Efficient and selective removal of cationic organic dyes from their aqueous solutions by a nanocomposite hydrogel, katira gum-cl-poly(acrylic acid-co-N, N-dimethylacrylamide) @bentonite

A pH sensitive nanocomposite (NC) hydrogel based on katira gum-cl-poly(acrylic acid-co-N, N-dimethylacrylamide) incorporated bentonite (BT) nano clay (KG-cl-poly(AA-co-DMA)@BT abbreviated as KGNCH) is prepared by in-situ crosslinked co-polymerization technique using N, N'-methylene-bis-acrylamide (MBA) as crosslinker and potassium peroxodisulphate (KPS) as a free radical initiator. Various nanocomposite hydrogels (KGNCH-1 to KGNCH-4) are prepared by varying weight percentage of bentonite clay. The best one is selected (KGNCH-3) with respect to their highest swelling percentage in aqueous medium. The prepared KGNCH-3 is characterized by the FTIR, FESEM, XRD and EDS analysis and is used for the removal of cationic dyes [Methylene blue (MB), Crystal violet (CV) and Auramine-O (AO)] from their aqueous solutions. The adsorption of cationic dyes onto the KGNCH-3 is found to be pH dependent, the adsorption isotherm and kinetic data are best fitted with the Freundlich isotherm and pseudo second order kinetic model respectively and maximum adsorption capacity (q(max)) is found to be at pH = 8.0 for MB, pH = 7.5 for CV and pH = 10 for AO. Calculation of different thermodynamic parameters shows the spontaneous and endothermic nature of the adsorption. The KGNCH-3 also exhibits excellent regeneration capacity at different pH using five cycle of adsorption-desorption studies. From the selectivity study the order of adsorption capacity of the KGNCH-3 is found to be MB > CV > AO.