Synthesis of Sodium Alginate-Cl-Poly-(N,N′-Dimethyl Acrylamide)@Pd/Reduced Graphene Oxide Nanocomposite Hydrogel and Its Application for the Dye and Pesticide Removal From Their Aqueous Solutions

Abstract

Sodium alginate (SA) cross-linked-poly-(N,N′-dimethyl acrylamide)@Pd/reduced graphene oxide nanocomposite hydrogel (SNCHG@Pd/RGO) is prepared by using sodium alginate cross-linked poly(N,N′-dimethyl acrylamide)/reduced graphene oxide (SNCHG@RGO) with PdCl₂ in aqueous medium. SNCHG@RGO is first prepared by reducing graphene oxide (GO) with SA, followed by a cross-linked graft copolymerization reaction with N,N′-dimethyl acrylamide (DMA) in the presence of N,N′-methylenebisacrylamide (MBA) as a cross-linker and K₂S₂O₈ as the radical initiator in situ. One other nanocomposite hydrogel, sodium alginate-Cl-poly-(N,N′-dimethyl acrylamide)@Pd (SNCHG@Pd), is also prepared separately. The nanocomposite hydrogels are characterized by FTIR spectroscopy, PXRD, FESEM, EDAX, BET and TGA. The water swelling behaviour of the three synthetic nanocomposite hydrogels is evaluated. The so-prepared hydrogels are used for the adsorption studies from the aqueous solutions of a textile dye, namely, rhodamine 6G (RH), and a pesticide, namely, dimethoate (DM). Among the three nanocomposite hydrogels, SNCHG@Pd/RGO shows superior water swelling behaviour (835% at pH = 5) and also the adsorption efficiency in comparison to the other two. The order of adsorption is SNCHG@Pd/RGO > SNCHG@Pd > SNCHG@RGO in both cases. The adsorption of dye and pesticide by the SNCHG@Pd/RGO follows pseudo-second-order kinetics and both Dubinin–Radushkevich isotherm model and Freundlich isotherm model with Q_max values of 1265.82 mg g⁻¹ for RH at pH = 6 and 833.33 mg g⁻¹ at pH = 4 for DM, respectively. The spontaneity of the adsorption process is confirmed by the negative ΔG value.