B. Vishalakshi

Swelling and Diffusion Characteristics of Stimuli-Responsive N-Isopropylacrylamide and κ-Carrageenan Semi-IPN Hydrogels

Semi-IPN formation has been achieved in a system comprising N-isopropylacrylamide and κ-carrageenan by an electron beam irradiation technique. The conditions for obtaining mechanically stable gels have been optimized. The gels were characterized by DSC, SEM, and FTIR techniques. Dynamic swelling measurements were carried out under different pH and temperature conditions. The results revealed the structure, pH, and temperature-dependent swelling behavior of the gels. The % swelling (S) of the hydrogels at various pH followed the order 9.0 < 1.2 <4.0 < 7.0. Also, the gels exhibited temperature dependence, with swelling being highest around 30°C. The “n” values for these hydrogels were in the range 0.31–0.79, indicating that the mechanism of water transport changes from Fickian to anomalous diffusion, with change in the network structure of the gel matrix.

Swelling and Metal Ion Adsorption Characteristics of Radiation Synthesized Stimuli Responsive PAAm-KC Semi – IPN Hydrogels

The preparation of super absorbent hydrogels based on Kappa-carrageenan and polyacrylamide was carried out by electron beam irradiation technique. The gels were characterized for their temperature and pH responsive behavior by equilibrium swelling experiments and for their structure by FTIR, DSC, and SEM techniques. The effect of polymer composition, dose applied, pH, and temperature on swelling was evaluated. The suitability of these systems as matrix materials for the uptake of Cu2+ and Ni2+ ions from aqueous solutions was studied. The influence of gel structure and pH conditions on metal ion uptake capacity of gels were investigated. The metal ion uptake capacity has been correlated with the swelling ability of the gels.

Evaluation of a pH-responsive guar gum-based hydrogel as adsorbent for cationic dyes: kinetic and modelling study

Interpenetrating network of guar gum and polyacrylamide has been made by simultaneous polymerization and crosslinking. Two different crosslinkers have been used to control the network structure. The amide groups in the network have been subsequently hydrolyzed by controlled saponification to obtain different degrees of ionic content in the gel. The gels containing –NH2 and –COOH functionalities have been characterized by FTIR, elemental analysis, DSC and TGA techniques. The swelling of the gel and pH responsiveness have been evaluated. The suitability of the gel as adsorbent material for removal of cationic dyes from aqueous solution has been investigated with crystal violet and azure B. The results revealed high degree of pH responsiveness and high dye adsorption capacity of gels. The adsorption–desorption processes were observed to be effective in repeated cycles, indicating the reusability of the gels for dye removal applications. The adsorption is observed to occur by Fickian diffusion and pseudo-second-order kinetic model appears to describe the adsorption. Crystal violet was absorbed to higher extent and bound stronger than azure B by the gel network. The adsorption is described by Langmuir model in case of crystal violet and Freundlich model for azure B. The thermodynamic parameters of adsorption indicate exothermic adsorption leading to ordered arrangement of dye molecules on the gel.

Heterocyclic modification of chitosan for the adsorption of Cu (II) and Cr (VI) ions

ABSTRACT A heterocyclic modification of chitosan has been attempted for development of an effective adsorbent material for removal of metal ions. The modified polymer was characterized using infrared (IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) techniques. The adsorption capacity exhibited for Cu (II) and Cr (VI) were 83.75 and 85.0 mgg−1, respectively, which is a significant improvement over chitosan. The adsorption on the modified polymer was a second-order kinetic process and followed Langmuir isotherm model. The thermodynamic analysis indicated exothermic and spontaneous nature of adsorption. About 80% of the adsorbed metal ions were desorbed in appropriate stripping solutions indicating reusability.

Silver nanoparticles embedded gum ghatti-graft-poly(N,N-dimethylacrylamide) biodegradable hydrogel: evaluation as matrix for controlled release of 2,4-dichlorophenoxyacetic acid

The present work explores the use of a nanocomposite hydrogel made using Gum ghatti (Gg), N,N-dimethylacrylamide (DMA) and N,N- methylene- bis-acrylamide (MBA) as a matrix for controlled release of 2,4-dichlorophenoxy acetic acid (2,4-D). Stable and uniformally distributed silver nanoparticles (Ag NP) were formed by the reduction of AgNO3 using TCS within the gel network. The Gg-g-PDMA and Ag NPs entrapped gel (Gg-g-PDMA-SN) were characterized by FT-IR, XRD, TGA, SEM, EDS and TEM techniques. The presence of Ag NPs is observed to enhance the swelling ability and the release efficiency of the Gg-g-PDMA gels significantly and also showed higher biodegradability. The gels exhibited prolonged release of the 2,4-D indicating good potential to be used as matrix for controlled release applications in agriculture.

Sustained Release of Atorvastatin from Radiation-Synthesized Stimuli-Responsive Hydrogels

The present paper deals with the study of suitability of interpenetrating network hydrogels comprising N-isopropylacrylamide and k-carrageenan as matrix materials for the sustained release of Atorvastatin. The drug was incorporated in various gels by the active-loading technique and the in-vitro release kinetics was studied at pH 1.2 and 7.4. When the release data were analyzed as per the Korsmeyer and Peppas equation, the release exponent “n” was observed to be dependent on temperature and pH conditions, indicating the influence of release conditions on gel structure and in turn on the drug release mechanism.

Effective removal of divalent metal ions: synthesis and characterization of pH-sensitive guar gum based hydrogels

AbstractThe present paper reports the modification of Guar gum network through grafting of acrylamide by free radical polymerization. The amide groups in the grafted network have been subsequently hydrolyzed by saponification. The hydrogels have been characterized by FTIR, Elemental Analysis, DSC, and TGA techniques. The nature and extent of swelling of these hydrogels is observed to be dependent on gel structure and pH. The pH dependence of uptake capacity of the hydrogels for metal ions Cu, Ni, Pb, and Zn2+ has been studied. The results reveal a very high metal uptake capacity of modified hydrogel attributed to the presence of carboxylic acid functionality. The metal adsorption is found to follow pseudo-first-order kinetics under pH 1.2 and pseudo-second-order kinetics under pH 7.0.

Adsorption Efficiency of Cr(VI) by Ethylene-1,2- Diamine-6-Deoxychitosan

Chitosan modified with ethylenediamine molecules has been evaluated as an effective adsorbent for Cr(VI) ions from aqueous system. The removal of Cr(VI) by adsorption was investigated at different pH conditions using UV-Vis spectrophotometry. The adsorption data were interpreted based on the Langmuir, Freundlich, and Temkin isotherm models. The isotherm constants were evaluated. The maximum adsorption capacity obtained from Langmuir model is 90.3 mg g−1 at 323 K and pH-3.0. The adsorption process was evaluated using the pseudo first-order, pseudo second-order, and intra-particle diffusion models and is observed to follow second order kinetics. The thermodynamic parameters of adsorption were evaluated. The result indicated the adsorption process to be spontaneous and endothermic. The sorbent was successfully regenerated using 0.5N NaOH and its reusability has been evaluated.

Pectin graft copolymer-montmorillonite composite: Synthesis, swelling and divalent metal ion adsorption

ABSTRACT A novel graft copolymer gel made up of pectin (Pec), 2-(methacryloyloxyethyl)trimethylammonium chloride (METAC), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and its composite with montmorillonite (MMT) were prepared using methylenebisacrylamide (MBA) as cross-linker via microwave irradiation and characterized using Fourier transform infrared (FTIR), Thermogravimetric Analysis (TGA) and Scanning electron microscopy (SEM) techniques. Swelling studies were carried out under different pH conditions. The graft copolymer gel and its composite showed maximum swelling in neural medium (pH 7.1) and the swelling process followed second order kinetics. The mechanism of water transport is found to be a Less Fickian diffusion process. The adsorption capacities of the graft copolymer gel and the composite towards divalent metal ions (Cu2+, Pb2+ and Hg2+) were evaluated. The adsorption capacity of the representative samples, Pec-g-poly(METAC-co-AMPS)-A5 and Pec-g-poly(METAC-co-AMPS)/MMT-C2 respectively for Cu2+ are 30.71 and 39.18 mg/g; for Pb2+ are 58.06 and 79.78 mg/g and for Hg2+ are 12.16 and 19.58 mg/g. The re-usability of the materials was also evaluated. The % recovery for the above two systems towards metals ion are 87.91 and 63.46 for Cu2+, 32.13 and 58.30 for Pb2+ and 78.53 and 51.92 for Hg2+. respectively. The adsorption isotherm studies indicated the adsorption of Pb2+, Cu2+ and Hg2+ in both samples is explained best by the Freundlich model except of Hg2+ by Pec-g-poly(METAC-co-AMPS)-A5, which is best explained by the Langmuir model.

Amphoteric gellan gum-based terpolymer–montmorillonite composite: synthesis, swelling, and dye adsorption studies

AbstractnA terpolymer gel, Gellan gum-graft-poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-dimethylaminopropyl methacrylamide) and its composite with the clay, Montmorillonite, was prepared by free-radical polymerization and crosslinking reactions in solution. The terpolymer gel and the clay composite were characterized using FTIR, TGA, SEM, and X-ray diffraction techniques. Swelling studies were carried out in different pH and salt solutions. The gel showed maximum swelling capacity in alkaline medium, while the composite showed higher swelling in neutral medium. The swelling of the gel and the composite followed second kinetics model and water transport is found to be a less Fickian diffusion process. The terpolymer gel and the composite were evaluated for the adsorption of rhodamine B (RhB) and chromotrope 2R (C2R) dyes. Rhodamine B is found to be adsorbed to a higher extent than chromotrope 2R and the adsorption isotherm studies suggested that adsorption of both RhB and C2R on the terpolymer gel was best explained by Langmuir model, while the adsorption on the Composite fitted best into Freundlich model. Similarly, the adsorption kinetics data for both RhB and C2R dyes followed the second-order kinetics.