Surface modification of sodium alginate-polyvinyl alcohol hydrogel beads using low-pressure cold plasma and application for methylene blue removal from water
Rizza Wijaya, Endar Hidayat, Seiichiro Yonemura, Sadaki Samitsu, Hiroyuki Harada, Yoshiharu Mitoma
Abstract
This study investigates the adsorption efficiency of methylene blue (MB) from aqueous solutions using sodium alginate-polyvinyl alcohol (SA/PVA) hydrogel beads modified through low-pressure cold plasma (LPCP) treatment. The LPCP process significantly enhanced the surface properties of the hydrogel beads, improving their adsorption capacity from 27.48 % (untreated) to 53.03 % (P15 treatment) at pH 8.2. Plasma-treated beads exhibited substantially higher MB removal compared to untreated beads, with the highest adsorption capacity of 175.506 mg g −1 under the P15 treatment condition. Adsorption followed the Freundlich model with high correlation coefficients ( R ² = 0.998), suggesting multilayer adsorption on a heterogeneous surface. Adsorption kinetics adhered to a pseudo-second-order model ( R ² > 0.98), indicating chemisorption as the dominant mechanism. Thermodynamic analysis demonstrated spontaneous and endothermic adsorption ( ΔG ° = −7.55 kJ mol −1 at 333 K). Plasma-treated hydrogel beads showed excellent reusability, maintaining over 85 % adsorption efficiency after three cycles. These findings highlight the potential of LPCP-treated hydrogel beads as an effective and sustainable solution for MB removal in wastewater treatment applications.