Kinetic and equilibrium modeling for adsorption of textile dyes in aqueous solutions by carboxymethyl cellulose/poly(acrylamide- co -hydroxyethyl methacrylate) semi-interpenetrating

Kinetic and Equilibrium Modeling for Adsorption ofTextile Dyes in Aqueous Solutions by CarboxymethylCellulose/Poly(acrylamide-co-hydroxyethylmethacrylate) Semi-interpenetrating Network Hydrogel

Ruma Bhattacharyya, Samit Kumar RayDepartment of Polymer Science and Technology, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India

Semi-interpenetrating network (IPN) hydrogels weresynthesized by free radical copolymerization of acryl-amide (AM) and hydroxyethyl methacrylate (HEMA) inaqueous solution of sodium carboxy methyl cellulose(CMC). The hydrogels were crosslinked with N,N0-methylene bisacrylamide (NMBA). Hydrogel was alsosynthesized from copolymerisation of AM and HEMA.This was designated as PAMHEMA. All of these hydro-gels were characterized by Fourier transforms infrared(FTIR) spectroscopy, scanning electron microscopy(SEM), X-ray diffraction (XRD), mechanical properties,and equilibrium swelling in deionized water. Thesehydrogels were used for adsorption of two importanttextile dyes, i.e., basic fuchsin and methyl violet fromwater at different experimental conditions. Thesehydrogels were found to show high removal% andadsorption of these two dyes from water for both lowand high feed concentration range. Experimental dyeadsorption data were fitted to five kinetic and sevenadsorption model equations with non-linear fittings.The experimental data were observed to fit well tomost of these model equations because of non-linearfitting. POLYM. ENG. SCI., 53:2439–2453, 2013. ª 2013Society of Plastics Engineers

INTRODUCTION

Synthetic dyes are of major concerns for our environ-

ment. More than 100,000 types of dyes are used in indus-

tries like plastics, paints, paper, textile, cosmetics etc. to

color various products [1]. It is reported that 2% of total

dyes produced in its manufacturing units and 10–20% of

dyes used for coloring different products are discharged in

effluent water [2]. However, most of the dyes are toxic

and carcinogenic. Because of very high tinctorial values

(\1 mg/L) discharge of very small quantity of dye in

water impart intense color which inhibits penetration of

sunlight. As a result photosynthesis of aquatic plants are

also disturbed [3]. Most of the textile dyes are made from

bio-recalcitrant synthetic aromatic compounds with low bi-

ological oxygen demand to chemical oxygen demand ratio

(�20%) [4]. Conventional methods like coagulation,

chemical precipitation, membrane extraction, complexa-

tion, solvent extraction, ozonation etc. can not effectively

remove dye from waste water [5]. However, adsorption is

a better candidate for dye–water treatment because of its

low cost, easy operation with simple design and insensitiv-

ity to toxic dye molecules [6]. Adsorbents like activated

carbon, fly ash, orange peel, jute etc. may effectively

remove low concentration of dyes from water [5]. In

recent years, various polymeric hydrogels based on acrylic

polymer/copolymers [7], semi- and full-interpenetrating

network (IPN) [8] and natural polymers like chitosan [9],

modified cellulose [2], alginates [6, 10] were tried for re-

moval of dye from water. Natural polymers are abundant,

renewable and biodegradable. However, structural integ-

rity of synthetic hydrogels is better [10]. Hence, hydrogels

based on both natural/semi-synthetic polymer and syn-

thetic polymers would be very effective. Carboxy methyl

cellulose (CMC) is water soluble ionic ether of cellulose

with wide spread commercial applications [8, 11]. Hydro-

gel obtained by crosslinking this cellulose ether would be

of poor gel strength [11] and because of its inherent crys-

tallinity the polymer can not absorb much of water. Thus

CMC was chemically modified with other synthetic poly-

mer to produce several hydrogels [8, 11, 12]. Interpenetra-

tion of two polymers followed by crosslinking of at least

one of the constituent polymers results in formation of

IPN type polymer with strong network structure [13]. IPN

formation is an effective way of enhancing mechanical

properties and toughness of a hydrogel. Further, polymers

with reactive functional groups can be combined into a

stable IPN blend to form a strong adsorbent. Thus, in

recent years CMC based IPN hydrogels have been widely

used for various applications. Bajpai and Misra [14] syn-

thesized IPN of acrylic acid and CMC and used it for

delivery of tetracycline drug. Xiao et al. synthesized pH

responsive IPN of CMC and polyvinyl alcohol [15]. In this

Correspondence to: Samit Kumar Ray; e-mail: [email protected]

DOI 10.1002/pen.23501

Published online in Wiley Online Library (wileyonlinelibrary.com).

VVC 2013 Society of Plastics Engineers

POLYMER ENGINEERING AND SCIENCE—-2013

hydrogel CMC was crosslinked with ferric chloride in

aqueous solution of polyvinyl alcohol. Ma et al. prepared

[16] clay loaded semi-IPN of CMC and N’isopropyl acryl-

amide with improved response rate and mechanical prop-

erties. Polyacrylamide is extensively used as hydrogel

materials. Metal and dye sorption of polyacrylamide is

increased by copolymerizing AM with maleic acid, ita-

conic acid, hydroxyethyl methacrylate (HEMA) etc. mono-

mers [17]. In this work, semi-IPN type hydrogels were syn-

thesized by free radical copolymerization of AM and

HEMA in aqueous solution of CMC. These hydrogels were

used for adsorption of two important synthetic dyes, i.e.,

basic fuchsin and methyl violet from water. These two dyes

are extensively used in Indian textile industries. Removal

of these dyes from water with a suitable adsorbent is indus-

trially very significant since both of these dyes are of high

tinctorial values and even a concentration as low as 1 mg/L

of these dyes produce color in water [3]. Thus, in this work,

the IPN hydrogels were used for adsorption of both low

(2.5–20 mg/L) and high range (100–1000 mg/L) of feed

concentration of these dyes. The effect of feed concentra-

tion, contact time, dosage of hydrogel, solution pH, and

ionic strength on adsorption of these dyes was studied.

EXPERIMENTAL

Materials

Monomers i.e., AM, HEMA, and N,N0-methylene bisa-

crylamide (NMBA; from Fluka), redox initiator pair, i.e.,

potassium peroxodisulphate (from Fluka) and sodium meta-

bisulfite (Merck), were of analytical grade and used without

further purification. CMC (degree of substitution 1.8 and

molecular mass 20,000) was obtained from S.d. fine chemi-

cals, Mumbai and used as obtained. Basic fuchsin (molecu-

lar mass 324, kmax ¼ 550 nm) and methyl violet (molecular

mass 408, kmax ¼ 585 nm) dye used in sorption studies,

were purchased from SRL Chemical, India.

Preparation of IPN Hydrogels

Three semi-IPN type hydrogels were synthesized in

aqueous solution of CMC by free radical crosslink copoly-

merization of AM, HEMA, and NMBA (comonomer cross-

linker) in a three-necked reactor at 658C for 3 h using po-

tassium peroxodisulfate and sodium metabisulfite(each, 0.5

mass% of the total monomer mass) as redox pair of initia-

tors. For this copolymerization reaction, AM:HEMA como-

nomer ratio was fixed at 10:1 while the amount of NMBA

was 0.5% (mass% of total monomer AM and HEMA).The

amount of CMC was 5, 7.5 and 10% (mass% of total como-

nomer) for these hydrogels and these were designated as

IPN1, IPN2, and IPN3, respectively. The gelled mass

resulting from this free radical crosslink copolymerization

was immersed in cold deionized water and kept for three

days to remove water soluble oligomer, uncrosslink poly-

mer and unreacted monomers from the gel. The gel

obtained was dried in a vacuum oven at 708C to a constant

weight. The dried gel was then disintegrated in a blender.

Characterization of the Hydrogel

Fourier Transforms Infrared Spectroscopy (FTIR). Va-

rious functional groups of the IPN hydrogels were charac-

terized by FTIR spectroscopy (Perkin Elmer model-Spec-

trum-2, Singapore) using KBr pellet made by mixing KBr

with fine powder of the polymer gel samples. (10:1 mass

ratio of KBr to polymer).

X-Ray Diffraction (XRD). The change of crystallinity

of the copolymer and CMC by IPN formation was charac-

terized by XRD. Wide angle XRD profile of the hydrogel

samples were studied at 258C with a diffractometer

(model: X’Pert PRO, made by PANalytical B.V., The

Netherlands) using Ni-filtered Cu Ka radiation (k ¼1.5418 A) and a scanning rate of 0.005 deg(2y)/s). The

angle of diffraction was varied from 2–72 degree.

Scanning Electron Microscopy (SEM). The morphol-

ogy of the dry and swollen hydrogels were characterized

by scanning electron microscopy (SEM, model no.

S3400N, VP SEM, Type-II, made by Hitachi, Japan) with

the accelerating voltage set to 15 kV. Hydrogels swollen

in dye solution were frozen in liquid nitrogen and then

freeze dried for SEM analysis.

Mechanical Properties. Mechanical properties of the

IPN hydrogels were also characterized with measurement

of tensile strength (TS) and elongation at break (EAB) by

an Instron-Tensile tester (Lloyd instruments, England).

The experiment was performed by a method reported else-

where [13]. In this work, cubic sample of 2 mm 3 2 mm

3 80 mm size was used. The crosshead speed of 100 mm

min21 was maintained. The cubic samples were elongated

at a strain rate of 5% min21. TS and EAB were calculated

on the basis of initial cross section area of the sample.

Equilibrium Swelling (ES%). The water uptake of the

hydrogels (WC) was determined by using the following Eq. 1.

WC ¼Wt �Wd

Wd

(1)

where Wt is the mass of swollen hydrogel polymer at time

‘‘t’’ and Wd is the mass of dry polymers. The amount of

water absorbed by the hydrogels under equilibrium condi-

tions, also called equilibrium swelling (ES) was obtained

when Wt did not change any more (Wa) with time.

Study of Dye Adsorption of the Hydrogels

Lower (2.5–20 mg/L) and higher (100–1000 mg/L)

range of feed concentration of basic fuchsin and methyl

2440 POLYMER ENGINEERING AND SCIENCE—-2013 DOI 10.1002/pen

violet dyes were prepared in distilled water at different

pH and also in distilled water with varied molar concen-

tration of sodium chloride and calcium chloride. Fifty

milligrams of hydrogel was taken in 50 mL of the dye so-

lution with continuous stirring on a magnetic stirrer until

equilibrium was reached. After equilibrium was reached,

the dye solution was separated by decantation from the

hydrogel. The concentration of dye solutions before and

after addition of hydrogel were determined by spectropho-

tometric measurement from a precalibrated curve of ab-

sorbance versus concentrations using Perkin Elmer lamda

2 5 UV–visible double beam Spectrophotometer. The ab-

sorbance of the dye solutions were measured at wave-

length of 550 nm for basic fuchsin and 585 nm for methyl

violet dye. The structure of basic fuchsin and methyl vio-

let dyes are shown in Fig. 1a and b, respectively. The

amount of dye uptake (Qe, mg/g) by unit mass (in g) of

the hydrogel at equilibrium was calculated using the fol-

lowing Eq. 1a

Qe ¼ðC0V0 � CeVÞ

Wd

(1a)

Here C0 and Ce are initial and final equilibrium

(after contact time t) concentration of dye solution

(mg/L) while V0 and V is volume (L) of the initial

and final dye solution containing the hydrogel and Wd

is mass (g) of the dry hydrogel polymer used for the

experiment. The removal% of dye by the hydrogel

polymers were determined by using the following

Eq. 2

Removal% ¼ ðC0V0 � CeVÞC0

� 100 (2)

The results for dye uptake experiments were reproduci-

ble and the errors inherent in the measurements were

less than 63%.

FIG. 1. (a) Basic Fuschin (BF) Dye, (b) methyl violet (MV) Dye, (c) IPN and its interaction with dye mole-

cule, (d) FTIR of the hydrogels.

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2013 2441

RESULTS AND DISCUSSION

Synthesis of Hydrogels

The IPN hdrogels were synthesized by free radical

copolymerization of AM and HEMA in presence of CMC.

In this case NMBA, a comonomer crosslinker also takes

part in the polymerization reaction. The reaction occurs

through free radical mechanism where primary radicals are

formed on all of these monomers, i.e. AM, HEMA and

NMBA. AM and HEMA radicals copolymerize while

NMBA being bifunctional (Fig. 1c) copolymerize with both

HEMA and AM resulting in formation of crosslink copoly-

mer. Hydroxy(-OH) and carboxyl(��COO2)functional

groups of CMC also interact with the copolymer through

electrostatic and hydrogen bonding interaction and thus a

double network of copolymer and CMC is formed [18].

The resulting polymer will be semi-IPN since only one

polymer of these double networks, i.e., the copolymer is

crosslinked. The possible structure of the IPN type hydrogel

and its interaction with dye molecule is shown in Fig. 1c.

Characterization of the Hydrogel

FTIR Analysis. The FTIR of CMC and the three IPN

hydrogels are shown in Fig. 1d. The stretching vibration

of carboxylic group of pure CMC is observed at 1580

cm21 while its CH2 scissoring and OH bending vibration

is observed at 1419 and 1326 cm21. 1, 4-b-D-Glucoside

stretching vibration of CMC is observed at 1036 cm21.

The broad band from 1203 cm21 to 1036 cm21 are due

to absorption of sugar ring of CMC [19, 20]. The band at

2950 cm21 corresponds to C��H stretching of alkane of

the hydrogels [21]. The N��H stretching of AM is

observed at around 3320 cm21 in the IPNs. The carbonyl

stretching of AM, NMBA, and HEMA are shifted at

around 1670 cm21. The carbonyl stretching of CMC is

also shifted to around 1650 cm21 in the IPN hydrogels.

CH2 scissoring of CMC is shifted in between 1423 and

1452 cm21 in the IPNs [21]. The C��O stretching band

of 1216 cm21 of HEMA comonomer is shifted to 1192

cm21 in the IPNs. The O��H bending vibration of HEMA

is also shifted to 1123 cm21 in the IPN. All of these shift-

ing clearly indicate interaction of CMC and PAMHEMA

in the double network of IPN.

SEM Analysis. The SEM of the dry IPN2 hydrogel is

shown in Fig. 2a. The globular morphology of CMC [22,

23] dispersed in continuous phase of the copolymer is evi-

dent from this figure. Other IPNs show similar type of SEM.

The SEM of IPN2 hydrogel swollen in dye solution is

shown in Fig. 2b. The swollen internal structure of the

hydrogel is clearly evident from its SEM. It also confirms

the three dimensional network structure of the hydrogel [20].

XRD Analysis. The XRD of CMC and the three IPNs

are shown in Fig. 3. The crystallinity of CMC arises from

intramolecular hydrogen bonding between hydroxy and

carboxylic functional groups of its structure. In-situcopolymerization of AM and HEMA reduces intramolecu-

lar hydrogen bonding. Hence crystallinity of CMC is also

reduced. Thus, from Fig. 3, it is observed that the crystal-

line peak of virgin CMC at 2y of 20 degree [24] is shifted

to 2y of 23 degree in the IPNs with much reduction in

peak intensity. In fact, polyacrylamide shows a low XRD

peak at 2y of around 21–32 degree [25]. Hence, the XRD

peak of the three IPNs at 2y of 23 degree may be due to

modified CMC and AM moiety of the copolymer.

Mechanical Properties. The TS and EAB of the hydro-

gel samples are given in Table 1. It is observed that with

increasing amount of CMC, TS of the hydrogel increases

while EAB decreases. IPN is formed by polymerization

FIG. 2. SEM of the hydrogel. (a) Dry IPN2, (b) Swollen IPN2.


of PAMHEMA copolymer in CMC with formation of

double networks. Entangled double networks of PAM-

HEMA and CMC increases its stiffness. Hence, with

increasing amount of CMC and interpenetration of the

IPN, TS increases while EAB decreases from PAM-

HEMA (0 wt% CMC) to IPN2. IPN3 shows slightly

lower TS which may be due to decrease in compatibility

of the copolymer and CMC in this IPN.

Equilibrium Swelling. The water uptake of initially dry

hydrogels was measured gravimetrically for a period of 48 h

at 308C and pH 7 using Eq. 1. It was observed that there was

no further change in mass of the hydrogel after 48 h of swel-

ling. Equilibrium swelling% (ES%) were determined from

the swelling curve (swelling % vs. time, not shown). The

ES% of the hydrogels is shown in Table 1. It is observed that

the IPN hydrogels show much higher ES% than the copoly-

mer hydrogel. The presence of CMC increases hydrophilicity

as well as ES% of the IPN hydrogels. In fact, the carboxylic

groups of CMC ionizes (pKa of CMC is 4.6 which is less

than solution pH 7) and repel one another. Thus, the network

structure expands to absorb more water. From Table 1, it is

observed that ES% increases with increase in amount of

CMC from IPN1 to IPN2. However, IPN3 containing higher

amount of CMC than IPN2 shows slightly lower ES%. This

may be due to increased interaction and entanglement

between CMC and the copolymer in this IPN [13].

Study of Dye Removal Capacity of the Hydrogels

Effect of Dosage of the Hydrogel. The dye adsorption

was studied in a batch experiment with 50 mL aqueous

solution of 5 mg/L basic fuchsin and methyl violet dyes

for 48 h at 258C. The dosage of hydrogel (IPN2) was var-

ied from 0.25 to 3 g/L. The experiment was carried out

for 48 h to ensure equilibrium of dye adsorption. It is

observed from Fig. 4a that removal% (R%) and equilib-

rium dye adsorption (Qe) increases with increasing dosage

of hydrogel. However, above 1 g/L of hydrogel, Qe

decreases though R% further increases to reach saturation

at around 2 g/L of hydrogel. Thus, at a hydrogel dosage

of 1 g/L, the IPN2 polymer is observed to show 62% BF

dye adsorption (R%) and adsorption capacity (Qe) of

3.1 mg/g while at hydrogel dosage of 2 g/L, Qe decreases

to 2.4 mg/g and R% increases to 95%. Similar kind of

FIG. 3. XRD of CMC and the three hydrogels.

TABLE 1. Composition, mechanical properties and equilibrium

swelling% (ES%) of the Hydrogels.

Name of the

polymer

hydrogel Composition

Tensile

strength

(MPa)

Elongation

at break

(%) ES%

PAMHEMA 10:1 copolymer of AM

and HEMA

35.13 55.21 1623

IPN1 10:0.5 mass ratio of

PAMHEMA and CMC

44.13 47.12 1693

IPN2 10:0.75 mass ratio of

PAMHEMA and CMC

49.23 39.11 1755

IPN3 10:1 mass ratio of

PAMHEMA and CMC

48.23 35.26 1731

FIG. 4. Effect of dosage of hydrogels and feed pH on Dye adsorption.

(a) Effect of Hydrogel dosage, (b) Effect of feed pH. Hydrogel-IPN2,

temperature 258C, dye concentration 5 mg/L, pH 7 for Fig. 4a, hydrogel

dosage 1 g/L for Fig. 4b.


trend is also observed for methyl violet dye adsorption.

The increase in % of dye adsorption (R%) with hydrogel

dosage may be attributed to increase in its surface area

which adsorbs more of the dye molecules. However, the

decrease in Qe at higher dosage of hydrogel (above 1 g/L)

may be due to competition among adsorbents and also

split in the concentration gradient [26]. In all of the sub-

sequent experiments, hydrogel dosage was fixed at 1 g/L

since at this dosage the hydrogel showed optimum per-

formance in terms of Qe and R%.

Effect of pH. The pH of the aqueous solution of dye

plays an important role for dye–hydrogel interaction. Dye

adsorption for IPN2 hydrogel was studied at different pH

of the dye solutions with dye concentration of 5 mg/L at

258C. Dilute aqueous solution of NaOH and HCl was

added to adjust the pH of the dye solutions. From Fig.

4b, it is observed that over the pH range of 2–9 the varia-

tion of dye adsorption or removal% (Qe or R%) for IPN2

hydrogel is marginal. Similar kind of trend lines was also

obtained with IPN1 and IPN3. Both Qe and R% decreases

above a pH of 8 which may be due to deprotonation of

the cationic dye [3]. In the subsequent experiments, solu-

tion pH was maintained at pH of 7.

Effect of Ionic Strength. Dye adsorption was also stud-

ied with similar experiments in presence of varied

concentration of monovalent and bivalent salts i.e. sodium

chloride and calcium chloride, respectively. For dying

textile fiber, sodium chloride is extensively used as it pro-

motes adsorption of dye [3, 27]. From Fig. 5a and b, it is

observed that with increase in concentration of both so-

dium chloride and calcium chloride both Qe and R%

decreases for basic fuchsin (Fig. 5a) and methyl violet

(Fig. 5b) dye. Ionic strength of the solution increases with

increase in salt concentration. As a result electrical double

layer surrounding the functional groups of the hydrogels

becomes compressed resulting in decreased adsorption of

dye. Because of higher ionic strength bivalent calcium

chloride is also observed to show lower adsorption than

monovalent sodium chloride for both basic fuchsin and

methyl violet dye.

Effect of Contact Time.

Two Distinct Stages of Adsorption. The variation of

adsorption of basic fuchsin dye with contact time in the

low and high concentration range is shown in Fig. 6a and

b, respectively. Similar kind of trendlines was also

observed for adsorption of methyl violet dye. From Fig.

6a and b, it is observed that for both concentration ranges

initially the rate of adsorption is very high. As the contact

time is further increased dye uptake rate becomes slower

and reaches almost a constant value. Initially all the func-

tional groups of the hydrogels are available for interacting

FIG. 5. Effect of salt on dye adsorption. (a) Sodium chloride, (b)

Calcium chloride. Solution pH 7, Polymer (IPN2) dosage 1 g/L,

Temperature 258C.

FIG. 6. Variation of adsorption of basic fucshin (BF) dye with time at

258C. (a) feed concentration 5 mg/L, (b) feed concentration 500 mg/L,

hydrogel dose 1 g/L, pH 7.


with dye molecules. Thus, initial rate of adsorption is

very high. As these functional groups exhaust by dye

adsorption, rate of adsorption becomes slower with time

and at a point of time it reaches a constant value. This

time is defined as equilibrium time when a dynamic equi-

librium is formed between the hydrogel and the dye solu-

tion, i.e., at this time the rate of desorption from the

hydrogel equals the rate of adsorption by the hydrogels

and dye adsorption reaches its maximum value.

Different Equilibrium Time for Hydrogels. From Fig.

6a, equilibrium time for dye uptake is observed to

increase in the following order: IPN1 (1315 min) \ IPN2

(1380 min) \ IPN3 (1521 min).

The different equilibrium times for the hydrogels may

be ascribed to its structure. Due to mutual interpenetration

and network formation of the two constituent polymers

(copolymer and CMC) the IPN hydrogels needed higher

contact time to reach saturation in the dye solution. With

increasing amount of CMC in the IPN hydrogel, inter-

penetration increases from IPN1 to IPN3 and thus IPN3

with the highest level of mutual interpenetration showed

the longest equilibrium time.

IPN Type and Adsorption. From Fig. 6a and b, it is

observed that for the same contact time dye adsorption

increases in the following order: PAMHEMA \ IPN1 \ I

PN2 [ IPN3. In this case as the amount of CMC increases

from 0% (PAMHEMA) to 7.5 % (IPN2), hydrophilicity of

the resulting hydrogel increases because of carboxylic and

hydroxy groups of CMC in the IPN. Thus, dye adsorption

increases due to increased interaction of dye molecules

with hydrogel (Fig. 1c). IPN3 showed slightly lower

adsorption than IPN2 which may be due to increased inter-

penetration and interactions between the two networks in

the hydrogel which reduces hydrogel-dye interaction [13].

Low and High Concentration. In comparison to low

feed dye concentration (5 mg/L, Fig. 6a) saturation of dye

adsorption occurs much earlier for high feed dye concentra-

tion (500 mg/L, Fig. 6b). In this case, within 180 min all of

the hydrogels reach equilibrium time. Dye adsorption by

hydrogel is governed by film diffusion of dye molecules

from solution to surface of the hydrogels followed by pore

diffusion into the interior of the hydrogel [27]. At higher

concentration range, mass transfer resistance for transport

of dye molecules is reduced and thus equilibrium time is

reached much faster. However, for all of the experiments an

equilibrium time of 48 h was given to ensure equilibrium

for both low and high concentration range of dye solution.

Effect of Initial Concentration of Dye. The variation

of dye up take properties of the hydrogels with feed con-

centration is shown for low feed concentration range of

2.5–20 mg/L and high concentration range of 100–1000

mg/L of basic fuchsin dye in Fig. 7a and b, respectively.

Similar type of isotherms was also obtained for methyl

violet dye. From these figures, it is observed that with

increase in equilibrium dye concentration in feed adsorp-

tion of dye molecules by the hydrogels increases. In fact,

dye adsorption by hydrogels is concentration dependant.

Mass transfer resistance of dye molecules between solid

(hydrogel) and liquid (dye solution) decreases with

increase in feed dye concentration. Thus, dye adsorption

increases with feed concentration. It is also observed that

removal% decreases with increase in feed concentration of

dye. A given amount of hydrogel can adsorb a fixed

amount of dye molecules. As the feed concentration inc-

reases, the % of this fixed amount decreases with respect

to increased feed concentration. Basic fuchsin and methyl

violet dye adsorption by IPN2 hydrogel for both high and

low feed dye concentrations is compared in Fig. 8a and b,

respectively. Similar kind of isotherms was also observed

for the other hydrogels. From these figures, it is observed

that for the same feed concentration the hydrogels show

much higher adsorption of basic fuchsin dye than methyl

violet dye. Both of these dyes are cationic. However, basic

fuchsin contains primary amine groups while methyl violet

contains tertiary amine groups. Primary amine is more ba-

sic (pKb ¼ 3.36) than tertiary amine (pKb ¼ 4.23) in

water. The methyl substituents of methyl violet dye may

cause some steric hindrance for approaching carboxylate

FIG. 7. Variation of adsorption of basic fucshin (BF) dye with feed

concentration at 258C. (a) Feed concentration range 2.5–20 mg/L, (b)

Feed concentration range 100–1000 mg/L.


anion of the hydrogel. The carboxylate anion of hydrogels

comes from its CMC and HEMA moieties. Further, the

primary amine of basic fuchsin dye forms hydrogen bond-

ing with hydroxy groups present in the IPN and also

shows strong electrostatic interaction with carboxylate

anion of CMC [18] (Fig. 1c). This may be the reason for

higher adsorption of basic fuchsin dye than methyl violet

dye by the hydrogels at any feed concentration of dye.

Adsorption Kinetics

The different rates of dye adsorption may be evaluated

by the following kinetic equations.

Lagergren Pseudo First Order Kinetics. Lagergren

pseudo first order kinetic equation is given by

dQt

dt¼ k1 Qe � Qtð Þ (3a)

Integrating the above Eq. 3a with boundary condition of

Q ¼ 0 at t ¼ 0 and Q ¼ Qt at t ¼ t, the following linear

Eq. 3b is obtained

lnðQe � QtÞ ¼ lnQe � k1t (3b)

The equation may also be expressed as

Qt ¼ Qe 1� expð�k1tÞ½ � (3c)

where Qe and Qt are dye adsorption (mg/g) at equilibrium time

and time t (min), respectively. The linear plotting of ln(Qe �Qt) against t using Eq. 3b or by non-linear fitting of Qt against

t using Eq. 3c yields the rate constant k (min�1) and theoretical

equilibrium adsorption (Qe) from slope and intercept (from

coefficients for non linear fittings) respectively.

Pseudo Second Order Kinetics. Pseudo second order

kinetic equation for equilibrium dye adsorption as given

by Ho and McKay [28, 29] is

dQt

dt¼ k2 Qe � Qtð Þ2 (4a)

Integrating the above equation with boundary condition of

Q ¼ 0 at t ¼ 0 and Q ¼ Qt at t ¼ t yields

t

Qt

¼ 1

k2Q2e

þ 1

Qe

t (4b)

On further simplification, Eq. 4b becomes

Qt ¼Q2

ek2t

1þ k2Qet(4c)

where k2 is second order rate constant (g/mg min) for dye

adsorption. The values of Qe and k2 is obtained from

slope and intercept of the linear trendlines of t/Qt against

t using Eq. 4b or by non-linear fitting of Qt against tusing Eq. 4c.

Intra Particle Diffusion Model. Intra particle diffusion

model as proposed by Weber and Morris [29] was tested

for the present system to understand diffusion mechanism.

According to this theory

Qt ¼ kpt1=2 þ c (5)

where c is intercept, intra particle rate constant kp (mg/g h1/2)

is obtained from linear plotting of Qt vs. t1/2. The diffusion of

dye molecules are only by intra particle diffusion if the trend

lines passes through origin (i.e., c ¼ 0). For some values of c(i.e. c = 0), diffusion is controlled by some other mecha-

nisms apart from intra particle diffusion. In fact, the curves

following intra particle diffusion have three different stages,

i.e., initial very fast surface adsorption (external mass

transfer) followed by a linear intra particle diffusion and

finally a plateau showing equilibrium sorption where intra

particle diffusion is very slow due to low concentration of

dye (solute) in solution [30].

Elovich Kinetic Model. This model assumes heteroge-

neous active sites of adsorbent and also different activa-

tion energies for sorption of organics like dye molecules.

FIG. 8. Comparison of adsorption and removal% for BF and MV dye

with IPN2 hydrogel. (a) High concentration (100–1000 mg/L), (b) low con-

centration (5–20 mg/L), hydrogel dose 1 g/L, Temperature 258C, pH 7.


It is given by the following Eq. 6a.

dQt

dt¼ a expð�bQtÞ (6a)

Integrating the above Eq. 6a with boundary condition of

Qt ¼ 0 at t ¼0 and Q ¼ Qt at t ¼ t, the above equation

becomes [31]

Qt ¼1

bln a:bð Þ þ 1

blnt (6b)

where a is initial rate of adsorption (mg g�1 min�1) andb is desorption rate constant for this adsorption. The val-ues of a and b are obtained from the slope and interceptof linear trendlines of Qt against lnt.

Bangham Kinetic Model. This kinetic equation is

given by

Qt ¼ kt t1m (7a)

The linear form of this model is given by

lnðQtÞ ¼ lnkt þ1

mlnðtÞ (7b)

where kt is rate constant for sorption and 1/m measures the

intensity of sorption. The non-linear fitting of Qt against tusing Eq. 7a or linear plot of ln(Qt) against ln(t) gives the val-

ues of rate constant kt and m. For Lagergren pseudo first order

and Ho and Mccay pseudo second order both linear and non-

linear regression were carried out with experimental adsorp-

tion data. For intra particle, Elovich and Bangham kinetic

models only linear regression was carried out since non-linear

regression would give the same statistical parameters.

Adsorption Isotherms

For absorption isotherms equilibrium dye absorption val-ues (Qe) at different feed dye concentrations (Ce) were fitted

to seven adsorption isotherms, i.e., two-parameter model

equations like Langmuir non-linear (Eq. 8a), and linear (Eq.

8b), Dubinin–Radushkevich linear (Eq. 9a) and non-linear

(Eq. 9b), Freundlich non-linear (Eq. 10), Tempkin non-linear

(Eq. 11), Redlich-Peterson non-linear (Eq. 12), Sips non-lin-

ear (Eq. 13a) and linear (Eq. 13b) and Fritz–Schlunder non-

linear (Eq. 14) models [32, 33] as given below.

Langmuir Isotherm. The non-linear and linear form of

this isotherm is given by Eqs. 8a and 8b, respectively.

Qe ¼QmaxKLCe

1þ KLCe

(8a)

1

Qe

¼ 1

QmaxKLCe

þ 1

Qmax

(8b)

The characteristic of Langmuir isotherm is expressed in

terms of dimensionless separation factor RL defined as

RL ¼1

KL þ Co

(8c)

where Co is the maximal dye concentration. The value of

RL indicates if the Langmuir process is unfavorable

(RL . 1), favorable (0 , RL , 1), linear (RL ¼ 1) or ir-

reversible (RL ¼ 0).

Dubinin–Radushkevich Isotherm. For heterogeneous

surface non-linear and linear form of this isotherm is

given by Eqs. 9a and 9b, respectively.

Qe ¼ Qmaxexp �be2� �

(9a)

lnQe ¼ ln Qmax�be2 (9b)

where

e ¼ RTln 1þ 1

Ce

8>:

9>; (9c)

The constant b is related to the energy of sorption E as

E ¼ 1ffiffiffibp (9d)

Freundlich Isotherm. The non-linear form of this equa-

tion is given by

Qe ¼ KF Ce1=n (10)

where KF is Freundlich constant and ‘‘1/n’’ signifies na-

ture of the isotherm. For linear adsorption n is unity.

When the adsorption is dominated by chemical sorption,

the value of n becomes less than unity. A value of n.1

indicates physical sorption.

Tempkin Isotherm. In this model, it is assumed that

heat of sorption of the molecules on the adsorbent surface

reduces linearly due to adsorbate–adsorbate interaction.

The non-linear form of this model is given by

Qe ¼RT

bT

ln ATCeð Þ (11)

where constant RT/bT ¼ Qmax, Qmax is maximum adsorp-

tion capacity, R is universal gas constant (8.314 J mol�1

K�1), T is absolute temperature (298 k). AT is TI constant

(L/mg) signifying maximum binding energy.

Redlich-Peterson Isotherm. The non-linear form of this

three-parameter model equation is given by Eq. 12,

Qe ¼KRPCe

1þ ARPCbRPe

(12)


Here KRP (L/mg) and ARP (L/g) are Redlich-Peterson iso-

therm constants. The value of bRP lies between 0 and 1.

For b ¼ 1, the Redlich-Peterson isotherm becomes identi-

cal with Langmuir isotherm while for b ¼ 0 the R-PI

becomes Henry’s law form.

Sips Isotherm Model. Like Redlich-Peterson isotherm

this model also combines Langmuir and Freundlich model

in one equation. The non-linear and linear form of this

model is given by Eqs. 13a and 13b

Qe ¼KSCbS

e

1þ ASCbSe

(13a)

� lnKS

Qe

8>>:

9>>; ¼ bSln Ceð Þ � ln ASð Þ (13b)

where Ks and As are Sips constant. This model is applica-

ble for adsorbent with heterogeneous surfaces. At low

concentration of dye, it becomes Freundlich isotherm

while at higher concentration it shows a mono layer

adsorption similar to Langmuir isotherm.

Fritz–Schlunder Model. Most of the above model

equations are combined in the following generalized five

parameter Fritz–Schlunder model Eq. 14

Qe ¼AFSCa

e

cþ BFSCbe

(14)

In most of the cases, c ¼ 1 and the above model

reduces to

Qe ¼AFSCa

e

1þ BFSCbe

(15)

where AFS and BFS are Fritz–Schlunder constants, while aand b are equation exponent. This model equation is

reduced to Sip model when a ¼ b and c ¼ 1, Redlich-Peter-

son model equation when a ¼ c ¼ 1, Langmuir model when

a ¼ c ¼ b ¼ 1 and Freundlich model when c ¼ 0.

Data Fitting to Model Equations. In most of the

reported works, linear regression is widely used for fitting

experimental data to linearized form of various model

equations. In linear regression a Gaussian distribution is

assumed for the trend lines where error distribution is

TABLE 2. Kinetic parameters of the hydrogels for low (2.5–20 mg/L) and high concentration (100–1000 mg/L) range of BF dye.

PAMHEMA IPN1 IPN2 IPN3

Model Low/high Low/high Low/high Low/high

Pseudo first order

Qeth(mg/g) 1.99/293 2.72/340 3.067/374.48 2.985/364.93

k1(min21) 0.0026/0.0221 0.0026/0.0227 0.00279/20.023 0.0027/20.0235

R2 0.9977/0.9963 0.9888/0.9965 0.9947/0.9953 0.9919/0.9950

v2 0.0016/33.48 0.0147/42.42 0.0088/67.52 0.0128/68.45

F value 9737/10150 2005/10897 4301/8340 2802/7899

Pseudo second order

Qeth (mg/g) .236/368 3.05/425.09 .449/466.07 3.36/452.21

K2(g/mg min) 0.0014/5.98E-05 0.0010/5.4E05 0.00097/5.02E-05 0.00098/5.34E-05

R2 0.9812/0.9898 0.9829/0.9909 0.99023/0.99116 0.9908/0.9889

v2 0.0136/91.62 0.0225/108 0.0163/127 0.0163/127

F value 1160/3705 1308/4251 2328/4404 2488/3632

1160.61/3705.87 1308.26/4251.88 2328.50128/4404.85

Intra particle

kp(mg/g min1/2) 0.023/21.99 0.034/25.392 0.038/27.853 0.0372/27.094

c 0.456/18.063 0.631/23.594 0.728/27.817 0.70101/28.82

R2 0.6615/0.9257 0.6903/0.9251 0.6984/0.9257 0.7109/0.9167

(v2) 0.2191/669 0.2191/900 0.3684/1073 0.4532/1151

F value 65.83/502 65.83/507 74/518.71 77.39/463

Elovich

a 0.0183/16.17 0.0257/19.43 0.02997/21.91 0.0291/21.69

b 2.479/0.0118 1.82/0.01029 1.620/0.0094 1.662/0.0096

R2 0.9226/0.9867 0.9345/0.9875 0.9426/0.9877 0.9472/0.9845

(v2) 0.0558/119 0.0866/149 0.09561/178 0.0832/214

F value 277/2840 335/3085 391/3159 426/2516

Bangham

Kb 0.05751/37.77 0.0869/45.58 0.103/51.33 0.102/51.53

m 2.23/2.487 2.30/2.532 2.33/2.560 2.34/2.596

R2 0.9026/0.9432 0.9086/0.9449 0.9086/0.9469 0.9122/0.9402

(v2) 0.079/512 0.069/662 0.0285/768 0.064/826

F value 60.96/658 73.32/692 83.55/727 85.26/647


same for each experimental value. However, after lineari-

zation of a model equation the error distribution gets

altered. In non-linear fitting experimental data are directly

fitted to the model equations and regression analysis is

carried out by adjusting parameter values through interac-

tion till convergence. For the present system, non-linear

regression was carried out for all of the five kinetic mod-

els and seven adsorption isotherms by directly fitting the

experimental Qt, t, Qe, and Ce values to the non-linear

model equations since it gives better fitting of experimen-

tal data [33, 34]. For comparison of these two types of

regression, both linear and non-linear fitting was carried

out for basic fuchsin dye in the low concentration range

for pseudo first order and pseudo second order kinetics.

For adsorption isotherms, both linear and non-linear fit-

tings were applied for Langmuir, Dubinin–Radushkevich,

and Sips adsorption isotherms. Both of these linear and

non-linear fittings were carried out by Origin-8 software.

The non-linear fitting with this software is based on

Levenberg-Marquardt (L-M) algorithm where parameter

TABLE 3. Adsorption parameters of the hydrogels for adsorption of low (2.5–20 mg/L) and high concentration (100–1000 mg/L) range of BF dye.


Model Low/High Low/High Low/High Low/High

Langmuir

KL (L/mg) 0.172/0.00120 0.247/0.00124 0.248/0.00127 0.241/0.00123

Qmax(mg/g) 5.08/705 5.27/847 5.96/920 5.842/899

RL 0.225/0.454 0.168/0.446 0.167/0.440 0.171/0.448

R2 0.9852/0.9571 0.9853/0.9597 0.9852/0.9597 0.9853/0.9592

v2 0.025/776 0.0303/1018 0.039/1204 0.037/1148

F value 1639/367 1797/389 1790/388 1772/387

Freundlich

n 0.087/1.59 0.4143/1.57 0.4143/1.573 0.538/1.57

KF (L/mg) 2.23/5.24 2.66/5.94 2.67/6.43 2.66/6.28

R2 0.941/0.938 0.9088/0.9421 0.9083/0.9420 0.9216/0.9419

v2 0.0061/1114 0.0068/1463 0.0069/1736 0.0058/1655

F value 747/254 695/269 692/268 760/268

Temkin

a 1.17/143 1.152/169 1.303/184 1.278/180

b 14/0.014 530/0.0139 29.14/0.013 34.14/0.014

R2 0.9467/0.9443 0.9210/0.9459 0.9205/0.9463 0.9272/0.9463

v2 0.0376/1009 0.055/1367 0.0716/1606 0.0716/1606

F value 978/281 974/288 1043/290 1080/290

DR

Qm (mg/g) 4.07/384 4.57/454 5.17/494 5.03/483

b (mol2/kJ2) 25.5E-06/0.0101 24.6E-06/0.010 4.6E-06/20.0103 4.6E-06/20.0102

R2 0.9790/0.8309 0.9852/0.8327 0.9851/0.8346 0.9817/0.8346

v2 0.036/2200 0.033/3046 0.0419/3046 0.041/3404

F value 919/127 1404/128 1399/129 1134/129

Sip

KS (L/mg) 0.736/0.094 0.953/0.122 1.07/0.126 1.15/0.123

b 1.15/1.41 1.29/1.4 1.30/1.40 1.19/1.40

AS 0.157/1.91E-04 0.199/2.05E-04 0.199/1.9E-04 0.2129/1.9E-04

R2 0.9836/0.9579 0. 9856/0.9601 0.9856/0.9605 0.9838/0.9604

v2 Sq 0.0274/763 0.029/1007 0.0380/1183 0.0405/1128

F value 988/262 1226/249 1223/264 1087/264

RP

KRP (L/mg) 0.005/0.062 0.0162/0.072 0.0185/0.077 0.016/0.076

ARP 21.0007/21.131 21.005/21.133 21.0053/21.132 21.004/21.131

B 20.008/20.0419 20.0243/20.0410 20.024/0.0407 20.0215/20.0408

R2 0.8897/0.9068 0.8293/0.9126 0.8287/9124 0.8438/0.9128

v2 0.1856/1688 0.3526/2208 0.4532/2620 0.3923/2499

F value 144/111 101/118 100/118 110/119

FS, AFS 34283/5.7Eþ09 4266/2.69Eþ09 4652/2.88Eþ09 18127/2.8Eþ09

A 22.62/22.27 21.95/22.14 21.94/22.13 22.35/22.13

BFS 39459/1.11Eþ10 3683/4.37Eþ09 3551/4.4Eþ09 13683/4.3Eþ09

B 23.22/23.31 22.52/23.16 22.51/23.16 22.88/23.16

R2 0.9932/0.9755 0.9942/0.9752 0.9942/0.9755 0.9932/0.9755

v2 0.0113/442 0.0119/626 0.0153/731 0.0171/697

F value 1798/323 2293/317 2279/321 1934/321

DR: Dubinin–Radushkevich; RP: Redlich–Peterson; FS: Fritz–Schlunder.


values of a model are adjusted in an iterative process

using chi-square (v2). The validity of the kinetic and

adsorption isotherm models were evaluated in terms of

regression coefficient (R2), non-linear v2 and F values

(obtained from Anova analysis in Origin). For a good fit-

ting, R2 should be close to unity, v2 should be low while

F value should be high [35]. The various kinetic and

model parameters along with regression coefficient, chi-

square, and F values are shown in Tables 2 and 3 for

adsorption of low and high concentration of basic fuchsin

dye by the four hydrogels. From Table 2, it is observed

that basic fuchsin dye shows good fitting for all of the ki-

netic models in high concentration range as evident from

respective R2, v2, and F values. In the low concentration

range, it also shows good fitting except intra particle dif-

fusion model. Methyl violet dye was also observed to

show similar fitting (not shown). From Table 3, it is

observed that basic fuchsin dye also shows good fitting to

all of the two-, three-, and four-parameter adsorption

models. Similar kind of fitting was also observed for

methyl violet dye. Favorable Langmuir adsorption is quite

evident from RL values as shown for Langmuir parame-

ters in Table 3. Similarly, all the hydrogels show chemical

adsorption for low concentration of dye and physical

adsorption for high concentration dye as observed from nvalues of Freundlich isotherm for basic fuchsin dye given

in Table 3. Methyl violet dye was also observed to show

similar trend (not shown). Linear and non-linear regression

for two kinetic models and three adsorption models are

shown in Table 4 for low concentration of basic fuchsin

dye. These linear (shown in inset) and non-linear fittings

are also shown in Fig. 9a and b (pseudo first and second

order), Fig. 10a and b (Langmuir and Dubinin–Radushke-

vich) and Fig. 11a (Sip isotherm). From these figures and

Table 4, it is observed that non-linear regression gives bet-

ter fitting of the experimental dye sorption data to the vari-

ous models used in this study. Accordingly, values of R2

for fitting to pseudo first order are observed to be less than

0.8 for all the hydrogels while non-linear fitting give R2 [0.98 with the same experimental data. Similar results are

observed to the other models as seen in Table 3. Among

the entire adsorption models four parameter Fritz–Schlun-

der model is observed to show the best fitting in terms of

statistical parameters as observed in Table 3 and Fig. 11b.

This model is very flexible to incorporate all of the other

models at various process conditions [34] which may be

responsible for its good fitting. In Fig. 12a and b, predicted

Qe based on various models are plotted against experimen-

tal Qe for basic fuchsin and methyl violet dyes at low

(Fig. 12a) and high (Fig. 12b) concentration range with

IPN2 hydrogel. Similar results were obtained with the other

three hydrogels. From these figures, it is observed that both

of these dyes show very good fitting at high concentration

TABLE 4. Comparison of linear and non-linear regression for adsorption of low concentration of BF dye.


Model Linear/Non-linear Linear/Non-linear Linear/Nonlinear Linear/Non-linear

Pseudo first order

Qeth (mg/g) 0.603/1.994 1.138/2.72 1.498/3.06716 1.606/2.985

k1 (L/mg) 0.0011/0.0026 0.0014/0.0023 9.6E-4/0.00279 8.8E-4/0.00277

R2 0.6351/0.9977 0.7304/0.9888 0.8007/0.99533 0.7557/0.99186

F value 21.73/9737 24.82/1089 31.67/4301.05 23.35/2802.24

Pseudo second order

Qeth (mg/g) 2.101/2.236 2.923/3.05 3.309/3.449 3.235/3.3606

k2(g/mg.min) 0.0018/0.0014 0.0013/0.00106 0.0011/0.00097 0.0012/0.00098

R2 0.9933/0.9812 0.9947/0.9829 0.9968/0.9902 0.9966/0.9908

F value 2696/1160 3462/1308 5677/2328 5564/2488

Qexpt(mg/g) for Low concentration BF 1.988 2.772 3.151 3.108

Langmuir

KL (L/mg) 0.183/0.172 0.233/0.247 0.234/0.248 0.240/0.248

Qmax(mg/g) 4.934/5.08 5.346/5.27 6.049/5.96 5.830/5.96

R2 0.9699/0.9852 0.9808/0.9853 0.9807/0.9852 0.9803/0.9852

F value 1064/1639 2212/1797 2203/1790 2224/1790

DR

Qm (mg/g) 3.57/4.07 4.12/4.57 4.66/5.17 4.52/5.03

b(mol2/kJ2) 1.3E-06/5.5E-06 1.12E-06/4.6E-06 1.11E-06/4.6E-06 1.09E-06/4.6E-06

R2 0.8302/0.9790 0.8881/0.9852 0.8883/0.9851 0.8697/0.9817

F value 35.23/919 56.55/1404 56.70/1399 47.75/1134

Sip

KS (L/mg) 1.01/0.736 1.03/0.953 1.02/1.07 1.05/1.15

B 0.446/1.15 0.374/1.29 0.376/1.30 0.371/1.19

AS 1.026/0.157 0.760/0.199 0.765/0.199 0.761/0.2129

R2 0.9414/0.9836 0.9088/0.9856 0.9083/0.9856 0.9216/0.9838

F value 682/988 758/1226 746/1223 890/1087


range. At low concentration range, methyl violet dye is

observed to show better fitting than basic fuchsin dye.

Regeneration and Reusability of the Hydrogels

For regeneration of the hydrogels, desorption experi-

ments similar to adsorption experiments were carried out

with dye loaded hydrogels at varied pH. No significant

desorption was observed at pH 7, while desorption was

maximum (up to 98.7%) at pH 3 indicating strong electro-

static interactions between dyes and hydrogels [36]. The

regenerated hydrogel was used for five numbers of

repeated adsorption /desorption cycles without any signifi-

cant change of adsorption% indicating efficient regenera-

tion and reusability of the hydrogels.

Comparison With Reported Work

The dye adsorption and removal% for basic fuchsin

and methyl violet dye are compared with reported works

with different hydrogels in Table 5. From the data given

in Table 5, it is observed that adsorption capacity of

different reported hydrogels (mg/g of hydrogels) varies

with feed concentration range (40–1000 mg/L) of dye.

Thus, poly(HEMA–g–GMA) was reported [3] to show

adsorption of 121.5 mg methyl violet dye/g of hydrogel for

feed concentration of 700 mg/L dye while poly(AM-co-

AA) hydrogel shows adsorption of only 6.38 mg methyl

violet dye/g of the gel for feed concentration of 50 mg/L

dye [41]. This kind of different dye adsorption for widely

varied feed concentration range was also obtained with

other reported works as shown in Table 5. In this work,

very low (2.5–20 mg/L) and very high range (100–1000

mg/L) of feed dye concentration was used. For the high

range of feed concentration, the present hydrogel is

observed to show much higher adsorption and removal%

than most of the reported work with similar feed dye con-

centration. The low range of concentration also shows high

adsorption and removal% though adsorption by other

hydrogels with similar feed dye concentration is yet to be

reported.

CONCLUSION

IPN type hydrogels were synthesized from PAM-

HEMA copolymer and CMC by free radical polymeriza-

FIG. 9. Fitting of experimental data of BF dye adsorption

to kinetic equation with non-linear and linear (shown in inset) regression.

(a) Pseudo first order kinetics, (b) Pseudo second order

kinetics. Dye concentration 5 mg/L, hydrogel dose 1 g/L, Temperature

258C, pH 7.

FIG. 10. Fitting of experimental data of BF dye adsorption to two-pa-

rameter adsorption isotherm equation with non-linear and linear (shown

in inset) regression. (a) Langmuir isotherm, (b) Dubinin–Radushkevich

model. Dye concentration 5 mg/L, Hydrogel dose 1 g/L, Temperature

258C, pH 7.


tion. The effect of dosage of hydrogel in water, solution

pH, initial feed dye concentration, and contact time on

dye adsorption and removal% for both low and high

range of two industrially important textile dyes, i.e., basic

fuchsin and methyl violet dye was studied. Mechanical

properties, equilibrium swelling, dye adsorption, and re-

moval% were observed to increase with increase in

amount of CMC in the hydrogel. The experimental dye

adsorption data were fitted to five kinetic models and

seven adsorption isotherm models by non-linear analysis.

The adsorption data of these hydrogels were found to

show best fitting for Fritz–Schlunder model. Non-linear

fitting was also compared with linear fitting using same

experimental data. Non-linear fittings were found to be

better than linear fitting in terms of values of various sta-

tistical parameters.

FIG. 12. Comparison of model fitting with BF and MV dye. (a) low

concentration (2.5–20 mg/L), (b) High concentration (100–1000 mg/L).

TABLE 5. Comparison of present work with reported data.

Name of hydrogel Dye used in water, concentration, pH Adsorption Performance mg/g resin Reference

Poly(HEMA-g-GMA 700 mg/L of MV, pH 5, Qmax ¼ 0.189 121.5 [3]

700 mg/L of BF, pH 5 68.7

Qmax ¼ 0.029

Jute stick 50 mg/L of Rhodamin B at pH 7 4.6 mg/g [5]

Poly(AA-co-AM)/attapulgite 200–1000 mg/L of MV at pH 7 917 for 1000 mg/L feed [18]

Soya ash pH 9, at 25.9 mg/L 4.209 [38]

Qm ¼ 5.76

Composite Poly(AA-co-VP) 40 mg/L of Crystal Violet at pH 7 4.1 [39]

Supramolecular and

composite gel of agarose

1000 mg/L of methyl violate at pH 7 Removal% 95.1 and 95.7% for supramolecular

gel and hybrid gel, respectively.

[40]

poly(AM-co-AA) 50 mg/L of methyl violet at pH7 6.38 [41]

Poly(VP-co-MA) 500 mg/L of methyl violet at pH 7 4.22 [42]

IPN2 For 2.5 mg/L feed dye (Ce) at pH 7, Temperature 258C 2.249 for BF, Qm ¼ 5.96 This work

1.723 for MV, Qm ¼ 3.93

IPN2 For 500 mg/L feed dye (Ce) at pH 7, Temperature 258C 368.70 for BF, Qm ¼ 920 This work

283.76 for MV, Qm ¼ 613.8

FIG. 11. Fitting of experimental data of BF dye adsorption to adsorp-

tion isotherm equation with non-linear and linear (shown in inset) regres-

sion. (a) three-parameter Sip isotherm, (b) Four-parameter Fritz–Schlun-

der model (only non-linear) dye concentration 5 mg/L, hydrogel dose 1

g/L, Temperature 258C, pH 7.


ACKNOWLEDGMENTS

The authors thank Council of Scientific and Industrial

Research (CSIR-EMR-22(0547)/11/EMR-II) and Depart-

ment of Science and Technology (DST-SERC-SR/S3/CE/

056/2009), Government of India for supporting the work.

Abbreviations

AM Acrylamide

CMC Carboxy methyl cellulose

EAB Elongation at break

FTIR Fourier transforms infrared

HEMA Hydroxyethyl methacrylate

IPN Interpenetrating network

NMBA N,N0-methylene bisacrylamide

SEM Scanning electron microscopy

TS Tensile strength

XRD X-ray diffraction

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