Sustainable Alginate/PVA/Silica Hydrogel Composites for Efficient Removal and Regeneration in Crystal Violet Adsorption

The development of reusable and sustainable adsorbents is essential for efficient dye remediation in wastewater treatment. In this study, alginate/polyvinyl alcohol/silica (APS) hydrogel composites were fabricated via a dual-crosslinking strategy using Ca2+ and boric acid to enhance structural stability and adsorption performance. Structural integration of the components was confirmed by FTIR and SEM–EDX analyses, revealing strong interactions among alginate, PVA, and silica within a reinforced network. The adsorption behavior toward crystal violet (CV) was systematically evaluated by varying pH, adsorbent dosage, contact time, and initial dye concentration. Under optimal conditions (pH 6, 40 mg adsorbent dosage, 250 mg L−1 CV, 120 min adsorption time), the APS composite achieved a maximum experimental adsorption capacity of 143.8 mg g−1. Non-linear kinetic modeling indicated that the pseudo-first-order model provided the best fit (R2 = 0.993), while equilibrium data were better described by the Langmuir isotherm (R2 = 0.984), with a predicted monolayer capacity of 169 mg g−1. Mechanistic analysis suggests that CV adsorption is governed by synergistic electrostatic attraction, hydrogen bonding, and partial ion-exchange interactions. Regeneration experiments demonstrated up to 69.7% CV desorption using 0.1 M KCl in ethanol/water, confirming the material's regeneration potential.