Response Surface Optimization of Graphene Oxide-Reinforced Dual-Crosslinked Alginate/Poly(Vinyl Alcohol) Hydrogel Beads for Methylene Blue Adsorption

摘要

Response surface methodology (RSM) was used to determine the optimal blend of alginate (ALG), poly(vinyl alcohol) (PVA) and graphene oxide (GO), as well as glutaraldehyde (GA) crosslinking solution concentration for the synthesis of dual-crosslinked ALG/PVA/GO nanocomposite hydrogel adsorbent beads for methylene blue (MB) removal. Statistical analyses show that PVA concentration contributes the largest effect to the adsorption capacity response, attributed to improved accessibility of MB molecules to adsorption sites. The optimal blend was determined to be 3% polymer with 50% PVA, 383.8384 ppm GO, crosslinked in 1% CaCl_2 and 5% GA. These results were validated, and the experimental value of the adsorption capacity deviated by only 1.702% from the RSM model prediction, suggesting good model predictability. Adsorption isotherm models were tested to provide a description of the adsorption process. The Sips isotherm model, suggesting monolayer adsorption over heterogeneous surface with action of cooperative adsorbate-adsorbate interactions, was the best fit to the experimental equilibrium data, with an R~2 of 0.9782. Furthermore, the ALG/PVA/GO beads demonstrated a maximum monolayer adsorption capacity of 1081.62 mg/g, showing superior performance compared to known biosorbents of MB.