SYNTHESIS AND CHARACTERIZATION OF NEW HYDROGELS …

SYNTHESIS AND CHARACTERIZATION OF NEW

HYDROGELS AND THEIR APPLICATIONS ON WATER

TREATMENT

Submitted to GC University Lahore

In partial fulfillment of the requirements

For the award of degree of

DOCTOR OF PHILOSOPHY

In

CHEMISTRY

By

AISHA HAMEED

SESSION 2014-2017

Registration No. 2014.PHD.CHEM.04

DEPARTMENT OF CHEMISTRY

GOVT COLLEGE UNIVERSITY

LAHORE (PAKISTAN)

In the Name of Allah, the most beneficent, the most Merciful

Praise is to Allah, Lord of the Worlds, The beneficent, the Merciful,

Master of the Day of judgment, Thee (alone) we worship thee

(alone) we ask for help. Show us the straight path, the path of those

whom Thou hast favored; Not the path of those who earn Thine

anger nor of those go astray.

DEDICATED TO:

My Great Father

Dr. Rana Abdul Hameed (Late)

Ex Principal Medical Officer,

Nishtar Medical University, Multan.

Who taught me

To believe upon ALLAH,

(Whatever the Circumstances),

Ask ALLAH

(Whatever I do need)

And

Always seek Guidance from ALLAH.

ABSTRACT

The present work in this thesis consists of Synthesis, Characterization and the

Applications of newly synthesized Carboxymethyl cellulose based Hydrogels. The

prepared hydrogels were characterized by studying their physical properties,

swelling behavior, Swelling kinetics, Fourier Transform Infrared spectroscopy

(FT-IR), scanning electron Microscopy (SEM), powdered x-ray diffractometery

(PXRD), thermogravimeteric analysis (TGA) and atomic absorption spectroscopy

to know their ability in removing heavy metal ions from water. In this work, the

synthesis of two novel hydrogels, Carboxymethyl cellulose/Potato Starch/Amylum

Strach (CMC/PS/AS) based Hydrgel (SAP). Modified Starch (MS) and Modified

Starch based Hydrogel (MSAP) were synthesized using Aluminium sulfate

octahydrate as a crosslinking agent. By taking into consideration, FT-IR analysis

done primarily to evaluate the structure of hydrogels, the structures in results were

according to the expected structures of hydrogels. The hydrogels then subjected to

the thermal gravimetric analysis to evaluate out the thermal stability of hydrogel

i.e. more than its ingredients. Hydrogels were then examined morphologically by

SEM. The swelling ability of both hydrogels were more in basic medium rather

than acidic, moreover it shows swelling and de-swelling behavior in water,

ethanol, acidic and basic buffers and in salt solutions when inferred by the swelling

experiment. A high swelling behavior was shown by SAP and MSAP in deionized

water, at pH 6.8 and 7.4 while no reasonable swelling at pH 1.2 was observed.

Furthermore, its potential as an intelligent drug delivery system was confirmed by

a remarkable swelling and de-swelling behavior of SAP in water and ethanol, in

acidic (pH 1.2) and basic (pH 7.4) media and in water and normal saline solution.

The thermal analysis of SAP and MSAP’s major degradation steps those takes

place above 200ºC represent their extra-ordinary stability. The PXRD anlysis

shows that there may be a distortion in the CMC’s crystallization and an increase in

SAP hydrogel’s amorphous region. The possible cause of it can be the chemical

crosslinking between the starches, CMC and SAP. These results indicate that due

to a reduction in the crystalline behavior during the gel formation. . The success of

the reaction in the FT-IR spectrum of SAP was revealed by an ester carbonyl

distinct signal’s appearance at 2341 cm−1 in spectra of CMC which was the major

constituent of hydrogel, jumps to a relatively higher wavenumber at 2345 cm−1

soon after the formation of its SAP. It also indicates the absorption of Carbon

dioxide at the time of reaction completion.

From the aqueous solution of Cd2+, Pb2+ and Fe2+ ions, these metal ions were then

separated by the hydrogel. The order of selectivity towards different metal ions of

the hydrogel as tested was Cd2+> Pb2+ >Fe2+. The observation revealed the fact

that the capacity of the hydrogel to bind with heavy metal ions was dependent on

the interaction of metal ions with the hydrogel monomers.

LIST OF ABBREVIATIONS

Description Abbreviation

Carboxymethyl Cellulose CMC

Carboxymethyl Cellulose Sodium CMC-Na

Modified Starch MS

Super Absorbent Polymer SAP

Modified Starch based Super Absorbent Polymer MSAP

Potato Starch PS

Amylum Starch AS

Fourier Transform Infrared Spectroscopy FT-IR

Scanning Electron Microscopy SEM

Powdered X- ray Diffractrometery PXRD

Thermogravimeteric Analysis TGA

Potassium Bromide KBr

Sodium Chloride NaCl

Micrometer μm

Nannometer nm

Centrifuge Retention Capacity CRC

Equilibrium degree of Swelling Qe

normalized degree of swelling Qt

Carr’s Index C

TABLE OF CONTENTS

Chapter 1

Introduction:

1.1: General…………………………………………………………………………

1

1.2: Classification of Carbohydrates……………………………………………….

1

1.2.1: Monosaccharides……………………………………………………………...

3

1.2.2: Disaccharides………………………………………………………………….

4

1.2.3: Oligo and Polysaccharides…………………………………………………...

5

1.3: Starches………………………………………………………………………...

7

1.4: The Properties of Hydrogels…………………………………………………..

8

i) Hydrogen Bonding……………………………………………………….

8

1.5: The Hydrogels………………………………………………………………...

9

1.6: Classification of Hydrogel……………………………………………………..

9

i) Classification on the Basis of Ionic Charge…………………………

10

1.7: Swelling Behavior of Hydrogels……………………………………………...

10

i) The Swelling De-swelling Behavior in response to External Stimuli. 10

1.8: Preparation of Hydrogel………………………………………………………. 11

1.9: Absorption of Metal ions……………………………………………………...

13

1.10: FTIR Spectroscopy……………………………………………………………

13

1.11: Powder X-ray Diffraction (PXRD)……………………………………………

15

1.12: Scanning Electron Microscopy (SEM)………………………………………...

16

1.13: Thermogravimetric Analysis…………………………………………………. 18

1.14: Atomic Absorption Spectroscopy……………………………………………... 20

1.15: Application of Hydrogel on Water Treatment……………………………….

21

Chapter 2

Review of Literature:

Chapter 3

22

Materials and Methods:

26

3.1:

Methodology…………………………………………………………………….

26

3.1.1: Preparation of Superabsorbent Polymer (SAP)………………………………….

26

3.1.2: Preparation of Modified Stach (MS)……………………………………………

26

3.1.3: Preparation of Modified Strach based superabsorbent polymer (MSAP)……. 26

3.2: Characterization…………………………………………………………………. 27

3.2.1: Flow-ability Parameters of SAP………………………………………………...

27

3.2.1.1: Angle of Repose. ………………………………………………………………..

27

3.2.1.2: Bulk and Tap Density. …………………………………………………………..

27

3.2.1.3: Hausner Ratio and Carr’s Index………………………………………………….

28

3.2.1.4: Moisture Content……………………………………………………………….. 28

3.2.1.5: Centrifuge Retention Capacity…………………………………………………

28

3.2.1.6: Swelling Capacity. ……………………………………………………………...

28

3.2.1.7: Dynamic and Equilibrium Swelling……………………………………………..

28

3.2.1.8: Swelling Kinetics………………………………………………………………..

29

3.2.1.9: The Swelling and de-swelling behavior in response to external stimuli………...

29

3.2.2: Scanning electron microscopy (SEM)…………………………………………..

30

3.2.3: FTIR Analysis…………………………………………………………………..

30

3.2.4: PXRD Analysis………………………………………………………………….

30

3.2.5: Thermogravimetric Analysis (TGA)…………………………………………….

31

3.3: Applications of Hydrogel on Water Treatment………………………………..

31

3.3.1: Atomic Absorption Spectroscopy………………………………………………

31

3.3.2: The Aims and Objectives of Study……………………………………………...

Chapter 4

32

Results and Discussion

34

4.1: Physical properties of SAP………………………………………………………

34

4.2: Swelling Behavior of Hydrogels and its Ingredients……………………………

36

4.2.1: Swelling Behavior of Potato Starch ……………………………………………

36

4.2.2: Swelling Behavior of Amylum Starch ………………………………………….

37

4.2.3: Swelling Behavior of Carboxymethyl cellulose………………………………..

38

4.2.4: Swelling Behavior of Modified Starch………………………………………….

39

4.2.5: Swelling Behavior of SAP………………………………………………………

40

4.2.6: Swelling Behavior of MSAP……………………………………………………

41

4.3: pH responsive swelling of Hydrogels…………………………………………..

42

4.3.1: pH responsive swelling of SAP…………………………………………………. 42

4.3.2: pH responsive swelling of MSAP………………………………………………

44

4.4: Swelling and de-swelling kinetics in response to external stimuli……………..

46

4.4.1:

Swelling and de-swelling behavior of SAP in water and ethanol……………….

47

4.4.2: Swelling and De-swelling behaviour of SAP in Acidic and Basic Buffers……..

48

4.5: Scanning Electron Microscopy (SEM)………………………………………..

49

4.5.1: SEM Micrographs of Potato Starch………………..…………………………...

50

4.5.2: SEM Micrographs of Amylum Starch…………………………………………

50

4.5.3: SEM Micrographs of Carboxymethyl Cellulose……………………………...... 51

4.5.4: SEM Micrographs of SAP……..……………………………………………….

52

4.5.5: SEM Micrographs of Modified Starch…………………………………………..

53

4.5.6: SEM Micrographs of Modified Starch based SAP…..…………………………

54

4.6: Fourier Transform Infrared Spectroscopy (FTIR)………………………………. 55

4.7: PXRD Analysis………………………………………………………………….

59

4.8: Thermogravimeteric Analysis…………………………………………………...

62

4.9: Applications of water treatment ………………………………………………..

68

4.9.1 Atomic Absorption spectroscopy 68

4.9.2 Adsorption Isotherms 69

4.10:

4.11:

Conclusion………………………………………………………………………..

Research work Published from this work………………………………………..

Chapter 5

References

73

75

76

LIST OF FIGURES

Fig 1.1: Illustration of a disaccharide maltose molecule’s glycosidic bond between

two molecules of glucose linked by an α-1,4-glycosidic

bond………………………………………………………………………..

2

Fig 1.2: Smallest monosaccharides “trioses”……………………………………… 3

Fig 1.3: Two structural formulae of glucose i.e. open chain and ring form ………. 4

Fig 1.4: Different forms of monosaccharrides in aqueous solution……………….. 4

Fig 1.5: Structure of common diasaccharides……………………………………... 5

Fig 1.6: Structure of some of the oligosaccharides………………………………... 6

Fig 1.7: Different types of polysaccharides 1st row: Non-mammalian 2nd row:

Mammalian polysaccharides………………………………………………

7

Fig 1.8: Structure of amylose and amylopectin in starch………………………….. 7

Fig 1.9: Illustration of hydrogen bonds (dotted line) in DNA by Watson and Crick’s

Model …………………………………………………………….

8

Fig 1.10: Schematic illustration of hydrogel structure having hydrophilic polymer

chains connected through cross-linking polymers………………………...

11

Fig 1.11: Hydrogen bonding in PVA………………………………………………. 11

Fig 1.12: Illustration of a hydrogel preparation……………………………………. 12

Fig 1.13: Schematic illustration of hydrogel network with different types of water.. 13

Fig 1.14: A block diagram of IR-imaging………………………………………….. 15

Fig 1.15: Major units in x-ray diffraction…………………………………………… 16

Fig 1.16: Construction of a scanning Electron microscopy………………………... 17

Fig 1.17: SEM image of a TiO2 nano-tubes……………………………………….. 18

Fig 1.18: A typical thermogravimetry apparatus with differential thermogravimetry

(DTG) facility…………………………………………

19

Fig 1.19: A typical thermogravimetric analysis plot of different compounds……… 19

Fig1.20(a&b): Single beam spectrometer (b) double beam spectrometer………………. 21

Fig 4.1(a): Swelling data of SAP obtained in water and buffers of pH 1.2, 6.8 and

7.4…………………………………………………………………………..

42

Fig. 4.1(b): Swelling data and kinetics of SAP obtained in buffers of pH 6.8 and 7.4..

43

Fig 4.1(c): Swelling data of SAP between time (min) and Qt(mg/g) obtained in water

and buffers of pH 1.2, 6.8 and 7.4…………………………………………

43

Fig4.1(d):

Fig 4.2(a):

Swelling data of SAP between time(min) and t/Qt(min(mg/g)) obtained in

water and buffers of pH 1.2, 6.8 and 7.4………………………………….

Swelling data of MSAP obtained in water and buffers(1.2,6.8 and 7.4)

44

44

Fig. 4.2(b): Swelling data and kinetics of MSAP obtained in buffers(6.8 and 7.4)……

45

Fig 4.2(c): Kinetic Studies of MSAP between time(min) and Qt (mg/g) at different

pH……………………………………………………………………………

45

Fig 4.2(d): Kinetic Studies of MSAP between time(min) and t/Qt (mg/g) at different

pH……………………………………………………………………………

46

Fig 4.3(a): The Swelling and de swelling of SAP in aqueous and ethanol media……..

46

Fig 4.3(b): The Swelling and de swelling of MSAP in aqueous and ethanol media…...

47

Fig 4.4(a): Swelling and de-swelling behavior of SAP in basic and acidic buffers…….

47

Fig 4.4(b): Swelling-deswelling behavior of MSAP in basic and acidic buffers……….

48

Fig 4.5(a): Swelling-deswelling behaviour of SAP in deionized water and 0.9% NaCl

solution………………………………………………………………………

49

Fig 4.5(b): Swelling-deswelling behaviour of MSAP in deionized water and

0.9%NaCl…………………………………………………………………….

49

Fig. 4.6: FTIR Spectra of Potato Starch………………………………………………. 56

Fig. 4.7: FTIR Spectra of Amylum Starch……………………………………………. 56

Fig. 4.8 : FTIR Spectra of Carboxymethyl cellulose………………………………….

56

Fig. 4.9: FTIR Spectra of SAP………………………………………………………...

57

Fig. 4.10: Combined FTIR Spectra of Potato, Amylum starches, CMC and SAP…….. 57

Fig 4.11: FTIR Analysis of MSAP…………………………………………………….

58

Fig.4.12: PXRD Analysis of Potato Starch……………………………………………

59

Fig.4.13: PXRD Analysis of Amylum Starch…………………………………………. 59

Fig.4.14: PXRD Analysis of Carboxymethyl cellulose-Sodium……………………… 60

Fig.4.15: PXRD Analysis of SAP……………………………………………………... 60

Fig 4.16: PXRD Analysis of Modified Starch…………………………………………

61

Fig 4.17:

PXRD Analysis of MSAP…………………………………………………...

61

Fig.4.18: Overlying graph of thermo-gravimetric (TG) straight line of SAP indicating

thermal stability of sorbent…………………………………………………..

62

Fig 4.19: Thermogravimeteric Analysis of Potato Starch……………………………..

62

Fig 4.20: Thermogravimeteric Analysis of Amylum Starch………………………….

63

Fig 4.21 Thermogravimeteric Analysis of Carboxymethyl Cellulose………………...

64

Fig 4.22 Overlying graph of thermo-gravimetric (TG) straight line of SAP,

indicating thermal stability imparted in sodic form of sorbent throughout

the degradation profile……………………………………………………….

64

Fig 4.23 Thermogravimeteric Analysis of Potato, Amylum Starchces,

Carboxymethyl Cellulose Sodium and SAP…………………………………

65

Fig 4.24 Thermogravimeteric Analysis of SAP (Graph between Temperature and

Weight Loss of both Derivatives)……………………………………………

65

Fig 4.25 Thermogravimeteric Analysis of Modified starch…………………………..

66

Fig 4.26 Thermogravimeteric Analysis of Modified Starch (Graph between

Temperature and Weight Loss of both Derivatives)…………………………

66

Fig 4.27 Thermogravimeteric Analysis of MSAP…………………………………….

66

Fig 4.28 Thermogravimeteric Analysis of MSAP (Graph between Temperature and

Weight Loss of both Derivatives)……………………………………………

67

Fig 4.29 Thermogravimeteric Analysis of Modified Starch, Carboxymethyl

Cellulose Sodium and Modified starch based SAP………………………….

67

Fig 4.30 Metal ion adsorption ratio profiles of SAP at room temperature…………… 68

Fig4.31 Metal ion adsorption ratio profiles of MSAP at room temperature……….

68

Fig 4.32 Graphical representation of Cadmium ion absorption in SAP between

Ce(mol/L) and Qe (mol/L)…………………………………………………...

69

Fig 4.33 Graphical representation of Cadmium ion absorption in MSAP between


69

Fig 4.34 Graphical representation of Fe2+ ion absorption in SAP between Ce(mol/L)

and Qe (mol/L)………………………………………………………………

70

Fig 4.35 Graphical representation of Fe2+ ion absorption in MSAP between


71

Fig 4.36 Graphical representation of Pb2+ ion absorption in SAP between Ce(mol/L)

&Qe (mol/L)…………………………………………………………………

71

Fig 4.37 Graphical representation of Pb2+ ion absorption in MSAP between


72

LIST OF TABLES

Table 1.1: Classification of Carbohydrates………………………………………… 2

Table 3.1: Conditions for PXRD Analysis for all six Samples……………………..

30

Table 4.1: Phyical Properties of SAP……………………………………………….

34

Table 4.2: Physical Properties of MSAP…………………………………………... 34

Table 4.3: Observed FT-IR bands and their Assignments………………………….

58

Table 4.4: Freundlich and Langmiur Equation fitted Parameters………………….. 72

LIST OF IMAGES

Image 4.1(a,b,c,d): SEM micrographs of Potato Starch………………………..

50

Image 4.2(a,b,c,d): SEM micrographs of Amylum Starch…………………… 50

Image 4.3(a,b,c,d): SEM micrographs of Carboxymethyl cellulose…………...

51

Image 4.4(a,b,c,d): SEM micrographs of SAP………………………………… 52

Image 4.5(a,b,c,d): SEM micrographs of Modified Starch based SAP ……….

53

Image 4.6(a,b,c,d): SEM micrographs of Modified starch ……….

54

Chapter 1

INTRODUCTION

Chapter 1: INTRODUCTION

Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 1

1.1 General

Carbohydrates are most abundant, natural organic compounds utilized by animals, plants as

well as micro-organisms. These are one of the macro-nutrients essential for human activity

providing metabolic energy by glucose oxidation. Not only as a source of energy, but a chief

source of fuel, clothes and building material. At molecular level, carbohydrates are the

essential components of neucleotides carrying the genetic information in all living animals.

Moreover, when they are conjugated with other biomolecules e.g. steroids, covert them water

dispersible and make them transportable from one part of body to other in the form of

glycosides [1]. Carbohydrates are divided into different classes depending on their molecular

weight and complexity. Types of carbohydrates include low-molecular-weight

monosaccharides (glucose, fructose, rabinose, xylose and mannose) and disaccharides

(maltose, sucrose and lactose), in addition to the high-molecular-weight oligosaccharides

(dextrins) and polysaccharides (chitin, cellulose, chitosan, agarose, inulin, xylan, amylose and

amylopectin) [2]. More simply, there exist two types of Carbohydrates; simple (glucose,

fructose, maltose and sucrose) and complex (cellubiose, amylose, dextrins, starch, cellulose

and fibres). Carbohydrates level in the body plays a part in physiological and metabolic

functions i.e. an increased intake of simple carbohydrates may lead to obesity and non-insulin

dependent diabetes which in turn, can lead to further disorders [3].

In many important biological processes, carbohydrates play an important role e.g. cell-cell

interactions, bacterial and viral infections and immune response. These are, not only and

important source of DNA and RNAs but also an important source of energy for many

organisms [4].

1.2 Classification of Carbohydrates

Carbohydrates can be classified as below

Simple carbohydrates as one to two sugar molecules combine by a simple chemical

reaction e.g. fructose, maltose, ribose, sucrose present in different types of foods like

carbonated beverages, fruit juice, table sugar and honey

Complex carbohydrates formed by a complex reaction of oligo or polysaccharides

e.g. cellobiose, amylose, dextrin and cellulose present in foods like broccoli, lentils,

apple and in brown rice having a gradual effect on level of blood sugar

Starches having glucose molecules in large number, produced by plants e.g.

chickpeas, pasta, wheat and potato.

Fiber: may be soluble or insoluble fibers help to decrease cholesterol and LDL level

and in regularity of bowel movements respectively. A non-digestible carbohydrate

having the main components pectin, cellulose and hemicellulose e.g. oats, fleshy

fruits, potato skins and brown rice [5].

The biological role of carbohydrates is prominent in assembly of organisms and complex

multicellular organs requiring an interaction between cells and their surrounding matrix.

Numerous macromolecules and cells in nature carry out a building block i.e. simple

sugar molecule attached covalently to other ones (monosaccharide) or a chain of sugar



molecules (oligosaccharides) generally referred as “glycans”. They are present on outer

surface of a cell or secreted macromolecules and many of them are capable to mediate

numerous cell-matrix, cell-molecules and cell-cell interactions for the function and

development of a complex multicellular organism or even in between different organism

i.e. between parasite, symbiont or pathogen to their hosts. Within the nucleus, protein-

bound glycans are most abundantly present in nucleus and cytoplasm serving as a

regulatory switch [6].

In nature, carbohydrates are present mostly in complex form by the joining of simpler

molecules through glycosidic linkages as well as in different structural forms i.e. ring or

open chain structure in which different atoms are substituted by other ones like

hydroxymethyl and N-acetyle etc. The different orientation and confromations of these

molecules make them complex ones for theory and experimental point of view [7]..

Fig 1.1: Illustration of a disaccharide maltose molecule’s glycosidic bond between two

molecules of glucose linked by an α-1,4-glycosidic bond [8].

According to recent research, excessive intake of carbohydrates specially sugars e.g. fructose

may lead to some detrimental metabolic effects. However, in mixed carbohydrate sources,

fructose doesn’t exert some specific metabolic effects and doesn’t take part primarily in an

increase of body weight. In a recent Asian cohort study, the excessive carbohydrate was not

associated with mortality of ischemic heart disease. In contrast to this, a diet shifts to a lower

carbohydrate intake, like vegetables, whole grain and fruits account for a lower risk of

ischemic heart disease [9].

Table 1.1: Classification of Carbohydrates [10]

Group Sub-group Principal components

Sugars (mono- and di-

saccharides)

Monosaccharides Fructose , Galactose,

Glucose

Disaccharides Trehalose, Sucrose, maltose,

lactose

Sugar-alcohols (polyols) Sorbitol, xylitol, lactitol,

maltitol, mannitol,

isomaltitol, erythritol



Oligosaccharides Maltooligosaccharides

(alpha-glucans)

Maltodextrins

Non-alpha-glucan

oligosaccharides

Raffinose, fructo- and

galacto-oligosaccharides,

polydextrose, inulin,

stachyose

Polysaccharides Starch (alpha-glucans) Modified starches, Amylose,

Amylopectin

Non-starch polysaccharides Pectins, Cellulose,

hemicellulose, hydrocolloids

(e.g., beta-glucans, gums,

mucilages)

1.2.1 Monosaccharides

Carbohydrates can be described in terms of polyhydroxyketones or polyhydroxyaldeheydes,

larger compounds and their simple derivatives, where the large compounds can be

hydrolyzed into simpler units. Monosacharides are defined as building blocks of

carbohydrates that can’t be hydrolyzed further having a carbonyl group on an inner carbon

atom (ketone) or at the carbon chain’s end (aldehyde). Thus can be ketoses or aldoses

respectively [6].

The empirical formula for monosaccharides is (CH2O)n. These are important building blocks

of many biological molecules carrying out cellular functions i.e. nucleic acids. D- and L-

glyceraldehyde and Dihydroxyacetone are simplest monosaccharides for which n=3 also

called as “trioses” while others with carbon atom ranging from four to seven are named as

tetroses, pentoses, hexoses and heptoses.

Fig 1.2: Smallest monosaccharides “trioses” [11].

In simple words, monosaccharides are the simplest, fundamental and most basic

carbohydrates having formula C6H12O6 e.g. glucose, fructose and galactose. They exist in the

form of five membered furanose form and six membered pyranose form adopting the shape to

minimize the eclipsing interactions [12].



Fig 1.3: Two structural formulae of glucose i.e. open chain and ring form [6]

In an aqueous solution, monosaccharides exist in different forms as describe below in figure:

Fig 1.4: Different forms of monosaccharrides in aqueous solution [13]

1.2.2 Disaccharides

Two monosaccharides are joined together via glycosidic linkage to form a disaccharide

molecule mostly by an O-glycosidic linkage. Examples of abundant disaccharides are

sucrose, maltose and lactose. These glycosidic linkages are cleaved by their respective

enzymes e.g. sucrose enzyme for the breakdown of sucrose into parent molecules.



Fig 1.5: Structure of common disaccharides [8]

1.2.3 Oligo and Polysaccharides

In living organisms, monosaccharides alone rarely occur in nature rather, they join with other

molecules of same specie or other to form large molecules. The most common of which is the

covalent linking of a sugar with an aglycone may be lipid, protein or other carried out by the

formation of a glycosidic linkage i.e. bond between the hydroxyl group of the aglycone and

anomeric carbon of sugar. The resulting specie thus called as oligosaccharide with less than

dozen monosaccharides or polysaccharides containing more than a dozen monosaccharides

and there may be repeating units in the structure of polysaccharides. This assemblage creates

a vast variety and diversity of macromolecules which makes carbohydrates to play functional

and vital role in living organisms [14].

Many types of oligosaccharides are occurring in nature and most important of them are

fructooligosaccharides (FOS), Lactulose derived galactooligosaccharides (LDGOS),

Galactooligosaccharides (GOS), Arabinooligosaccharides (AOS), Xylooligosaccharides

(XOS) and algae derived marine oligosaccharides (ADMO).

In recent research, pre-biotics of oligosaccharides are gaining attention as their effect is now

extended as an anti-obesity, antidiarrheal substance in addition to its promising role in

suppressing diabetes type 2. In future, there may be a development of pre-biotic and pro-

biotic combination for a synergistic effect which can used to combat many ailments in human

beings [15].



Fig 1.6: Structure of some of the oligosaccharides [15]

In polysaccharides, there present a diverse range of functional groups like ester, hydroxyl,

carboxylate and amino groups. Therefore, they can be modified to attain a diverse group of

derivatives [16]. Basically, polysaccharides are classified into two main classes on the basis

of their structure i.e. homopolysaccharides or homoglycans and heteropolysaccharides or

heteroglycans. The first defines the formation of polysaccharide chain by same

monosaccharides e.g. glycogen, starch, chitin and cellulose while the later one is formed by

two or more types of monosaccharides e.g. glycosaminoglycans. Another classification of

polysaccharides is based on morphology i.e. long chains or branched molecules or on their

function i.e. structural polysaccharides (agar, chitin and pectin) or storage polysaccharides

(starch, glycogen). Some living organisms also secrete polysaccharides in order to prevent

themselves from drying out as an evolutionary adaptation or to get adhered to the surface like

bacteria, fungi and algae. In addition, polysaccharides can also be divided on the basis of

their electrical charge i.e. cationic, neutral and anionic as well as by their sources i.e. plants,

micro-organisms and animals [17].



Fig 1.7: Different types of polysaccharides 1st row: Non-mammalian 2nd row:

Mammalian polysaccharides [18]

1.3 Starches

A type of polysaccharides and a mixture of two glucose polymers i.e. amylopectin a highly

branched molecules (with (1→6) α-linkages as well as (1→4) α-linkages) and may comprise

over 100,000 glucose residues and amylose, which has (1→4) α-linked chains comprises up

to several thousand glucose units. Amylose occurs mostly in tuber starch than cereal ones

having a few long branches but highly branched. Most of the starches contains 70-80%

amylopectin while, 20-30% amylose and their ratio can be altered by transgenic engineering

or some mutations in biosynthetic pathway [19].

Fig 1.8: Structure of amylose and amylopectin in starch [20]



In a starch granule, about 30% of its mass is considered as crystalline mainly composed of

amylopectin while, 70% is considered as amorphous having amylose as major component

with a considerable amount of amylopectin. The gelatinization of starch is a three step

mechanism involving thermal hydration-plasticization of the polymeric network in which

first step includes the swelling of hydrophilic starch granule by the absorption of water while,

the second step is destruction of the granular structure by dissolving it thermally and resulting

in leaching of amylose. The major third step is the retrogradation step in which by cooling,

the starch-hydrogel network is created, recrystallization occurs partially and polysaccharide

structure is regenerated. Temperature of gelatinization and the amount of starch are the two

main factors affecting the gel formation [20].

1.4 The Properties of Hydrogels

1.4.1 Hydrogen Bonding

It is a type of interaction between an electronegative acceptor atom “Y” (usually N, O or F)

and an electropositive donor covalent bond group X-H. The bond thus created X-H----Y

imposes different properties chemically and physically in a compound in correlation with the

electronegative atom. This hydrogen bonding is crucial to carry out major metabolic events in

living organisms as well as in the formation of essential biomolecules e.g. nucleic acids,

proteins and many others. Various factors like pressure, temperature, electronegativity of

donors and acceptors, bond angle, bond length and the local dielectric constant [21].

Fig 1.9: Illustration of hydrogen bonds (dotted line) in DNA by Watson and Crick’s

Model [22]



We can say, conventional bonds of hydrogen in a biomolecular structure respresent a major

stabilizing force. This bond is usually shared between a donor and an acceptor atom by a

slightly varying degree. The most common way to discover hydrogen bond is by measuring

the bond length between the groups of donors and acceptors. Moreover, spectroscopic

signature is also a common way to detect hydrogen bond with some accuracy [23].

1.5 The Hydrogels

Also called the hydrophilic gels, these are actually the polymeric networks swollen

extensively with water, sometimes found as colloidal gels in dispersion medium as water. In

other words, hydrogel is a water swollen, cross-linked polymeric network produced by

monomers, having the ability to retain a large volume of water within its structure without

dissolving in it [24].

The first reference to hydrogels appeared in 1894 claiming it a colloidal gel made up of

inorganic salt. The term “hydrogels” was then used to describe a 3D network of polymers

formed chemically of physically. The idea of biological use of hydrogels was devised in

1960 by Wichterle and Lim and since then, a large number of ideas were applied on

hydrogels providing useful evidences in biomedical research. The term “smart hydrogels”

refers to a type of hydrogels which respond to a minute change in its environment differing

with ordinary hydrogels which undergo only a swelling and de-swelling behavior in water

medium. Smart hydrogels undergo volume and structural phase transition in response to

external stimuli providing a potential for scientific observation and different technological

applications [25].

1.6 Classification of Hydrogel

Two main classes of hydrogels include the natural and synthetic hydrogels. Among these,

natural hydrogels include fibrin, collagen, matrigel, hyaluronic acid and derivatives of natural

products e.g. chitosan and alginate. These are the physiological hydrogels as they are the

components of extracellular metrix in vivo. Drawbacks of natural hydrogels include their

final properties and microstructures which are difficult to control reproducibly in addition to

their difference in properties due to natural origin. Synthetic hydrogels include poly (acryl

amide), poly (ethylene glycol) diacrylate, poly (vinyl alcohol) which are more reproducible

but their final structure also depends on polymerization condition. They can be tuned or

selected to be biodegradable and hydrolysable over selected period of time [26]. The

resistance to dissolution and their ability to absorb water are due to functional-groups

attached to their backbone and their cross-linked network respectively. Due to high gel

strength, long service life and high capacity of water absorption, synthetic hydrogels are now

widely used today. Fortunately, the synthetic hydrogels possess well-defined structures that

can be tailored for the required functionality and degradability [24].

Due to their unique properties, hydrogels are used commonly for a wide range of

experimental and clinical practices as diagnostics, cellular immobilization, tissue engineering

and regenerative medicine, separation of cells or biomolecules and as barrier molecules for

the regulation of biological adhesions [27].



1.6.1 Classification on the Basis of Ionic Charge

Based on ionic charge, method of preparation or physical character, hydrogels are divided

into different categories. Hydrogels having ionic charge on backbone polymer are called

ionic hydrogels and are classified as neutral hydrogels (uncharged), anionic hydrogels

(negative charge only), cationic hydrogels (positively charged hydrogels) and ampholytic

hydrogels (having both positive and negative charges). On the basis of method of preparation,

hydrogels are classified as homopolymer hydrogels (made by cross-linking of only one type

of hydrophilic monomer unit), copolymer hydrogels (made by cross-linking of chains having

at least one hydrophilic unit to make them water swellable) and multi-polymer hydrogels

(produced by reaction of three or more comonomers). By considering the physico-chemical

properties, hydrogels are divided as amorphous (possessing covalent cross-links) and semi-

crystalline (may or may not possess covalent bond) hydrogels [28].

1.7 Swelling Behavior of Hydrogels

In other words, hydrogels are macromolecular networks having ability to absorb water and

then releasing it in specific environmental stimuli. This specific behavior to a specific stimuli,

make it a suitable substance to design a smart device in various fields of technology and

biomedical sciences [29]. The swelling behavior of hydrogels occurs in relation to the

presence of hydrophilic groups in their polymeric chain, elasticity of network in hydrogel, the

porosity and extent of the cross-linker. A super-porous hydrogel SPH is composed of a 3D

network of polymer having the ability to absorb a large amount of water in a relatively less

time due to the interconnected microscopic pores network [30]. New ideas regarding

hydrogels include enhanced mechanical hydrogels structures, super-porous hydrogels, comb-

type grafted structure having a fast response time and self-assembled hydrogels made from

specific co-polymers [31].

1.7.1 The Swelling De-swelling Behavior in Response to External Stimuli

Today, hydrogels can be formed with responses that can be controlled accordingly as to

expand or shrink desirably with some changes in the environment. Dramatic transitions in

volume of hydrogels can be observed with chemical or physical stimuli as physical stimuli

include pressure, sound, electric or magnetic fields and temperature, while, chemical stimuli

include solvent type and composition, pH, molecular species and ionic strength [24].

Swelling and de-swelling in response to a particular stimulus is a unique property carried out

by hydrogels. The extent of swelling tells about the network and structure of hydrogels and it

depends on the following four important parameters;

The ratio of swelling i.e. involvement of mass swelling ratio (Qm) and the volume

swelling ratio (Qv)

The polymer volume fraction in the swollen state (υ2,s)

The number average molecular weight between cross-links (Mc)

The network mesh size (ξ)



Fig 1.10: Schematic illustration of hydrogel structure having hydrophilic

polymer chains connected through cross-linking polymers [32]

As previously described, hydrogels have a three dimensional structure in which molecules are

held together by some specific type of forces i.e. Van der Waals forces, hydrogen bonding

and covalent bonds. The most important factors in the preparation of a hydrogel are type of

cross-linker and its concentration, types of initiator, monomers and their concentration,

inorganic particle types (if used), rate of stirring, surfactant type, reactor type, polymerization

method and the temperature of reaction [20].

1.8 Preparation of Hydrogel

Preparation of hydrogel basically involves the polymerization of molecules under optimum

temperature and pressure for the reactants to react. Cross-linking the molecules is the basic

technique in the preparation of a hydrogel. Two methods of cross-linking are applied in the

preparation a hydrogel i.e. physical crosslinking and chemical cross-linking. Physically cross-

linked gels got an attention due to the absence of special cross-linkers used in the preparation.

Following are the physical methods to introduce cross-linking in molecules;

By hydrogen bonds (e.g. polymethacrylic acid and polyacrylic acid complex with

PEG, PVA)

Fig 1.11: Hydrogen bonding in PVA [33]



By ampiphilic grafting and block polymers (e.g. polymers of PLGA and PEG)

Cross-linking by crystallization in homopolymer system (Polyvinyl alcohol) and by

stereocomplex formation (mixture of PLLA and PDLA at 230ºC)

By ionic interactions (Alginate gels)

By protein interaction from genetically engineered proteins (biocompatible

ProLastins) and by antigen-antibody interactions (grafting of IgG to chemically cross-

linked polyacrylamide)

Some of the chemical methods for cross-linking are given below;

By chemical reaction of complementary groups i.e. with aldehydes (PVA cross-

linking with glutaraldehyde), by addition reactions (Polysaccharides cross-linking by

1,6-hexamethylenediisocyanate) and by condensation reactions (e.g. gelatin

hydrogels)

By high energy radiation i.e. gamma rays to polymerize unsaturated compounds

By free radical polymerization i.e. from enzyme as catalysts or by UV polymerization

Using enzymes e.g. reaction between the ε-amine group of lysine and γ-carboxamide

group of the PEG-Qa catalyzed by transglutaminase [34].

Fig 1.12: Illustration of a hydrogel preparation [35]

Presence of water is hydrogel is a most important tool to carry out all the transport of active

ingredients through the gel. A hydrogel is associated with different types of water i.e. bound,

semi-bound, interstitial and free or bulk water as given below in figure;



Fig 1.13: Schematic illustration of hydrogel network with different types of water [33]

1.9 Absorption of Metal ions

Hydrogels possess a unique property to absorb metal ions from aqueous solutions. This

property leads to some of the most important applications. The absorption of metal ions by

hydrogels can be calculated by concentration of metal ions in initial and equilibrium phase in

aqueous solution, the volume of hydrogel used and by the weight of hydrogel. Moreover, the

metal absorption is affected by the salt concentration of solution and pH [36].

In recent times, various methods are employed to treat the polluted water by means of

physical and chemical methods e.g. removal of heavy metal ions. Various studies analyzed

the methods of using hydrogels for the removal of heavy metal ions and reported

considerable results [37]. In this study, we will examine the treatment of contaminated water

with heavy metal ions by the use of hydrogels.

1.10 FTIR Spectroscopy

Fourier transform IR (FTIR) spectroscopy is a technique to assess the biochemical

information and images and widely used for research purposes. The spectral domain obtained

after the FTIR spectroscopy, helps in chemical identification, and when used with

microscope, the examination of heterogeneous samples and complex tissues becomes

possible. An IR active substance comprises of molecules having an electric dipole moment

that can be changed by atomic displacements having some natural vibrations. An IR

spectroscopy measures these vibrational modes quantitatively and provides a label-free

method to study the composition and dynamics of molecules without changing or affecting

the sample [38].

It is a widely used technique for the investigation of samples in gaseous, solid or liquid phase

based on the interaction of natural vibrations of chemical bonds present in atoms and

electromagnetic radiation. There are two conditions for an element to absorb the infrared

radiations,

i) The frequencies between the molecular vibrations and the infrared radiations must

resonate



ii) There must be a change in dipole moment during vibration by natural vibrations

Two types of vibrations are present in a molecule; one of them changes the bond angle and

the other, bond length. Moreover, wavelength (λ) is used to represent the position of the

absorption band spectra. However, the commonly used term used in IR spectra is

wavenumber (v¯) having the unit cm-1, and is directly prop. to frequency (v) and energy (E)

of the radiation as given below;

E= h v = h c / λ

C= Speed of light in vacuum

H= Plank’s constant

Absorbance and transmittance are two terms used to describe the band intensity.

Transmittance (T) is defined as the ratio between intensities of the transmitted (I) and

incident (Io) beams. On the other hand, absorbance (A) is the logarithm (base 10) of the

reciprocal of the transmittance;

A =log10 (1/T) = log10 (Io /I)

The transmitted radiant energy depends on the thickness (x) and absorption coefficient (α) of

the sample

I = I0eαx

In Infrared, there are three spectral regions, i.e., the near (NIR – from 4,000 to approx. 14,000

cm-1), mid (MIR – from 400 to 4,000 cm-1) and far-infrared (FIR – from approx. 25 to 400

cm-1) regions [39].

The intensities of absorbance and frequencies of the infrared bands don’t contain isolated

peaks rather complex contours and unique bands are displayed for the quantification,

characterization and isolation of the sample under consideration [40].

Modern IR spectrometer are mostly Fourier transformed in which the main part is

Michealson’s Interferometer, the main technique of which is the interference of two beams of

light produced by a broadband light source [41]. A discrete fourier transform is a

mathematical function which is able to transform a function from time to frequency domain.

A fast fourier transform algorithm is present which makes the discrete fourier transfer to

compute so there is a recognizable absorbance spectrum by these raw signals inversely

besides this interferometer. Moreover, the analysis of samples in different conditions (liquid,

suspended, powered or dehydrated) is responsible for the expansion in scientific and

technical applications by the use of chemo-metric tools by which quantitative and qualitative

analysis can be done by the spectra. A standardized experimental protocol which is available

for media preparation, temperature and incubation time, sample preparation, cell harvesting

conditions and FT-IR measurement should be followed in order to obtain a reproducible data

[40].



In many research areas, the combination of FTIR and chemometric techniques is being used

as a reliable tool for quantitative and qualitative analysis. There exists a varierty of

chemometric methods used to carry out analysis which includes Canonical Variate Analysis

(CVA), Hierarchical Cluster Analysis (HCA), Principal Component Analysis (PCA), Partial

Least Squares Regression (PLS), Soft Independent Modelling by Class Analogy (SIMCA),

Artificial Neural Network (ANN) and Discriminant Analysis (DA). The use of FTIR

spectroscopic technique has a wide range of applications from the analysis of microscopic

organisms to the geographical discrimination and classification of seeds, pods and fruits [42].

Fig 1.14: A block diagram of IR-imaging [43]

1.11 Powder X-ray Diffraction (PXRD)

Powder X-ray diffraction is a source to obtain an accurate structural data of polycrystalline

substance since early 90s. A crystalline structure can be successfully determined by the use of

PXRD data. Moreover, the further use of solid-state NMR spectroscope can validate and

significantly enhance the data obtained by the PXRD analysis [44]. A type of X-ray

diffraction in which the sample is used in the form of powder and is considered as a non-

destructive, non-invasive and a quick tool for the identification of solid phases. The pattern of

PXRD analysis is unique for a particular crystalline form, so identification of the compound

can be done by it. This technique is mostly used for the pharmaceutical ingredients for the

identification of drugs also known as “bulk characterization method” because it uses a bulk

mass of powder to analyze it [45].

Powdered X-ray diffraction is a modified form of X-ray diffraction whose history lies in 1912

when Max Van Loue and co-workers discovered that crystalline substances can work as a 3D

diffraction grating for x-ray wavelengths. Later, it became a successful tool for the

identification of crystal lattice and atomic structure. An x-ray diffratcometer work is based on

the constructive interference of a crystalline sample and monochromatic x-rays in which a

cathode ray tube produces x-rays and then collimated to make them concentrated and



directional towards the sample under study. This interaction produces a constructive

interference when Bragg’s law is conditioned:

nλ= 2dsinθ

n = an integer

λ = wavelength of the X-rays

d = the inter-planar spacing generating the diffraction

θ= diffraction angle.

This law relates the spacing of a lattice in a crystalline sample and wavelength of

electromagnetic radiation to the diffraction angle. These diffracted X-rays are then detected,

processed, and counted and all possible diffraction directions of the lattice can be attained by

scanning the sample through a range of 2θ angles due to the random orientation of the

powdered material. Due to unique d-spacings for each compound, we can convert the

diffraction peaks to d-spacings that allow identification of the sample. More elaborately, we

can achieve this by comparing d-spacings with some standard reference pattern [46].

Fig 1.15: Major units in x-ray diffraction [45]

Many types of XRD are present today, PXRD is one of them which allow the non-invasive

and accurate imaging of the powdered sample under study and we can say, PXRD patterns

are actually the fingerprints of crystalline substances. The data collection time is 20-30min

for identification purposes. Identification of the peaks is done in phases of a straight-forward

automatic technique by matching the ones obtained by sample against all the possible peaks

of a crystalline compound in the powder diffraction file and a computer software is available

for this purpose [47].

1.12 Scanning Electron Microscopy (SEM)

It is a modified form of “Transmission electron microscopy (TEM)” which is introduced in

late 1930s. SEM was made by attaching scan coils to a TEM and first introduced

commercially by Cambridge Instrument Company in 1965 as the “Stereoscan” and first scan

of nylon fibres was done in US where it was shipped firstly. Since that time, SEM has been

used as a most useful tool to gather information even at sub-nanometer scale and widely used



as a research and analytical tool. Due to the use of electron instead of light as a source for

illumination, it can resolve or evaluate structure as tiny as 0.4nm [48].

A SEM has the ability to magnify a sample 20–130,000× and provides an intense detail and

high-quality resolution image. A vacuum is necessary in SEM for the electron source to shoot

off electrons, in this way; the electrons are directed with electromagnets and can be focused

to hit the sample to produce a topographical image in a scanning manner. Moreover, this

vacuum environment helps the electrons in preventing to come in contact with air particulates

and gas molecules which in turn, prevent them from interacting with the sample, which can

result in a poor-quality image [49].

Fig 1.16: Construction of a scanning Electron microscopy [50]

The detectors in SEM are of various types having the ability to ensure the most detailing

image of the sample and to detect the composition of a substance. SEM gives a 3D

topographical image that reveals even minor or nano details of a substance. It has a wide

range of applications including the examination of food particles, ingredients, biological

substances, micro-organisms etc. The SEM and associated software are easy to use yet

expensive to operate. The main advantage of SEM is its limitation to inorganic and solid

sample that can be adjusted inside the vacuum chamber [50, 51].

Modification in SEM is useful in carrying out the desired visualization of the sample by using

affordable methods. In this way; we get different types of SEM i.e. atmospheric scanning

electron microscopy, Field Emission Scanning Electron Microscope (FESEM), and ultra-high

resolution SEM etc [52,53] By using elastically scattered electrons, mass measurements can

now be done regularly on a wide range of molecular and supra-molecular structures. The

scanning transmission electron microscope it is an efficient tool for mapping the chemical

composition of biological samples according to the recent progress in the acquisition and

analysis of electron energy-loss spectroscopy data [54].



Fig 1.17: SEM image of a TiO2 nano-tubes [55]

1.13 Thermogravimetric Analysis

It is a thermoanalytical technique in which a thermobalance measures changes in sample

mass, where, thermobalance is consists of an appropriate temperature controller and an

electronic microbalance with a furnace. A thermogravimetric analysis is done to findout the

weight loss in different procedures like oxidation, loss of volatiles (moisture in a temperature

range) and decomposition giving the data in the form of a plot most of the times as a

temperature (or time)/mass (or mass percentage) plot. Though there arises some difficulty in

interpreting the polt data of composite compounds, but can be overcome by comparing the

plot with reference plots or adequate samples to carry out the compositional analysis.

Moreover, it is a useful tool to determine the life expectancy of a compound, the oxidative

and thermal stability, moisture and volatile contents and decomposition profile [56].

More precisely, it is a rapid technique of thermal analysis which, under a set of conditions

and at a fixed rate heats a substance and change is mass is measured as a function of

temperature. This loss of mass tells much about a compound’s properties in addition to its

kinetic parameters and energy of activation may require to design and operate the

thermochemical conversion equipment [57].



Fig 1.18: A typical thermogravimetry apparatus with differential thermogravimetry

(DTG) facility [58]

Fig 1.19: A typical thermogravimetric analysis plot of different compounds [59]

Likewise other equipment, TG apparatus also couples with other instruments to get desired

results e.g. coupling it with mass spectrometer which can help in the identification of gaseous

compounds in the process of combustion [60].



TG has a wide range of applications from the energy analysis of electronic waste products to

the estimation of carbon release from silicone products to estimate the effects on pollution

[61,62]. Not only for research purposes, TG can be useful in identifying the polymer in

forensic sciences [63]. TG analysis can predict the thermal stability and vapor pressure

behavior of a volatile substance [64]. Moreover, in pharmaceutical development, it is a useful

tool in accurate measurement of even a tiny heat change to develop a more suitable drug

product in addition to its wide range of application in quality control of pharmaceuticals [65].

It is helpful in determining the components of biomass e.g. lignocellulosic and fuels in

addition to their energy estimation [66, 67].

1.14 Atomic Absorption Spectroscopy

It is an analytical technique used to get information about any compound quantitatively. The

technique based on the absorbance of the electromagnetic radiation by gaseous atoms at some

specific wavelength to produces signals which can be detected and identified further. In the

optical path, the concentration of those free absorbing atoms influences the absorption signal.

This whole operation requires the conversion of the sample into gaseous state and for this

purpose, an atomizer is used. Atomic absorption spectrometry (AAS) is of categorized into

two types on the basis of atomizer i.e. flame atomic absorption spectrometry (FAAS) and

electrothermal atomic absorption spectrometry (ETAAS). The former type provides the

continuous signals while the later provides the signals in discontinuous mode i.e. 2-

4min/sample. In both types of AAS, the liquid samples are introduced to the analyzer easily

and more elaborately, an aerosol while using FAAS and microliter sample in case of ETAAS.

The methods of cold vaporization and hydride generation introduces gas molecules in

atomizer [68].

It is relatively an inexpensive technique used for the quantitative analysis and widely used for

low-budget research projects. There exist many types of AAS on the basis of its construction

having respective pros and cons and can be selected easily on the basis of type of analyte

[69].

A spectrometer consists of a light source, an atomizer, a wavelength detector and a signal

detector. Based on the configuration, two types of AAS are developed i.e. single beam

spectrometer in which light source, atomizer and detector are aligned and the selected

wavelength is directed to the detector, double-beam spectrometer which has a beam-splitter

by which beam splits to an atomizer and other acts as a reference for a continuous

comparison of the two lights [70].



Fig. 1.20(a): Single beam spectrometer (b) double beam spectrometer [70]

1.15 Application of Hydrogels on Water Treatment

Hydrogels possess a unique property to absorb metal ions from aqueous solutions. This

property leads to some of the most important applications. The absorption of metal ions by

hydrogels can be calculated by concentration of metal ions in initial and equilibrium phase in

aqueous solution, the volume of hydrogel used and by the weight of hydrogel. Moreover, the

metal absorption is affected by the salt concentration of solution and pH [36].

In recent times, various methods are employed to treat the polluted water by means of

physical and chemical methods e.g. removal of heavy metal ions. Various studies analyzed

the methods of using hydrogels for the removal of heavy metal ions and reported

considerable results [37]. In this study, we will examine the treatment of contaminated water

with heavy metal ions by the use of hydrogels.



Chapter 2

LITERATURE REVIEW

Chapter 2: REVIEW OF LITERATURE


2. REVIEW OF LITERATURE:

Since after the first preparation of hydrogels, it is widely studied and researched and many of

its properties are evaluated.

(Slaughter et al., 2009) studied their properties, methods of preparation, biocompatibility

and their physical characters, they can be used in regenerative medicine [71].

(Gong et al.,2010) revealed another progress for hydrogels is the formation of a double

network gel having a relatively high toughness and strength mainly consisting of two types of

networks with opposite in nature. This double network gel showed some common features

with ductile and brittle nano composite materials e.g. dentins and bones [72].

( Bhattarai et al.,2010) made use of chitosan as a polymeric material in the gel led the

formation of a drug delivery vehicle that releases the payloads in varying stimuli

Furthermore, chitosan possesses the superiority over other polymers being biodegradable,

low toxic and biocompatible substance [73].

(Nguyen et al., 2010) prepared injectable biodegradable copolymer hydrogels which undergo

a sol-gel transition under stimuli of pH and temperature have found uses in biomedical and

pharmaceutical sciences e.g. drug delivery and cell-growth [74].

(Burdick et al., 2010) worked in the field of tissue regeneration, hyaluronic acid derived

hydrogels present a promising effect in tissue repair and regeneration by delivering the cells

and therapeutic agents [75].

(Sun et al.,2012) find out that the hydrogels have uses in various fields from tissue

engineering to drug delivery as a vehicle, from optics and fluidics as actuator to biological

studies as model extracellular metrices However, sometimes their role gets limited due to

their mechanical properties as most of the hydrogels do not show high stretchability like

alginate hydrogels, some are brittle. The gel’s toughness may be attributed to two main

factors i.e. hysteresis by unzipping the network of ionic crosslinks and crack bridging by the

network of covalent crosslinks. In contrast, the crosslinking property of the hydrogel can

preserve its initial state upon unloading and the un-zipped network though can cause damage

but can be re-zipped [76].

(Hennink et al.,2012) used hydrogels as a vehicle for drug delivery, the hydrogel’s strength

can be increased by the use of chemical cross-linkers which can be toxic and may give

unwanted reactions. However, physical cross-linkers may substitute these chemical

compounds) [77].

(Appel et al.,2012) prepared another type supramolecular crosslinkers lead the formation of

novel supramolecular polymeric hydrogels having directional, specific and dynamic non-

covalent interactions which can be the basis for many new discoveries [78].



(Phadke et al.,2012) find out permanently cross-linked hydrogels can be edited or engineered

to make them a self-healing substance in an aqueous environment and this kind of hydrogel

can withstand multiple cycles of self-healing without compromising its mechanical status and

kinetics [79].

(Malda et al.,2013) find out the Biofabrication is the formation of a bio-engineered tissue

made by cells and biomaterials. Cell-laden hydrogels are an important part of this

biofabrication process and also called as “bio-inks” as they have the features of natural extra

cellular matrix and they permit the encapsulation of cells in a hydrated 3D environment [80].

(Sun et al.,2013) studied another type of molecules called the polyampholytes polymers

having some randomly dispersed cationic and anionic repeat groups, have the ability to make

a viscoelastic and tough hydrogels having comparable multiple mechanical properties. This

approach may prove helpful in the formation of a tough hydrogels for further applications

[81]. Incorporation of the nano-particles within the polymeric structure yield out a

nanocomposite having superiority in physical, chemical and biological properties opening out

a field for further research and study [82].

(Gaharwar, et al.,2014) studied Dynamic modulations in the hydrogel structure physically

and chemically lead to changes in its properties which in turn, may open doors of further

research and study [83].

(Lee et al.,2018) recently discovered that hydrogels can take part in deciding the cell fate.

The stress/strain time dependent changes in interaction with cells, the degradation process by

the cell mediation and synthesis of matrix can influence cell status and tissue repairing. This

can be categorized as a biophysical property of hydrogels [84].

(Caliari et al.,2016) determined that the standard cell culture does not play a significant role

in recapitulating native cellular milieus, hydrogels most importantly the commercially

available hydrogel may take part as a cell culture medium due to their unique properties [85].

(Bodenberger et al.,2016) found that by biofabrication of hydrogels, their structure can be

manipulated i.e. creation of a pore in structure of the hydrogel may alter the physicochemical

properties of hydrogel a bit and cancer cell lines were seen adhered to the wall of the pore

[86].

(Li et al.,2016) working in the field of pharmaceutical manufacturing found that the

hydrogels play a significant role as drug delivery, release time, degradation and dissolution

when employed with drug dosage form. In this way, hydrogels have the ability to carry out

the spatial and temporal control over the drug whether macromolecular of having small

molecules in its formation [87]. Apart from the hydrogel structure manipulating, 3D printing,

double network cross-linking and drug release development, hydrogels can be used as a

cartilage repair.

(Vega et al.,2017) studied the hydrogels structure with respective mechanical properties can

be supplemented within the cartilage structure that may improve its quality and strength [88].



(Perale et al.,2011) developed a technique in which the biomaterial is injected to the site of

injury which carries the cells or drugs and delivers it at the site of injury. Among these

biomaterials, synthetic, natural or composite hydrogels are considered as a reasonable

substance which swells when comes in contact with water. These hydrogels may improve the

healing process of the spinal cord injury [89].

(Kornev et al.,2018) studied in biomedical sciences, hydrogels may possess the ability to

repair or replace the damaged brain cell inside the brain. These 3D structures can act as a

promising tool for regeneration of brain tissues due to their biological, physical and chemical

properties. Hydrogels prepared from different polymers i.e. hyaluronic acid, chitosan,

alginate, collagen type I, methylcellulose, fibrin, gellan gum, Matrigel, proteins and self-

assembling peptides, poly(ethylene glycol), methacrylamides and methacrylates are

implemented in recent brain injury studies. And among them, self-assembling peptide and

collagen I based hydrogels showed an attractive properties for neuroregeration [90].

(Kirshner et al.,2012) employed hydrogels in a bio-sensitive system by embedding a thin,

pH-responsive hydrogel within the sensor in which it can sensed a tiny change in pH by

triggering the pressure sensor due to its swelling properties. So as with volume changes, the

hydrogel was tuned to sense volume changes in response to pathological pH values [91].

(Gao et al.,2016) In another study, nanoparticle-hydrogel system was employed for drug

delivery and called it “NP-gel”. This NP-gel showed a promising response in drug delivery

(passively-controlled, stimuli-responsive, site specific) and detoxification. Integration of

therapeutic nano-particles with hydrogels makes a hybrid biomaterial system that extensively

affected the localized delivery of drug [92].

(Gao et al.,2016) did modification of naturally occurring extracellular matrix

glycosaminoglycan hyaluronic acid (HA) was studied in a recent study so that it may release

photo-crosslinkable hydrogels having an increased long-term stability and mechanical

stiffness with little or no decrease in cytocompatibility. These tailor-made methacrylated

hyaluronic acid (MeHA) gels proved useful for bone tissue engineering and 3D bioprinting

within a narrow window of concentration [93].

(Gao et al.,2015) Employed hydrogels to recycle rare earth metals. The immobilized gel

particles were formed by doping poly-γ-glutamate (PGA) and sodium alginate (SA). This

composition showed an excellent capacity in the absorption of rare earth metals. By applying

different techniques like Scanning electron microscopy (SEM) and Fourier transform infrared

(FT-IR) spectroscopy, it was revealed that carboxyl group in the composite played a major

role in absorbing and recycling the rare earth metals from waste water [94].

(Lau et al.,2015) Formation of a multicompartment hydrogels having unique properties

imparted its role in biomaterials with desired properties. This multicompartment system with

engineered enhanced mechanical properties presented multiple biological properties and

implemented its role in tissue engineering, cancer and gene therapy [95].



(Lauren et al.,2017) In another study in biomedical sciences, the surgical sutures were

employed with nanofibrillar cellulose-alginate (NFCA) in rats and mice tissues. Adding 8%

sodium alginate in NCFA hydrogel system increased its viscosity and coating strength. The

study showed that these NFCA coated sutures presented as a useful tool in cell-based therapy

and in treatment after the surgery [96].

(Pérez-Luna et al.,2018) studied the cross-linked nature of hydrogels is not only suitable for

the delivery of proteins at the site of action, but they can be used to encapsulate the cells with

therapeutic drugs. They can form a system for the controlled release of drugs from the

encapsulated cells thus making them a really helpful and easy way in combating the disease

[97].



Chapter 3

MATERIALS AND METHODS

Chapter 3: MATERIALS AND METHODS


3. Materials and Methods

The Commercially available powders of Potato starch (laboratory grade), Amylum starch

(laboratory grade with no further purification) and sodium salt of Carboxymethyl cellulose

were purchased from scientific store located in Lahore, Pakistan (average molecular

weight=90000) (DS = 0.7). The Carboxymethylcellulose along with these starches was used

for the synthesis of superabsorbent polymers (SAP) [118]. To crosslink the polymer complex,

Aluminum sulfate octadecahydrate (reagent grade) was also used [119].

3.1 Method

3.1.1 Preparation of Superabsorbent Polymer (SAP)

By using a magnetic stirrer in a large beaker, about 20g of sodium salt of Carboxymethyl

cellulose was mixed with distilled water (2.0L). Soon after the mixing, these two starch types

(1.2g) were subjected to gelatinization at 80°C in distilled water (50ml) for 45 min. In CMC

solution, previously gelatinized starch was added and they were allowed to mix for 1hour.

Aluminum sulfate in some variable amounts was then introduced in to the beaker for another

30 minutes and the whole mixture was allowed to mix thoroughly. The whole solution was

placed on Teflon baking pans and dried at 70°C till the formation of a film. With the help of a

blender and pestle mortar, the film was shredded and grinded into a powder respectively

[120-121]. Soon after the addition of more than 2.3% of Aluminium sulfate, the polymer

exhibited an over-crosslinked complex. The resulting complex develops into a structure

carrying a lot of connections rendering too small voids for optimal water absorbency [122].

3.1.2 Preparation of Modified Starch (MS)

Native potato starch, hydrochloric acid 37 %, ethanol and sodium hydroxide were purchased

from Merck. All other chemicals were of analytical grade and used without further

purification. Distilled water was used throughout the work. The granular cold water-soluble

starch was prepared following the method of Chen and Jane (1994a) with slight

modifications. 10g starch was suspended in 40 g ethanol (40 %) at two different temperatures

(25 and 35 °C) and stirred mechanically for 10 min. This was followed by adding 12 g NaOH

(3 M on the solvent basis) at rate of 4 g/min. The suspension was gently stirred for 15 min;

afterwards an additional 40 g ethanol (40 %) was added slowly and stirred for another 10

min. The slurry was left at room temperature (25 °C) for 30 min in order to give sufficient

time for the treated starch to settle down. The settled granules were washed with fresh ethanol

solution (40 %), neutralized with 3MHCl in absolute ethanol, and then washed with 60 % and

95 % ethanol solutions. The obtained starch was dehydrated with absolute ethanol, and

finally oven-dried at 80 °C for 3 h.



3.1.3 Preparation of Modified Strach based Superabsorbent Polymer (MSAP)

Carboxymethyl cellulose sodium salt (20 g) was mixed with 2.0 L of distilled water in a

large beaker using a magnetic stirrer. Modified starch (2.4g) was gelatinized in 50 mL of

distilled water at 80°C for 45 min. The gelatinized starch was added to the CMC solution and

allowed to mix for 1 h. Then varying amounts of aluminum sulfate were added to the beaker

and the solution was allowed to mix for another 30 min. The solution was then spread on

Teflon baking pans and dried at 70°C until a film is formed. The film was shredded with a

blender and then ground into a powder with a mortar and pestle [120-121]. The addition of

more than 2.3% of Aluminium sulfate, it was observed that polymer was over-crosslinked

and the complex had too many connections making the void spaces too small for optimal

water absorbency [122].

3.2 Characterizations

3.2.1 Flow-ability Parameters of SAP

3.2.1.1 Angle of Repose.

Fixed funnel method was used to find out angle of repose for the purpose of studying

the flow property of hydrogel [123]. Through a fixed funnel placed previously on a graph

paper, hydrogel (powdered) was then allowed to fall. Angle of repose (θ) was calculated by

the following equation;

h

Tanr

(1)

h=height of heap

r=radius of heap

3.2.1.2 Bulk and Tap Density.

By the placement of the hydrogel (1.0 g) in graduated cylinder, we can measure the volume

of hydrogel Vb. The tapped volume (Vt) was noted after tapping 100 times the graduated

cylinder. Tap density (Dt) and Bulk density (Db) were calculated by using equations (2) and

(3) respectively;

( )

t

t

WeightofHydrogelD

VolumeofHydrogel V (2)

( )

b

b

WeightofHydrogelD

VolumeofHydrogel V (3)



3.2.1.3 Hausner Ratio and Carr’s Index.

The specific hydrogel’s flow properties can be determined by means of Hausner ratio and

Carr’s index [123]. “Hausner ratio is the ratio of tap density to bulk density” as mentioned in

equation (4);

( ) t

b

DHausnerratio h

D (4)

“Carr’s index is the percentage ratio which represents arrangement of particles” and it can be

measured by using the equation (5);

'sin ( ) 100 (1 )t

b

DCarr dex C

D (5)

Where Db and Dt are bulk and tap densities, respectively.

3.2.1.4 Moisture Content.

Before and after drying, the weight of hydrogel was calculated at 105 °C (1 hour).

3.2.1.5 Centrifuge Retention Capacity.

“Water retention capacity is the ratio of wet sediment mass to dried mass”. Centrifuge

retention capacity or water retention capacity was measured by centrifuging the freshly

prepared solution of hydrogel (1% w/w) at 4500 rpm (30 min) in deionized water at 25ºC.

Weight of wet paste was measured after decanting the supernatant. Weight of the dried mass

was checked after completely drying the paste at 70°C [124-125].

3.2.1.6 Swelling Capacity.

The tapped volume was measured by tapping the graduated cylinder 100 times in which the

powdered hydrogel (1.0g) was placed. Then, in de-ionized water, hydrogel was mixed

thoroughly and the volume was adjusted to 100 cm3. After keeping for 24 hours of these

swollen hydrogel’s sediment, its volume was observed and Swelling Capacity(v/v) was

calculated by using equation (6);

SwellingCapacity(v/ v)SwollenVolume

TappedVolume (6)

3.2.1.7 Dynamic and Equilibrium Swelling.

In order to find out the pH dependent swelling, SAP (0.1 g each) were placed in the

bags of cellophane which were soaked into phosphate buffers (pH 6.8 and 7.4), HCl buffer

(pH 1.2) and deionized water for 24 hours. The weights of these swollen hydrogels were



checked after regular intervals for 24 hours. The swelling capacity (g/g) in each case was

calculated as;

( / ) t O c

O

W W WSwellingCapacity g g

W

(7)

Wt = weight of swollen hydrogel (with wet cellophane bag)

W0= weight of dry hydrogel

Wc= weight of wet cellophane bag

The normalized degree of swelling (Qt) is a ratio between media (buffers of pH 1.2, 6.8, 7.4

and de-ionized water) penetrated into gel and initial weight of hydrogel at time t as given in

equation (8).

s d tt

d d

W W WQ

W W

(8)

Ws =weight of swollen hydrogel at time t

Wd =weight of dried hydrogel at time t=0

Wt =weight of water penetrated into hydrogel at time t.

Qe =(Normalized equilibrium degree of swelling) is the ratio of media penetrated into

hydrogel

at t∞ to weight of dried hydrogel at t=0. It can be calculated by equation (9);

d ee

d d

W W WQ

W W

(9)

W∞=weight of swollen hydrogel at time t∞ (swelling remains constant)

Wd =weight of dried hydrogel (t=0)

We =amount of water absorbed by hydrogel (t∞)

3.2.1.8 Swelling Kinetics.

To find out the kinetic order of swelling, normalized degree of swelling (Qt) and normalized

equilibrium degree of swelling (Qe) values can be used [126]. The second order kinetics

equation (10) can be calculated by using the following equation [127].

2

1

t ee

t t

Q KQ Q (10)

3.2.1.9 The Swelling and De-swelling Behavior in Response to External Stimuli.

SAP has ability to show swelling and de swelling in different aqueous and non-aqueous

media. The Gravimetric method was employed for its analysis.



1. The swelling of hydrogel was observed while keeping its cellophane bag (0.1g) in

deionized water, allowed to stand for 1hour and its weight was measured . Then by

placing it in pure ethanol for 1 hour, its weight was again measured as a function of its

de-swelling time.

2. By using buffer solutions (pH 7.4 and 1.2), the swelling & de-swelling behaviors were

studied in another experiment. The swelling was observed by keeping its cellophane

bag (0.1g) in a buffer (pH 7.4) for 1 hour and after that its de-swelling was observed

by keeping in another buffer solution (pH 1.2) for one more hour.

3. As above mentioned, the swelling and de-swelling behavior was also observed in

water and aqueous NaCl solution (0.9%).

As decrease in the osmotic pressure occurs due to addition of salt between hydrogel and

water, similar phenomenon happens in the present case and the swelling decreases and vice

versa. In other words de-swelling occurs due to the fact that water molecules moves out of

hydrogel rendering it flaccid [128-129].

3.2.2 Scanning Electron Microscopy (SEM)

The internal structure and superficial morphology of SAP was analyzed by a 10 kV operating

scanning electron microscope (NanoSEM 450, FEI Nova). In deionized water (2ml), dried

hydrogel (0.1 g) was allowed to mix by mixer mill. This mixture was subjected to sonication

for 30 min in order to remove air bubbles from it. Then, resulting swollen SAP was placed at

-20°C, allowing it to get frozen and was subjected to freeze-drying. Moreover, sharp blade

was used to get the cross-sections of hydrogel transversely and vertically to reveal its porous

nature.

3.2.3 FTIR Analysis

Fourier transform infrared spectroscopy (FT-IR, KBr, 4000–400 cm−1) was performed on

Carboxymethyl cellulose Sodium (CMC.Na), Potato, Amylum starches, and SAP by using an

IR-Prestige-21instrument (Shimadzu, Japan). The obtained spectra by FT-IR were measured.

3.2.4 PXRD Analysis

Powdered X-ray Diffractrometry of all four samples was performed under the given

conditions.

Table 3.1: Conditions for PXRD Analysis for all six Samples

Anode material Cu

Generator voltage 40

Tube current 40

Monochromator used NO



K-Alpha1 wavelength 1.540598

K-Alpha2 wavelength 1.544426

Ratio K-Alpha2/K-Alpha 0.5

File date and time 13-08-18 12:42

h k l 0 0 0

Scan type CONTINUOUS

Scan axis Gonio

Scan range 20-80

Scan step size 0.02

No. of points 3000

Phi 0

Time per step 0.2

3.2.5 Thermogravimetric Analysis (TGA)

Thermogravimetric Analysis (TGA) was performed on all four samples i.e Carboxymethyl

cellulose Sodium (CMC.Na), Potato, Amylum starches, and SAP. On the basis of results

obtained from the above said method, the maximum and final thermal decomposition

temperatures were investigated. The obtained data was analyzed by using Universal Analysis

2000 and Microsoft Excel 2010 software.

3.3 Applications of Hydrogels on Water Treatment

The novel gel was then used in dried form for removal of metal ions from their standard

solutions, for this purpose Atomic Absorption Spectrophotometer was used.

3.3.1 Atomic Absorption Spectroscopy

To get the optimized amount, the 10, 20, 40, 60,80 and 100 mg of SAP was used to add in

100 mg/L solutions of Cd+2 , Pb+2,Fe+2 and then stirred at the temperature of 298K, at the rate

of 130r/min for 30 minutes. The samples were analyzed on “Flame Atomic Absorption

Spectrophotometer; Shimadzu AA-7000F”. All values of metal analysis were recorded in

parts per million (ppm: mg/L). For calibration curve, four standards i.e. 0.5, 1.0, 2.0 and

4.0ppm were also used. To study the adsorption behavior, two empirical adsorption models

named Freundlich and Langmuir models were used. The obtained experimental data at pH 7



was analyzed by applying Freundlich and Langmuir equations. The Freundlich and Langmuir

isotherms are given by eq. (10) and (11), respectively:

KF= Freundlich constants related to adsorption capacity

N = Freundlich constants related to intensity

Ce =equilibrium concentration of metal ion in the solution.

Ce/Qe = Ce/Qmax + 1/bQmax (11)

Qmax and b = Langmuir constants related to maximum monolayer adsorption capacity and

adsorption energy

3.3.2 The Aims and Objectives of Study

A hydrogel can be defined specifically as a substance consists of hydrophilic polymers

arranged in a three-dimensional pattern to form a network. The wide range of applications of

a hydrogel is attributed to its ability to absorb a large amount of water by swelling up and

keeping its structure retained. It is all due to its cross-linked structure with solutions or water

molecules and this fact was reported firstly by Lím and Wichterle in 1960 [98]. A hydrogel

normally contains 10% water of its weight. The hydrogels possess relatively high grade

flexibility because of their high water contents like natural tissues. Moreover, hydrogels may

show a hydrophilic property because of the presence of some hydrophilic groups (-COOH, -

NH2, -OH, -CONH2 and SO3H [98]. On the basis of their flow behavior, they can be

categorized into weak and strong hydrogels [99]. Because of the wide range of their

applications , they’re also used in the food industry i.e. some edible gels are used as gelling

polysaccharides at a large scale [100]. In short, the term hydrogel may be described as a

structure of three-dimensional network with cross-linked molecules. Irrespective of their

source, either obtained from synthetic or natural class of polymers, they contain similar a

property of swelling up by absorbing a significant amount of water [101].

Heavy metal pollution is considered as one of the serious environmental hazards not

only for human beings but also for all living organisms due to its toxic and carcinogenic

effects. In recent years, the methods like ion exchange, chemical precipitation, membranous

separation and adsorption have been employed to reduce such a type of environmental

pollution. Due to its economic and technical applications among all the above discussed

methods, the most reliable choice to reduce this type of pollution is the method of adsorption.

[102-103].

Human activities like mining, smelting, alloy manufacturing, textile operations, use of

pesticides, fertilizers, electronics and paint industry, resultantly cause Cadmium(Cd2+)

Iron(Fe2+) and lead(Pb2+) to accumulate these highly toxic environmental pollutants in the

ground water reservoirs[104-105]. Almost all these above mentioned activities can also result

in accumulation of heavy metals in environment and ultimately these metals penetrate in the

living tissues and become a part of food chain [106]. High levels of these metal ions in



human body can lead to some serious and major problems i.e. cancer [107-108], kidney

dysfunction, prostate carcinogenesis[109], multiple bone fractures, hypertension [110] and

weight loss [111]. Some cellulosic materials such as agriculture waste [112-113] and

carboxylated cellulose nano-crystals [114], fruit peels and plant barks[115] (low-cost

sorbents) are reported to depict a relatively high capability for metal binding and removal of

heavy metal ions and they can be considered useful as they are abundant and renewable

sources in nature. In view of above described hazards, there arises an increased need of an

efficient method with a high and defined sorption capacity with a specific type of functional

group preferably. Among all the renewable biopolymers occurring naturally, cellulose

possesses some modifiable hydroxyl groups [116]. By modifying these hydroxyl groups and

grafting the polysaccharides on the resulting carboxylate group, the exchange of cations in

aqueous solutions can be made possible [117].

Therefore, by chemically modifying the substances containing cellulose/

polysaccharide structures, we can enhance its ability to uptake of metal ions from the

solution. Synthesis of a super-absorbent hydrogel by commercially available low cost

polysaccharide, i.e. Carboxymethylcellulose, combined with other starch, i.e. Potato and

Amylum starch was studied extensively in the following described experiments. Moreover,

the cross-linked polymer complexes (CMC) associated with aluminum ions by non-

permanent chemical bonds were also studied, when further observed in the presence of water,

which showed their swelling behavior. These cross-linked starch and CMC can create an

environment friendly biopolymer based SAP which may help to reduce the hazardous metal

ions from human consumption substances [117].



Chapter 4

RESULTS AND DISCUSSION

CHAPTER 4: RESULT AND DISCUSSION


4. Results and Discussion

The Novel gel was investigated and characterized by

1. Analysis of its Physical Properties

2. Swelling Behavior on the basis of changes in pH temperature and medium with time laps

3. FTIR (Fourier Transform Infared Spectroscopy)

4. SEM (Scanning Electron Microscopy)

5. TGA (Thermogravimeteric Analysis)

6. PXRD (Powdered X-ray Difractrometery)

4.1Physical Properties of SAP

The physical properties of hydrogel are as follow;

Table 4.1: Phyical Properties of SAP

Moisture content (%) 20 ± 0.20

Average particle size (μm) ≈228

Angle of repose 3± 0.25

Bulk density (g/cm3) 0.8 ± 0.01

Tapped density (g/cm3) 0.66 ± 0.01

Carr’s index (%) 17.5 ±1.50

Hausner ratio .825 ± 0.06

Swelling capacity on 24 h (g/g) 37.33±2.00

Centrifuge retention capacity

(%) 70 ± 1.11

Table 4.1and 4.2 reflects different parameters obtained from physical study of prepared hydrogel

(SAP) and (MSAP). These results were obtained by grinding the completely dried gel with pistal

and mortar and by passing through sieve of 0.5 mesh.

Table 4.2: Physical Properties of MSAP

Moisture content (%) 19 ± 0.20

Average particle size (μm) ≈172



Angle of response 2.6± 0.25

Bulk density (g/cm3)

Tapped density (g/cm3) 0.66 ± 0.01

Carr’s index (%) 17.5 ±1.50

Hausner ratio .825 ± 0.06

Swelling capacity on 24 h (g/g) 35.2±2.00

Centrifuge retention capacity (%) 66 ± 1.11

Hausner ratio, Carr’s index and angle of repose are indicative of poor flow property of powdered

SAP and MSAP.



4.2 Swelling behavior of Hydrogels and its Ingredients

4.2.1 Swelling Behavior of Potato Starch

a:Swelling Behavior at 30oC b:Swelling Behavior at 37OC

c:Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8

e: Swelling Behavior at pH 7.4

y = 0.0029x + 0.2141R² = 0.4655

0

0.05

0.1

0.15

0.2

0.25

0.3

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swal

low

ing

(g)

Time (min)

y = 0.0029x + 0.2141R² = 0.4655

0

0.05

0.1

0.15

0.2

0.25

0.3

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0403x + 1.1637R² = 0.7354

0

0.5

1

1.5

2

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0296x + 0.7367R² = 0.6925

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.09x + 0.532R² = 0.8056

0

0.5

1

1.5

2

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)



4.2.2 Swelling Behavior of Amylum Starch

a:Swelling Behavior at pH 30OC b:Swelling Behavior at pH 37oC



y = 0.0144x + 0.2323R² = 0.6428

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0573x + 1.247R² = 0.6709

0

0.5

1

1.5

2

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0244x + 0.2323R² = 0.5807

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0571x + 0.7037R² = 0.8863

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0988x + 0.524R² = 0.6476

0

0.5

1

1.5

2

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)



4.2.3 Swelling Behavior of Carboxymethyl cellulose

a:Swelling Behavior at 30oC b:Swelling Behavior at 37oC


e:Swelling Behavior at pH 7.4

y = 0.0822x + 0.544R² = 0.8791

0

0.5

1

1.5

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.1082x + 0.2883R² = 0.8605

0

0.5

1

1.5

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0373x + 0.354R² = 0.6586

0

0.2

0.4

0.6

0.8

1

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0434x + 0.4273R² = 0.7239

0

0.2

0.4

0.6

0.8

1

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0741x + 0.6597R² = 0.8181

0

0.5

1

1.5

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)



4.2.4 Swelling Behavior of Modified Starch




y = 0.0324x + 0.3953R² = 0.5864

0

0.2

0.4

0.6

0.8

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0343x + 0.672R² = 0.5716

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0773x + 0.74R² = 0.8316

0

0.5

1

1.5

2

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0243x + 0.5567R² = 0.8034

0

0.2

0.4

0.6

0.8

1

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0252x + 0.1683R² = 0.9236

0

0.1

0.2

0.3

0.4

0.5

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)



4.2.5 Swelling Behavior of SAP


c: Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8


y = 0.0296x + 0.4817R² = 0.6983

0

0.2

0.4

0.6

0.8

1

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0645x + 0.833R² = 0.7508

0

0.5

1

1.5

2

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0506x + 0.7757R² = 0.779

0

0.5

1

1.5

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0449x + 0.4423R² = 0.8361

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0277x + 0.3413R² = 0.8146

0

0.2

0.4

0.6

0.8

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)



4.2.6 Swelling Behavior of MSAP



e:Swelling Behavior at pH 7.4

y = 0.0327x + 0.2483R² = 0.9607

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0428x + 0.5647R² = 0.5297

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0182x + 0.2133R² = 0.8754

0

0.1

0.2

0.3

0.4

0.5

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0378x + 0.26R² = 0.8412

0

0.2

0.4

0.6

0.8

0 5 10 15Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)

y = 0.0193x + 0.1467R² = 0.8179

0

0.1

0.2

0.3

0.4

0.5

0 5 10 15

Wei

ght

of

Sam

ple

aft

er

swel

low

ing

(g)

Time (min)



4.3. pH Responsive Swelling of Hydrogels

4.3.1 pH Responsive Swelling of SAP

Buffers of pH 1.2, 6.8 and 7.4 were made according to the pH values of stomach, and the

different parts of intestine, to check the swelling behavior of SAP upon them. The swelling

behavior of hydrogel in deionized water was found to be more as compared to acidic and basic

buffers(pH 1.2, 6.8, 7.4). We can infer that it may be due to the protonation of carboxylic groups,

located at the terminal ends of polymer chains. The capability of anion formation of carboxylic

acid increases as the pH rises in contrast with the alkaline media. Moreover in basic buffers,

there appeared a relatively low swelling capacity in comparison to its behavior in deionized

water. In alkaline media, the screening effect of excess cations may be responsible for this

relatively low swelling capacity which stops the anion-anion repulsions due to carboxylate

anion’s shielding effect. According to the literature, many other hydrogels’s water absorbent

property depend upon their pH values. [128-129].As explained by 2nd order kinetic mode, the

pH dependent swelling of hydrogel is controlled by the relaxation of polymer chain and diffusion

of solvent [36].

Figure 4.1(a): Swelling data of SAP obtained in water and buffers of pH 1.2, 6.8 and 7.4

On the basis of data obtained from swelling study it depicts the property of prepared hydrogel to

show more swelling behavior more in basic rather than acidic medium, i.e at pH 7.4 and 6.8.

The kinetic study that was performed on data obtained by the swelling behavior of SAP shown in

buffers of pH 6.8 and 7.4 and in deionized water is given below;

0

1

2

3

4

5

6

7

0 200 400 600 800 1000 1200

We

igh

t (g

)

Time (min)

water

pH 2.1

pH 6.8



The swelling behavior of hydrogel in deionized water was found to be more as compared to

acidic and basic buffers(pH 1.2, 6.8, 7.4).

Fig. 4.1(b): Swelling data and kinetics of SAP obtained in buffers of pH 6.8 and 7.4

From the swelling data, the values of Qt (mg/g) and t/Qt (min/(mg/g)) were finded out, and were

plotted against the time(min).

Figure 4.1(c): Swelling data of SAP between time (min) and Qt(mg/g) obtained in water and

buffers of pH 1.2, 6.8 and 7.4

The swelling behavior of hydrogel in deionized water was found to be less as compared to

basic buffers(pH 6.8, 7.4) and more than acidic one (pH 2.1).

0

1

2

3

4

5

6

7

0 200 400 600 800 1000 1200

We

igh

t (g

)

Time (min)

pH 6.8

pH 7.4

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200

Qt(

mg/

g)

Time (min)

Qt (Water)

Qt (Ph 2.1)

Qt (Ph 6.8)



Figure 4.1(d): Swelling data of SAP between time(min) and t/Qt(min(mg/g)) obtained in

water and buffers of pH 1.2, 6.8 and 7.4

In practical applications, a higher swelling rate is required as well as a higher swelling capacity.

The swelling kinetics for the absorbents is significantly influenced by factors such as swelling

capacity, size distribution of powder particles, specific size area, and composition of polymer.

4.3.2 pH Responsive Swelling of MSAP

The kinetic studies were performed on swelling data of Modified starch based SAP obtained in

water and at pH 6.8 and 7.4. Fig.1(a) and (b)

0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000 1200

t/Q

t(m

in/(

mg/

g))

Time (min)

t/Qt (Water)

t/Qt (Ph 2.1)

t/Q (Ph 6.8)

t/Qt (Ph 7.4)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 200 400 600 800 1000 1200

We

igh

t (g

)

Time (min)

water

pH 2.1

pH 6.8

pH 7.4



Figure 4.2(a): Swelling data of MSAP obtained in water and buffers(1.2,6.8 and 7.4)

It has been observed that the swelling behavior of MSAP hydrogel was more in basic buffers

(pH6.8, 7.4) than in acidic buffer (pH 2.1).

Fig. 4.2(b): Swelling data and kinetics of MSAP obtained in buffers(6.8 and 7.4)

. The swelling behavior of MSAP hydrogel in deionized water was found to be less as compared

to acidic and basic buffers(pH 1.2, 6.8, 7.4).

Fig 4.2(c): Kinetic Studies of MSAP between time(min) and Qt (mg/g) at different pH

0

1

2

3

4

5

0 200 400 600 800 1000 1200

We

igh

t (g

)

Time (min)

pH 6.8

pH 7.4

0

5

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1000 1200

Qt

(mg/

g)

Time (min)

Qt (Water)

Qt (pH 2.1)

Qt (pH 6.8)

Qt (pH 7.4)



Fig 4.2(d): Kinetic Studies of MSAP between time(min) and t/Qt (mg/g) at different pH

When the graph was plotted against time and t/Qt (min/mg/g) it was found to be opposite as

compared to time versus weight.i e distilled water has heighest values than those of all buffers.

4.4 Swelling and De-swelling Kinetics in Response to External Stimuli

4.4.1 Swelling and De-swelling Behavior of SAP in Water and Ethanol

Due to the less affinity of ethanol with hydrogel than water, the hydrogels usually de-swells

rapidly in ethanol (Fig. 2). In contrast, the dielectric constant (24.55) and a low polarity of

ethanol than that of water (80.40) are responsible for formation of hydrogen bonding to a lesser

extent with ethanol. Moreover, a less dielectric constant causes a drop in swelling capacity i.e.

de-swelling of the polymer and ionization of ionizable groups.

Fig 4.3(a): The Swelling and de swelling of SAP in aqueous and ethanol media

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200

t/Q

t (m

in/m

g/g)

Time (min)

t/Qt (water)

t/Qt (pH 2.1)

t/Qt (pH 6.8)

t/Qt (pH 7.4)

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350 400

We

igh

t (g

)

Time (min)



Once the SAP swells by keeping in distilled water, by immersing the gel bag in ethanol

suddenly washes out all the water molecules when observed by weighing it after regular

intervals. The swelling of hydrogel after placing it again in water is probably due to the result of

extensive hydrogen bonding with water and a swift wash out of ethanol molecules.

Fig 4.3(b): The Swelling and de swelling of MSAP in aqueous and ethanol media

The same phenomena of swift wash out of water molecules happens on immersing MSAP

hydrogel in absolute ethanol as discussed earlier.

4.4.2 Swelling and De-swelling Behaviour of SAP in Acidic and Basic Buffers

By using different types of buffers, swelling and de-swelling behavior of hydrogel in acidic and

basic media was evaluated. According to the observations, SAP swells in basic buffer (pH 7.4)

whereas a de-swelling behavior was shown by the hydrogel in acidic buffer (pH 1.2). This

swelling and de-swelling behavior of SAP was observed four times and the measurements of

these experiments (off and on) were recorded in form of a graph as shown in Fig.

Fig. 4.4(a): Swelling and de-swelling behavior of SAP in basic and acidic buffers.

0

0.5

1

1.5

2

2.5

3

3.5

4

0 50 100 150 200 250 300 350 400

We

igh

t (g

)

Time(min)

0

1

2

3

4

5

6

0 100 200 300 400

We

igh

t (g

)

Time (min)



Fig. 4.4(b): Swelling-deswelling behavior of MSAP in basic and acidic buffers.

Maximum swelling (99 g/g) was obtained at pH 8. In the pH region from 1 to 3, most

carboxylate groups were in the form of OCOOH, and the low swelling values of the hydrogels

could be attributed to the presence of nonionic hydrophilic COOH and OOH groups in the

hydrogel network. The swelling ratio increased rapidly as the pH of the solutions was increased

from 4 to 8. At higher pHs (4–8), some carboxylate groups were ionized, and the electrostatic

repulsion between COOH groups caused an enhancement of the swelling

capacity. The reason for the swelling loss of the highly basic solutions (pH 8) was the charge-

screening effect of excess Na in the swelling media, which shielded the carboxylate anions and

prevented effective anion–anion repulsion. Similar swelling pH dependence has been reported

for other hydrogel systems.

4.4.3 Swelling and De-swelling Behavior of SAP in NaCl Solution and Deionized Water

By immersing SAP in water and Sodium Chloride (0.9%) solution, the swelling and de-swelling

of SAP was observed respectively. Generally, the swelling ability of anionic hydrogels in various

salt solutions is appreciably decreased in comparison with the swelling values in distilled water.

This well-known undesired swelling loss is often attributed to a charge-screening effect of the

additional cations causing a nonperfect anion–anion electrostatic repulsion. Therefore, according

to the Donnan membrane equilibrium theory, the osmotic pressure resulting from the mobile ion

concentration difference between the gel and aqueous phases decreased, and consequently, the

absorbency decreased. In addition, in the case of salt solutions with multivalent cations,

ionic crosslinking at the surfaces of the particles caused an appreciable reduction in the swelling

capacity.

0

1

2

3

4

5

0 50 100 150 200 250 300 350 400

We

igh

t(g)

Time(min)



Fig. 4.5(a): Swelling-deswelling behaviour of SAP in deionized water and 0.9% NaCl

solution

Fig. 4.5(b): Swelling-deswelling behaviour of MSAP in deionized water and 0.9% NaCl

When studied at regular intervals, SAP shows a swelling behavior in de-ionized water while

shrinkage observed in the solution of NaCl (Fig. 4). Among hydrogel and water, the addition of

salt causes a decrease in osmotic pressure making the water molecules moved out of hydrogel

render it to shrink was measured in various salt solutions (Figs. 4.5(a) 4.5(b))

4.5 Scanning Electron Microscopy (SEM).

In order to study the surface morphology and porosity of a dried SAP, Scanning electron

microscopy (SEM) was used. The presence of interconnected macropores were confirmed by the

SEM photographs of transversely cut cross sections of a hydrogel (Fig. 5) ranging the size of 228

μm. When analyzed by SEM, the longitudinal cross sections of hydrogel, an inter-connected

network of macropores were also observed in the form of macroporous tubes, through which the

transfer of solvents and water takes place. By this investigation, we can expect, that SAP may be

used for water treatment, diapers, cosmetics, pharmaceuticals and controlled drug release.

0

1

2

3

4

5

6

7

0 100 200 300 400

We

igh

t (g

)

Time (min)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 100 200 300 400

We

igh

t (g

)

Time(min)



4.5.1 SEM Micrographs of Potato Starch

Image 4.1(a,b,c,d): SEM images of Potato Starch

Fig shows the micrographs of little granules of potato starch, partially soluble in water having

capability of gel formation along with CMC in presence of a crosslinking agent .some r small

enough with 225nm while some particles r large with 600nm.

4.5.2 SEM Micrographs of Amylum Starch



Image 4.2(a,b,c,d): SEM images of Amylum Starch

Fig shows the micrographs of hexagonal granules of Amylum starch, partially soluble in water

with multiple surfaces for water interaction having capability of gel formation along with CMC

in presence of a crosslinking agent .some r small enough with 190nm while some particles r

large with 400nm.

4.5.3 SEM Micrographs of Carboxymethyl Cellulose

Image 4.3(a,b,c,d): SEM images of Carboxymethyl cellulose



The micrographs of CMC.Na shows a rough irregular surface and amorphous nature with

10micrometer to 1 micrometer resolution of electron microscope.

4.5.4 SEM Micrographs of SAP

Image 4.4(a,b,c,d): SEM images of SAP

Scanning electron micrographs of transverse (a) and (b) with average pore size 228 μm at

different magnifications.The fig shows the magnified images of prepared hydrogel, in which

empty spaces between gel folds can be seen clearly. The hydrophilic groups present in the empty

spaces may have an ability to trap the smaller ions e.g. Fe2+, Cd2+, Pb2+.



4.5.5 SEM Micrographs of MSAP

Image 4.5(a,b,c,d): SEM images of MSAP

To reveal the relationship between structure and water-holding capacity of the hydrogels with

different ions , SEM images of the cross-sections of the lyophilized hydrogels (Fig4.5 a,b,c,d)

were observed . The porous structure could be observed in the cross-section surface of both SAP

and MSAP, and the pore size of entry SAP was larger than that of entry MSAP. This indicates

that SAP N=23.5 × 10−3could swell a large amount of water, but its loose structure could also

hold water molecules inside of the gel as compared to the highly developed structure of MSAP

where n= 36.3 × 10−3. In the case of entry 1 whose n=6.4 × 10−3, a porous structure in the cross-

section surface could not be observed, and thus the structure could not retain water inside of the

gel, thereby resulting in the low water absorbency and low water-holding capacities.



4.5.6 SEM Micrographs of Modified Starch

Image 4.6(a,b,c,d): SEM images of Modified starch

Amorphous small granules like structure of modified starch with very small particle size was

observed in micrographs.



4.6 Fourier Transform Infrared Spectroscopy (FTIR)

FTIR was performed on all of the four samples i.e. CMC.Na, Potato and Amylum starches and

SAP respectively.

Fig. 4.6: FTIR Spectra of Potato Starch

The figure shows Infrared Spectrum of cationic potato starch, microwave assisted.3200, 2800,

1572, 1315, 1134, 980, 652 cm-1. For the cationic potato starch, (Figure 3), the broad peak at

3300cm-1 is due to the H2O stretching vibration. The two bands at, 2880cm-1 are due to

antisymmetric and symmetric stretch respectively, and 1134 cm-1 are due to the C–O stretching

vibration. The peak at 1572cm-1 is due to the first overtone of O–H bending or H2O

deformation. The band at 1315 cm-1 is due to CH2, CH deformation. The bands at 980 cm-1 are

due C-OH stretch vibration, and the band at 652cm-1 CH2–O–CH2 correspond at ring mode

stretching vibration.

Fig. 4.7: FTIR Spectra of Amylum Starch

The figure shows Infrared Spectrum of Amylum starch, microwave assisted. 3227, 2890, 1593,

1101, 980, 650 cm-1. For the Amylum starch, the broad peak at 3300cm-1 is due to the H2O

stretching vibration. The two bands at, 2890cm-1 are due to antisymmetric and symmetric

65

2.2

84

98

0.2

9 11

34

.97

13

15

.75

15

72

.94

28

98

.01

32

57

.69

0

20

40

60

80

100

120

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Inte

nsi

ty (

T%)

Wave number (cm-1)

65

0.4

2

98

0.2

9 11

01

.43

11

72

.25

15

93

.44

28

92

.41

32

27

.87

0

20

40

60

80

100

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Inte

nsi

ty (

T%)

Wave number (cm-1)



stretch respectively, and 1101 cm-1 are due to the C–O stretching vibration. The peak at 1593cm-

1 is due to the first overtone of O–H bending or H2O deformation. The bands at 980 cm-1 are due

C-OH stretch vibration, and the band at 650cm-1 CH2–O–CH2 correspond at ring mode

stretching vibration.

Fig. 4.8 : FTIR Spectra of Carboxymethyl cellulose

The figure shows Infrared Spectrum of carboxymethyl cellulose sodium, microwave assisted.

1521, 1177, 489, 386, 273,176 cm-1 .In fingerprint region, bands that show the ether bond in

CMC are 1050 cm-1. The presence of a new and strong absorption band around 1520 cm-1 is

confirms the stretching vibration of the carboxyl group (COO¯) and 1177 cm-1 is assigned to

carboxyl groups as it salts.

Fig. 4.9: FTIR Spectra of SAP

17

6 27

3

38

6

48

9 11

77

15

21

0

20

40

60

80

100

120

0 500 1000 1500 2000

Inte

nsi

ty (

T%)

Wave number (cm-1)

CMC

65

0.4

2

97

0.9

72

15

30

.07

28

12

.28

0

20

40

60

80

100

120

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Inte

nsi

ty (

T%)

Wave number (cm-1)

SAP



Fig. 4.10: Combined FTIR Spectra of Potato, Amylum starches, CMC and SAP

The absorption was observed at 3270 cm-1 (hydroxyl stretch influenced by hydrogen bond), 1569

cm-1 and 1388 cm-1 (carbonyl stretch), 980 cm-1 (b-1,4-glycosidic bond) and 2942 cm-1 and 2838

cm-1 (methylene), which were characteristic absorptions in cellulose and methylcellulose

structures. The obtained FT-IR (KBr), by the analysis of potato, Amylum starches, CMC and

SAP are clearly shown in figures above in order to elaborate the desired modifications.

Fig 4.11: FTIR Analysis of MSAP

The success of the reaction in the FT-IR spectrum of SAP was revealed by an ester carbonyl

distinct signal’s appearance at 2000 cm−1 in spectra of CMC which was the major constituent of

hydrogel, jumps to a relatively higher wavenumber at 2812 cm−1 soon after the formation of its

SAP. It also indicates the absorption of Carbon dioxide at the time of completion of reaction. In

98

0.2

9

28

38

.37

32

76

.33

98

0.2

9

13

88

.43

15

69

.21

32

07

.37

0

20

40

60

80

100

120

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Inte

nsi

ty (

T%)

Wave Number (cm-1)

Potato Strach

Amylum Starch

CMC

SAP

0

20

40

60

80

100

120

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Inte

nsi

ty

Wave number cm-1

CMC

Modified Starch

Hydrogel



addition. The salt formation can be indicated by the absorption of carboxylate ion in the

spectrum from 460 cm−1 of CMC to 464cm-1 of SAP.

Table 4.3: Observed FT-IR bands and their Assignments

Material

v(O

-H)

v(C

-H) A

liphatic

HO

H D

eform

ation

𝛅(O

-H) In

plan

e

𝛅(C

H2 )

𝛅(C

H)

𝛅A

SY

M b

ridged

oxygen

v(C

-O-C

)

V(C

-C) A

rabin

osy

l side

Chain

𝛅A

SY

M (O

ut o

f plan

e 𝛃-

Gly

cosid

ic bond

Poly

mer B

ackbone

Unassig

ned

Potato

Starch

3134,

3560

296

0

164

9

-

142

1

1350

124

0

107

0

-

995,92

3,852

653,

605

1139,

2140

Amylum

Starch

3466,

3487

290

4

164

1

-

142

7

1350,

1338

- -

101

0

952,85

0

651,

553

1132,

2904

Carboxy

methyl

cellulose

3552

288

5

159

7

146

2

- - -

106

6

- 916

648,

590

704

Modified

Starch

3209

287

7

168

1

-

140

9

- - -

100

1

999,93

1,860

661,

559

2175,

1132

SAP

3444,

3361

287

9

160

2

-

142

7

1336 -

106

6

-

985,92

7.879

665,

586

833,6

65

MSAP 3585

288

1

164

5

-

141

7

1327 - -

100

1

912

663,

570

1525

Table 4.3 represents the remarkable peaks of both hydrogels and their ingredients



4.7 PXRD Analysis

Some very clear and sharp diffraction signals can be seen at 28,33,38,45,68,70,74, and 80 in the

CMC’s diffractogram by X-ray diffraction (XRD) method (Figure 4.12-4.17),

Fig.4.12: PXRD Analysis of Potato Starch

Potato starch has its strongest diffraction peak at around 17° 2 θ , relatively medium peaks at

around 5°, 15°, 22°, and 24° 2 θ and a couple of weak peaks scattered around 10° and 19° 2 θ .

The pattern of peaks seen in the diffractogram of potato starch is characteristic of a B-type

crystalline structure.

Fig.4.13: PXRD Analysis of Amylum Starch

Amylum starch has its strongest diffraction peak at around 21° 22 θ , relatively medium peaks at

around 24°, 26°, 27°, and 36° 2 θ and a couple of weak peaks scattered around 17° and 19° 2 θ .

The pattern of peaks seen in the diffractogram of potato starch is characteristic of a B-type

crystalline structure.

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70 80 90

Inte

nsi

ty (

T%)

Diffraction angle ()

0

50

100

150

200

0 10 20 30 40 50 60 70 80 90

Inte

nsi

ty (

T%)

Difraction Angle ()



Fig.4.14: PXRD Analysis of Carboxymethyl cellulose-Sodium

CMC represented two prominent peaks at 2 θ = 30.60° and 36.12°, whereas the crystalline state

of CMC was also evident in its PXRD diffractogram; displaying intense and characteristics

peaks at 2 θ = 20.75, 22.23°, 23.03°, 24.85°, 28° and 34.43.

Fig.4.15: PXRD Analysis of SAP

SAP represented two prominent peaks at 2 θ = 25.33° and 35.07°, whereas the crystalline state of

SAP was also evident in its PXRD diffractogram, displaying intense and characteristics peaks at

2 θ = 21.75, 25.33°, 30.87°, 35.84°, 46.93° and 51.85. which are actually a characteristic of

cellulose. In contrast, these diffraction signals at 28,33,38,45,68,70,74, and 80 were not observed

in the XRD diffractogram of SAP, only some peaks at 38, 67 and 68 were observed i.e. there

may be a distortion in the CMC’s crystallization and an increase in SAP hydrogel’s amorphous

region. Its possible cause may be the chemical crosslinking between the starches, CMC and SAP.

These results indicate a reduction in the crystalline behavior during the gel formation and

resultantly metal ions can easily penetrate into the hydrogel folds. In view of above description,

we can say that the SAP hydrogel beads may have a relatively high tendency for metal ions

absorption.

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90

Inte

nsi

ty (

T%)

Difffraction Angle ()

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70 80 90

Inte

nsi

ty (

T%)

Diffraction angle ()



Fig 4.16: PXRD Analysis of Modified Starch

Modified starch represented two prominent peaks at 2 θ = 31.59° and 42.25°, whereas the

crystalline state of MS was also evident in its PXRD diffractogram; displaying intense and

characteristics peaks at 2 θ= 56.49,66.01, 75.23.

Fig 4.17: PXRD Analysis of MSAP

The maximum intensity of peaks of Potato starch, Amylum, CMC were at 127, 156, 56

respectively while that of SAP was at 128 represents the crosslinking between both starches and

CMC, however, the diffraction peaks have completely vanished in case of SAP. Thus, we can

reasonably assume the reason lying behind i.e. the formation of co-ordination bonds of hydrogel

with the carboxyl groups of CMC and starches.

Carboxymethyl cellulose sodium shows some crystallinity due to hydrogen bonding among its

hydroxyl groups. However, during IPN formation with copolymer, these hydroxyl functional

0

20

40

60

80

100

120

140

0 20 40 60 80 100

Inte

nsi

ty T

%

Diffraction Angle ()

0

10

20

30

40

50

60

0 20 40 60 80 100

Inte

nsi

ty T

%

Diffraction Angle ()



groups forms chemical bond with copolymers (as it was also evident from free carboxyl % and

FTIR analysis) and thus crystalline peaks of diffractogram of carboxymethyl cellulose sodium is

not likely to be present in its IPN with copolymer. XRD of CMC sodium, SAP and MSAP gel is

shown in Fig. From this figure it is observed that CMC sodium shows three crystalline peaks at

14.3◦, 21.3◦ and 37.1.The hydrogel SAP, being amorphous shows no crystalline peak.

However, the crystalline peaks of CMC sodium are absent in its graph i.e. as observed in the

same figure.

4.8 Thermogravimeteric Analysis

The thermal analysis of Potato starch, Amylum Strach, CMC-Na and SAP were recorded for

comparison

Fig.4.18: Overlying graph of thermo-gravimetric (TG) straight line of SAP, indicating

thermal stability of sorbent.

By analyzing the thermal analysis of SAP’s major degradation steps above 200ºC, we can

conclude that the SAP possesses a relatively higher thermal stability as indicated in graph given

below. This increase in thermal stability can be helpful for the purpose of increasing the

sorbent’s shelf-life, suggesting its future use in some commercial applications.

y = 6.5889x + 55.119R² = 0.9812

0

100

200

300

400

500

600

700

-20 0 20 40 60 80 100

Tem

pe

ratu

re (

ºC)

Weight Loss (%)

y = 4.9937x + 77.486R² = 0.9543

0

200

400

600

800

-20 0 20 40 60 80 100 120

Tem

pe

ratu

re D

eg

C

Weight Loss



Fig 4.19: Thermogravimeteric Analysis of Potato Starch

Fig 4.19 shows the thermogravimetric curves of potato starch at different heating rates. These

curves present three primary mass loss parts. The initial temperature of each part was identified

as the critical point in the TG curves. The initial stage is the desiccation, which starts instantly

when the temperature just rises and ends at about 120 °C. The percentage of mass loss in this

part depends on the moisture content of the starch samples. The second stage is the main

degradation stage, which finishes at around 400 °C. Pyrolysis of starches in this step has been

reported to release water, carbon dioxide, carbon monoxide, acetaldehyde, furan, and 2-methyl

furan. Thermal decomposition has usually been regarded as the important process associated

with the degradation mechanisms of starches. The degradation of amylose and amylopectin

happened in this step. The last step ends with the formation of carbon black between 300 and 600

°C. The foremost degradation temperatures were 60, 65, 76, and 80 °C at heating rates of 5, 10,

15, and 20 °C·min−1, respectively.

Fig 4.20: Thermogravimeteric Analysis of Amylum Starch

Fig 4.20 shows the thermogravimetric curves of Amylum starch at different heating rates. These

curves present three primary mass loss parts. The initial temperature of each part was identified

as the critical point in the TG curves. The initial stage is the desiccation, which starts instantly

when the temperature just rises and ends at about 120 °C. The percentage of mass loss in this

part depends on the moisture content of the starch samples.

y = 4.7599x + 85.435R² = 0.9442

0

100

200

300

400

500

600

700

-20 0 20 40 60 80 100 120

Tem

pe

ratu

re D

egC

Weight Loss



Fig 4.21: Thermogravimeteric Analysis of Carboxymethyl Cellulose

The TGA of CMC showed residual weight of 19.6 and 34.2%, respectively, at 600 °C, which

indicates the presence of a fraction of non-volatile components.

Fig 4.22: Overlying graph of thermo-gravimetric (TG) straight line of SAP, indicating

thermal stability imparted in sodic form of sorbent throughout the degradation profile.

As shown by the thermal analysis of SAP’s major degradation steps that takes place above

200ºC, above to potato Amylum and CMC-Na, therefore we can conclude that the SAP

possesses a thermal stability that is extraordinary in some ways, which can also be observed

throughout the TG straight line. This increase in thermal stability can be helpful for the purpose

of increasing the sorbent’s shelf-life, revealing its future use in some commercial applications.

y = 6.7192x + 31.689R² = 0.883

0

100

200

300

400

500

600

700

-20 0 20 40 60 80 100

Tem

pe

ratu

re D

eg

C

Weight Loss

y = 6.5889x + 55.119R² = 0.9812

0

100

200

300

400

500

600

700

-20 0 20 40 60 80 100

Tem

pe

ratu

re

Weight Loss



Fig 4.23: Thermogravimeteric Analysis of Potato, Amylum Starchces, Carboxymethyl

Cellulose Sodium and SAP

From the figure it is clear that the major degradation of all the ingredients from 280-320oC.and

complete weigh loss of all potato amylum and SAP takes place except that of CMC having some

of the residual products like water, carbon dioxide, carbon monoxide, acetaldehyde, furan, and 2-

methyl furan.

Fig 4.24: Thermogravimeteric Analysis of SAP (Graph between Temperature and Weight

Loss of both Derivatives)

SAP is reported to produce two derivatives at250 and 280OC respectively and decomposes at

300-3200C.and complete decomposition takes place at 6000C.

0

20

40

60

80

100

120

-20

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700

We

igh

t lo

ss %

Temperature (DegC)

PotatoStrach

AmylumStarch

CMC

-3

-2

-1

0

1

2

-1

0

1

2

3

4

5

0 200 400 600 800

We

igh

t Lo

ss

Temerature DegC

1st Derivative

2nd Derivative



Fig 4.25: Thermogravimeteric Analysis of Modified starch

Fig 4.26: Thermogravimeteric Analysis of Modified Starch (Graph between Temperature

and Weight Loss of both Derivatives)

MS is reported to produce two derivatives at250OC respectively and decomposes at 295-

3200C.and complete decomposition takes place at 6000C.

Fig 4.27: Thermogravimeteric Analysis of MSAP

y = 0.0222x - 23.787R² = 0.9172

-20

0

20

40

60

80

100

0 1000 2000 3000 4000 5000 6000

Tem

pe

ratu

re D

egC

Weight Loss

-4

-3

-2

-1

0

1

2

3

4

5

-1

0

1

2

3

4

5

6

7

8

0 100 200 300 400 500 600 700

We

igh

t Lo

ss (

1st

De

riva

tive

)

Temperature DegC

1st Derivative

2nd Derivative

y = 6.0907x + 45.078R² = 0.9922

0

200

400

600

800

-20 0 20 40 60 80 100

Tem

pe

ratu

re D

egC

Weight Loss



Fig 4.28: Thermogravimeteric Analysis of MSAP (Graph between Temperature and

Weight Loss of both Derivatives)

MSAP is reported to produce two derivatives at 228-205OC respectively and decomposes at 251-

2740C.and complete decomposition takes place at 6000C.

Fig 4.29: Thermogravimeteric Analysis of Modified Starch, Carboxymethyl Cellulose

Sodium and Modified starch based SAP

The thermal analysis of Potato starch, Amylum Strach, CMC-Na and SAP were recorded for

comparison. Fig. 4.23 and 4.29 show an overlying pattern of the TG Curves of all the ingredients

and SAP, and a straight line for the decomposition of SAP. The minimum degradation (Tdm) in

SAP’s first degradation step appeared at 231.46°C, which is slightly higher than the Tdm of both

starches whereas less than that of CMC-Na. Likewise, Tdi of SAP’s second degradation step was

596ºC and almost 35ºC higher than starches whereas equal to that of CMC-Na. In the last

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

0 100 200 300 400 500 600 700

We

igh

t Lo

ss

Temperature DegC

1stDerivative(data)2ndDerivative(data)

-10

0

10

20

30

40

50

60

70

80

90

0

100

200

300

400

500

600

700

-20 0 20 40 60 80 100

SAP



degradation step, with the remaining wt. of 21.97%, a complete decomposition of the starches

were observed. From major degradation steps, the obtained thermal data reveals significantly

higher values of Tdi, Tdm and Tdf of SAP as compared to its ingredients. As observed throughout

the TG curves, we may infer an extraordinary thermal stability of the sorbent. In order to

increase the sorbent’s shelf life; this increase in thermal stability can be used as a beneficial tool

especially for commercial applications.

4.9 Applications on Water Treatment

4.9.1. Atomic Absorption Spectroscopy

Fig 4.30: Metal ion adsorption ratio profiles of SAP at room temperature

Fig 4.31: Metal ion adsorption ratio profiles of MSAP at room temperature

The above figure shows the metal ion absorption rates in the SAP solution. An increase in

concentration of SAP results an increase in the adsorbed quantity of metal ions. The 14, 12, and

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120

Me

tal D

ete

cte

d (

pp

m)

Weight of Hydrogel (mg)

Detection forCadmium (ppm)

Detection for Iron(ppm)

Detection for Lead(ppm)

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120

Me

tal D

ete

cte

d (

pp

m)

Weight of Hydrogel (mg)

Detection forCadmium (ppm)

Detection for Iron(ppm)

Detection for Lead(ppm)



10ppm concentration for Cd2+, Pb2+, and Fe2+ indicates maximum absorption respectively. In

fact, a relatively stronger attraction of oxygen atom of carboxyl group is the reason for an

increased absorption rate of Cd+2 ion than other metal ions, which is helpful in reaction with

Cd(II), Fe(II) or Pb(II) forming a relatively stable complexes with Cd(II) [131]. When the

concentration of metal ions get lower than 0.2 mmol/L, the absorption ratio for Fe(II) exceeds to

95% and the absorption percentage for Cd(II) and Pb(II) becomes higher than 99%. An increase

in the concentration causes the adsorption ratio to decrease and a better adsorption capacity was

seen by hydrogel for the metals under consideration, hence we can infer a relatively higher

adsorption capacity of the SAP hydrogel beads ,so the hydrogel can be taken into consideration

for the recovery of metal ions from solutions.

Qe = (Co-Ce) V/W (12)

Km = (1-Ce/Co) 100 (13)

Where Co and Ce are the initial and equilibrium metal ions concentrations (mol/L), respectively.

V is the volume of the solution (L) and W is the weight of the dried hydrogel beads (g).

4.9.2 Adsorption Isotherms

To study the adsorption behavior, two empirical adsorption models named Freundlich and

Langmuir models were used. In this work, the analysis was done by applying Freundlich and

Langmuir equations on the experimental data obtained at pH 7. [132-133] The Freundlich and

Langmuir isotherms are given by eq. (11) and (12), respectively:

Log Qe = log KF + 1/n log Ce (14)

KF= Freundlich constants related to adsorption capacity

N = Freundlich constants related to intensity

Ce =equilibrium concentration of metal ion in the solution

Fig 4.32: Graphical representation of Cadmium ion absorption in SAP between Ce(mol/L)

and Qe (mol/L)

y = 28.503x + 0.0001R² = 0.6679

0

0.001

0.002

0.003

0.004

0.005

0 0.000020.000040.000060.00008 0.0001 0.00012

Qe

(m

ol/

L)

Ce (mol/L



Fig 4.33: Graphical representation of Cadmium ion absorption in MSAP between

Ce(mol/L) and Qe (mol/L)

According to the results shown in (Fig 4.32 -4.33) and taking into account the values of the

correlation coefficients (R2 ), which are between 0.66 and 0.59, in case of SAP and MSAP.

These values show less adsorption of Cd2+ than that of Pb2+ but more than Fe2+. We conclude that

the results conform to the Langmuir model. It was generally observed that the adsorption values

are high and increase with increasing pore size of the matrix, pore volume and water content.

Fig 4.34: Graphical representation of Fe2+ ion absorption in SAP between Ce(mol/L) and

Qe (mol/L)

y = 19.014x + 0.0003R² = 0.5925

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 0.000020.000040.000060.00008 0.0001 0.00012Q

e (

mo

l/L)

Ce (mol/L)

y = 18.75x + 0.0004R² = 0.3371

0

0.001

0.002

0.003

0.004

0.005

0 0.000020.000040.000060.00008 0.0001 0.00012

Qe

(m

ol/

L)

Ce (mol/L)



Fig 4.35: Graphical representation of Fe2+ ion absorption in MSAP between Ce(mol/L) and

Qe (mol/L)

Variation of the mass of the hydrogel correlated with the less adsorption of Fe2+ ions R2=.33 for

SAP swollen in water. From the above isotherm for Fe2+ that increasing the concentration of the

ion in the solution increases the electrostatic repulsion between the charged groups on the

network and a concentration gradient inside and outside the hydrogel governed by the Donnan

potential. On the other hand, it is also possible that is occurred the displacement of water

molecules by the Fe2+ ions that are directed into the polymer matrix.

Fig 4.36: Graphical representation of Pb2+ ion absorption in SAP between Ce(mol/L) &Qe

(mol/L)

According to the results shown in Fig 4.36 -4.37 and taking into account the values of the

correlation coefficients (R2 ), which are between 0.95 and 0.87, We conclude that the results

conform to the Langmuir model. It was generally observed that the adsorption values are high

and increase with increasing pore size of the matrix, pore volume and water content. The

deviation in case of Cd2+ and Fe2+ isotherm is behavior is attributed to the fact that having a

lower density of crosslinking in the matrix, there is a greater possibility of diffusion, higher

y = 15.969x + 0.0004R² = 0.8154

0

0.001

0.002

0.003

0.004

0.005

0 0.00005 0.0001 0.00015 0.0002 0.00025

Qe

(m

iol/

L)

Ce (mol/)

y = 13.07x + 0.0003R² = 0.9501

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 0.00001 0.00002 0.00003 0.00004 0.00005 0.00006 0.00007

Qe

(m

ol/

L)

Ce (mol/L)



density of adsorption sites and adsorption volumetric capacity and that the functional groups

capable of complexing the metal, can be rearranged more easily.

Fig 4.37: Graphical representation of Pb2+ ion absorption in MSAP between Ce(mol/L) and

Qe (mol/L)

The sorption capacity depends on the extent of crosslinking and decreases with the increase in

the extent of crosslinking. This is because of the restricted diffusion of the ions through the

polymer networks and reduced chain flexibility. Metal ion uptake of the modified SAP was

more than SAP. Partitioning of ions between polymeric matrices and liquid phase is reflected

with high values of partition coefficients (Kd). Structure of polymeric networks has significant

effect on ion-uptake, which is reflected in low retention capacities (Qr).

Table 4.4: Freundlich and Langmiur Equation fitted Parameters

Freundlich

Equation

Metal Ions KF n R2

SAP Cd2+ 1.63 1.85 .898

Fe2+ 1.008 .88 .798

Pb2+ 1.57 2.22 .955

MSAP Cd2+ 1.46 2.38 .726

Fe2+ 1.56 2.42 .923

Pb2+ 1.47 1.69 .881

Langmiur

Equation

Metal Ions Qmax b R2

SAP Cd2+ 222 .095 .923

Fe2+ 476 .026 .882

Pb2+ 84 .16 .716

MSAP Cd2+ 111 .136 .955

Fe2+ 100 .128 .898

Pb2+ 222 .09 .798

From Freundlich Eqaution, the observed KF values for Cd2+, Fe2+ and Pb2+are 1.63, 1.008,

1.57for SAP and1.46, 1.56, 1.47 for MSAP respectively. The adsorption studies demonstrate that

the both hydrogels have a potential application in removal and recovery of heavy metal ions

from waste water.

y = 19.602x + 0.0002R² = 0.8726

0

0.0005

0.001

0.0015

0 0.00001 0.00002 0.00003 0.00004 0.00005

Qe

(m

ol/

L)

Ce (mol/L)



4.10 Conclusion

The prepared hydrogels were characterized by studying their physical properties, Swelling

behavior, Swelling kinetics, Fourier Transform Infrared spectroscopy (FT-IR), Scanning electron

Microscopy (SEM), Powdered X-ray diffractometery (PXRD), Thermogravimeteric analysis

(TGA) and Atomic Absorption spectroscopy to know their ability in removing heavy metal ions

from water. In this work, the synthesis of two novel Hydrogels, Carboxymethyl cellulose/Potato

Starch/Amylum Strach (CMC/PS/AS) based Hydrgel (SAP), A Modified Starch (MS) and a

Modified Starch based Hydrogel (MSAP) were synthesized by using Aluminium Sulfate

Octahydrate as a crosslinking agent. By taking into consideration, FT-IR analysis done primarily

to evaluate the structure of hydrogels, the structures in results were according to the expected

structures of hydrogels. The hydrogels then subjected to the thermal gravimetric analysis to

evaluate out the thermal stability of hydrogel i.e. more than its ingredients. Hydrogels were then

examined morphologically by SEM. The swelling ability of both hydrogels were more in basic

medium rather than acidic, moreover it shows swelling and de-swelling behavior in water,

ethanol, acidic and basic buffers and in salt solutions when inferred by the swelling experiment.

A high swelling behavior was shown by SAP and MSAP in deionized water, at pH 6.8 and 7.4

while no reasonable swelling at pH 1.2 was observed. Furthermore, its potential as an intelligent

drug delivery system was confirmed by a remarkable swelling and de-swelling behavior of SAP

in water and ethanol, in acidic(pH 1.2) and basic (pH 7.4) media and in water and normal saline

solution. The thermal analysis of SAP and MSAP’s major degradation steps that takes place

above 200ºC,which represents their extra-ordinary stability. The PXRD anlysis shows that there

may be a distortion in the CMC’s crystallization and an increase in SAP hydrogel’s amorphous

region. The possible cause of it can be the chemical crosslinking between the starches, CMC and

SAP. These results indicate that due to a reduction in the crystalline behavior during the gel

formation. . The success of the reaction in the FT-IR spectrum of SAP was revealed by an ester

carbonyl distinct signal’s appearance at 2341 cm−1 in spectra of CMC which was the major

constituent of hydrogel, jumps to a relatively higher wavenumber at 2345 cm−1 soon after the

formation of its SAP. It also indicates the absorption of Carbon dioxide at the time of reaction

completion.

From the aqueous solution of Cd+2, Pb+2 and Fe+2 ions, these metal ions were then separated

by the hydrogel. The order of selectivity towards different metal ions of the hydrogel as tested

was Cd+2> Pb+2 >Fe+2. The observation revealed the fact that the capacity of the hydrogel to

bind with heavy metal ions was dependent on the interaction of metal ions with the hydrogel

monomers.

A high swelling behavior was shown by SAP and MSAP in deionized water, at pH 6.8 and 7.4

while no reasonable swelling at pH 1.2 was observed. Furthermore, its potential as an intelligent

drug delivery system was confirmed by a remarkable swelling and de-swelling behavior of SAP

in water and ethanol, in acidic(pH 1.2) and basic (pH 7.4) media and in water and normal saline

solution. The FT-IR spectrum of SAP, by the appearance of a distinct ester carbonyl signal at



2341 cm−1 in spectra of CMC (the major constituent of hydrogel), moved to higher wavenumber

at 2345 cm−1 after its SAP formation and it all revealed the success of the reaction. The

macroporous nature of dried hydrogel by SEM analysis was confirmed predicting it a

superabsorbent material. SAP proves itself not only a potential candidate for water treatment, but

an effective substance in targeted and sustained delivery of drugs in colon and small intestine on

the basis of higher adsorption in basic media. XRD Spectra revealed a lower the crystalline

property of hydrogel beads in comparison to that of the pure CMC. It is proved that Tdi, Tdm

and Tdf of SAP are significantly higher than those of ingredients as the thermal data of major

degradation steps was analyzed. It is therefore inferred that the sorbent has thermal stability at

some extraordinary level which can be observed throughout the TG curve. In view of the whole

study, it is concluded that these hydrogels have a higher selectivity towards Cd(II) and Pb(II) and

over 90% recovery was attained after repeating its use for almost five times. From Freundlich

Eqaution, the observed KF values for Cd2+, Fe2+ and Pb2+are 1.63, 1.008, 1.57for SAP and1.46,

1.56, 1.47 for MSAP respectively. The adsorption studies demonstrate that the both hydrogels

have a potential application in removal and recovery of heavy metal ions from waste water.



Publications

Synthesis and Characterization of Carboxymethyl cellulose based Hydrogel and its Applications

on water Treatment.

(Desalination and Water Treatment Journal) (Published)

Synthesis, Characterization and Metal Ion removing Capability of Novel Carboxymethyl

Cellulose based Hydrogel.

(Journal Of Envoironmental Chemistry) (Submitted)



Chapter 5

REFERENCES

REFERENCES


References

1. Mathur, N. K. Industrial Galactomannan Polysaccharides; CRC Press, 2016.

2 Zakrzewska, M. E.; Bogel-Łukasik, E.; Bogel-Łukasik, R. Solubility of Carbohydrates in

Ionic Liquids. Energy Fuels 2010, 24 (2), 737–745. https://doi.org/10.1021/ef901215m.

3 Holesh, J. E.; Bhimji, S. S. Dietary, Carbohydrates; StatPearls Publishing, 2017.

4 Gunasekara, R. W.; Zhao, Y. A General Method for Selective Recognition of

Monosaccharides and Oligosaccharides in Water. J. Am. Chem. Soc. 2017, 139 (2), 829–835.

https://doi.org/10.1021/jacs.6b10773.

5 Holesh, J. E.; Martin, A. Physiology, Carbohydrates. In StatPearls; StatPearls Publishing:

Treasure Island (FL), 2019.

6 Varki, A.; Kornfeld, S. Historical Background and Overview. In Essentials of

Glycobiology; Varki, A., Cummings, R. D., Esko, J. D., Stanley, P., Hart, G. W., Aebi, M.,

Darvill, A. G., Kinoshita, T., Packer, N. H., Prestegard, J. H., et al., Eds.; Cold Spring Harbor

Laboratory Press: Cold Spring Harbor (NY), 2015.

7 Raich, L.; Nin-Hill, A.; Ardèvol, A.; Rovira, C. Enzymatic Cleavage of Glycosidic

Bonds: Strategies on How to Set Up and Control a QM/MM Metadynamics Simulation. Methods

Enzymol. 2016, 577, 159–183. https://doi.org/10.1016/bs.mie.2016.05.015.

8 Berg, J. M.; Tymoczko, J. L.; Stryer, L. Complex Carbohydrates Are Formed by Linkage

of Monosaccharides. Biochem. 5th Ed. 2002.

9 Slavin, J.; Carlson, J. Advances in Nutrition, Carbohydrates. 2014, 5 (6), 760–761.

https://doi.org/10.3945/an.114.006163.

10 Aller, E. E. J. G.; Abete, I.; Astrup, A.; Martinez, J. A.; van Baak, M. A. Starches, Sugars

and Obesity. Nutrients 2011, 3 (3), 341–369. https://doi.org/10.3390/nu3030341.

11 Berg, J. M.; Tymoczko, J. L.; Stryer, L. Monosaccharides Are Aldehydes or Ketones

with Multiple Hydroxyl Groups. Biochem. 5th Ed. 2002.

12 Fraser-Reid, B. O.; Tatsuta, K.; Thiem, J. Glycoscience: Chemistry and Chemical

Biology I–III; Springer Science & Business Media, 2012.

13 Lelong, G.; Howells, W. S.; Brady, J. W.; Talon, C.; Price, D. L.; Saboungi, M.-L.

Translational and Rotational Dynamics of Monosaccharide Solutions. J. Phys. Chem. B 2009,

113 (39), 13079–13085. https://doi.org/10.1021/jp905001q.

REFERENCES


14 Prestegard, J. H.; Liu, J.; Widmalm, G. Oligosaccharides and Polysaccharides. In

Essentials of Glycobiology; Varki, A., Cummings, R. D., Esko, J. D., Stanley, P., Hart, G. W.,

Aebi, M., Darvill, A. G., Kinoshita, T., Packer, N. H., Prestegard, J. H., et al., Eds.; Cold Spring

Harbor Laboratory Press: Cold Spring Harbor (NY), 2015.

15 Belorkar, S. A.; Gupta, A. K. Oligosaccharides: A Boon from Nature’s Desk. AMB

Express 2016, 6 (1), 82. https://doi.org/10.1186/s13568-016-0253-5.

16 Seidi, F.; Jenjob, R.; Phakkeeree, T.; Crespy, D. Saccharides, Oligosaccharides, and

Polysaccharides Nanoparticles for Biomedical Applications. J. Controlled Release 2018, 284,

188–212. https://doi.org/10.1016/j.jconrel.2018.06.026.

17 Bačáková, L.; Novotná, K.; Pařízek, M. Polysaccharides as Cell Carriers for Tissue

Engineering: The Use of Cellulose in Vascular Wall Reconstruction. Physiol. Res. 2014, 63

Suppl 1, S29-47.

18 Yang, X.; Zhao, Y.; Zhou, Y.; Lv, Y.; Mao, J.; Zhao, P. Component and Antioxidant

Properties of Polysaccharide Fractions Isolated from Angelica Sinensis (OLIV.) DIELS. Biol.

Pharm. Bull. 2007, 30 (10), 1884–1890.

19 Lovegrove, A.; Edwards, C. H.; De Noni, I.; Patel, H.; El, S. N.; Grassby, T.; Zielke, C.;

Ulmius, M.; Nilsson, L.; Butterworth, P. J.; et al. Role of Polysaccharides in Food, Digestion,

and Health. Crit. Rev. Food Sci. Nutr. 2017, 57 (2), 237–253.

https://doi.org/10.1080/10408398.2014.939263.

20 Ismail, H.; Irani, M.; Ahmad, Z. Starch-Based Hydrogels: Present Status and

Applications. Int. J. Polym. Mater. Polym. Biomater. 2013, 62 (7), 411–420.

https://doi.org/10.1080/00914037.2012.719141.

21 Li, Y.; Yang, Y.; Ding, Y. The New Competitive Mechanism of Hydrogen Bonding

Interactions and Transition Process for the Hydroxyphenyl Imidazo [1, 2-a] Pyridine in Mixed

Liquid Solution. Sci. Rep. 2017, 7. https://doi.org/10.1038/s41598-017-01780-7.

22 Harding, S. E.; Channell, G.; Phillips-Jones, M. K. The Discovery of Hydrogen Bonds in

DNA and a Re-Evaluation of the 1948 Creeth Two-Chain Model for Its Structure. Biochem. Soc.

Trans. 2018, 46 (5), 1171–1182. https://doi.org/10.1042/BST20180158.

23 Horowitz, S.; Trievel, R. C. Carbon-Oxygen Hydrogen Bonding in Biological Structure

and Function. J. Biol. Chem. 2012, 287 (50), 41576–41582.

https://doi.org/10.1074/jbc.R112.418574.

24 Ahmed, E. M. Hydrogel: Preparation, Characterization, and Applications: A Review. J.

Adv. Res. 2015, 6 (2), 105–121. https://doi.org/10.1016/j.jare.2013.07.006.

REFERENCES


25 Lee, S. C.; Kwon, I. K.; Park, K. Hydrogels for Delivery of Bioactive Agents: A

Historical Perspective. Adv. Drug Deliv. Rev. 2013, 65 (1), 17–20.

https://doi.org/10.1016/j.addr.2012.07.015.

26 Yahia, Lh.; Chirani, N.; Gritsch, L.; Motta, F. L.; SoumiaChirani; Fare, S. History and

Applications of Hydrogels. J. Biomed. Sci. 2015, 4 (2). https://doi.org/10.4172/2254-

609X.100013.

27 Hoare, T. R.; Kohane, D. S. Hydrogels in Drug Delivery: Progress and Challenges.

Polymer 2008, 49 (8), 1993–2007. https://doi.org/10.1016/j.polymer.2008.01.027.

28 Peppas, N. A.; Hoffman, A. S. Chapter I.2.5 - Hydrogels. In Biomaterials Science (Third

Edition); Ratner, B. D., Hoffman, A. S., Schoen, F. J., Lemons, J. E., Eds.; Academic Press,

2013; pp 166–179. https://doi.org/10.1016/B978-0-08-087780-8.00020-6.

29 Ambrosio, L.; Demitri, C.; Sannino, A. 2 - Superabsorbent Cellulose-Based Hydrogels

for Biomedical Applications. In Biomedical Hydrogels; Rimmer, S., Ed.; Woodhead Publishing

Series in Biomaterials; Woodhead Publishing, 2011; pp 25–50.

https://doi.org/10.1533/9780857091383.1.25.

30 Vishal Gupta, N.; Shivakumar, H. G. Preparation and Characterization of Superporous

Hydrogels as Gastroretentive Drug Delivery System for Rosiglitazone Maleate. DARU J. Pharm.

Sci. 2010, 18 (3), 200–210.

31 Kopeček, J. Hydrogel Biomaterials: A Smart Future? Biomaterials 2007, 28 (34), 5185–

5192. https://doi.org/10.1016/j.biomaterials.2007.07.044.

32 Zhu, J.; Marchant, R. E. Design Properties of Hydrogel Tissue-Engineering Scaffolds.

Expert Rev. Med. Devices 2011, 8 (5), 607–626. https://doi.org/10.1586/erd.11.27.

33 parhi, R. Cross-Linked Hydrogel for Pharmaceutical Applications: A Review. Adv.

Pharm. Bull. 2017, 7 (4), 515–530. https://doi.org/10.15171/apb.2017.064.

34 Akhtar, M. F.; Hanif, M.; Ranjha, N. M. Methods of Synthesis of Hydrogels … A

Review. Saudi Pharm. J. SPJ 2016, 24 (5), 554–559. https://doi.org/10.1016/j.jsps.2015.03.022.

35 Shetye, S. P.; Godbole, D. A.; Shilpa, D.; Gajare, P. Hydrogels: Introduction,

Preparation, Characterization and Applications. 2015, 1, 25.

36 Katime, I.; Rodríguez, E. Absorption of Metal Ions and Swelling Properties of

Poly(Acrylic Acid-Co-Itaconic Acid) Hydrogels. J. Macromol. Sci. Part A 2001, 38 (5–6), 543–

558. https://doi.org/10.1081/MA-100103366.

REFERENCES


37 Andrés, Á. C. C.; Alberto, C. O. J.; Andrés, Á. C. C.; Alberto, C. O. J. Use of PH-

Thermosensitive Hydrogels for Nickel Ion Removal and Recovery. Polímeros 2017, 27 (1), 35–

40. https://doi.org/10.1590/0104-1428.2298.

38 Baker, M. J.; Trevisan, J.; Bassan, P.; Bhargava, R.; Butler, H. J.; Dorling, K. M.;

Fielden, P. R.; Fogarty, S. W.; Fullwood, N. J.; Heys, K. A.; et al. Using Fourier Transform IR

Spectroscopy to Analyze Biological Materials. Nat. Protoc. 2014, 9 (8), 1771–1791.

https://doi.org/10.1038/nprot.2014.110.

39 Moraes, L. G. P.; Rocha, R. S. F.; Menegazzo, L. M.; AraÚjo, E. B. de; Yukimitu, K.;

Moraes, J. C. S. INFRARED SPECTROSCOPY: A TOOL FOR DETERMINATION OF THE

DEGREE OF CONVERSION IN DENTAL COMPOSITES. J. Appl. Oral Sci. 2008, 16 (2),

145. https://doi.org/10.1590/S1678-77572008000200012.

40 Alvarez-Ordóñez, A.; Mouwen, D. J. M.; López, M.; Prieto, M. Fourier Transform

Infrared Spectroscopy as a Tool to Characterize Molecular Composition and Stress Response in

Foodborne Pathogenic Bacteria. J. Microbiol. Methods 2011, 84 (3), 369–378.

https://doi.org/10.1016/j.mimet.2011.01.009.

41 Carbonaro, M.; Nucara, A. Secondary Structure of Food Proteins by Fourier Transform

Spectroscopy in the Mid-Infrared Region. Amino Acids 2010, 38 (3), 679–690.

https://doi.org/10.1007/s00726-009-0274-3.

42 Christou, C.; Agapiou, A.; Kokkinofta, R. Use of FTIR Spectroscopy and Chemometrics

for the Classification of Carobs Origin. J. Adv. Res. 2017, 10, 1–8.

https://doi.org/10.1016/j.jare.2017.12.001.

43 Türker-Kaya, S.; Huck, C. W. A Review of Mid-Infrared and Near-Infrared Imaging:

Principles, Concepts and Applications in Plant Tissue Analysis. Molecules 2017, 22 (1), 168.

https://doi.org/10.3390/molecules22010168.

44 Hughes, C. E.; Reddy, G. N. M.; Masiero, S.; Brown, S. P.; Williams, P. A.; Harris, K. D.

M. Determination of a Complex Crystal Structure in the Absence of Single Crystals: Analysis of

Powder X-Ray Diffraction Data, Guided by Solid-State NMR and Periodic DFT Calculations,

Reveals a New 2′-Deoxyguanosine Structural Motif †The Experimental Datasets for This Study

and the Magres Output (.Magres) Files from the CASTEP Calculations Are Available from the

Cardiff University Data Catalogue at Http://Doi.Org/10.17035/d.2017.0031643370 ‡Electronic

Supplementary Information (ESI) Available. CCDC 1535685. For ESI and Crystallographic Data

in CIF or Other Electronic Format See DOI: 10.1039/C7sc00587c Click Here for Additional

Data File. Click Here for Additional Data File. Chem. Sci. 2017, 8 (5), 3971–3979.

https://doi.org/10.1039/c7sc00587c.

REFERENCES


45 Thakral, N. K.; Zanon, R. L.; Kelly, R. C.; Thakral, S. Applications of Powder X-Ray

Diffraction in Small Molecule Pharmaceuticals: Achievements and Aspirations. J. Pharm. Sci.

2018, 107 (12), 2969–2982. https://doi.org/10.1016/j.xphs.2018.08.010.

46 Bunaciu, A. A.; Udriştioiu, E. G.; Aboul-Enein, H. Y. X-Ray Diffraction:

Instrumentation and Applications. Crit. Rev. Anal. Chem. 2015, 45 (4), 289–299.

https://doi.org/10.1080/10408347.2014.949616.

47 Artioli, G. X-Ray Diffraction, Studies of Inorganic Compounds and Minerals. In

Encyclopedia of Spectroscopy and Spectrometry (Third Edition); Lindon, J. C., Tranter, G. E.,

Koppenaal, D. W., Eds.; Academic Press: Oxford, 2017; pp 676–683.

https://doi.org/10.1016/B978-0-12-803224-4.00176-X.

48 Jones, C. G. Scanning Electron Microscopy: Preparation and Imaging for SEM. Methods

Mol. Biol. Clifton NJ 2012, 915, 1–20. https://doi.org/10.1007/978-1-61779-977-8_1.

49 Nguyen, J. N. T.; Harbison, A. M. Scanning Electron Microscopy Sample Preparation

and Imaging. Methods Mol. Biol. Clifton NJ 2017, 1606, 71–84. https://doi.org/10.1007/978-1-

4939-6990-6_5.

50 Singh, A. K. Chapter 4 - Experimental Methodologies for the Characterization of

Nanoparticles. In Engineered Nanoparticles; Singh, A. K., Ed.; Academic Press: Boston, 2016;

pp 125–170. https://doi.org/10.1016/B978-0-12-801406-6.00004-2.

51 Webb, J.; Holgate, J. H. MICROSCOPY | Scanning Electron Microscopy. In

Encyclopedia of Food Sciences and Nutrition (Second Edition); Caballero, B., Ed.; Academic

Press: Oxford, 2003; pp 3922–3928. https://doi.org/10.1016/B0-12-227055-X/00779-3.

52 Hubbs, A.; Porter, D. W.; Mercer, R.; Castranova, V.; Sargent, L.; Sriram, K. Chapter 43

- Nanoparticulates. In Haschek and Rousseaux’s Handbook of Toxicologic Pathology (Third

Edition); Haschek, W. M., Rousseaux, C. G., Wallig, M. A., Eds.; Academic Press: Boston,

2013; pp 1373–1419. https://doi.org/10.1016/B978-0-12-415759-0.00043-1.

53 Sato, C.; Kinoshita, T.; Memtily, N.; Sato, M.; Nishihara, S.; Yamazawa, T.; Sugimoto,

S. Chapter 10 - Correlative Light–Electron Microscopy in Liquid Using an Inverted SEM

(ASEM). In Methods in Cell Biology; Müller-Reichert, T., Verkade, P., Eds.; Correlative Light

and Electron Microscopy III; Academic Press, 2017; Vol. 140, pp 187–213.

https://doi.org/10.1016/bs.mcb.2017.03.015.

54 Raghavendra, P.; Pullaiah, T. Chapter 4 - Biomedical Imaging Role in Cellular and

Molecular Diagnostics. In Advances in Cell and Molecular Diagnostics; Raghavendra, P.,

Pullaiah, T., Eds.; Academic Press, 2018; pp 85–111. https://doi.org/10.1016/B978-0-12-

813679-9.00004-X.

REFERENCES


55 Brabazon, D. Chapter 16 - Nanocharacterization Techniques for Dental Implant

Development. In Emerging Nanotechnologies in Dentistry (Second Edition); Subramani, K.,

Ahmed, W., Eds.; Micro and Nano Technologies; William Andrew Publishing, 2018; pp 327–

354. https://doi.org/10.1016/B978-0-12-812291-4.00016-9.

56 Polini, A.; Yang, F. 5 - Physicochemical Characterization of Nanofiber Composites. In

Nanofiber Composites for Biomedical Applications; Ramalingam, M., Ramakrishna, S., Eds.;

Woodhead Publishing, 2017; pp 97–115. https://doi.org/10.1016/B978-0-08-100173-8.00005-3.

57 Acquah, G. E.; Via, B. K.; Fasina, O. O.; Adhikari, S.; Billor, N.; Eckhardt, L. G.

Chemometric Modeling of Thermogravimetric Data for the Compositional Analysis of Forest

Biomass. PLoS ONE 2017, 12 (3). https://doi.org/10.1371/journal.pone.0172999.

58 Wunderlich, B. Thermal Analysis. In Encyclopedia of Materials: Science and

Technology; Buschow, K. H. J., Cahn, R. W., Flemings, M. C., Ilschner, B., Kramer, E. J.,

Mahajan, S., Veyssière, P., Eds.; Elsevier: Oxford, 2001; pp 9134–9141.

https://doi.org/10.1016/B0-08-043152-6/01648-X.

59 Al Mamun, A.; Nikousaleh, M. A.; Feldmann, M.; Rüppel, A.; Sauer, V.; Kleinhans, S.;

Heim, H.-P. 8 - Lignin Reinforcement in Bioplastic Composites. In Lignin in Polymer

Composites; Faruk, O., Sain, M., Eds.; William Andrew Publishing, 2016; pp 153–165.

https://doi.org/10.1016/B978-0-323-35565-0.00008-4.

60 Loof, D.; Hiller, M.; Oschkinat, H.; Koschek, K. Quantitative and Qualitative Analysis of

Surface Modified Cellulose Utilizing TGA-MS. Materials 2016, 9 (6).

https://doi.org/10.3390/ma9060415.

61 Quan, C.; Li, A.; Gao, N. Thermogravimetric Analysis and Kinetic Study on Large

Particles of Printed Circuit Board Wastes. Waste Manag. 2009, 29 (8), 2353–2360.

https://doi.org/10.1016/j.wasman.2009.03.020.

62 Vazquez-Pufleau, M.; Chadha, T. S.; Yablonsky, G.; Biswas, P. Carbon Elimination from

Silicon Kerf: Thermogravimetric Analysis and Mechanistic Considerations. Sci. Rep. 2017, 7.

https://doi.org/10.1038/srep40535.

63 Ihms, E. C.; Brinkman, D. W. Thermogravimetric Analysis as a Polymer Identification

Technique in Forensic Applications. J. Forensic Sci. 2004, 49 (3), 505–510.

64 Tatavarti, A. S.; Dollimore, D.; Alexander, K. S. A Thermogravimetric Analysis of Non-

Polymeric Pharmaceutical Plasticizers: Kinetic Analysis, Method Validation, and Thermal

Stability Evaluation. AAPS PharmSci 2002, 4 (4), 231–242. https://doi.org/10.1208/ps040445.

REFERENCES


65 Saber, R. A.; Attia, A. K.; Salem, W. M. Thermal Analysis Study of Antihypertensive

Drugs Telmisartan and Cilazapril. Adv. Pharm. Bull. 2014, 4 (3), 283–287.

https://doi.org/10.5681/apb.2014.041.

66 Pazó, J. A.; Granada, E.; Saavedra, Á.; Eguía, P.; Collazo, J. Biomass Thermogravimetric

Analysis: Uncertainty Determination Methodology and Sampling Maps Generation. Int. J. Mol.

Sci. 2010, 11 (7), 2701–2714. https://doi.org/10.3390/ijms11072701.

67 Zhang, J.; Feng, L.; Wang, D.; Zhang, R.; Liu, G.; Cheng, G. Thermogravimetric

Analysis of Lignocellulosic Biomass with Ionic Liquid Pretreatment. Bioresour. Technol. 2014,

153, 379–382. https://doi.org/10.1016/j.biortech.2013.12.004.

68 Fernández, B.; Lobo, L.; Pereiro, R. Atomic Absorpton Spectrometry | Fundamentals,

Instrumentation and Capabilities. In Encyclopedia of Analytical Science (Third Edition);

Worsfold, P., Poole, C., Townshend, A., Miró, M., Eds.; Academic Press: Oxford, 2019; pp 137–

143. https://doi.org/10.1016/B978-0-12-409547-2.14116-2.

69 Michalke, B.; Nischwitz, V. Chapter 22 - Speciation and Element-Specific Detection. In

Liquid Chromatography; Fanali, S., Haddad, P. R., Poole, C. F., Schoenmakers, P., Lloyd, D.,

Eds.; Elsevier: Amsterdam, 2013; pp 633–649. https://doi.org/10.1016/B978-0-12-415806-

1.00022-X.

70 SANZ-MEDEL, A.; Pereiro, R.; Costa-Fernandez, J. A General Overview of Atomic

Spectrometric Techniques. RSC Anal. Spectrosc. Ser. 2009.

71 Slaughter, B. V.; Khurshid, S. S.; Fisher, O. Z.; Khademhosseini, A.; Peppas, N. A.

Hydrogels in Regenerative Medicine. Adv. Mater. 2009, 21 (32‐33), 3307–3329.

https://doi.org/10.1002/adma.200802106.

72 Gong, J. P. Why Are Double Network Hydrogels so Tough? Soft Matter 2010, 6 (12),

2583–2590. https://doi.org/10.1039/B924290B.

73 Bhattarai, N.; Gunn, J.; Zhang, M. Chitosan-Based Hydrogels for Controlled, Localized

Drug Delivery. Adv. Drug Deliv. Rev. 2010, 62 (1), 83–99.

https://doi.org/10.1016/j.addr.2009.07.019.

74 Nguyen, M. K.; Lee, D. S. Injectable Biodegradable Hydrogels. Macromol. Biosci. 2010,

10 (6), 563–579. https://doi.org/10.1002/mabi.200900402.

75 Burdick, J. A.; Prestwich, G. D. Hyaluronic Acid Hydrogels for Biomedical Applications.

Adv. Mater. 2011, 23 (12), H41–H56. https://doi.org/10.1002/adma.201003963.

76 Sun, J.-Y.; Zhao, X.; Illeperuma, W. R. K.; Chaudhuri, O.; Oh, K. H.; Mooney, D. J.;

Vlassak, J. J.; Suo, Z. Highly Stretchable and Tough Hydrogels. Nature 2012, 489 (7414), 133–

136. https://doi.org/10.1038/nature11409.

REFERENCES


(77 Hennink, W. E.; van Nostrum, C. F. Novel Crosslinking Methods to Design Hydrogels.

Adv. Drug Deliv. Rev. 2012, 64, 223–236. https://doi.org/10.1016/j.addr.2012.09.009.

78 Appel, E. A.; Barrio, J. del; Loh, X. J.; Scherman, O. A. Supramolecular Polymeric

Hydrogels. Chem. Soc. Rev. 2012, 41 (18), 6195–6214. https://doi.org/10.1039/C2CS35264H.

79 Phadke, A.; Zhang, C.; Arman, B.; Hsu, C.-C.; Mashelkar, R. A.; Lele, A. K.; Tauber, M.

J.; Arya, G.; Varghese, S. Rapid Self-Healing Hydrogels. Proc. Natl. Acad. Sci. 2012, 109 (12),

4383–4388. https://doi.org/10.1073/pnas.1201122109.

80 Malda, J.; Visser, J.; Melchels, F. P.; Jüngst, T.; Hennink, W. E.; Dhert, W. J. A.; Groll,

J.; Hutmacher, D. W. 25th Anniversary Article: Engineering Hydrogels for Biofabrication. Adv.

Mater. 2013, 25 (36), 5011–5028. https://doi.org/10.1002/adma.201302042.

81 Sun, T. L.; Kurokawa, T.; Kuroda, S.; Ihsan, A. B.; Akasaki, T.; Sato, K.; Haque, M. A.;

Nakajima, T.; Gong, J. P. Physical Hydrogels Composed of Polyampholytes Demonstrate High

Toughness and Viscoelasticity. Nat. Mater. 2013, 12 (10), 932–937.

https://doi.org/10.1038/nmat3713.

82 Gaharwar, A. K.; Peppas, N. A.; Khademhosseini, A. Nanocomposite Hydrogels for

Biomedical Applications. Biotechnol. Bioeng. 2014, 111 (3), 441–453.

https://doi.org/10.1002/bit.25160.

83 Zhang, Y. S.; Khademhosseini, A. Advances in Engineering Hydrogels. Science 2017,

356 (6337), eaaf3627. https://doi.org/10.1126/science.aaf3627.

84 Lee, J.-H.; Kim, H.-W. Emerging Properties of Hydrogels in Tissue Engineering. J.

Tissue Eng. 2018, 9. https://doi.org/10.1177/2041731418768285.

85 Caliari, S. R.; Burdick, J. A. A Practical Guide to Hydrogels for Cell Culture. Nat.

Methods 2016, 13 (5), 405–414. https://doi.org/10.1038/nmeth.3839.

86 Bodenberger, N.; Kubiczek, D.; Abrosimova, I.; Scharm, A.; Kipper, F.; Walther, P.;

Rosenau, F. Evaluation of Methods for Pore Generation and Their Influence on Physio-Chemical

Properties of a Protein Based Hydrogel. Biotechnol. Rep. 2016, 12, 6.

https://doi.org/10.1016/j.btre.2016.09.001.

87 Li, J.; Mooney, D. J. Designing Hydrogels for Controlled Drug Delivery. Nat. Rev.

Mater. 2016, 1 (12). https://doi.org/10.1038/natrevmats.2016.71.

88 Vega, S. L.; Kwon, M. Y.; Burdick, J. A. RECENT ADVANCES IN HYDROGELS

FOR CARTILAGE TISSUE ENGINEERING. Eur. Cell. Mater. 2017, 33, 59–75.

https://doi.org/10.22203/eCM.v033a05.

REFERENCES


89 Perale, G.; Rossi, F.; Sundstrom, E.; Bacchiega, S.; Masi, M.; Forloni, G.; Veglianese, P.

Hydrogels in Spinal Cord Injury Repair Strategies. ACS Chem. Neurosci. 2011, 2 (7), 336–345.

https://doi.org/10.1021/cn200030w.

90 Kornev, V. A.; Grebenik, E. A.; Solovieva, A. B.; Dmitriev, R. I.; Timashev, P. S.

Hydrogel-Assisted Neuroregeneration Approaches towards Brain Injury Therapy: A State-of-the-

Art Review. Comput. Struct. Biotechnol. J. 2018, 16, 488–502.

https://doi.org/10.1016/j.csbj.2018.10.011.

91 Kirschner, C. M.; Anseth, K. S. Hydrogels in Healthcare: From Static to Dynamic

Material Microenvironments. Acta Mater. 2013, 61 (3), 931–944.

https://doi.org/10.1016/j.actamat.2012.10.037.

92 Gao, W.; Zhang, Y.; Zhang, Q.; Zhang, L. Nanoparticle-Hydrogel: A Hybrid Biomaterial

System for Localized Drug Delivery. Ann. Biomed. Eng. 2016, 44 (6), 2049–2061.

https://doi.org/10.1007/s10439-016-1583-9.

93 Poldervaart, M. T.; Goversen, B.; Ruijter, M. de; Abbadessa, A.; Melchels, F. P. W.;

Öner, F. C.; Dhert, W. J. A.; Vermonden, T.; Alblas, J. 3D Bioprinting of Methacrylated

Hyaluronic Acid (MeHA) Hydrogel with Intrinsic Osteogenicity. PLOS ONE 2017, 12 (6),

e0177628. https://doi.org/10.1371/journal.pone.0177628.

94 Xu, S.; Wang, Z.; Gao, Y.; Zhang, S.; Wu, K. Adsorption of Rare Earths(Ⅲ) Using an

Efficient Sodium Alginate Hydrogel Cross-Linked with Poly-γ-Glutamate. PLOS ONE 2015, 10

(5), e0124826. https://doi.org/10.1371/journal.pone.0124826.

95 Lau, H. K.; Kiick, K. L. Opportunities for Multicomponent Hybrid Hydrogels in

Biomedical Applications. Biomacromolecules 2015, 16 (1), 28–42.

https://doi.org/10.1021/bm501361c.

96 Laurén, P.; Somersalo, P.; Pitkänen, I.; Lou, Y.-R.; Urtti, A.; Partanen, J.; Seppälä, J.;

Madetoja, M.; Laaksonen, T.; Mäkitie, A.; et al. Nanofibrillar Cellulose-Alginate Hydrogel

Coated Surgical Sutures as Cell-Carrier Systems. PLOS ONE 2017, 12 (8), e0183487.

https://doi.org/10.1371/journal.pone.0183487.

97 Pérez-Luna, V. H.; González-Reynoso, O. Encapsulation of Biological Agents in

Hydrogels for Therapeutic Applications. Gels 2018, 4 (3). https://doi.org/10.3390/gels4030061.

98.O. Wichterleand D. Lim, Hydrophilic gels for biological use, Nature, 185 (1960) 117-118.

32.S.W. Won, P. Kotte, W. Wei, A. Limand Y.-S. Yun, Biosorbents for recovery of precious metals,

Bioresour. Technol., 160 (2014) 203-212.

99.J.D. Ferry, Viscoelastic properties of polymers, John Wiley & Sons, 1980.

3.G. Pass, G. Phillipsand D. Wedlock, Interaction of univalent and divalent cations with carrageenans in

aqueous solution, Macromolecules, 10 (1977) 197-201.

REFERENCES


100.J.M. Rosiakand F. Yoshii, Hydrogels and their medical applications, Nucl. Instrum. Methods Phys.

Res., B., 151 (1999) 56-64.

101.Q. Zhuand Z. Li, Hydrogel-supported nanosized hydrous manganese dioxide: synthesis,

characterization, and adsorption behavior study for Pb2+, Cu2+, Cd2+ and Ni2+ removal from water,

Chem. Eng., 281 (2015) 69-80.

102.T.E. Dudu, M. Sahiner, D. Alpaslan, S. Demirciand N. Aktas, Removal of As (V), Cr (III) and Cr

(VI) from aqueous environments by poly (acrylonitril-co-acrylamidopropyl-trimethyl ammonium

chloride)-based hydrogels, J. Environ. Manag., 161 (2015) 243-251.

103.R. Huaand Z. Li, Sulfhydryl functionalized hydrogel with magnetism: Synthesis, characterization,

and adsorption behavior study for heavy metal removal, Chem. Eng., 249 (2014) 189-200.

104.P. Soudaand L. Sreejith, Magnetic hydrogel for better adsorption of heavy metals from aqueous

solutions, J. Environ. Chem. Eng., 3 (2015) 1882-1891.

105.T. Nguyen, H. Ngo, W. Guo, J. Zhang, S. Liang, Q. Yue, Q. Liand T. Nguyen, Applicability of

agricultural waste and by-products for adsorptive removal of heavy metals from wastewater, Bioresour.

Technol., 148 (2013) 574-585.

106.L. Yan, Y. Huang, J. Cuiand C. Jing, Simultaneous As (III) and Cd removal from copper smelting

wastewater using granular TiO2 columns, Water Res., 68 (2015) 572-579.

107.J. Duan, J. Tan, J. Haoand F. Chai, Size distribution, characteristics and sources of heavy metals in

haze episod in Beijing, J. Environ. Sci., 26 (2014) 189-196.

108.T. Liu, X. Yang, Z.-L. Wangand X. Yan, Enhanced chitosan beads-supported Fe0-nanoparticles for

removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Res., 47

(2013) 6691-6700.

109.H. Zhang, Y. Tian, L. Wang, L. Zhangand L. Dai, Ecophysiological characteristics and biogas

production of cadmium-contaminated crops, Bioresource technology, 146 (2013) 628-636.

110.K. Khan, Y. Lu, H. Khan, S. Zakir, S. Khan, A.A. Khan, L. Weiand T. Wang, Health risks associated

with heavy metals in the drinking water of Swat, northern Pakistan, J. Environ. Sci., 25 (2013) 2003-

2013.

111.A.C. Davis, P. Wu, X. Zhang, X. Houand B.T. Jones, Determination of cadmium in biological

samples, Appl. Spectrosc. Rev., 41 (2006) 35-75.

112.M. Tellez-Plaza, A. Navas-Acien, C.M. Crainiceanuand E. Guallar, Cadmium exposure and

hypertension in the 1999–2004 National Health and Nutrition Examination Survey (NHANES),

Environmental health perspectives, 116 (2008) 51-56.

113.D. Sud, G. Mahajanand M. Kaur, Agricultural waste material as potential adsorbent for sequestering

heavy metal ions from aqueous solutions–A review, Bioresour. Technol., 99 (2008) 6017-6027.

114.S.W. Won, P. Kotte, W. Wei, A. Limand Y.-S. Yun, Biosorbents for recovery of precious metals,

Bioresour. Technol., 160 (2014) 203-212.

115.L.V.A. Gurgel, O.K. Junior, R.P. de Freitas Giland L.F. Gil, Adsorption of Cu (II), Cd (II), and Pb

(II) from aqueous single metal solutions by cellulose and mercerized cellulose chemically modified with

succinic anhydride, Bioresour. Technol. ,99 (2008 )3077-3083.

116.S. Prapagdee, S. Piyatiratitivorakuland A. Petsom, Activation of Cassava Stem Biochar by Physico-

Chemical Method for Stimulating Cadmium Removal Efficiency from Aqueous Solution,

EnvironmentAsia, 7 (2014).

117.X. Yu, S. Tong, M. Ge, L. Wu, J. Zuo, C. Caoand W. Song, Adsorption of heavy metal ions from

aqueous solution by carboxylated cellulose nanocrystals, J. Environ. Sci., 25 (2013) 933-943.

REFERENCES


118.M.A. Hussain, Alternative routes of polysaccharide acylation: synthesis, structural analysis,

properties, in, 2004.

119.J.C. de Melo, E.C. da Silva Filho, S.A. Santanaand C. Airoldi, Maleic anhydride incorporated onto

cellulose and thermodynamics of cation-exchange process at the solid/liquid interface, Colloids Surf. A

Physicochem. Eng. Asp., 346 (2009) 138-145.

120.M.M. Zohourian and K. Kabiri, Superabsorbent polymer materials: a review, Iran. Polym. J.,

17(2008)451-447.

121. 27.M. Summers, M. Aulton, M. Aulton, J. Staniforth, M. Aulton, Z. Summers, M. Aultonand M.

Rubinstein, Pharmaceutics: The science of dosage form design, (2007).

122.A. Suo, J. Qian, Y. Yaoand W. Zhang, Synthesis and properties of carboxymethyl cellulose‐graft‐

poly (acrylic acid‐co‐acrylamide) as a novel cellulose‐based superabsorbent, J. Appl. Polym., 103 (2007)

1382-1388.

123.S.A. Weerawarna, Method for making biodegradable superabsorbent particles, in, Google Patents,

2011.

124.F. Esposito, M.A. Del Nobile, G. Mensitieriand L. Nicolais, Water sorption in cellulose‐based

hydrogels, J. Appl. Polym. Sci., 60 (1996) 2403-2407.

125.M.E. Aulton, Pharmaceutics: The science of dosage form design, Churchill livingstone, 2002.

126.S. Ring, Some studies on starch gelation, Starch‐Stärke, 37 (1985) 80-83.

127. 20.J. Peerapattana, P. Phuvarit, V. Srijesdaruk, D. Preechagoonand A. Tattawasart, Pregelatinized

glutinous rice starch as a sustained release agent for tablet preparations, Carbohydr. Polym., 80 (2010)

453-459.

128.E. Diez-Pena, I. Quijada-Garridoand J. Barrales-Rienda, On the water swelling behaviour of poly (N-

isopropylacrylamide)[P (N-iPAAm)], poly (methacrylic acid)[P (MAA)], their random copolymers and

sequential interpenetrating polymer networks (IPNs), Polymers, 43 (2002) 4341-4348.

129.M.K. Krušićand J. Filipović, Copolymer hydrogels based on N-isopropylacrylamide and itaconic

acid, Polymer, 47 (2006) 148-155.

130.Ν. Peppasand B. Barr-Howell, In Hydrogels in Medicine and Pharmacy, Vol. 1; Peppas, ΝΑ, Ed, in,

CRC Press: Boca Raton, FL, 1986.

131.G. Pass, G. Phillipsand D. Wedlock, Interaction of univalent and divalent cations with carrageenans

in aqueous solution, Macromolecules, 10 (1977) 197-201.

132.S. Ghasemi, M. Mousavi, M. Shamsipurand H. Karami, Sonochemical-assisted synthesis of nano-

structured lead dioxide, Ultrason. Sonochem., 15 (2008) 448-455.

133.C. Liu, R. Baiand Q. San Ly, Selective removal of copper and lead ions by diethylenetriamine-

functionalized adsorbent: behaviors and mechanisms, Water Res., 42 (2008) 1511-1522

REFERENCES


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