Surface modification of sodium alginate-polyvinyl alcohol hydrogel beads using low-pressure cold plasma and application for methylene blue removal from water

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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 (R² = 0.998), suggesting multilayer adsorption on a heterogeneous surface. Adsorption kinetics adhered to a pseudo-second-order model (R² > 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.