Green adsorbents based on polyacrylic acid-acrylamide grafted starch hydrogels: the new approach for enhanced adsorption of malachite green dye from aqueous solution

Effective removal of Malachite Green (MG) dye was recorded using environmental friendly starch-based hydrogel adsorbents. Because of its full biodegradability, zero-toxicity and sustainability, Starch has received further consideration for designing sustainable hydrogels by combining with natural sources or synthetics. In this research, the graft copolymerisation of polyacrylic acid and/or acrylamide onto potato starch is among the most successful techniques to introduce specific functional groups that significantly change their physico-chemical characteristics. Starch grafted acrylic acid-acrylamide hydrogels were synthesised utilising a technique of aqueous solution polymerisation and examined their performance for MG adsorption. The effect of initiator concentration, monomer concentration and polymerisation temperature was discussed. FTIR, XRD and SEM analysis techniques characterised the optimised and most efficient hydrogel. The swelling behaviour has been indicated as a swelling time function. The influence on the dye removal by different operating parameters: hydrogel dose, contact time, initial dye concentration and temperature was studied. The adsorption models of Langmuir, Freundlich and Temkin have been implemented to study the isothermic adsorption. The pseudo-second-order model outlined the MG adsorption well. Dye adsorption improved with increasing temperature proposing the endothermic nature of the adsorption. For five cycles, the stability of the most efficient hydrogel has been examined.