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Journal of Environmental Management 162 (2015) 37e45

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Journal of Environmental Management

journal homepage: www.elsevier .com/locate/ jenvman

Research article

Biodegradable and conducting hydrogels based on Guar gumpolysaccharide for antibacterial and dye removal applications

Reena Sharma a, Balbir S. Kaith b, Susheel Kalia c, *, D. Pathania a, Amit Kumar a,Neha Sharma d, Reva M. Street e, Caroline Schauer e

a School of Chemistry, Shoolini University, Bajhol, Solan, Himachal Pradesh, Indiab Department of Chemistry, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar, Punjab, Indiac Department of Chemistry, Army Cadet College Wing, Indian Military Academy, Dehradun, 248007 (UK) Indiad School of Biotechnology, Shoolini University, Bajhol, Solan, Himachal Pradesh, Indiae Department of Materials Science and Engineering, Drexel University, Philadelphia, PA, USA

a r t i c l e i n f o

Article history:Received 9 May 2015Received in revised form17 July 2015Accepted 19 July 2015Available online xxx

Keywords:HydrogelConductivityDye adsorptionAntibacterial properties

* Corresponding author.E-mail address: susheel.kalia@gmail.com (S. Kalia)

http://dx.doi.org/10.1016/j.jenvman.2015.07.0440301-4797/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

Conducting hydrogels possessing antibacterial activity were developed using a two-step free-radicalaqueous polymerization method to incorporate polyaniline chains into an adsorbent Guar gum/acrylicacid hydrogel network. The material properties of the synthesized samples were characterized using FTIRspectroscopy, thermal analysis and scanning electron microscopy techniques. Conducting hydrogels weretested for antibacterial activities against gram-positive Staphylococcus aureus and gram-negativeEscherichia coli bacteria and demonstrated antibacterial activity. Synthesized hydrogel samples can bepotential adsorbent materials for dye removal applications.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Hydrogels are polymer networks possessing the ability toabsorb water-based fluids, swelling to form a hydrated interlinkednetwork (Shi et al., 2011 Peppas et al., 2000). The water-inducedswelling of the network depends on the type of polymer back-bone, monomeric composition and extent of cross-linking(Mundargi et al., 2007a, 2007b; Zhang et al., 2005). Modificationsof crosslinked hydrogels with conducting polymers (CPs) lead tomultifunctional electrically conductive materials that retain thebeneficial absorption properties of hydrogels (Fan et al., 2008).Polyaniline (PANI) is an attractive conductive polymer because ofits simple methods of synthesis, high stability, variable structure, aswell as unique optical, magnetic, electrical, electrochemical andelectromechanical properties (Karami et al., 2003; Malhotra et al.,1990; Tiwari et al., 2013; Prokes and Stejskal, 2003; Han et al.,2002). Other useful characteristics include the varied physi-ochemical properties of different forms of PANI (Feast et al., 1996),as well as the tunable conductivity of PANI, which can be controlled

.

by the protonation of the imine sites present on the main polymerchain (Pron et al., 1988; Syed and Dinesan, 1991; Cortes and Sierra,2006). Such polymers have potential applications in numerousfields such as the removal of dyes from wastewater (Perju andDragan, 2010), bioactive electrode coatings (Rylie et al., 2010),electrochemical devices (Zhao et al., 2013) and super capacitors(Ghosh and Inganas, 1999). Such cross-linked polymer networksare gaining importance due to their applications in a variety ofdifferent fields including biomedical and environmental engineer-ing, agriculture and water purification (Thakur and Thakur, 2014;Liu et al., 2014).

One of the most environmentally significant applications ofhydrogels is in their uses for reducing industrial contamination ofnatural water sources. Industries such as dye, textile, paper, plastic,plating andmining can release effluents containing toxic pollutantsand heavy metals, which may be extremely harmful to people andthe environment. Many dyes and pigments are toxic and havecarcinogenic and mutagenic effects that influence the environmentand human life also. Different adsorbents have been used forremoving colored effluents from aqueous solutions. Absorption ofpollutants by hydrogel swelling, an inexpensive and simple design,can be used to remove dye contamination from aqueous

R. Sharma et al. / Journal of Environmental Management 162 (2015) 37e4538

environments. The presence of ionic groups in the superabsorbenthydrogel polymer structure can also increase loading due to largerspace for liquid uptake due to ioneion repulsion (Jiuhui, 2008).Hydrogels are three-dimensional cross-linked polymer networks offlexible chains, which are able to absorb and retainwater and solutemolecules. The possibility of using hydrogel as a potential adsor-bent is due to the presence of ionizable carboxylic and hydroxylgroups in the polymer network.

Senay et al. (2015) have recently developed a new morpholog-ical approach for removing acid dye from leather wastewater. Theysynthesized p(HEMAeGMA) poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) spherical particulated membranes by UV-photopolymerization. Synthesized membranes were coupled withiminodiacetic acid, chelated with Cr(III) ions as ligand and used forremoving acid dye. Adsorption properties of the membranes wereinvestigated under different conditions and results showed that themetal-membranes were effective sorbent systems removing aciddye from leather wastewater.

Several options of decolourisation of textile wastewater bychemical means have been suggested by Verma et al. (2012). Thedirect discharge of wastewater into environment affects itsecological status by causing various undesirable changes. Re-searchers and industries are finding novel solutions for developingtechnologies that can reduce the environmental damage. Colorremoval from textile wastewater by means of cheaper and envi-ronmental friendly technologies is still a major challenge. Theyhave emphasized and encouraged the use of natural materials asthe viable alternative because of their eco-friendly nature.

Guar gum polysaccharide is a biodegradable, non-toxic, low costand renewable raw material and can potentially be used for highperformance applications. Research work on the graft copolymer-ization of vinyl monomers onto Guar gum (Ggum) was reported(Kono et al., 2014; Pandey et al., 2014; Shahid et al., 2013; Yadavet al., 2013; Tiwari, 2007; Tiwari and Singh, 2008), but there isscant information in literature about the synthesis of Ggum-cl-poly(AA/PANI) conducting interpenetrating networks (IPNs).Therefore, Guar gum-acrylic acid (AA) based crosslinked hydrogelswere interpenetrated with PANI and evaluated for conductivity,antibacterial properties and dye adsorption application.

2. Materials and methods

2.1. Materials

Guar gum (Ggum) and ammonium persulfate (APS) were pur-chased from Loba-Chemie Pvt. Ltd. Hexamine and acrylic acids (AA)were purchased from S D Fine-Chem Pvt. Ltd. Aniline,1-methyl-2-pyrrolidone and acetone were procured from Merck India. Methy-lene blue (MB) dye used for the dye adsorption study was pur-chased from SigmaeAldrich. Gram-positive Staphylococcus aureus(MTCC 737) and gram-negative Escherichia coli (MTCC 739) used forantibacterial investigations were obtained from the Microbial TypeCulture Collection and Gene Bank (MTCC).

Table 1Optimized process parameters for the synthesis of Semi-IPNs and IPNs.

Sample Optimized reaction parameters

Initiator [APS] � 10�1

mol L�1Time(min)

Solvent(ml)

Ggum-cl-poly(AA) 0.262 150 17.5Ggum-cl-poly(AA-ipn-aniline)-

undoped0.262 150 17.5

Ggum-cl-poly(AA-ipn-aniline)-doped

0.262 150 17.5

2.2. Synthesis of Ggum-cl-poly(AA-ipn-aniline) IPN

Guar gum (1 g) was mixed with 17.5 mL of distilled waterfollowed by the addition of a calculated amount ofAPS (0.262 � 10�1mol L�1) as an initiator and hexa-amine (0.356 � 10�1mol L�1) as cross-linker. Acrylic acid(0.145 � 10�3mol L�1) was added drop-wise to the solution withcontinuous stirring to improve homogeneity. The resulting solu-tion was incubated at 60 �C for 3 h and the final product waswashed with distilled water in order to remove unreacted ho-mopolymer and then dried in a vacuum oven. Ggum-cl-poly(AA)was used for the preparation of Ggum-cl-poly(AA-ipn-aniline)under neutral (undoped) and acidic (doped) conditions. Differentreaction parameters were tested at a range of values to get themaximum percentage swelling in the resultant hydrogel at opti-mum concentrations. The percentage swelling (Ps) was calculatedusing the following equation (Kaith et al., 2012),

Ps ¼ Ws �Wd

Wd� 100 (1)

Where, Ws and Wd are the weight of the swelled and dry samples,respectively.

The reaction parameters were varied in following manner;initiator concentration: 0.0131e0.0306 mol L�1, reaction time:120e240 min, solvent volume: 15e25 mL, monomer concentra-tion: 0.145e0.729 � 10�3 mol L�1, pH: 3e7, reaction temperature:50e90 �C, crosslinker concentration: 0.0214e0.0499 mol L�1andaniline concentration: 0.109e0.767 � 10�3 mol L�1in case of bothneutral (undoped) and acidic (doped) conditions. Doping was car-ried out in different concentrations of aqueous HCl varying from0.5 N to 2.5 N.

One gram of Ggum-cl-poly(AA) was added to optimized anilinemonomer in aqueous solution for the synthesis of IPNs underneutral (undoped) condition. Optimized amount of APS and hex-amine were added with continuous stirring at 80 �C for 150 min.Progress of the reaction was visually assessed by the color changecaused by the formation and protonation of PANI chains. Theresulting IPN, Ggum-cl-poly-(AA-ipn-aniline), was washed with 1-methyl-2-pyrrolidone to remove the unreacted homopolymer andfinally the product was dried in oven at 50 �C. A similar procedurewas followed to synthesize Ggum-cl-poly(AA-ipn-aniline) underacidic (doped) conditions (0.5 N aqueous solution of HCl) andsummary of these optimized conditions can be found in Table 1.

2.3. Instrumental analysis

The Fourier transform infrared (FTIR) spectrums of the sampleswere recorded with a Model 8300 Shimadzu IR spectrophotometer.Thermal behavior of samples was assessed using a ShimadzuSimultaneous Thermal Analyzer from 50 to 700 �C in a nitrogenatmosphere with a heating rate of 10 �C/min. Scanning electronmicroscope (SEM) images were obtained using a Jeol Steroscan 150

Ps

Monomer � mol L�1 pH Cross-linker [hexamine] � 10�1

mol L�1Temp.(�C)

0.145 � 10�3 7 0.356 80 2345.060.548 � 10�3 7 0.356 80 666.60

0.329 � 10�3 7 0.356 80 306.06

R. Sharma et al. / Journal of Environmental Management 162 (2015) 37e45 39

microscope. The currentevoltage (IeV) characteristics were stud-ied using a Keithley source meter and a 2-probe instrument.

2.4. Antibacterial study

Gram-positive Staphylococcus aureus (MTCC 737) and gram-negative Escherichia coli (MTCC 739) bacteria were used as testmicroorganisms using agar as a growth medium in an agar overlaytechnique. Briefly, agar plates were seeded with test microorgan-isms and incubated at room temperature for 30 min until the so-lidification of the medium. Synthesized hydrogel samples of sameweight were placed on the solidified agar and controls withouthydrogel samples were also prepared (Abdel Kader and Seddkey,1995). Plates were incubated at 37 �C to allow bacterial growth.At 24 h, the growth inhibition zone surrounding the test sampleswas measured in millimeters and recorded as the antibacterialeffect.

2.5. Dye adsorption

To determine the degree of dye adsorption, 250 mg of each testsample was immersed in 100 mL aqueous solution of methyleneblue dye (2 � 10�5 mol L�1) for 4 h at room temperature. The su-pernatant was analyzed spectrophotometrically using a UVeVISspectrometer at 662 nm at 40 min intervals in order to know theremaining dye concentration. The effect of different parameterssuch as time, pH, amount of sample and temperature on the dyeremoval were studied with respect to maximum dye uptake. Thepercentage of MB removal was calculated using the followingexpression (Chatterjee et al., 2011):

Dye adsorptionð%Þ ¼ ðCo � CtÞCo

� 100 (2)

Where Co is the initial absorbance of MB dye and Ct represents theabsorbance at the time measured.

3. Results and discussions

3.1. Optimization of different reaction conditions

Reaction parameters such as initiator, crosslinker and monomerconcentration, reaction time, amount of solvent, pH and tempera-ture were optimized in order to get the crosslinked hydrogel withmaximum water uptake capacity (Fig. 1). Ggum-cl-poly(AA)exhibited 2345.06% swelling at 0.262 � 10�1 mol L�1,0.145 � 10�3 mol L�1 and 0.356 � 10�1 mol L�1 concentrations ofAPS, AA and hexamine, respectively. The optimal reaction time,temperature, pH and volume of reaction mediumwere found to be150 min, 80 �C, 7.0 and 17.5 mL, respectively.

Water uptake capacity was decreased with further increases inreaction parameters beyond optimal. This was due to an increase incrosslinking site density with further increase in reaction param-eters beyond optimal and results in decreased pore size (Sharmaet al., 2014; Wang and Wang, 2010).

Ps was found to increase with increase in pH and maximum Pswas obtained at 7.0 pH value. Increased ioneion repulsion wasobserved between the polymeric chains with an increase in pHvalue, which results in more space for liquid uptake. Anotherpossible cause of this trend may be a decreased Hþ screening effectwith increasing pH values. Further, decreased ioneion repulsionwas observed as sodium ion screening effect dominates at higherpH values and hence a reduced Ps was obtained (Sharma et al.,2014).

3.2. Optimization of aniline concentration during the synthesis ofIPNs

The effect of aniline concentration on Ps of IPNs was studiedunder both un-doped (neutral) and doped (acidic) conditions whilekeeping other reaction parameters constant (Fig. 1h and i). It hasbeen observed that there was an increase in Ps with initial increasein aniline concentration. However a decreasing trend was obtainedwith further increase in aniline concentration. Maximum Ps(666.60%) was observed in undoped sample in comparison todoped one (306.06%). This was likely due to increased incorpora-tion of PANI chains in the doped conditions, which results in acompact IPN with decreased pore size and hence a reduced per-centage swelling (Tiwari and Singh, 2008).

3.3. Doping effect of HCl and CurrenteVoltage characteristics

The surface resistivity and currentevoltage (IeV) characteristicsof the samples was measured at room temperature using a stan-dard two-probe method in order to evaluate the effect of HClconcentration on the conductivity behavior of the cross-linked IPNstructure (Fig. 2). Overall trends in the data indicate that all thesamples demonstrate IeV characteristics that are linear in natureand obey Ohm's law. Better conductivity was observed with anincrease in HCl concentrations up to 1.5 N. However further in-crease results in a decreased conductivity. This was due to thedistribution of charge carriers over polyaniline chain (mechanismof charge transport) (Kaufman et al., 1984). The net positive chargedensity on the polyaniline chains was increased during protonationand a stretch configuration was obtained due to mutual repulsiveeffects (Stejskal et al., 2010). A high conductivity at initial increaseHCl concentration was due to the high degree of protonation ofpolyaniline imine groups, continuous crosslinked network and welldoped quinoid rings (Thanpitcha et al., 2006). Decreased delocal-ization length of polyaniline chains due to over-protonation andhindrance in the movement of electrons between the valence bandand conduction band was responsible for low electrical conduc-tivity at higher HCl concentrations (Sharma et al., 2014).

3.4. FTIR spectra

FTIR transmittance spectra of the backbone, cross-linked sampleand IPN were assessed to know the incorporation of poly(AA) chainonto Guar gum and interpenetration of PANI chains in the Ggum-cl-poly(AA) matrix (Fig. 3). In case of Ggum, the broad peak at3428.57 cm�1 indicates the presence of eOH stretching vibrationsand peaks at 2924.59 cm�1,1018.55 cm�1 and 1650.59 cm�1 showedCeH stretching, OeH bending vibrations and C]O stretching ofcarbonyl group, respectively (Fig. 3a). In case of Ggum-cl-poly(AA),the absorption spectrum shows an additional peaks after thegrafting of poly(AA) chains onto Guar gum. This new peak wasobserved at 1723.52 cm�1due to carbonyl stretching of carboxylicacid and confirms the formation of graft copolymers (Fig. 3b). FTIRspectra of Ggum-cl-poly(AA-ipn-aniline) showed the characteristicpeaks of PANI as well as Ggum-cl-poly(AA). An additional peaks inthe range of 1200e1410 cm�1 was observed due to CeN stretchingof amine groups, which confirms the formation of IPNs (Bajpai,1999) (Fig. 3c and d). Additionally, the peak at 1603.35 cm�1

(CeN vibration), 1498.35 cm�1 (CeC stretching of quinoid ring) and1725 cm�1 (COO� stretching vibration) confirm the formation ofIPNs (Huang andWan, 2002). The band at 1156 cm�1 represents themeasure of degree of delocalization of electrons, which is an indi-cation of high conductivity (Bajpai, 1999). Overall, FTIR studiesconfirm that poly(AA) chains were grafted onto the Guar gumbackbone and PANI chains were successfully interpenetrated

Fig. 2. Currentevoltage characteristics for various concentration of HCl-dopedGgum-cl-poly(AA-ipn-aniline).

Fig. 1. Variation of percentage swelling with (a) initiator concentration (b) reaction time (c) solvent (d) monomer concentration (e) pH (f) Temperature (g) crosslinker concentration(h) aniline concentration in neutral medium (i) aniline concentration in acidic medium.

R. Sharma et al. / Journal of Environmental Management 162 (2015) 37e4540

within the Ggum-cl-poly(AA) matrix.

3.5. Thermogravimetric analysis

The effect of grafting and crosslinking of poly(AA) chains ontoGuar gum and interpenetration of PANI chains within the Ggum-cl-poly(AA) matrix on the thermal stability of Guar gum was studied.TGA curves of Ggum, Ggum-cl-poly(AA) and Ggum-cl-poly(AA-ipn-aniline)illustrated that the mechanism of decomposition wasdifferent in each case (Fig. 4). A two-stage decomposition mecha-nism was observed in case of Ggum. Whereas, three-stagedecomposition mechanism was found in the crosslinked samplesand IPNs. Maximum weight loss was observed after the first stagedecomposition of crosslinked samples and this indicates thechemical modification of Ggum. In case of Ggum, the initial minorweight loss (9.1%) up to 247 �C was due to the removal of moistureand volatile components. Maximum weight loss (54.9%) was

Fig. 3. FTIR spectra of (a) Guar gum (b) Ggum-cl-poly(AA) and (c) Undoped Ggum-cl-poly(AA-ipn-aniline) (d) Doped Ggum-cl-poly(AA-ipn-aniline).

Fig. 4. TGA of (a) Guar gum (b) Ggum-cl-poly(AA) (c) Undoped Ggum-cl-poly(AA-ipn-aniline) (d) Doped Ggum-cl-poly(AA-ipn-aniline).

R. Sharma et al. / Journal of Environmental Management 162 (2015) 37e45 41

observed in the temperature range of 247 �Ce330 �C due to thedegradation of backbone polymer. Only 13.55% and 4.23% weightloss was observed in the temperature range of 330 �Ce500 �C and500 �Ce700 �C, respectively (Table 2).

In case of Ggum-cl-poly(AA) and Ggum-cl-poly(AA-ipn-aniline),three stage decomposition was observed. In case of Ggum-cl-poly(AA), initial decomposition temperature (IDT) was 213 �Cwith 8.995% weight loss, which is likely due to the loss of moistureor volatile compounds. The second stage weight loss (41.246%) wasobserved in the temperature range of 300 �Ce400 �C due to theelimination of side chains. Finally, third stage decomposition wasobserved at 400 �Ce500 �C with 68.475% wt. loss due to thebreakdown of the crosslinked structure.

Table 2TGA Data of Ggum, Semi-IPN and IPNs.

Sample code IDT (�C) Weight loss (%) in the t

100e200 �C 2

Ggum 239.87 7.328 6Ggum-cl-poly(AA) 208.86 6.061 4Ggum-cl-poly(AA-ipn-aniline)-U 228.12 12.916 4Ggum-cl-poly(AA-ipn-aniline)-D 204.59 12.018 3

Where, IDT ¼ Initial Decomposition Temperature, FDT ¼ Final Decomposition Temperat

In comparison, the rate of decomposition was lower in case ofIPNs than Ggum-cl-poly(AA) and pure Ggum. The cross-linkedsamples and IPNs showed enhanced thermal stability due to theformation of cross-links between different polymeric chainsthrough covalent bonding and interpenetration of PANI chainswithin the Ggum-cl-poly(AA) matrix.

3.6. Surface morphology

The surfacemorphology of the samples was investigated by SEM(Fig. 5). Scanning electron micrographs showed that surface of thecrosslinked hydrogels (Fig. 5bed) was found to be rougher incomparison to pure Guar gum, which has a smooth surface (Fig. 5a).Surface roughness was more intense in case of doped crosslinkedsamples (Fig. 5c) than undoped samples (Fig. 5d). The change insurface morphology was due to the formation of covalent bondsbetween different polymeric chains and crosslinking with hexam-ine. This is in a well agreement with TGA analysis, which showedthat thermal stability was improved after grafting and crosslinking.

3.7. Antibacterial study

A zoneinhibition assay, the preliminary step to screen for anti-bacterial activity, was performed on the synthesized samplesagainst gram-negative pathogenic bacteria Escherichia coli, andgram-positive pathogenic bacteria Staphylococcus aureus (Fig. 6). Itwas observed that pure Guar gum is inactive against both testbacteria. Whereas synthesized samples showed inhibition zones inboth the cases (Fig. 6, Table 3). In case of Ggum-cl-poly(AA),undoped Ggum-cl-poly(AA-ipn-aniline) and doped Ggum-cl-poly(AA-ipn-aniline), the zone of inhibition was found to be

emperature range FDT (�C) Residual left (%)

00e400 �C 400e600 �C

2.257 10.533 547.09 15.3532.926 23.005 571.53 26.2912.767 16.319 582.34 26.226.714 20.494 592.91 28.965

ure.

Fig. 5. SEM images of (a) Guar gum (b) Ggum-cl-poly(AA) (c) Undoped Ggum-cl-poly(AA-ipn-aniline) (d) Doped Ggum-cl-poly(AA-ipn-aniline).

Fig. 6. Antibacterial activity of Guar gum based crosslinked hydrogels.

R. Sharma et al. / Journal of Environmental Management 162 (2015) 37e4542

22.5 mm, 13 mm and 12 mm, respectively against E. coli, and11 mm, 17.5 mm and 20 mm, respectively against S. aureus.

The antibacterial behavior of synthesized samples was due tothe interactions between charged polymeric hydrogel and chargespresent on the surface of bacterial membrane. The cell wall of

gram-positive S. aureus has thick layers of peptidoglycan com-plexed with negatively charged teichoic acids. However in gram-negative E. coli, the presence of negatively charged lipopolysac-charide contributes to an overall negative charge on the cell sur-face. Porosity of the hydrogel structure facilitates the frequent

Table 3Antibacterial activity of synthesized hydrogels against bacterium E. coli andS. aureus.

Sample Inhibition zone(mm) (E. coli)

Inhibition zone (mm)(S. aureus)

Guar gum (Ggum) Inactive Least activeGgum-cl-poly(AA) (HA) 22.5 11.0Ggum-cl-poly(AA-ipn-aniline)

(HAC5)-Undoped13 17.5

Ggum-cl-poly(AA-ipn-aniline)(HACc)-doped

12.0 20

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diffusion of liquid media across the hydrogels and may contributeto the size of the inhibition zone (Cabeen and Wagner, 2005).Further, the contact of poly(AA) and PANI chains with lipid layer ofbacterial cell membrane disrupts the protein synthesis inside thecell and stops the enzymatic activities required for the survival ofcell (Vimala et al., 2011; Murali et al., 2007).

3.8. Dye removal studies

Sorption is one of the most frequently applied methods toremove pesticides, dissolved organic pollutants and other hazard-ous chemicals fromwaste-water. Removal of MB dye from aqueousmedium takes place by different mechanisms such as chemisorp-tion, physical adsorption and electrostatic removal. Tremendousresearch work was reported on the adsorptive removal of methy-lene blue using low-cost adsorbents. Due to low adsorption ca-pacity of these adsorbents, environmental chemists have focusedtheir attention on developing synthetic polymeric materials as new

Fig. 7. Effect of different parameters on (%) adsorption of MB dye in case of Grafting of poly((d) Temperature.

class of adsorbents with fair adsorption capacity. Several polymerswith different functional groups have attracted great attention dueto their high adsorption capacity (Senkal and Yavuz, 2006). Today,there is growing interest in developing natural low-cost alterna-tives to synthetic polymers. In particular, the increasing cost ofconventional adsorbents undoubtedly makes biopolymer-basedmaterials one of the most attractive biosorbents for waste-watertreatment. Therefore, we have explored an alternative conductingadsorbent for removing cationic dyes i.e. methylene blue fromaqueous solutions. The performance and applicability of raw gumsare still limited due to their fixed structure and functional groups aswell as poor resistance to enzyme corrosion. Thus many effortshave been engaged to develop the derivatives of gums by theirreaction with active modification agents for introducing various ormore functional groups (i.e., eNH2, eCOOH, eOCH3, eCH]CH2,eOC2H5, eSO3

2�). The introduction of new functional groupschanged the charges, aggregation state of molecular chains,hydrophilic-hydrophobic capability, complexing capacity, stimuli-responsive ability and rheological behavior of gums and applica-tion domain of natural gums was greatly extended. The hydrogelsare non-toxic, easy to handle and also their reusability makes thempromising material for water purification (Rath and Singh, 1998).The effect of different parameters on the percentage removal of MBdye by semi-IPNs and IPNs was studied.

3.8.1. Effect of contact timeFig. 7a shows the removal of MB dye with respect to contact

time using Ggum-cl-poly(AA) and doped and undoped Ggum-cl-poly(AA-ipn-aniline) samples. Percentage removal was increasedgradually for all samples with contact time of 4 h and 61.839%,

AA) Chains and PANI onto Ggum (a) Contact Time, (b) Amount of Adsorbent, (c) pH and

R. Sharma et al. / Journal of Environmental Management 162 (2015) 37e4544

54.684% and 52.981% dye was removed by Ggum-cl-poly(AA),undoped Ggum-cl-poly(AA-ipn-aniline) and doped Ggum-cl-poly(AA-ipn-aniline) samples, respectively. Initially, high dyeremoval was observed due to more interaction of sample activesites with MB dye molecules (Saber-Samandari et al., 2012). After4 h, decreased dye removal was observed due to the saturation ofactive sites of semi-IPNs and IPNs.

3.8.2. Effect of adsorbent dosageThe amount of hydrogel samples on the removal of methylene

blue dye was optimized (Fig. 7b). A high sample dosage improvedthe dye removal efficiency with an increase in active sites. 64.4%dye was removed by 300 mg dose of Ggum-cl-poly(AA). Whereas,56.4% and 54.9% dye was removed by similar amount of undopedand doped Ggum-cl-poly(AA-ipn-aniline), respectively.

3.8.3. Effect of pHAdsorption studies were carried out at different pH (1e10) of the

adsorbate solution. Dye removal capacity of the cross-linked sam-ple and IPNs improved with an increase in pH of adsorbate (Fig. 7c).The grafted sample Ggum-cl-poly(AA) showed 69.165% dyeremoval at pH 10. Whereas, undoped and doped Ggum-cl-poly(AA-ipn-aniline) samples removed 64.224% and 62.606% of MB dye,respectively. The poor dye removal at low pH of the adsorbate wasdue to either competitive adsorption between Hþ ions and cationicMBþ molecules or H-bonding between the eCOOH group and MBdye molecules. Enhanced dye uptake at higher pH values ofadsorbate solution was due to ionization and increased electro-static attraction between the positively charged sorbate andnegatively charged sorbent (Fil et al., 2012).

3.8.4. Effect of temperatureFig. 7d shows the relationship between temperature and per-

centage dye adsorption by Ggum-cl-poly(AA) and undoped anddoped Ggum-cl-poly(AA-ipn-aniline). The percentage dye removalwas increased with increase in temperature due to the high degreeof adsorption. The increased temperature results in highmobility oflarge dye ions, sample swelling, growth of adsorbent porosity anddecreased viscosity of the medium (Bajpai et al., 2012). Ggum-cl-poly(AA) showed 93.867% dye removal, while undoped anddoped Ggum-cl-poly(AA-ipn-aniline) exhibited 88.756% and85.689% dye removal, respectively at 70 �C. This showed that semi-IPNs exhibited higher dye removal efficiency than correspondingIPNs (Liu et al., 2010).

4. Conclusions

Guar gum suffers drawbacks such as uncontrollable rate of hy-dration, instability of its solutions for longer time and susceptibilityto microbial contamination. Natural gums can chemically bemodified on order to minimize these drawbacks and to supplementnew properties without any major changes to its natural charac-teristics. The property profile of Guar gum was improved via freeradical polymerization and antibacterial crosslinked semi-IPNs andIPNs were successfully synthesized. Cross-linked hydrogels sam-ples were found to absorb large quantities of water within theirstructure. Surface morphology of Guar gum was changed aftergrafting and cross-linking and synthesized hydrogels showed bet-ter thermal stability. Semi-IPNs and IPNs exhibited antibacterialactivity against E. coli and S. aureu strains. Synthesized hydrogelscan potentially remove the toxic methylene blue dye from waste-water. Thus, synthesized cross-linked samples are important fromtechnological point of view.

Acknowledgments

The authors are grateful to the National Institute of Technology,Jalandhar (Punjab) for providing laboratories facilities and CentralInstrumentation Laboratory, Panjab University, Chandigarh forcharacterization of samples.

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