Eco-friendly poly(vinyl alcohol)/partially hydrolyzed polyacrylamide/graphene oxide semi-IPN nanocomposite hydrogel as a reusable and efficient adsorbent of cationic dye methylene blue from water

Abstract

Eco-friendly semi-interpenetrating polymer network (IPN) nanocomposite hydrogels composed of poly(vinyl alcohol) (PVA) chains and graphene oxide (GO) nanosheets embedded within the cross-linked partially hydrolyzed polyacrylamide (PHPAm) network were prepared in a one-stage approach via the internal ionic gelation in an aqueous solution. After full characterizations by various techniques, optimization of the hydrogel synthesis reaction condition based on the equilibrium swelling ratio criterion was performed by using Taguchi standard method. The performance of the prepared PVA/PHPAm/GO semi-IPN nanocomposite hydrogel as methylene blue (MB) adsorbent was evaluated by treating aqueous solutions in batch mode and kinetic models and isothermal models were used to describe the adsorption mechanism. The experimental results indicated that the incorporation of GO in the semi-IPN nanocomposite formulation enhanced the thermal stability, swelling ability and (MB) removal efficiency by 49% compared to empty hydrogels. Adsorption kinetics and equilibrium adsorption isotherm fitted the pseudo-second-order kinetic model and Langmuir isotherm model well, respectively. Moreover, the prepared semi-IPN hydrogel had good stability and reusability as it exhibited excellent removal efficiency of 70% after five consecutive adsorption-desorption cycles. The maximum adsorption capacity calculated from the Langmuir isotherm model reached qmax = 714.8 mg.g−1 at 30°C, obviously higher than the hydrogel prepared without this addition (293.8 mg.g−1). According to the calculated thermodynamic parameters ΔG°, ΔH°, and ΔS°, MB adsorption onto the adsorbent was a spontaneous, endothermic, and physical adsorption process.