GUIDED ASSEMBLY OF MAGNETIC NANOCOMPOSITE

FOR REMOVING POLLUTANT(S) FROM AQUEOUS

ENVIRONMENT

By

GWEE SHANG JUN

Report submitted in partial fulfillment of the requirements for the degree

of Bachelor of Chemical Engineering

JUNE 2014

ii

ACKNOWLEDGEMENTS

First and foremost, I would like to take this opportunity to express my utmost

gratitude towards everyone involved in my development as both a person, and of

course, in the completion of my Final Year Project.

In the preliminary, I wish to acknowledge my supervisor, Dr. Lim Jit Kang,

who has been providing me with invaluable guidance and advices throughout my

tenure as a final year student in my last two semesters here. Not only he has been

lending me his knowledge and expertise, supporting me whenever I encounter any

difficulties in my lab works or report writings, but he has also never failed encouraging

me to pursue my career pathway and goals, despite the role I play here is just trivial

and perhaps redundant. For that, I really appreciate his effort.

Besides, I would like to show my deepest appreciation to senior Che Hui Xin,

my post graduate student friend who has constantly been guiding me especially in my

lab works. Not to forget mentioning senior Yeap Swee Pin too, another post graduate

student friend of mine whom such selflessly he has been to me by always lending me

his helping hand as much as he could whenever I needed it most. I wish them all the

best in their future undertakings.

Furthermore, I feel glad to have such caring, kind and selfless lab mates like

Joanna Tai, senior Toh Pei Yi, senior Sum Jing Yao and all the lab technicians who

have been assisting me without any hesitation during my lab works. I feel blessed I

must say, to have been able to be part of it.

Last but not least, I am grateful to my parents who have all the way been

supportive to me when I started my studies here. Their continual moral support has

proven to be one of the pivotal driving forces in the completion of my final year project.

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TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ii

TABLE OF CONTENTS iii

LIST OF TABLES vii

LIST OF FIGURES viii

LIST OF SYMBOLS x

LIST OF ABBREVIATION xi

ABSTRAK xii

ABSTRACT xiv

CHAPTER ONE: INTRODUCTION

1.1 Introduction 1

1.1.1 Nanoparticles (NPs) 1

1.1.2 Polyelectrolytes 2

1.1.3 Dyes 3

1.1.4 Impacts to Society 3

1.2 Problem Statement 4

1.3 Research Objectives 6

1.4 Organization of Thesis 6

iv

CHAPTER: TWO LITERATURE REVIEW

2.1 Properties of Magnetic Iron Oxide Nanoparticles (MIONPs) 7

2.1.1 Magnetophoresis 7

2.1.2 Catalytic Property 9

2.2 Problems Associated with Application of MIONPs 11

2.2.1 Agglomeration 11

2.2.2 Nanotoxicology 12

2.3 Polyelectrolytes as Binding Agents 16

2.3.1 Layer by Layer (LBL) Technique 18

2.4 Nanocomposite as One Unified Structure 21

2.4.1 Advantages of Nanocomposite 21

2.4.2 Application of Nanocomposite in Environmental Remediation 23

CHAPTER: THREE MATERIALS AND METHODS

3.1 Materials and Equipment 25

3.1.1 Chemicals and Materials 25

3.1.2 Facilities and Equipment 26

3.2 Research Methodology 27

3.3 Experimental Methods 28

3.3.1 Preparation of Silica Nanotemplate 28

3.3.2 Size Distribution and Zeta Potential Measurements 29

3.3.3 Preparation of PDDA Solution 29

v

3.3.4 Preparation of PSS Solution 30

3.3.5 Preparation of PEI Solution 30

3.3.6 Preparation of Iron Oxide Nanoparticles Solution 30

3.3.7 Preparation of Polymeric-Coated Silica Nanoparticles 31

3.3.8 Preparation of Silica-Polyelectrolyte(s)-MIONPs Nanocomposite 32

3.3.9 Preparation of Methylene Blue (MB) Dye 33

3.3.10 Preparation of Methyl Orange (MO) Dye 33

3.3.11 Dye Removal 34

CHAPTER: FOUR RESULTS AND DISCUSSION

4.1 Characterization and Observation 36

4.1.1 Synthesis of Silica Nanoparticles 36

4.1.2 Synthesis of Polymeric-Coated Silica Nanoparticles 37

4.1.3 Synthesis of Iron Oxide Nanoparticles 38

4.1.4 Synthesis of Silica-Polyelectrolyte(s)-MIONPs Nanocomposite 39

4.1.5 Zeta Potential and Particle Size 42

4.2 Performance Evaluation 46

4.2.1 Removal of 20 ppm Methylene Blue Dye 46

4.2.2 Removal of 20 ppm Methyl Orange Dye 51

4.2.3 Removal of MB and MO Dyes by Ultimate Nanostructures 58

vi

CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion 63

5.2 Recommendations 65

REFERENCES 66

APPENDICES

vii

LIST OF TABLES

Page

Table 3.1: Chemicals used in this research 25

Table 3.2: Equipment used in this research 26

Table 4.1: Zeta potential and hydrodynamic diameter of single layered

silica-PDDA-iron oxide nanocomposite

44

Table 4.2: Zeta potential and hydrodynamic diameter of multilayered

silica-PDDA-PSS-PDDA-iron oxide nanocomposite

45

Table 4.3: Zeta potential and hydrodynamic diameter of single-layered

silica-PEI-iron oxide nanocomposite

46

viii

LIST OF FIGURES

Page

Figure 2.1: Relationship between specific surface area (m2 kg-1) of a

spherical particle and its size (diameter in nm) with a density

of 1000 kg m-3 as an example (Navarro et al., 2008)

12

Figure 2.2: Schematic illustration of LBL adsorption of polyelectrolyte

multilayers (Decher, 1997)

18

Figure 3.1: Process research schematic flow 27

Figure 3.2: Schematic diagram portraying major steps involved in LBL

assembly of silica-polyelectrolyte(s)-MIONPs

nanocomposite (Che et al., 2014)

29

Figure 4.1: Silica NP suspension 37

Figure 4.2: (a) PDDA-PSS-PDDA-modified silica NP suspension, and

(b) PEI-modified silica NP suspension

38

Figure 4.3: Collection of iron oxide NP suspension with a magnetic bar 39

Figure 4.4: TEM micrograph of iron oxide NP aggregration 40

Figure 4.5: TEM micrographs of polymeric-modified latices exposed to

deposition of iron oxide NPs on (a) a PDDA-modified silica

core, (b) a PDDA-PSS-PDDA-modified silica core, and (c) a

PEI-modified silica core

41

Figure 4.6: (a) MB structural formula and (b) MB solution before and

after reaction

48

Figure 4.7: Percentage removals for 20 ppm MB tests using silica-

PDDA-iron oxide nanocomposite

49

ix

Figure 4.8: Percentage removals for 20 ppm MB tests using silica-PEI-

iron oxide nanocomposite

50

Figure 4.9: Percentage removals for 20 ppm MB tests using silica-

PDDA-PSS-PDDA-iron oxide nanocomposite

51

Figure 4.10: (a) MO structural formula and (b) MO solution before and

after reaction

52

Figure 4.11: Percentage removals for 20 ppm MO tests using silica-

PDDA-iron oxide nanocomposite

53

Figure 4.12: Percentage removals for 20 ppm MO tests using silica-PEI-

iron oxide nanocomposite

55

Figure 4.13: Percentage removals for 20 ppm MO tests using silica-

PDDA-PSS-PDDA-iron oxide nanocomposite

56

Figure 4.14: Schematic diagram showing electrostatic interactions and

mechanisms involved for MB and MO removal by (a) silica

colloid, (b) PDDA-coated silica colloid, and (c) silica-

PDDA-iron oxide nanocomposite (Che et al., 2014)

59

Figure 4.15: Collection of magnetic NC suspension with a magnetic bar 60

Figure 4.16: Percentage removal tests using three ultimate

nanocomposites for (a) MB and (b) MO dyes

61

x

LIST OF SYMBOLS

Symbol Description

% Percentage

μL Microliters

mg or g Milligram or gram

min Minutes

mM Millimolar

mL Mililiters

nm Nanometer

ppm Parts per million

rpm Revolution per minute

xi

LIST OF ABBREVIATION

DI Deionized

DLS Dynamic Light Scattering

Fe2+ Ferrous ion

Fe3+ Ferric ion

FeCl3 Iron (III) chloride

FeCl2.4H2O Iron (II) chloride

Fe3O4 or (Fe3II/IIIO4) Magnetite

H2O2 Hydrogen peroxide

IO Iron oxide

LBL Layer-by-layer

MB Methylene blue

MIONPs Magnetic iron oxide nanoparticles

MO Methyl orange

NaCl Sodium Chloride

NC Nanocomposite

NPs Nanoparticles

H2O∙/O2∙ Superoxide radicals

PDDA Poly(diallyldimethylammonium chloride)

PEI Poly(ethyleneimine)

PSS Poly(styrenesulfonate)

TEM Transmission Electron Microscopy

TEOS Tetraethylorthosilicate

∙OH Hydroxyl radicals

xii

PEMASANGAN PERPANDU NANOKOMPOSIT MAGNET UNTUK

MENGALIHKAN BAHAN PENCEMARAN DARI ALAM SEKITAR

AKUEUS

ABSTRAK

Nanopartikel oksida besi magnet yang terdedah adalah cenderung untuk

mengalami aglomerasi disebabkan oleh van der Waals dan tarikan magnet yang

dialami oleh partikel-partikel tersebut. Tambahan pula dengan nanoketoksikan mereka,

nanostruktur novel di mana nanopartikel oksida besi magnet tersebut diintegrasikan

dengan tiga jenis rangkaian polimer yang berbeza yang dilapiskan di atas permukaan

koloid silika telah disintesiskan melalui teknik lapisan demi lapisan. Penyelerak

Cahaya Dinamik (DLS) telah digunakan untuk mengawasi evolusi struktur-struktur

tersebut dari koloid silika ke koloid silika-polielektrolit-komposite oksida besi. Di

samping itu, Mikroskop Elektron Transmisi (TEM) juga digunakan untuk menyiasat

morfologi struktur nanostruktur yang telah disintesiskan dalam setiap peringkat.

Nanostruktur-nanostruktur muktamad tersebut menunjukkan kestabilan koloid dan

pemangkin yang bagus, kerana sintesis tersebut membolehkan permukaan-permukaan

koloid silika tersebut untuk diubahsuai dan difungsionalisasikan dengan nanopartikel

oksida besi magnet untuk mempunyai fungsi magnet dan pemangkin dalam satu

nanostruktur bergabungan. Koloid silika dipilih untuk menjadi cangkerang teras

disebabkan kestabilan meraka yang amat tinggi yang membolehkan mereka

mengurangkan kecenderungan nanopartikel oksida besi magnet membentuk kluster-

kluster, dan juga oleh kerana kebolehan mereka untuk menyediakan perlindungan

terhadap ketoksikan oksida besi. Pada masa yang sama, rangkaian-rangkaian polimer

yang mengelilingi nanotemplate silika tersebut memerangkap substrat dengan

xiii

bertindak sebagai penyekat untuk menyetempatkan nanopartikel oksida besi magnet

dan substrat tersebut dalam ruang terkurung di mana ini menambahbaikkan sentuhan

fizikal mereka dan seterusnya menyenangkan degradasi pemangkin nanopartikel

oksida besi. Hasilnya, satu entiti di mana kestabilan kimia yang lebih baik, keupayaan

dispersi yang lebih tinggi, nanoketoksikan yang lebih rendah dengan fungsi-fungsi

yang dipertingkatkan seperti penjerapan yang bagus, keterdegradasikan yang

dipertingkatkan dan kebolehpisahan magnet telah berjaya diperolehi. Di sini, aplikasi

nanokomposit-nanokomposit tersebut yang berpotensi dalam kejuruteraan alam

sekitar telah diperagakan menggunakan pewarna organik, iaitu Metilena Biru (MB)

dan Metilena Oren (MO) sebagai sistem model kami. Eksperimen telah dijalankan

untuk menguji kebolehan ketiga-tiga nanokomposit muktamad dalam mengurangkan

pewarna tersebut bersama dengan nanobahan mereka yang telah disintesiskan pada

setiap peringkat, iaitu koloid silika, koloid silika-polielektrolit (silika-PDDA dan

silika-PEI), dan koloid silika-polielektrolit-nanokomposite oksida besi (silika-PDDA-

nanopartikel oksida besi, silika-PDDA-PSS-PDDA-nanopartikel oksida besi dan

silika-PEI-nanopartikel oksida besi). Dengan mengambil kira interaksi elektrostatik di

antara molekul-molekul pewarna dan nanobahan-nanobahan yang telah disintesis

tersebut, kami berjaya mengesahkan bahawa ketiga-tiga koloid silika-polielektrolit-

nanokomposite oksida besi muktamad tersebut menunjukkan prestasi pengurangan

pewarna yang lebih baik dibandingkan dengan nanopartikel-nanopartikel yang tidak

difungsionalisasikan, disebabkan oleh sifat pemangkin mereka. Kami juga berjaya

mewajarkan bahawa silika-PEI-nanokomposite oksida besi merupakan

nanokomposite yang paling unggul di antara semua, oleh kerana konfigurasi

polielektrolit yang digunakan adalah berlapis tunggal dan bercabang.

xiv

GUIDED ASSEMBLY OF MAGNETIC NANOCOMPOSITE FOR

REMOVING POLLUTANT(S) FROM AQUEOUS ENVIRONMENT

ABSTRACT

Bare magnetic iron oxide nanoparticles (MIONPs) are prone to fast

agglomeration due to van der Waals and magnetic attraction experienced among them.

Coupled with their nanotoxicity induced, novel nanostructures of MIONPs being

integrated into three different types of polymeric networks assembled onto silica

colloid surfaces have been synthesized via layer-by-layer technique. Dynamic Light

Scattering (DLS) was employed to monitor the evolution of these structures from silica

colloid to silica colloid-polyelectrolyte(s)-iron oxide composite. Moreover,

Transmission Electron Microscope (TEM) was utilized to investigate the structural

morphology of nanostructure synthesized at each stage. The ultimate nanostructures

manifested good colloidal and catalytic stability, as the synthesis allowed the silica

colloids surfaces to be modified and functionalized with MIONPs in order to possess

both the magnetic and catalytic bifunctionalities in one unified nanostructure. Silica

nanoscale colloids were selected to be the core shell due to their exceptional stability

subsequently minimizing the tendency of MIONPs to form clusters, and ability to

provide better protection against toxicity. Meanwhile, polymeric networks

surrounding the silica nanotemplate were to entrap substrates by acting as barriers to

localize the MIONPs and substrates in a confined space, improving their physical

contacts thus easing the catalytic degradation by MIONPs. As a result, an entity of

better chemical stability, higher dispersion capability, less nanotoxicity with enhanced

functionalities combined with its good adsorptivity, upgraded degradability and

magnetic separability was acquired. Here, the potential environmental engineering

xv

application of these nanocomposites was demonstrated by taking organic dyes,

Methylene Blue (MB) and Methyl Orange (MO) as our model system. The experiment

was conducted by assessing the dye-removing capabilities of the three final

nanocomposites along with their respective nanomaterials synthesized at each stage,

namely silica colloid, polyelectrolyte(s)-functionalized silica colloid (silica-PDDA

and silica-PEI), and silica colloid-polyelectrolyte(s)-iron oxide nanocomposites

(silica-PDDA-MIONPs, silica-PDDA-PSS-PDDA-MIONPs and silica-PEI-MIONPs).

By taking into consideration of electrostatic interactions between the dye molecules

and the aforesynthesized nanomaterials, it was verified that all three ultimate silica

colloid-polyelectrolyte(s)-iron oxide nanocomposites showed better dye-removing

capabilities as compared to their unfunctionalized counterparts, primarily due to their

catalytic property. We also justified that silica-PEI-MIONPs nanocomposite was the

most superior among all, because of the single-layered and branched configuration of

its polyelectrolyte registered.

1

CHAPTER ONE

INTRODUCTION

1.1 Introduction

In this globalized epoch with rapid urbanization, magnetic nanoparticle

technologies are becoming a boon, especially in areas of biomedical engineering (Hee

Kim et al., 2005), bio-sensing development (Josephson et al., 2001, Gijs et al., 2009,

Fornara et al., 2008), and bio-separation technologies (Taylor et al., 2000, Son et al.,

2005). Ubiquitously, the application of magnetic nanoparticle technology to solve

environmental problems has received considerable attention (Jiang et al., 2012). Due

to their reactive surfaces and large specific surface areas, magnetic nanoparticles have

been a choice of most, as largely seen in applications in the adsorption of various dyes

(Saha et al., 2011). Bear in mind that it is imperative for these industrial applications

to have their pollutant-removing agents recovered easily from the treated wastewater;

thus, excellent magnetic responsivity is necessary for magnetic separation of the

recovery of nanocomposite adsorbent from treated effluents in practical application

(Jiang et al., 2012).

1.1.1 Nanoparticles (NPs)

In this study, magnetic iron oxide nanoparticles (MIONPs) are chosen since

they have great potential to be used for selective wastewater purification for dye

removal applications due to their unique magnetic and catalytic characteristics (Saha

et al., 2011). Besides, this nanostructure is also readily separable from water treated

by magnetophoretic collection (Yavuz et al., 2006). Furthermore, catalytic function of

iron oxide nanoparticles facilitates Fenton’s reaction that is able to degrade dyes in

wastewater effectively (Yang et al., 2009). Fenton’s reaction is one type of advanced

oxidative process that involves the generation of hydroxyl radicals which can degrade

2

most of the organic compounds to carbon dioxide and water of dye/organic matter

efficiently (de Souza et al., 2006).

There are handful of chemical methods that can be used to synthesize magnetic

nanoparticles namely microemulsions (Chin and Yaacob, 2007), sol-gel syntheses

(Albornoz and Jacobo, 2006), sonochemical reactions (Hee Kim et al., 2005) and so

on. The synthesis of these magnetic nanoparticles is a complex process due to their

colloidal nature (Laurent et al., 2008). However, the most common method for the

production of magnetite nanoparticles is the chemical co-precipitation technique of

iron salts (Martínez-Mera et al., 2007, Morrison et al., 2005, Lee et al., 2004). This

method will be employed in this study since it is the simplest and most efficient

chemical pathway to obtain magnetic particles, not to forget mentioning that large

amount of nanoparticles can be synthesized through this method (Laurent et al., 2008).

1.1.2 Polyelectrolytes

Therefore, polyelectrolytes - polymers bearing electrolytes namely polycations

and polyanions, are utilized because they act as the linker or binder between silica

colloids and iron oxide nanoparticles in the whole unified nanocomposite structure. In

our approach, layer-by-layer (LBL) self-assembly technique (Decher and Hong, 1991)

is applied to the coating of polymer colloids. For over the last 15 years, the LBL

deposition of polyelectrolytes have become established techniques for the formation

of a wide range of thin films (Bruening et al., 2008). The assembly of magnetite

nanoparticle and layers of polycation and polyanion onto silica microspheres to form

magnetic core-shell microspheres is performed in this research.

3

1.1.3 Dyes

Here, dyes namely methylene blue and methyl orange were chosen as

pollutants from aqueous environment to evaluate the feasibility of our idea due to the

ease of their detection by calorimetric method during their exterminations. Wastewater

effluents from different industries, namely textiles, rubber, paper, and plastics, contain

several kinds of synthetic dyestuffs (Chiou et al., 2004). The release of these colored

waters to the environment is a considerable source of nonaesthetic pollution and

eutrophication (Jiang et al., 2012), at the same time, posing serious problems because

of their color, low biochemical oxygen demand (BOD) and high chemical oxygen

demand (COD) (Kusvuran et al., 2005). Because of the complex aromatic structure

and the stability of these dyes, conventional biological treatment methods are

ineffective for decolorization (Razo-Flores et al., 1997). Hence, the magnetic-catalytic

bifunctionalities of MIONPs come into the picture for a better efficiency of dye

removal as mentioned previously.

1.1.4 Impacts to Society

As stated above, iron oxide nanoparticles are superior in water treatment

purposes as they have high specific areas to volume ratio. As a result, their high

reactivity coupled with their high catalytic properties are capable of degrading other

pollutants in aqueous environment more easily. However, due to the same nanoscopic

nature of iron oxide nanoparticles themselves, they actually possess nanotoxicity

which is attributable by oxidative stress and generation of free radicals. Of course,

human exposure is ineluctable then since they are becoming more widely used

nowadays. Therefore, they have to be integrated into another system such as silica

or/and polymeric matrices to minimize their adverse effects on humans.

4

1.2 Problem Statement

Bare MIONPs tend to be agglomerated easily (Phenrat et al., 2007),

predominantly due to both long-range van der Waals and magnetic attraction

experienced among the particles (Lim et al., 2009), reducing their catalytic and

selectivity (Zhao et al., 1998). Hence, it is desirable that the nanoparticles are isolated

by inert materials such as silica and polymers (Im et al., 2005, Sun et al., 2005, Xu et

al., 2006) as their capping ligands (Barnakov et al., 2005) to avoid aggregation of the

nanoparticles in the application systems (Matsumoto et al., 2009). Furthermore, iron

oxide nanoparticles induce nanotoxicity resulted by oxidative stress and generation of

free radicals (Jeong et al., 2011).

Thus, in this research, MIONPs are functionalized beforehand in order to

stabilize them (Illés and Tombácz, 2006), where they will be incorporated into

polymeric network assembled on silica colloid surfaces. In this case, silica colloids are

chosen to serve as nanotemplates for layer-by-layer assemblies of MIONPs for their

traits of being able to prevent agglomeration of MIONPs in liquid, improve their

chemical stability and provide better protection against toxicity (Lesnikovich et al.,

1990). This coating of silica actually stabilizes the magnetic nanoparticles in two

distinct ways (Sun et al., 2005); one is by shielding the magnetic dipole interaction of

the MIONPs with the silica shells, another is through the enhancement of the coulomb

repulsion of the MIONPs with the silica NPs since the latter is also negatively charged

(Laurent et al., 2008).

On the other hand, different configurations of polymer to be employed here are

of linear and branched polyelectrolytes. These architectures are proposed with the

intention to have a better grasp on their behaviors particularly in terms of their

containment and capturing rate of iron oxide NPs. However, the actual working

5

mechanism is not known yet. Hence, it is hypothesized that the differences in

configuration of polymeric surfaces would somehow affect their performances in

pollutant removal capabilities which are made possible either by; having more iron

oxide being able to be embedded in branched more easily compared to their linear

counterparts at the very first place after their integration, or in spite having the same

amount of iron oxide content on both the finished nanostructures initially but when it

comes to dye removing part only then the branching comes into the picture, degrading

pollutants more effectively. Therefore, the assimilation of the magnetic and catalytic

properties of magnetic nanoparticles into one unified nanostructure is undergone for

dye removal application.

6

1.3 Research Objectives

There are two objectives needed to be achieved in this study and are listed

below.

1. To synthesize surface functionalized silica-core/iron oxide-shell nanoparticles

using different configurations of polymers registered as their linkage.

2. To compare the environmental engineering feasibility of the aforementioned

structures in terms of their dye removing abilities from aqueous environment.

1.4 Organization of Thesis

This thesis has been organized in five chapters. Chapter One is an introductory

chapter where a superficial glimpse of what the whole thesis is all about is presented.

Meanwhile, Chapter Two contains pertinent literature reviews related to our field of

study and findings. Chapter Three presents the methodology of the experiments where

materials and methods synthesizing various nanostructures and performing dye

removals are included here. On the other hand, Chapter Four comprises results and

discussion of the whole research. Last but not least, conclusion and recommendations

of this study are presented in Chapter Five.

7

CHAPTER TWO

LITERATURE REVIEW

2.1 Properties of Magnetic Iron Oxide Nanoparticles (MIONPs)

2.1.1 Magnetophoresis

Commonly, this physical phenomena has been used to separate magnetic

material from a non-magnetic medium (Moeser et al., 2004). Herein, magnetic

separation methods can be classified into two main types; the first type, separand

which is intrinsically magnetic, so that magnetic separation can occur without any

modification and meanwhile, for the second type, one or more non-magnetic

components of a mixture have to be rendered magnetic by the attachment of a

magnetic-responsive entity and can be manipulated using an external field

(Karumanchi et al., 2002). Here, MIONPs possess such properties, where they respond

to magnetophoresis and their motion is controlled by an external magnetic force.

Effectively, this magnetophoretic mobility is the velocity of an immunomagnetically

labeled cell in a magnetic energy gradient divided by the magnitude of that magnetic

energy gradient, where the velocity is the result of a magnetic force created on the cell

by the interaction of the magnetic-susceptible material with the imposed magnetic

energy gradient (McCloskey et al., 2003). For the past few decades, magnetic

separation has been consistently utilized and applied to rather complex separations

through the use of functionalized magnetic particles tailored specifically to selectively

remove cells (Šafařık and Šafařıková, 1999), proteins (Bucak et al., 2003, Hubbuch

and Thomas, 2002), environmental contaminants (Buchholz et al., 1996), heavy metal

ions (Kaminski and Nunez, 1999, Leun and SenGupta, 2000), dyes (Šafařík, 1995) and

nonpolar organic contaminants (Moeser et al., 2002).

8

Application of this magnetic separation is getting more prominent nowadays,

preponderantly in areas dealing with environmental issues. Unlike other techniques

such as biological treatment (Kornaros and Lyberatos, 2006), coagulation/flocculation

(Sadri Moghaddam et al., 2010), chemical oxidation (Dutta et al., 2001), membrane

filtration (Capar et al., 2006), ion-exchange (Karcher et al., 2002) and photocatalytic

degradation (Gao et al., 2012), magnetic separation has the upper hand by having

purification method that does not produce secondary pollutions whereby the material

can be easily retrieved, recollected and reused (Ma et al., 2009). In fact, it has been

widely recognized that iron-based nanoparticles are the first generation nanomaterial

used in nanorelated environmental technologies (Sun et al., 2006, Tratnyek and

Johnson, 2006). As a result, MIONPs exhibiting magnetic characteristic are highly in

demand to perform quick and effective magnetic separation (Bolto, 1990).

Generally, this process works such a way that when a magnetic field is applied,

MIONPs are magnetically induced creating field or locally induced magnetic moment

that contributes to the net field sensed by the colloidal particles (Gerber and Birss,

1983). When the magnetic force created by the field is sufficiently greater than

opposing force producing large field gradients around the particles, MIONPs will be

attracted to the magnetic field (Gerber and Birss, 1983). Once the magnetic field is

turned off, the nanoparticles are released and are allowed to disperse back into solution.

Therefore, magnetic forces on the particles themselves have to be able to suppress and

overcome opposing forces, singularly viscous drag and Brownian motion (Yavuz et al.,

2006, Lim et al., 2010), which is different from forces like inertial, gravitational and

buoyant forces that can be neglected owing to their extremely nanosized particles

(Cotten and Eldredge, 2002). Otherwise, no magnetic separation will be triggered. So,

to exert a larger magnetic force on the particles to overpower the rivalling forces

9

resulted from small particle sizes, a more powerful magnetic field gradient has to be

used, giving rise to the theory that magnetic force being proportional to external

magnetic field gradient (Bek et al., 2008).

2.1.2 Catalytic Property

Another fundamental application of the MIONPs is their catalytic property

with Fenton reactions as the dominant driving forces behind their working mechanism.

Since the 1990s, Fenton and photoassisted Fenton reactions have been conventionally

employed in the degradation of aromatic organic compounds in industrial wastewater

(Feng et al., 2003), not to forget mentioning the various forms of phenols (Zazo et al.,

2005, Watts et al., 1999, Zimbron and Reardon, 2009), aromatics (Matta et al., 2007),

acetic acid (Pignatello, 1992), formaldehyde (Murphy et al., 1989) and dyes (Kuo,

1992) as well. Their effectiveness is a sequel from the fact that the generated hydroxyl

radicals (∙OH), are highly reactive and nonselective to the extent that they are capable

to decompose numerous organic compounds (Faust and Hoigne, 1990). Thus, ∙OH

radicals are the main players in the degradation process since they are able to detoxify

a number of substrates owing to their strong oxidation abilities (Dutta et al., 2001).

Iron oxide nanoparticles possess excellent catalytic function aiding Fenton’s reaction,

degrading organic pollutants more effectively; hence, are favorably preferred in the

elimination of toxic and recalcitrant organic pollutants from aqueous environment

(Kusvuran et al., 2005).

In fact, the Fenton reaction is an advanced oxidation process (AOP) that

underlines the production of reactive hydroxyl radicals (∙OH) from a mixture of ferrous

ions (Fe2+) and hydrogen peroxide (H2O2) (Jiang et al., 2010). Since both the H2O2 and

Fe2+ are uncomplicated, easy to handle and environmental friendly, much efforts have

been poured in during these recent years to establish the classic Fenton’s reaction

10

(Brillas et al., 2000, Gözmen et al., 2003, Neyens and Baeyens, 2003). Interestingly,

Fenton-like reactions in which ferric ions (Fe3+) or other transition metal ions utilized

are normally treated as the prototype of the developed Fenton reactions (Jiang et al.,

2010).

As a whole, the underlying working mechanism controlling the Fe3+/H2O2

Fenton-like reaction is dependent on the formation of a complex called Fe(III)-H2O2

complex, followed by decomposition of the complex in a uni-molecular method to

generate Fe2+ ions and radicals of H2O∙/O2∙ (Jiang et al., 2010). Subsequently, the

decomposition of H2O2 is catalyzed by the previously yielded Fe2+ ions in order to

produce hydroxyl radicals (∙OH) (De Laat and Gallard, 1999). Typically, Fenton and

Fenton-like reactions are not considered as one but classically, shifting of Fe(II) to

Fe(III) happens frequently with a rapid presence of Fe(II) during Fenton-like reaction

(Jiang et al., 2010). In other words, both the Fenton and Fenton-like reactions exhibit

the possibilities of inherent concurrence and conversion (Jiang et al., 2010).

11

2.2 Problems Associated with Application of MIONPs

2.2.1 Agglomeration

As known, MIONPs have the ability to swiftly convert unwanted

environmental contaminants to benign products and are emerging as one of the most

promising (Henn and Waddill, 2006) and flexible in-situ remediation agents in

aqueous environment (Phenrat et al., 2007). Unfortunately, being reactive alone is not

sufficient enough. In order to be able to effectively live up to their top billing, these

particles should be stable and readily dispersible in water in a way that it can be

migrated through water-saturated porous media to the contaminated area (Phenrat et

al., 2007). Studies have shown that for bare unsupported MIONPs, they exhibit limited

mobility when saturated in porous media where they have practical transport distances

of only a dew centimeters or less (Schrick et al., 2004). In other words, the aggregation

of MIONPs occurs, which could result in pore plugging that limits transport (Saleh et

al., 2007).

Therefore, colloidal stability plays a pivotal role in fulfilling the potentials of

MIONPs in environmental aspects. Else, these clusters would lead to low chemical

reactivity to the particles as their exposed specific surface area is tremendously

diminished upon precipitation (Schrick et al., 2004). Technically, colloidal stability is

defined as the capacity of a particle to defy agglomeration within a specified time

(Sonntag et al., 1987), and is further accelerated by the existence of an energy barrier

in the interparticle interaction potential (Phenrat et al., 2007). Reason MIONPs having

a higher tendency to form clusters are mainly due to the van der Waals and magnetic

interaction undergone by the particles (Lim et al., 2009), thus altering their dispersion

stability (De Vicente et al., 2000). The influence of the magnetic properties of

MIONPs on their amalgamation is even more obvious under an applied magnetic field,

12

where ferromagnetic or paramagnetic distributions result in chain-like lumps in which

the dipoles are oriented in a head-tail configuration along the direction of the field (De

Vicente et al., 2000, Promislow et al., 1995, De Gennes and Pincus, 1970). Despite

after having dried with the absence of a magnetic field, these chain-like

conglomerations of magnetic nanoparticles still exist (Butter et al., 2003). Hence, in

addition, the scattering of MIONPs might undergo dipole-dipole attraction between

the magnetic moments of the particles which may affect their size and dispersion

stability (Phenrat et al., 2007).

2.2.2 Nanotoxicology

As portrayed in Figure 2.1, the specific surface area increases as particles

become more nanoscaled. Escalating progress made in materials science has enabled

the synthesis and fabrication of various nanostructures with superior physicochemical

properties, primarily because of such exponential increase in surface-to-volume ratio

compared to their bulk counterparts (Rivera Gil et al., 2010, Jang, 2006), particularly

porous NPs (Maurer-Jones et al., 2010).

Figure 2.1: Relationship between specific surface area (m2 kg-1) of a spherical

particle and its size (diameter in nm) with a density of 1000 kg m-3 as an example

(Navarro et al., 2008)

13

In the past decade, the use of nanoparticles in research and in industrial

production is seeing a drastic surge, which in turn leading to feuds on the potential

toxicity of such nanomaterials (Lewinski et al., 2008, Meng et al., 2009).

Corresponding to this controversy, nanoparticles are beginning to come under scrutiny

and discussions on the potential adverse effects of these nanomaterials have increased

steadily in recent years (Nowack and Bucheli, 2007), inevitably giving rise to the field

of nanotoxicology (Rivera Gil et al., 2010). With the anticipated increasing exposures

to nanoparticles, for instance, intentionally in the field of medical diagnostics (Pons et

al., 2010, McCarthy and Weissleder, 2008) and unintentionally in occupational

settings (Lee et al., 2010) and chemical waste streams, nanotoxicology has suddenly

become a crucial element in the assessments of nanomaterials in terms of their safety

aspect (Rivera Gil et al., 2010).

Omnipresently, researchers in cytotoxicity studies have dedicated their time

and attention to different physicochemical properties of nanostructures namely sizes,

shapes, surface functionalities, crystallinities, and dopants (George et al., 2009, Oh et

al., 2010). The question of whether the nanoparticulate itself contributes to toxicity

remains imperative (Rivera Gil et al., 2010). As mentioned, nanoparticles own higher

surface-to-volume ratio, which could mean that catalytic or other active sites on the

particular surface are exposed (Barnard and Xu, 2008, Xia et al., 2008). Increased

surface area may also promote dissolution of the materials, resulting in the release of

potentially toxic ions which would be very unwelcome especially heavy metals like

Cd or Ag (Kirchner et al., 2005, AshaRani et al., 2008).

14

2.2.2.1 Nanotoxicity towards Humans

This extraordinary physicochemical characteristics of nanomaterials might

cause devastating implications to human organs (Lewinski et al., 2008, Nabeshi et al.,

2011, Lee et al., 2011). Due to their nanoscopic nature, these small, subcellular scale

of nanoparticles can expedite their notorious entry to intracellular domains, thereby

invading cellular defenses (Daughton, 2004), causing them to be retained in many cells

and organs to a larger extent as compared to their bulkier forms (Nativo et al., 2008,

Hess and Tseng, 2007). Conceivably, outcomes of the reactive material at the same

concentration can be higher at the intracellular level than at the extracellular level

(Chang et al., 2006) because of the solubilization and degradation occurring inside

cells (Thubagere and Reinhard, 2010). With prolonged exposure to these

nanomaterials, accumulation and retention in the organism, singularly spleen and liver

(Casals et al., 2008) would be unescapable, since the shape of nanoparticles plays a

vital role in a determining response (Albanese et al., 2010, Liu et al., 2009, Hutter et

al., 2010). Furthermore, their geometric effects have been hyped up by the examples

of needle-shaped nanotubes, which have the ability to impale the entire cells (Poland

et al., 2008, Miyawaki et al., 2008). In addition, proteins present in biological media

can readily associate with the nanoparticle surface, specifically protein corona which

alters the features of their interaction with cells (Walczyk et al., 2010, Casals et al.,

2010). Moreover, simply the sorption of endogenous proteins to nanoparticles within

an organism could theoretically elicit an immune response as a result of changing the

native conformation of the exposed protein (Daughton, 2004).

15

2.2.2.2 Nanotoxicity towards Environments

In context here, nanoparticles, in this sense, are examples of indirect toxicants,

where exposure to the parent chemical is not a prerequisite for adverse effects, since

nanoscale by-products from nanotechnology industries would eventually find their

ways and enter aqueous environment (Daughton, 2004). Ecotoxicological studies

show that NPs pose threats to aquatic organisms, both to unicellular organisms (e.g.

bacteria or protozoa) and animals (e.g. Daphnia or fish) (Nowack and Bucheli, 2007).

Potential uptake impacts include direct ingestion or entry across epithelial boundaries

such as gills or body wall (Nowack and Bucheli, 2007). At the cellular level

prokaryotes like bacteria may be largely protected against the uptake of many types of

NPs since they do not have mechanisms for transport of colloidal particles across the

cell wall; unfortunately for eukaryotes, e.g. protists and metazoans, the situation is

different since they have processes for the cellular internalization of nanoscale or

microscale particles, namely endocytosis and phagocytosis (Moore, 2006). Also, there

were reports that latex NPs have been consumed by fish Oryzias latipes, accumulating

those particles not only in their gills and intestine but in brain, testis, liver and blood

as well (Kashiwada, 2006). Meanwhile, plants like algae and fungi could be

detrimentally affected too. Inside their cells, NPs might directly provoke alterations of

membranes and other cell structures and molecules, as well as protective mechanisms

(Navarro et al., 2008). Indirect effects of these NPs depend on their chemical and

physical properties and may include physical restraints (clogging effects),

solubilization of toxic NP compounds, or production of reactive oxygen species

(Navarro et al., 2008).

16

2.3 Polyelectrolytes as Binding Agents

To date, polymers functionalized MIONPs are getting more and more into the

limelight owing to the advantages of polymer coating which increases repulsive forces

to balance the magnetic and van der Waals attractive forces acting on the NPs (Wu et

al., 2008). The formation of these polyelectrolyte adlayers offers electrosteric

repulsions among particles (Runkana et al., 2006) to overcome the attractive

interactions when two particles approach each other at distances less than twice the

adlayer thickness (Lim et al., 2009, Seebergh and Berg, 1994). The synthesis and

fabrication of micro- and nanosized capsules or shells enabling the encapsulation of

diversified structures are of both scientific and technological interest (Langer and

Chasin, 1990). Such particles can be prepared by interfacial polymerization or by

phase separation from a polymer-solvent mixture (Slomkowski and Miksa, 1995), with

these linkers combining the advantages of thin organic films of polyelectrolytes

coupled with the easy handling and applications of colloids (Donath et al., 1998). The

most important novel features of the fabricated polyelectrolyte shells are that firstly,

the composition and thickness of the shells can be controlled; secondly, they can be

fabricated with controlled physical and chemical properties; thirdly, they offer novel

structures for micro- and nanocompartmentalization of materials (Donath et al., 1998).

Additionally, unlike liposome structures (Lasic, 1993), the fabricated shells are readily

permeable by small polar molecules (Caruso et al., 1998b) and are rather stable against

chemical and physical influences (Donath et al., 1998).

It is fascinating to see that various types of species can be embedded and built-

in into one whole unified nanostructure, furnishing specialized and desired customized

properties, making them a huge boon for a wide range of applications (Donath et al.,

1998). One of the most promising alternatives includes the incorporation of catalytic

17

materials like MIONPs inside or onto their inner surface; coupled with the ease of

diffusion of reaction products and substrates, it is undoubtedly a really effective way

to both control and manipulate the efficiency of catalytic processes (Donath et al.,

1998). The control of the chemical composition of the inner surface, or likewise for

outer surface, can be fully utilized to produce nucleation centers for eventual crystal

growth in constrained surroundings, which is a novel way nanocomposites are

produced (Donath et al., 1998).

As for now, a variety of materials for instance, biological macromolecules,

surfactants, phospholipids, nanoparticles, inorganic crystals, and multivalent dyes

have been successfully integrated into polyelectrolyte films by replacing one of the

polyelectrolytes with another species of the same charge to fabricate composite

polyelectrolyte multilayer films (Caruso et al., 1997, Sukhorukov et al., 1996). In this

paper, it is intended that the benefits of these polyelectrolytes can bring about are

wholly employed.

18

2.3.1 Layer by Layer (LBL) Technique

The homogeneities in particle size and loading of magnetic component into

silica particles were not high enough to be applied to highly quantitative analysis

(Matsumoto et al., 2009). Therefore, an approach to obtain monodispersed composite

particles with homogeneous loading of functional component to each particle has been

studied and performed which is the electrostatic heterocoagulation between oppositely

charged particles (Furusawa et al., 1994, Caruso et al., 1999). From here, layer-by-

layer (LBL) technique was born, where it has been used to heterocoagulate MIONPs

onto polystyrene particles (Caruso et al., 1999, Caruso et al., 2001) and silica particles

(Zhu et al., 2003). Among the many methods of preparing thin films, the deposition of

LBL of interdependent polymers has loomed large as a particularly versatile, robust

and flexible technique for gaining control of film thickness and its functionality

(Bruening and Adusumilli). Here, a convenient method to design a bifunctional hybrid

composite integrating the catalytic and magnetic performance together is provided,

because the catalytic sites would not be obstructed and blocked as NPs are effectively

immobilized in the polyelectrolyte layer (Li et al., 2011). Figure 2.2 shows the most

typical form of the LBL method, which is the alternating adsorption of polycations and

polyanions.

Figure 2.2: Schematic illustration of LBL adsorption of polyelectrolyte multilayers

(Decher, 1997)

19

Operationally, this method undergoes through simple, stepwise film formation

by consecutive exposure of the colloids to polyelectrolytes of alternating charge, with

excess unadsorbed polyelectrolyte and supernatants being removed by cycles of

centrifugation and rinsing before the next layer is deposited (Donath et al., 1998,

Bruening and Adusumilli). LBL methods have the advantage that ionic attraction

between opposite charges being the driving force for the multilayer buildup (Decher

et al., 1992), which is in contrast to chemisorption techniques (Merrifield, 1965, Maoz

et al., 1988, Lee et al., 1988) that require a reaction yield of 100% in order to maintain

surface functional density in each layer where no covalent bonds need to be formed

(Decher et al., 1992).

Early studies showed that LBL methods can also use a much broader range of

multiply charged species, including proteins, viruses, NPs, and exfoliated inorganic

materials (Bertrand et al., 2000). Now, in most cases, this method also capitalizes on

other interactions such as hydrogen bonding or covalent linkages (Quinn et al., 2007).

The LBL strategy has the upper hands over most thin film forming methods due to

firstly, this technique offers control over film thickness at nanometer scale because a

single adsorption step can deposit as little as a few angstroms of polymer (Quinn et al.,

2007). Secondly, conformal adsorption happens on substrates with a huge range of

geometries, allowing coating of 3-dimensional objects namely NPs and porous

membranes (Dotzauer et al., 2006, Becker et al., 2010).

The key feature in the deposition of polyelectrolyte multilayers is charge

overcompensation, where the initial layer adsorbs onto the substrate by electrostatic or

hydrophobic interactions and either creates a charged surface or reverses the substrate

surface charge (Schlenoff and Dubas, 2001). Adsorption of subsequent layers again

overcompensates the charge on its surface to reverse the substrate’s charge, permitting

20

adsorption of the next layer (Schlenoff and Dubas, 2001). Most of the time, the

thickness of multilayer polyelectrolyte films increases linearly with the number of

adsorbed layer, suggesting that the extent of charge overcompensation does not differ

dramatically with the number of adsorped layers, so the amount of polyelectrolyte

deposited in each step is approximately constant (Bruening and Adusumilli). It is

suggested that the exponential growth occurs when one of the polyelectrolytes diffuses

“into” the entire film during deposition (Lavalle et al., 2004). Upon addition of the

oppositely charged polyelectrolyte, the previously adsorbed polyelectrolyte diffuses

“out” of the whole film to form a very thick polyanion-polycation complex at the

surface, resulting in an increment of thickness of the multilayer films (Hoda and

Larson, 2009). The LBL approach allows a rich variety of structures to be assembled,

both on planar substrates (Decher, 1997) and on colloidal templates (Caruso, 2000),

allowing a greater degree and extent of structural complexity and numerous

components to be introduced into defined layers, thereby permitting the establishment

of new materials with enormous potentials in broad ranging applications (Caruso et al.,

2001).

21

2.4 Nanocomposite as One Unified Structure

In this everchanging world with the expeditious progress shown in the field of

nanoscience and nanotechnology, the combination of different nanomaterials to afford

multifunctional unified composite nanomaterials is no longer just a myth (Shevchenko

et al., 2006). Recently, intensive work has been done to design unique nanostructures

for composite nanomaterials, at the same time to achieve the combination of properties

of each component or cooperatively enhanced performances (Mann, 2009, Jenekhe

and Chen, 1998, Caruso et al., 1998a, Deng et al., 2009). These days, core-shell

structured nanocomposites have gained much more interest due to their enormously

improved properties when compared to their counterparts as mentioned earlier.

2.4.1 Advantages of Nanocomposite

Despite the fact that naked MIONPs can still fulfil their purposes in

environmental remediation by exterminating pollutants from aquatic sources without

the need for further functionalization (Hu et al., 2004), modification on surfaces of

these NPs beforehand is still a prerequisite in achieving more significant results in

order to acquire the desired unique properties of high magnetic saturation, stability,

biocompatibility and interactive functions at the surface (Wu et al., 2008). Otherwise,

the main culprit which is none other than their high tendency to form lumps or

agglomeration as discussed previously would definitely be a huge hindrance in

achieving our objectives.

As mentioned, silica nanoscale colloids are selected to be the core shell due to

their ability to host and support wide ranges of guests owing to their remarkable

stability, possibility to be reused, relative swiftness in achieving equilibrium, high

mechanical resistance and high surface area (Mahmoudi et al., 2011). Not to forget

mentioning their high negative zeta potential as well (Parida et al., 2006), subsequently

22

giving rise to a better dispersion stability hence less proneness to amalgamation of

particles later on. The negatively charged characteristic of these silica colloids

undoubtedly facilitates the adsorption of electron deficient species (Parida et al., 2006)

such as polycations whose positive charge provides the perfect opportunity for the

adsorption process to be initiated through electrostatic attraction. In this case, various

polyelectrolytes are to be employed, where they will firstly be integrated onto these

colloids via LBL method, forming an outermost positive charged layer prior to be

coated with negatively charged iron oxide particles. Sometimes, pH adjustment is also

needed to ensure oppositely charged condition happens between MIONPs and the

coated polycation in which the physisorption of both nanostructures will then be

favoured (Yeap et al., 2012).

This revolutionary and highly sophisticated nanomaterial has been designed

and destined to perform better together as compared to their pure counterparts owing

to their vastly enhanced functionalities coupled with superior improvisation of their

properties in a single unified nanostructure, because this novel nanocomposite exhibits

the best trait from everything else. In other words, highly monodispersed silica NPs

will aid in stabilization of composite in solution, diminishing their tendency to form

clusters and aggregates which affect their performance; polymeric network

surrounding the silica nanotemplate whose function is to entrap the substrates in a

confined space, easing and fastening the catalytic degradation on the substrates by iron

oxide NPs and acting as their binding agents; and at the same time, still retaining the

magnetophoretic and catalytic characteristics of MIONPs. As a result, it can be said

that this entity will have better thermal and chemical stabilities, higher dispersion

capability, lesser nanotoxicity with upgraded functionalities and properties combined

with its good adsorptivity, improved degradabilitiy and magnetic separability. Last but

23

not least, by having a better grasp and full understanding on controlled structure and

interface interactions between these nanoparticles, nanocomposites can further possess

greater novel physical and chemical characteristics that will be crucial for future

technological applications as well (Wu et al., 2008).

2.4.2 Application of Nanocomposite in Environmental Remediation

The use of different types of dyes in textile, paper, leather, cosmetics and other

industries is well known (Reed et al., 1998). These industries dispose tremendous

amount of dye contents causing devastating turmoil and problems such as increasing

the COD and reducing light penetration and visibility (Murray and Parsons, 2004).

Since dyes are stable, recalcitrant, colorant, and even potentially carcinogenic and

toxic (Wu and Tseng, 2008), their release into the environment results in aesthetical

and detrimental health problems (Saha et al., 2011). Thus, this scenario has become

increasingly worrying and needs to be paid attention to for the potential hazards posed.

Therefore, herein, one of the most prominent properties of magnetic

nanocomposites, that is their advantages of easy isolation via magnetic separation

which is more selective and rapid as compared to both centrifugation and filtration

(Hirschbein et al., 1982, Chang et al., 2005) is fully utilized. This is mainly because

each MIONP exists as a single domain (Faraji et al., 2010) with huge magnetic

moment (Mathew and Juang, 2007), so it could be easily magnetized and removed by

an external applied magnetic field (Vatta et al., 2006). This exceptionally remarkable

magnetic collectability of such nanocomposites is sure to be one of the key

contributors to acting as the emerging paradigm in pollutant removal applications,

albeit factors influencing their collectability such as effect of surface modification

employed have not been completely known and understood yet (Yeap et al., 2012).

24

However, bear in mind that these magnetic nanocomposites deliberately

combined for water remediation purposes have to be separated out eventually so that

pollutant-bound particles would be halted from re-entering into the environment once

again (Yavuz et al., 2006). Upon its certainty in contributing to severe toxicity to

aquatic lives (Nel et al., 2006), it is unacceptable for the magnetic nanocomposites to

be released in a vast amount without proper recovery system. Consequently, effective

clarification technologies (Limbach et al., 2008) are needed and must act as the frontier

area of research before pilot-scale applications of nanocomposites for water

reclamation are intended to be performed (Ambashta and Sillanpää, 2010). Hence,

questions and doubts regarding on how to improve the stability and availability of

functionalized iron oxide NPs in extreme environmental conditions, how to develop

efficient, robust and orderly magnetic nanoassembly structures, and how to realize

large-scale or industrial synthesis need to be urgently solved and overcome for

obtaining an ideal functionalized MIONPs (Wu et al., 2008). In a nutshell, the future

work in this area must be focused on preparing all these functionalized NPs via green

chemistry routes, minimizing environmental pollutions as much as possible.

25

CHAPTER THREE

MATERIALS AND METHODS

3.1 Materials and Equipment

3.1.1 Chemicals and Materials

Table 3.1: Chemicals used in this research

Chemicals Supplier Principle of usage

Ethanol (absolute) Fisher Scientific

(M) Sdn. Bhd.

To act as a medium for

silica synthesis

Ammonia solution 25% Merck To act as a catalyst for silica

synthesis

Tetraethylorthosilicate (TEOS),

98%

Acros Organics To act as a precursor to

silica synthesis

Poly(diallyldimethylammonium

chloride) (PDDA), low

molecular weight, 20wt% in

water

Aldrich

Chemistry

To act as a linkage to iron

oxide to be coated onto

silica colloids

Poly(styrenesulfonate) (PSS),

low molecular weight in

powder form

Aldrich

Chemistry

To act as a linkage to iron

oxide to be coated onto

silica colloids

Poly(ethyleneimine) (PEI),

branched in solution form

Aldrich

Chemistry

To act as a linkage to iron

oxide to be coated onto

silica colloids

Iron (III) chloride (FeCl3, 98%

pure, anhydrous)

Acros Organics To act as a precursor to iron

oxide synthesis

Iron (II) chloride (FeCl2.4H2O,

99%)

Acros Organics To act as a precursor to iron

oxide synthesis

Hydrogen peroxide 100

volumes>30%w/v

Nanostructured &

Amorphous

Materials Inc.

To be integrated in

polymeric silica providing

catalytic and magnetic

functions

1000 ppm Methyl Orange

(MO)

Merck To evaluate the performance

of nanocomposites

1000 ppm Methylene Blue

(MB)

Merck To evaluate the performance

of nanocomposites

Deionized water Analytical Lab To wash off unreacted

reactants and to dilute dyes

26

3.1.2 Facilities and Equipment

Table 3.2: Equipment used in this research

Equipment Supplier Principle of usage

Ultrasonic Cleaner Branson Ultrasonics

Corporation

To sonicate for better solution

dispersion

Centrifuge 4000 Kubota Corporation To separate sediments from

supernatants

UV-Vis

Spectrophotometer

Fisher Scientific(M) Sdn.

Bhd.

To observe the dye

absorbance values

Zetasizer Nanoseries

(Malvern)

DKSH Technology Sdn.

Bhd.

To investigation the size

distribution and zeta potential

of synthesized particles

Water bath

(Memmert)

Sterling Ascent Sdn.

Bhd.

To maintain polyelectrolytes

at 40oC

Rotator Stuart To uniformly distribute the

solution

Magnetic stirrer with

magnetic bar

Heidolph To mechanically stir the

solution without heating

Aluminium foil Diamond To act as a protector for

various chemicals

Electronic balance Shimadzu AC 220 To weigh various chemicals

Transmission Electron

Microscope (TEM)

Philips CM12 with Docu

Version 3.2 image

analysis

To determine the morphology

of nanocomposites

27

3.2 Research Methodology

Figure 3.1: Process research schematic flow

Identification of Research Objectives

Selection of Types of Polyelectrolytes

Synthesis of Various Precusors and Nanoparticles

Coating of Polyelectrolytes on Silica by LBL Technique

Incorporation of Iron Oxide Nanoparticles on Polymeric Silica

Analysis of Nanoscopic Properties of Nanostructures

Conduction of Dye Removal Experiments

Results and Discussions

Conclusion and Recommendations

28

3.3 Experimental Methods

The pictorial representation of major steps involved in the silica colloid-

polyelectrolyte(s)-MIONPs nanocomposites is illustrated in Figure 3.2.

Figure 3.2: Schematic diagram portraying major steps involved in LBL assembly of

silica-polyelectrolyte(s)-MIONPs nanocomposite (Che et al., 2014)

3.3.1 Preparation of Silica Nanotemplate

Firstly, silica particles were synthesized via Stöber process under room

temperature with the hydrolysis of TEOS in ethanol and further condensation with

ammonia (Stöber et al., 1968). A 60 ml of absolute ethanol was measured and poured

into a 250 ml beaker. A magnetic stirrer bar was dropped into the beaker, where the

latter was put onto a magnetic stirrer with stirring of the mixture at a lower speed. Next,

a 2 ml of tetraethylorthosilicate (TEOS) followed by another 6 ml of ammonia (NH3)

were pipetted dropwise into the mixture in the beaker, and stopwatch was started

immediately. At the same time, the speed of the stirrer was slowly increased to 500

rpm to avoid the mixture from splitting out. Then, parafilm was used to seal the beaker

to prevent ethanol from evaporating out. After the mixture was left to stir for 2 hours,

the initially colourless solution would turn cloudy indicating that silica had been

formed and suspended in solution. The stirrer was turned off and a magnetic bar was

29

used to separate the solution out of the beaker. A total of 68 ml of solution was then

poured into two separate 50 ml centrifugal tubes, where centrifugation of 7000x g for

25 minutes was done. Subsequently, the supernatants from the tubes were poured out

and washed with deionized (DI) water immediately. The precipitates were redispersed

in DI using a sonicator, and DI washing step was repeated for another three times.

Finally, the solutions from both tubes were combined into one, where the silica was

synthesized, ready for size distribution and zeta potential measurements.

3.3.2 Size Distribution and Zeta Potential Measurements

For any samples, the procedures were all the same. For size distribution

measurement, firstly, a 3 ml of DI water was prepared in a cuvette. Then, a 20 μL of

sample was pipetted into the cuvette, before being sonicated in ultrasonic cleaner for

few minutes. Subsequently, the whole solution was transferred to another smooth

cuvette before being measured by Zetasizer Nanoseries. Meanwhile for zeta potential

measurement, a 1 ml of 1 mM NaCl was prepared in a cuvette as well, where another

20 μL of sample was dropped into it and sonicated. Lastly, a 750 μL of the mixture was

pipetted into a folded capillary cell meant only for zeta potential measurement.

3.3.3 Preparation of PDDA Solution

For ease of calculation, a 0.01 g/ml concentration was standardized for all the

solutions involved. A concentration of 0.01 g/ml of PDDA solution was used to coat

the silica nanoparticles. Firstly, a 45 ml of DI water was measured and poured into a

50 ml centrifugal tube. Next, a 433 μL of pure PDDA was added into the tube, with a

subsequent of 1 hour sonication in an ultrasonic cleaner for its dispersion. Then, the

dispersed PDDA solution was left in water bath at 40oC for a day, ready for size

distribution and zeta potential measurements.

30

3.3.4 Preparation of PSS Solution

A 0.01 g/ml concentration of PSS solution was prepared by having 0.45 g of

PSS powder mixed with 45 ml of DI water in a centrifugal tube. Again, the solution

was left for sonication for an hour in an ultrasonic cleaner and left in water bath at

40oC for a day, ready for size distribution and zeta potential measurements.

3.3.5 Preparation of PEI Solution

A 0.01 g/ml concentration of PEI solution was prepared by having 0.45 g of

PEI solution (due to its extremely high viscosity) mixed with 45 ml of DI water in a

centrifugal tube. The solution was also left for sonication for an hour in an ultrasonic

cleaner and left in water bath at 40oC for a day, ready for size distribution and zeta

potential measurements.

3.3.6 Preparation of Iron Oxide Nanoparticles Solution

Here, iron oxide nanoparticles were synthesized through Co-Precipitation

Method, with its theoretical background of:

𝐹𝑒2+ + 2𝐹𝑒3+ + 8𝑂𝐻− → 𝐹𝑒3𝑂4 + 4𝐻2𝑂

Best ratio Fe3+ / Fe2+ = 2/1

Firstly, a 60 ml of DI water was prepared inside a 3-neck round bottom flask

placed on a magnetic stirrer and was bubbled with Argon gas for a period of 20 minutes.

The flow rate of the gas was set to 400 ml/min with a pressure of 1 bar. Then, the

openings of the flask were covered with a cork and few layers of parafilms respectively,

with 2 syringe holes poked on top of the parafilm layer of the centre neck. Next, iron

(III) chloride (FeCl3) and iron (II) chloride (FeCl2.4H2O) as precursors were prepared

at a mole ratio of 2:1, which is (0.3244:0.1988) g. The prepared salts were added and

dissolved into the treated DI water. Subsequently, a rapid stirring at 700 rpm with a

31

magnetic stirrer bar with the continued bubbling of argon gas was done, and the

mixture was left to stir for another 20 minutes. Once done, argon gas was removed and

openings of flask (centre and argon gas) were covered with few parafilm layers. Then,

the mixture was heated using a temperature controller with thermocouple. Once the

temperature was left to reach 70oC, a 5 ml of 2.5 M NaOH solution was injected into

the mixture using a syringe, causing a change in colour for the mixture from light

brown to black. The reaction was allowed to continue for another 30 minutes before

the black precipitate was collected by permanent magnet. The iron oxide nanoparticles

synthesized were washed with DI water to remove the supernatants, and was

centrifuged at 10000x g for 10 minutes. Lastly, the precipitate was redispersed in DI

water. The iron oxide nanoparticles solution was synthesized, ready for concentration

measurement.

3.3.7 Preparation of Polymeric-Coated Silica Nanoparticles

A precursor film was formed by the alternate adsorptions of PDDA, PSS and

PDDA polymers from aqueous solutions onto the silica microspheres by sequential

layering approach. All the steps employed to coat these polymers on silica core shell

were performed in an ultrasonic cleaner to facilitate a better and more uniform particle

dispersion and coating. For the first PDDA layer coating, after some calculations, a

0.506 ml of 0.01 g/ml silica colloid solution was needed to be added into the 45 ml of

0.01 g/ml PDDA solution, Firstly, both of the solutions prepared earlier were sonicated

in ultrasonic cleaner for 15 minutes, before the 0.506 ml silica was pipetted out and

dropped slowly into the centrifugal tube of 45 ml PDDA solution. Next, the whole

0.01 g/ml solution was sonicated in ultrasonic cleaner for 1 hour, prior to being left at

a rotator with 37 rpm for a day. After one day, the solution was centrifuged at 3500x

g for 10 minutes, and supernatants were separated out followed by DI water washing

32

as done previously. The centrifugation was repeated once more, before DI water was

flushed in until a 2 ml of solution was obtained. The PDDA coated silica solution was

synthesized, ready for size distribution and zeta potential measurements. For PSS

coating, the 2 ml of 0.01 g/ml silica-PDDA solution prepared earlier was also sonicated

15 minutes hour beforehand together with the prepared 45 ml of 0.01 g/ml PSS

solution. Then, the whole 2 ml of silica-PDDA solution was pipetted dropwise into the

centrifugal tube of the 45 ml PSS solution. Steps of sonication, rotation, centrifugation

and washing with DI water were repeated again. Lastly, a 2 ml of silica-PDDA-PSS

solution was synthesized, ready for size distribution and zeta potential measurements.

For the subsequent PDDA layer coating, again, the steps above were repeated by just

replacing the 2 ml of 0.01 g/ml silica-PDDA solution with the 2 ml of 0.01 g/ml silica-

PDDA-PSS synthesized earlier. Finally, a 2 ml of silica-PDDA-PSS-PDDA solution

was synthesized, ready for size distribution and zeta potential measurements. The

amount of iron oxide needed to be pipetted out from the stock was then calculated.

For PEI and a single PDDA coating during the 2nd and 3rd experiments, the

whole procedure was repeated by replacing the first layer of PDDA coating earlier

with just a layer of PEI and a layer of PDDA respectively. Lastly, a silica-PEI and

silica-PDDA solutions were synthesized, ready for size distribution and zeta potential

measurements. The amount of iron oxide needed was then calculated as well.

3.3.8 Preparation of Silica-Polyelectrolyte(s)-MIONPs Nanocomposite

Firstly, the iron oxide stock prepared earlier was sonicated along with the

silica-PDDA-PSS-PDDA for an hour. Then, a 3.96 ml of iron oxide from stock

calculated earlier was added into a 50 ml of DI water dropwise in a centrifuged tube,

done in ultrasonic cleaner to have uniform coating. After sonication of an hour, the

iron oxide NPs were ready for size distribution and zeta potential measurements. Once

33

done, coating of 1 ml silica-PDDA-PSS-PDDA was continued by having it dropped

into the centrifuged tube and left at the rotator for one day. After one day, the solution

was centrifuged at 10000x g for 10 minutes, and supernatants were separated out aided

by an external magnet. Lastly, the unified silica-PDDA-PSS-PDDA-iron oxide

nanocomposite was obtained, ready for size distribution and zeta potential

measurements. The whole step was repeated using silica-PEI and silica-PDDA

structures as well.

3.3.9 Preparation of Methylene Blue (MB) Dye

A 20 ppm of MB solution was prepared from 10000 ppm of MB solution to

make up a total of 10 mL solution with 1 mL 0.01g/mL silica suspension solution.

Therefore, 8.98 mL of DI was transferred into 200 mL beaker followed by the addition

of 0.02 mL of 10000 ppm MB solution. The 200 mL beaker containing the total volume

of 9 mL MB solution was covered with parafilm before dispersing it in an ultrasonic

cleaner for 1 hour. After sonicating the solution for an hour, the solution was stored in

dark conditions ready to be used.

3.3.10 Preparation of Methyl Orange (MO) Dye

A 20 ppm of MO solution was prepared from 2000 ppm of MO solution to

make up a total of 10 mL solution with 1 mL 0.01g/mL silica suspension solution.

Therefore, 8.98 mL of DI was transferred into 200 mL beaker followed by the addition

of 0.1 mL of 2000 ppm MO solution. The 200 mL beaker containing the total volume

of 9 mL MO solution was covered with parafilm before dispersing it in an ultrasonic

cleaner for 1 hour. After sonicating the solution for an hour, the solution was stored in

dark conditions ready to be used.

34

3.3.11 Dye Removal

1 ml of each sample namely silica, various polymeric silica and iron oxide-

polymeric silica nanocomposite solutions was placed in a vial. Then, a 9 ml of 20 ppm

MB was added into the solution, left at rotator for 15 minutes (reaction time). For

nanocomposites, an additional step in which an external magnet was first used to

collect the magnetic nanocomposite in the mixture obtaining the initial supernatant

before its 1 ml from the total 10 ml mixture solution was taken and poured into a

centrifugal tube, centrifuged at a speed of 10000 rpm for 30 minutes to obtain the

remaining supernatant for the absorbance analysis in order to observe the dye remained.

Different reaction times up to 360 minutes were employed and repeated. Subsequently,

the procedure for the MO dye removal was performed with the same steps above.

The whole procedure was repeated again only with the difference of an 8.5 ml

of 20 ppm MB and MO instead of the 9.0 ml previously, with an addition of 0.5 ml of

H2O2 into the vial.

35

CHAPTER FOUR

RESULTS AND DISCUSSION

Silica NPs were chosen to serve as nanotemplates for the synthesis of

nanocomposite fabrications in this study using three different types of polyelectrolytes:

(1) a single layer of PDDA, (2) a three multilayer of PDDA, PSS and PDDA and, (3)

a single layer of PEI. In the first experiment, since silica NP is negatively charged, the

introduction of a single layer of PDDA polycation would modify the silica NPs to

become positively charged before negatively charged iron oxide NPs could be

incorporated into silica NPs, exhibiting catalytic and magnetic bifunctionalities in one

unified nanostructure for environmental remediation. Another two experiments were

repeated with: the alternating coating of polycations and polyanion which are the

PDDA, PSS and PDDA multilayers through the LBL method instead of just a single

layer of PDDA; and a single layer of PEI as the polyelectrolyte respectively. In the

second experiment, the establishment of the first layer of PDDA would also modify

the silica NPs to become positively charged before being realtered by PSS polyanion

to become negatively charged, only to be remodified again by another layer of PDDA

to become positively charged once more, before negatively charged iron oxide NPs

were again incorporated into the silica core. In the third experiment, PEI was used

instead of the PDDA layer from the first experiment. Both PDDA and PSS are linear

polyelectrolytes while PEI is of branched configuration. These synthesized

nanomaterials were observed and analyzed under Dynamic Light Scattering (DLS) and

Transmission Electron Microscope (TEM) equipment. From these experiments, it

could be said that these nanocomposites showed good dye removal efficiencies.

36

4.1 Characterization and Observation

This LBL technique was used to necessitate the consecutive adsorption of

oppositely charged nanocomponents onto colloidal core particles where

polyelectrolytes play their roles as binding agents by acting as intermediate layers for

integration of iron oxide NPs, retaining both their magnetophoretic and catalytic

characteristics. Formation of the ultimate structure of PDDA, PDDA-PSS-PDDA and

PEI polyelectrolye-modified nanosized silica core were visualized using TEM.

4.1.1 Synthesis of Silica Nanoparticles

Silica NPs were synthesized via Stober Process as mentioned with hydrolysis

of TEOS in ethanol followed by further condensation with ammonia. The initial

colorless TEOS, ethanol and ammonia mixture solution turned cloudy, indicating that

silica was produced and suspended in solution as portrayed in Figure 4.1. From DLS,

these silica NPs had average diameters between 200-300 nm and were negatively

charged.

Figure 4.1: Silica NP suspension

37

4.1.2 Synthesis of Polymeric-Coated Silica Nanoparticles

Colorless pure PDDA reagent, PEI highly-viscous liquid and PSS powder were

all mixed with DI water to prepare their respective solutions. These polymeric-

modified silica NPs synthesized were analyzed under DLS in determining their sizes

and zeta potentials before proceeding to latter stages. The ever-occurring reversals of

zeta potential values observed at each stage of new coated nanoparticles synthesis

compared to their previous NPs suggested that the subsequent desired layers were

successfully coated on the core and prior NP surfaces (Che et al., 2014). The PDDA-

PSS-PDDA and PEI modified silica NP suspensions were shown in Figure 4.2 (a) and

(b) respectively, also in milky colors but with less intensities after dilution with DI

water.

Figure 4.2: (a) PDDA-PSS-PDDA-modified silica NP suspension, and (b) PEI-

modified silica NP suspension

a b

38

4.1.3 Synthesis of Iron Oxide Nanoparticles

Iron oxide NPs were synthesized through Co-Precipitation Method described

previously. The black precipitate was collected by an external magnet as shown in

Figure 4.3, so that the MIONPs synthesized could be washed with DI water to remove

supernatants. Zeta potential of negative value was made sure to be obtained under DLS,

so that MIONPs could be amalgamated onto oppositely charged polymeric matrix

surfaces synthesized earlier. Since at low pH, iron oxides are positively charged and

attract negatively charged ligands; hence, when solution pH (DI water) was above the

isoelectric point (pH = ~8), the oxide surface became negatively charged and could

form surface complexes with cations (Sun et al., 2006) such as PDDA and PEI

polycations as our outermost layers in all three experiments here. Therefore, DI water

was ensured to always be in between pH of 8 to 10 in order to have the oxide surface

negatively charged. Meanwhile, Figure 4.4 depicted TEM micrograph of MIONPs,

where their clustering was due to magnetic interactions (Phenrat et al., 2007).

Figure 4.3: Collection of iron oxide NP suspension with a magnetic bar

39

Figure 4.4: TEM micrograph of iron oxide NP aggregration

4.1.4 Synthesis of Silica-Polyelectrolyte(s)-MIONPs Nanocomposite

These polymeric-modified silica NPs were dropped into iron oxide NP solution

to be coated in order to synthesize the desired nanocomposites. In the meantime, the

heterocoagulation between MIONPs on the surface of a PDDA-modified silica core, a

PDDA-PSS-PDDA-modified silica core and a PEI-modified silica core could be

visualized through TEM micrographs in Figure 4.5 (a), (b) and (c) respectively.

40

Figure 4.5: TEM micrographs of polymeric-modified latices exposed to deposition of

iron oxide NPs on (a) a PDDA-modified silica core, (b) a PDDA-PSS-PDDA-

modified silica core, and (c) a PEI-modified silica core

a

b

c

41

It was seen that all three TEM images differed from each other through their

structural morphologies. As mentioned in problem statement, these architectures were

proposed with the intention to understand more on their behaviors in terms of their

confinement of iron oxide NPs through dye removal performance which will be

discussed later. From their structural morphologies, it was illustrated that the one in

Figure 4.5 (a) has the thinnest outermost iron oxide NPs layered structure as compared

to that in (b) and (c), where both the latters have thicker layers covered on their silica

cores. This was due to the simple fact that only a single linear layer of polyelectrolyte

was formed in (a) but three layers of alternatingly charged polyelectrolytes were

fabricated in (b). As in uniformities, (c) showed more irregularities to (a) and (b),

which was attributable to the difference in their polymeric configurations. The single

layer PDDA and multilayer PDDA-PSS-PDDA polyelectrolytes in (a) and (b) are all

linear, while the single layer of PEI polyelectrolyte (c) is a branched type, where it was

believed to have caused the latter to possess a higher total surface area to volume ratio.

42

4.1.5 Zeta Potential and Particle Size

The zeta potential and particle size of various synthesized NPs were analyzed

using Malvern Zetasizer Nanoseries and were summarized in Table 4.1 to 4.3.

For the first experiment seen in Table 4.1, from DLS, the uncoated silica NP

yielded a zeta potential of -58.4 mV in 1 mM NaCl. The presence of PDDA

polyelectrolyte caused a reversal in its zeta potential to +52.4 mV, a value consistent

with the outer layer being a polycation. The zeta potential value turned positive when

this layer of PDDA formed the outer layer and in between -26.0 mV of iron oxide NPs

as the outermost layer, acting as a bridging agent to facilitate the assimilation of iron

oxide NPs by electrostatic attraction to synthesize the magnetic nanocomposite. At the

end of the day, the ultimate nanocomposite exhibited an overall zeta potential of +23.7

mV instead of the localized negative value of zeta potential from iron oxide NPs. This

result indicated that the iron oxide NPs incorporated into the polymeric matrix have

successfully suppressed the more highly positively charged PDDA, leading to a net

lower value of positively charged nanocomposite.

The colloidal stability of the coated nanocomposite was higher when PDDA,

rather than iron oxide, formed the outlayer as slow flocculation of the multilayer-

coated nanocomposite happened when the latter was the outermost layer (Zhu et al.,

2003). This was due to electrosteric stabilization of the NPs conferred by the

polyelectrolyte (Caruso et al., 1999, Lvov et al., 1997, Caruso and Möhwald, 1999).

However, the nanocomposite was easily redispersable by gentle shaking.

As for the hydrodynamic diameters, from DLS, coating silica NP with PDDA

layer increased its diameter from 209.4 nm to 234.4 nm. Meanwhile, iron oxide NPs

43

had hydrodynamic diameter of 144.9 nm before being integrated into the polymeric

matrices, further increasing its hydrodynamic diameter to 260.2 nm.

Table 4.1: Zeta potential and hydrodynamic diameter of single layered silica-PDDA-

iron oxide nanocomposite

Zeta potential

(mV)

Hydrodynamic

diameter (nm)

Silica NP -58.4 209.4

Silica-PDDA NP +52.4 234.4

Iron oxide NP -26.0 144.9

Silica-PDDA-iron oxide NC +23.7 260.2

In the second experiment from Table 4.2, the uncoated silica NP also yielded

a zeta potential of -58.4 mV in 1 mM NaCl since it was taken from the same stock

solution. The presence of PDDA polyelectrolyte triggered a reversal in its zeta

potential to +56.9 mV, a value compatible with the outer layer being a polycation.

Subsequent deposition of PSS polyanion onto the coated silica reversed the zeta

potential to -46.0 mV. Alternating zeta potential was once observed again with the

further deposition of another layer of PDDA polycation. The zeta potential value

turned +46.4 mV when this third layer of PDDA formed the outer layer and in between

-26.0 mV of iron oxide NPs as the outermost layer. The alternating zeta potentials

observed were characteristics of stepwise growth of multiplayer films on microspheres

(Zhu et al., 2003). Lastly, the ultimate nanocomposite possessed an overall zeta

potential of +10.7 mV instead of the localized negative value of zeta potential from

iron oxide NPs. This phenomenon depicted that the MIONPs incorporated into the

polymeric matrices managed to subdue the more positively charged PDDA as well,

resulting in a net lower value of positively charged nanocomposite.

The colloidal stability of the coated nanocomposite was also higher with

PDDA, rather than iron oxide, as the outmost layer due to the same reason mentioned

44

above, as evidently proven by the higher zeta potential values observed when PDDA

became the outmost layer (Zhu et al., 2003).

As for the hydrodynamic diameters, from DLS, the coating of silica NP with

the first PDDA layer increased its diameter from 209.4 nm to 229.9 nm, with

subsequent alternating coatings of PSS and PDDA layers giving rise to an increase to

249.5 nm and 264.8 nm. Nevertheless, iron oxide NPs manifesting hydrodynamic

diameter of 144.9 nm were also incorporated into the polymeric matrices, further

increasing its hydrodynamic diameter to 274.6 nm.

Table 4.2: Zeta potential and hydrodynamic diameter of multilayered silica-PDDA-

PSS-PDDA-iron oxide nanocomposite

Zeta potential

(mV)

Hydrodynamic

diameter (nm)

Silica NP -58.4 209.4

Silica-PDDA NP +56.9 229.9

Silica-PDDA-PSS NP -46.0 249.5

Silica-PDDA-PSS-PDDA NP +46.4 264.8

Iron oxide NP -26.0 144.9

Silica-PDDA-PSS-PDDA-iron oxide NC +10.7 274.6

On the other hand in Table 4.3, for the third experiment, the uncoated silica NP

also yielded a zeta potential of -58.4 mV in 1 mM NaCl since it was taken from the

same stock solution as well. The presence of a single layered PEI polyelectrolyte

caused a reversal in its zeta potential to +48.8 mV. The zeta potential value turned

positive again as explained in the first two experiments. Last but not least, the ultimate

nanocomposite had an overall zeta potential of +13.7 mV instead of the localized -26.0

mV negative value of zeta potential from iron oxide NPs. This scenario has illustrated

that the MIONPs incorporated into the polymeric matrices have again charge-

45

neutralized the more positively charged PEI as well, resulting to a net lower value of

positively charged nanocomposite.

The colloidal stability of the coated nanocomposite was also higher with PEI,

rather than iron oxide, as the outmost layer as shown by the higher zeta potential values

observed when PEI being the outermost layer (Zhu et al., 2003).

As for the hydrodynamic diameters, the deposition of silica NP with PEI

increased its diameter from 209.4 nm to 264.8 nm. Meanwhile, iron oxide NPs

exhibiting hydrodynamic diameter of 144.9 nm were amalgamated into the polymeric

matrices, further increasing its hydrodynamic diameter to 318.2 nm.

Table 4.3: Zeta potential and hydrodynamic diameter of single-layered silica-PEI-

iron oxide nanocomposite

Zeta potential

(mV)

Hydrodynamic

diameter (nm)

Silica NP -58.4 209.4

Silica-PEI NP +48.8 264.8

Iron oxide NP -26.0 144.9

Silica-PEI-iron oxide NC +13.7 318.2

46

4.2 Performance Evaluation

The absorbance values of dyes were analyzed using UV-Vis

Spectrophotometer with maximum absorbance wavelength for MB at 665 nm and MO

at 465 nm. The concentration of dyes in the reaction mixture was determined by

measuring the absorption intensity at respective wavelengths and with calibration

curves at different reaction times, from 15 minutes up to 6 hours. Inevitably, the

absorbance values decreased after the degradation and removal processes since the

remaining concentration of dye was reduced. Prior to that, calibration curves were

acquired using the standard MB and MO solutions with known concentrations. The

dye decolorization efficiency is defined as:

𝐷𝑒𝑐𝑜𝑙𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 (%) = (1 −𝐶𝑡

𝐶0) × 100%

where C0 is the initial concentration of dyes and Ct is the concentration of dyes at

certain reaction time, t (min).

4.2.1 Removal of 20 ppm Methylene Blue Dye

Figure 4.6 (a) portrayed the structural formula of positively charged MB, and

(b) showed two vials after the removal process in one of the timelines, where the vial

on the left was before and on the right was after the reaction time. Meanwhile from

Figure 4.7 to 4.9, various time intervals (from 15 minutes to 6 hours) of dye removal

using MB were employed to compare the removal efficiency by different decolorizing

agents from various nanocomposites.

47

Figure 4.6: (a) MB structural formula and (b) MB solution before and after reaction

In the first experiment involving single layered PDDA nanocomposite shown

in Figure 4.7, silica achieved 94.6 %, silica-PDDA with 20.3 %, silica-PDDA-iron

oxide with 61.0 % (absorption only) and silica-PDDA-iron oxide (absorption with

Fenton reaction) achieved 90.1 % of removal efficiencies in MB removal tests.

Silica NP was able to decolorize MB with the highest percentage among all

due to the electrostatic driven process conferred. Positively charged MB was most

favored to highly negatively charged silica and thus, was attracted and adsorbed by

silica the most resulting in the highest removal efficiency. However, the surface charge

of silica core was reversed to positive charge once silica NPs were coated with a layer

of PDDA polycation. Therefore, due to electrostatic repulsion between both positively

charged MB and silica-PDDA, adsorption of MB by silica-PDDA was unfavorable,

giving rise to the lowest removal efficiency. MB could be removed better by lower

degree of positively charged silica-PDDA-iron oxide nanocomposite as compared with

a b

48

higher degree of positively charged silica-PDDA NP for there was still electrostatic

attraction between positively charged MB to the localized outmost layer of negatively

charged iron oxide NPs, albeit slightly. Further degradation process of MB via Fenton

reaction attributed by iron oxide NPs and H2O2 reagent enhanced the removal

efficiency of this silica-PDDA-iron oxide nanocomposite.

Figure 4.7: Percentage removals for 20 ppm MB tests using silica-PDDA-iron oxide

nanocomposite

In the third experiment involving PEI single layered nanocomposite shown in

Figure 4.8, silica from the same stock achieved 94.6 % as well, silica-PEI with 22.1 %,

silica-PEI-iron oxide with 63.1 % (absorption only) and silica-PEI-iron oxide

(absorption with Fenton reaction) achieved 92.6 % of removal efficiencies in MB

removal tests.

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica Silica-PDDA Silica-PDDA-IO Silica-PDDA-IO (with Fenton)

49

Similar to the previous test, silica NP was able to decolorize MB with the

highest percentage among all due to the highest electrostatic driven process conferred

with MB. However, the surface charge of silica core was reversed to positive charge

once silica NPs were coated with a layer of PEI polycation. Adsorption of MB by

silica-PEI was most non-favorable, due to electrostatic repulsion between both

positively charged MB and silica-PEI. MB could be adsorbed better by lower degree

of positively charged silica-PEI-iron oxide nanocomposite as compared with higher

degree of positively charged silica-PEI NP since there was still electrostatic attraction

between positively charged MB to the localized outmost layer of negatively charged

iron oxide NPs as well. Again, further degradation process of MB via Fenton reaction

attributed by iron oxide NPs and H2O2 reagent enhanced the removal efficiency of this

nanocomposite.

Figure 4.8: Percentage removals for 20 ppm MB tests using silica-PEI-iron oxide

nanocomposite

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica Silica-PEI Silica-PEI-IO Silica-PEI-IO (with Fenton)

50

Meanwhile, for the second experiment seen in Figure 4.9, there was only one

decolorizing agent being studied which was the ultimate three-multilayer

nanostructure. Here, comparisons were made only between silica-PDDA-PSS-PDDA-

iron oxide (absorption only) achieving 54.4 % with silica-PDDA-PSS-PDDA-iron

oxide (absorption with Fenton reaction) managing 88.6 % removal efficiencies in this

MB test. As mentioned previously, the latter’s performance was contributed by Fenton

reaction contributed by iron oxide NPs and H2O2 reagent.

Figure 4.9: Percentage removals for 20 ppm MB tests using silica-PDDA-PSS-

PDDA-iron oxide nanocomposite

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica-PDDA-PSS-PDDA-IO Silica-PDDA-PSS-PDDA-IO (with Fenton)

51

4.2.2 Removal of 20 ppm Methyl Orange Dye

Figure 4.10 (a) illustrated the structural formula of negatively charged MO, and

(b) depicted two vials after removal process in one of the timelines, where the vial on

the left was before and on the right was after the reaction time. From Figure 4.11 to

4.13, various time intervals of dye removal (from 15 minutes to 6 hours) using MO

were employed to compare the removal efficiency by various decolorizing agents from

different nanocomposites.

Figure 4.10: (a) MO structural formula and (b) MO solution before and after reaction

In the first experiment involving single layered PDDA nanocomposite shown

in Figure 4.11, silica achieved 3.4 %, silica-PDDA with 52.6 %, silica-PDDA-iron

oxide with 50.9 % (absorption only) and silica-PDDA-iron oxide (absorption with

Fenton reaction) achieved 57.8 % of removal efficiencies in MO removal tests.

Unlike in MB test, silica NP had the lowest percentage efficiency here due to

electrostatic repulsion of both negatively charged silica and MO, causing limitations

a b

52

for the adsorption of MO by silica. However, after a PDDA layer was coated onto the

silica core, it became highly positively charged which favored the adsorption of

oppositely charged MO. Once iron oxide NPs were introduced forming silica-PDDA-

iron oxide nanocomposite (absorption only), it could still manage to adsorb the

negatively charged MO despite being less positive due to the still present electrostatic

attraction. Nonetheless, silica-PDDA-iron oxide nanocomposite (absorption with

Fenton reaction) emerged with the highest efficiency percentage among all since the

MO removal was enhanced further by Fenton reaction attributed by iron oxide NPs

and H2O2 reagent, other than the electrostatic attraction alone.

Figure 4.11: Percentage removals for 20 ppm MO tests using silica-PDDA-iron

oxide nanocomposite

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica Silica-PDDA Silica-PDDA-IO Silica-PDDA-IO (with Fenton)

53

In the third experiment involving PEI single layered nanocomposite shown in

Figure 4.12, silica from the same stock had 3.4 %, silica-PEI with 58.4 %, silica-PEI-

iron oxide with 52.2 % (absorption only) and silica-PEI-iron oxide (absorption with

Fenton reaction) achieved 60.0 % of removal efficiencies in MO removal tests.

Similar to the previous test, silica NP had the lowest percentage efficiency

owing to electrostatic repulsion between both negatively charged silica and MO,

causing restrictions for the adsorption of MO by silica. However, after a PEI layer was

coated onto the silica core, it turned into highly positive charge favoring the adsorption

of negatively charged MO. When negatively charged iron oxide NPs were assimilated

producing silica-PEI-iron oxide nanocomposite (absorption only), it was still able to

adsorb the MO despite having a lower net positive charge because electrostatic

attraction was still playing its role. Silica-PEI-iron oxide nanocomposite (absorption

with Fenton reaction) had the highest efficiency percentage among all due to the fact

that the MO removal was again aided by Fenton reaction contributed by iron oxide

NPs and H2O2 reagent.

54

Figure 4.12: Percentage removals for 20 ppm MO tests using silica-PEI-iron oxide

nanocomposite

In the meantime, for the second experiment seen in Figure 4.13, there was also

only one decolorizing agent involved which was the finished nanostructure of the

three-multilayer PDDA-PSS-PDDA nanocomposite. Comparisons were made only

between silica-PDDA-PSS-PDDA-iron oxide (absorption only) achieving 45.9 % with

silica-PDDA-PSS-PDDA-iron oxide (absorption with Fenton reaction) managing 56.0 %

removal efficiencies in this MO test. Similarly, it could be seen that the upgraded

performance was attributable by Fenton reaction contributed by iron oxide NPs and

H2O2 reagent.

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica Silica-PEI Silica-PEI-IO Silica-PEI-IO (with Fenton)

55

Figure 4.13: Percentage removals for 20 ppm MO tests using silica-PDDA-PSS-

PDDA-iron oxide nanocomposite

Silica NPs synthesized manifested high negative charge as proven from DLS

analysis previously. Consequently, silica NPs have high colloidal stabilities, giving

rise to being extremely well monodispersed in solution (Mahmoodi et al., 2011).

Within the same time interval, silica NPs were able to decolorize positively charged

MB much more efficiently compared to negatively charged MO due to the electrostatic

interactions between them. Opposite charges between silica NPs and MB would

inevitably cause the latter to be attracted and adsorbed onto the former, significantly

reducing the blue solution of MB. On the other hand, there was electrostatic repulsion

between both the negatively charged silica NPs and MO, whereby the adsorption of

MO by silica NPs was limited, thus, the orange solution remained slightly unchanged.

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica-PDDA-PSS-PDDA-IO Silica-PDDA-PSS-PDDA-IO (with Fenton)

56

Subsequently, silica NPs were modified by having their surfaces coated with

positively charged polycations such as PDDA and PEI via electrostatic interaction as

well. The coating turned the silica-PDDA/PEI NPs highly positive, as a result, they

were able to remove negatively charged MO very effectively compared to positively

charged MB, simply due to the electrostatic attraction between the polymeric silica

and MO, and the electrostatic repulsion taking place between the polymeric silica and

MB. Hence, the orange MO was reduced tremendously while the blue MB remained

unchanged.

Then, the polymeric-modified silica core was again incorporated with

negatively charged iron oxide NPs, becoming the finished nanocomposites. At almost

neutral pH, nanocomposite analyzed by DLS showed an overall lower value of positive

charge, indicating that the negatively charged iron oxide NPs had suppressed the

highly positive charge of the polycations to have nanostructure of a lower net

magnitude of positive charge. So, being an anionic dye, MO could be decolorized

better compared to the cationic MB since MO was more preferably attracted and

adsorbed by the nanocomposite. Their MO removals were slightly less effective than

that of polymeric-modified silica core, since their counterparts have higher magnitudes

of positive charge resulting in stronger electrostatic attraction. However, MB could

still be decolorized slightly by the nanocomposite probably due to the ever-present

electrostatic attraction between the positive MB and the localized negatively charged

iron oxide NPs on the surface of nanocomposite.

However, without the addition of H2O2 reagent, it was just pure absorption

processes involved only. Once added, there would be an additional reaction plying its

trade called the Fenton reaction attributable to iron oxide NPs and the H2O2 reagent.

After the adsorption processes, MB and MO would be further catalytically degraded

57

by ∙OH decomposing from H2O2 on the catalyst surface where ∙OH is a nonspecific

oxidant reacting with most organic compounds, whereby both MB and MO would be

first adsorbed onto Fe3O4/FeMnOx before being decomposed by hydroxyl radical in

heterogeneous catalytic reaction processes (Xing et al., 2011). In other words, there

were two rounds of mechanisms playing their roles here. Once the adsorptive or the

binding sites were fully occupied by adsorption process, the remaining removals were

facilitated by the Fenton reaction processes. As a result, their removal efficiencies were

greatly enhanced as compared to their counterparts with only adsorption processes

involved. In addition, according to Che and coworkers (Che et al., 2014), these

nanocomposites are less susceptible to the thermal randomization energy compared to

individual particle and experience much greater magnetophoretic force to overcome

the viscous drag. These scenarios would enable rapid magnetic collection of

nanocomposite which composed of magnetic particle clusters after their usages in

water remediation, as evidenced by one of the tests done by Che and coworkers (Che

et al., 2014), where their finding implies that the ultimate nanocomposite has excellent

reusability and recyclability, making them a superior candidate for water treatment

purposes as they can always be used repeatedly and their performances are not

dependent on the charges of targeted pollutants alone (Che et al., 2014).

Taking silica-PDDA-iron oxide nanocomposite as an example, the pictorial

representation of its nanomaterial synthesized at each stage during dye-removing

processes is illustrated in Figure 4.14 below. For processes mainly driven by

adsorption such as those in (a) and (b), electrostatic interactions play important roles

in either promoting or suppressing the MB and MO removal depending on the charges

of adsorbate (dye molecules) and adsorbent (silica colloid and PDDA-coated silica

colloid). For silica-PDDA-iron oxide nanocomposite in process (c), the influence of

58

electrostatic interaction is negligible as Fenton-reaction dominates the removal

mechanism.

Figure 4.14: Schematic diagram showing electrostatic interactions and mechanisms

involved for MB and MO removal by (a) silica colloid, (b) PDDA-coated silica

colloid, and (c) silica-PDDA-iron oxide nanocomposite (Che et al., 2014)

4.2.3 Removal of MB and MO Dyes by Ultimate Nanostructures

In this study, the three desired finished nanocomposites: (1) silica-PDDA-iron

oxide, (2) silica-PDDA-PSS-PDDA-iron oxide, and (3) silica-PEI-iron oxide were

utilized for dye removal processes shown in Figure 4.15, where after a certain reaction

time, a magnetic bar was first used to collect the magnetic nanocomposite in the

mixture solution obtaining the dye supernatant before being centrifuged.

59

Figure 4.15: Collection of magnetic NC suspension with a magnetic bar

All three final nanocomposites were then compared relatively in terms of their

MB and MO removing capabilities as portrayed in Figure 4.16 (a) and (b) respectively,

in which all were added with H2O2 reagents prior to the removal processes, indicating

that both adsorption and Fenton reaction processes took place. Here in (a), it was seen

that silica-PDDA achieved 90.1 %, silica-PDDA-PSS-PDDA-iron oxide had 88.6 %,

with silica-PEI-iron oxide managing 92.6 % of dye removal efficiencies in MB

removal test. Meanwhile in (b), silica-PDDA-iron oxide achieved 57.8 %, silica-

PDDA-PSS-PDDA-iron oxide had 56.0 %, while silica-PEI-iron oxide managing 60.0 %

of dye removal efficiencies in MO removal test.

60

Figure 4.16: Percentage removal tests using three ultimate nanocomposites for (a)

MB and (b) MO dyes

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica-PDDA-IO Silica-PDDA-PSS-PDDA-IO Silica-PEI-IO

a

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300 350 400

Per

cen

tage

rem

ova

l, %

Time, min

Silica-PDDA-IO Silica-PDDA-PSS-PDDA-IO Silica-PEI-IO

b

61

Among all three synthesized nanocomposites, silica-PEI-iron oxide

nanocomposite had the highest percentage removal among all, while silica-PDDA-iron

oxide showed better efficiency than silica-PDDA-PSS-PDDA-iron oxide in both MB

and MO removals. From Figure 4.5 (a), there was only a thin single layer of PDDA

coated on silica core rather than the thick multilayers of polyelectrolytes seen in (b).

When there was only a single layer, the electrostatic barrier existing between the dyes

and nanocomposites was far less than that of multilayers. Since dyes needed to

penetrate through more layers in order to reach the core of the nanocomposites, it led

to the prerequisite of having to overcome higher electrostatic barriers, resulting in

lower dye removal performance for silica-PDDA-PSS-PDDA-iron oxide

nanocomposite despite having higher iron oxide content embedded on its surfaces in

Figure 4.5 (b) as compared to silica-PDDA-iron oxide shown in (a). Also, it is

understood that these multilayers were not assembled in an absolute-layered manner,

but they were in fact interpenetrable. This has inexorably given rise to the existence of

electroneutrality condition. Here, the local electroneutrality was assumed with the

electroneutrality balance having contributions from (Biesheuvel and Wittemann, 2005)

the alternatingly opposite charge of each layer of polyelectrolyte. Albeit these layers

were globally balanced to each other in terms of their charge distribution as one whole

layer adjacently, due to their interpenetrability however, they were not likely to be

locally balanced as well, causing them to experience imbalanced charge distribution,

where the dyes would have had to cope with these conditions every time they pass

through each layer. Without the imbalanced charge distribution experienced in the

single PDDA layered nanocomposite, the MB and MO particles would have less

obstacles or barriers to reach out for the core, indirectly increasing their dye removing

capabilities.

62

As for the silica-PEI-iron oxide nanocomposite illustrated by its structural

morphology in Figure 4.5 (c), it showed more irregularities in terms of its uniformity

of iron oxide NPs embedded as compared to (a) and (b). As mentioned, the

polyelectrolytes involved in (a) and (b) were all linear whereas PEI (c) was a branched

polycation. This difference in their structural configurations played essential roles in

the ways MO and MB dyes were being removed. It is clearly seen that the confinement

of iron oxide NPs onto the polymeric-silica matrices was almost similar between silica-

PDDA-PSS-PDDA-iron oxide and silica-PEI-iron oxide judging from the particle

distributions portrayed in Figure 4.5 (b) and (c). However, the key difference was that

not only the branching part of PEI was able to possess a much higher total surface area

to volume ratio, but to also own a more open fractal structure compared to its linear

counterparts. This fractal dynamics (Toroczkai et al., 1998) ineluctably brought to a

higher degree of voidness or openness in its nanostructure, resulting in a distribution

of iron oxide NPs that differs entirely from the formers that could degrade the dyes

more effectively in a way that its linear counterparts could not. Coupled with the fact

that this PEI layer registered was of single layer, it was no fluke that the dye removing

percentage efficiency of this type of configuration soared highest.

63

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

The synthesis of these revolutionary and sophisticated nanocomposites have

been destined to perform better as evidenced by the results and findings obtained, as

compared to their pure counterparts owing to their vastly enhanced functionalities

together with superior improvisations of their properties in a single unified

nanostructure, as these novel nanocomposites exhibit the best trait from each

nanomaterial. The highly monodispersed silica NPs aided in the stabilization of

composites in solution, diminishing their proneness to form lumps and clusters; while

polymeric networks surrounding the silica nanotemplate were responsible to entrap

dyes in a confined space, easing and fastening the removal processes and acting as

binding agents between the silica core and MIONPs by improving their physical

contacts; along with the magnetophoretic and catalytic bifunctionalities of iron oxide

NPs still being retained.

In this paper, two main agendas were focused on and studied. Firstly, the

mechanisms involved in dye removal processes which were the adsorption and

catalytic degradation processes; secondly, on how would the number of layers or

thickness of polyelectrolytes registered, and the difference in fractal dimension of

polymeric network, either linear or branched, influence the dye removal performance

of nanocomposites. Firstly, high removal efficiencies of MB by silica NPs and that of

MO by polyelectrolyte-modified silica NPs were dominated by electrostatic-driven

interactions, whereas the additional enhancements of dye removals by the ultimate

nanocomposites were contributed by Fenton and Fenton-like reactions facilitated by

iron oxide NPs and H2O2 reagent, catalytically degrading the dyes other than the

64

adsorption processes. Therefore, it is suggested that Fenton reactions have to be

involved for dye removal processes since during adsorption, the adsorptive sites are

always limited and will be saturated slowly but surely, and the pollutants will always

be retained within the polymeric matrix itself. Meanwhile during catalytic degradation,

iron oxides NPs are the active sites, can be used for multiple times and leaves no trace

of pollutants in its aftermath since they have already been degraded. In the second

highlight of this work, a single layer of PDDA and three multilayers of PDDA, PSS

and PDDA nanocomposites were respectively synthesized, where the former was more

effective in removing MO and MB dyes due to the less electrostatic barrier and less

imbalanced charge distribution experienced. Regarding the configurations of

polyelectrolytes employed, in which the more highly branched they are, the higher dye

removing capabilities they have because of their higher surface area to volume ratio

and their more open fractal structures, leading to a higher degree of voidness or

openness in the nanostructure. Thus, in a nutshell, with all the supported data and

findings, it is strongly validated that a single layered, branched polyelectrolyte will

make a far more interesting and superior nanocomposite, and hopefully, this will not

be merely a speculation.

65

5.2 Recommendations

These are some of the recommendations and suggestions that can be done to

further improvise and study the synthesis and application of nanocomposite.

1. Iron oxide NPs to be coated with polyelectrolytes prior being attached on silica

nanosphere surfaces rather than incorporating the iron oxide NPs only after the

silica NPs have been polyelectrolyte-modified.

2. More types of polyelectrolytes acting as the intermediate layer(s) to be

explored and employed in order to identify any branched polyelectrolytes with

better fractal dimension.

3. Reaction kinetics of nanocomposites for dye removal application to be studied

in order to have better insights on their underlying working mechanisms.

66

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APPENDICES

Appendix A

Figure A.1: Maximum wavelength of 665nm of MB from UV-Vis Cary 60

Figure A.2: Calibration curve of MB dye solution

y = 3.8378xR² = 0.9989

0

5

10

15

20

25

30

35

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

Ab

sorb

ance

Concentration, mg/L

80

Figure A.3: Calibration curve of MO dye solution

y = 12.618xR² = 0.9961

0

5

10

15

20

25

30

35

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Ab

sorb

ance

Concentration, mg/L

81

Appendix B

Table B.1: Data of dye removal of silica-PDDA-iron oxide nanocomposite

MO=20 ppm Co (ppm)= 16.87197 MB=20 ppm Co (ppm)= 16.45092

time abs C (ppm) % time abs C (ppm) %

abs 1 abs 2 abs 3 abs av abs 1 abs 2 abs 3 abs av

0 1.57 1.5744 1.5749 1.5731 16.871969 0 0 0.5044 0.5044 0.5041 0.5043 16.450921 0

15 0.2376 0.2376 0.2377 0.237633 8.9953722 46.68452 15 0.0151 0.0151 0.0151 0.0151 3.4770468 78.86412

30 0.2076 0.2076 0.2075 0.207567 7.8572286 53.43028 30 0.0122 0.0122 0.0121 0.012167 2.801594 82.96999

60 0.2075 0.2075 0.2077 0.207567 7.8572286 53.43028 60 0.0101 0.01 0.01 0.010033 2.3103556 85.95607

180 0.2047 0.2046 0.2046 0.204633 7.7461902 54.08841 180 0.008 0.0081 0.0081 0.008067 1.8574952 88.70887

360 0.1883 0.1882 0.1882 0.188233 7.1253846 57.76791 360 0.0071 0.007 0.0072 0.0071 1.6349028 90.06194

82

Table B.2: Data of dye removal of silica-PDDA-PSS-PDDA-iron oxide nanocomposite

MO=20 ppm Co (ppm)= 16.53233 MB=20 ppm Co (ppm)= 16.72168

time abs C (ppm) % time abs C (ppm) %

abs 1 abs 2 abs 3 abs av abs 1 abs 2 abs 3 abs av

0 1.5417 1.5415 1.5411 1.541433 16.53233493 0 0 0.5128 0.5125 0.5125 0.5126 16.72167838 0

15 0.22 0.221 0.222 0.221 8.365734 49.39775 15 0.0245 0.0246 0.0245 0.024533 5.6492416 66.21606

30 0.2154 0.2154 0.2154 0.2154 8.1537516 50.67998 30 0.0222 0.0222 0.0222 0.0222 5.1119496 69.42921

60 0.21 0.21 0.2099 0.209967 7.9480782 51.92404 60 0.0197 0.0197 0.0197 0.0197 4.5362796 72.87186

180 0.203 0.202 0.202 0.202333 7.659126 53.67184 180 0.0121 0.0121 0.0122 0.012133 2.7939184 83.29164

360 0.1919 0.192 0.1921 0.192 7.267968 56.03786 360 0.0083 0.0083 0.0083 0.0083 1.9112244 88.57038

Table B.3: Data of dye removal of silica-PEI-iron oxide nanocomposite

MO=20 ppm Co (ppm)= 16.87197 MB=20 ppm Co (ppm)= 16.45092

time abs C (ppm) % time abs C (ppm) %

abs 1 abs 2 abs 3 abs av abs 1 abs 2 abs 3 abs av

0 1.57 1.5744 1.5749 1.5731 16.87196943 0 0 0.5044 0.5044 0.5041 0.5043 16.45092159 0

15 0.208 0.209 0.208 0.208333 7.88625 53.25827 15 0.025 0.0249 0.0249 0.024933 2.8706744 82.55007

30 0.203 0.203 0.202 0.202667 7.671744 54.52965 30 0.02 0.019 0.021 0.02 2.30268 86.00273

60 0.1981 0.198 0.1981 0.198067 7.4976156 55.5617 60 0.015 0.0151 0.015 0.015033 1.7308478 89.47872

180 0.188 0.187 0.189 0.188 7.116552 57.82026 180 0.0115 0.0116 0.0117 0.0116 1.3355544 91.88158

360 0.1781 0.1782 0.178 0.1781 6.7417974 60.04143 360 0.0106 0.0105 0.0106 0.010567 1.2165826 92.60478