Synergistically active magnetic Fe3O4–VO2/polydopamine hydrogel for photocatalytic degradation of malachite green and tetracycline

The synergistic integration of photocatalytic nanomaterials with hydrogel matrices has emerged as a promising strategy for sustainable wastewater treatment due to their biocompatibility, stability, and cost-effectiveness. In this study, a multifunctional hydrogel was fabricated through a green synthesis route by embedding Fe₃O₄@VO₂–polydopamine (PDA) composites into a sodium alginate (SA) network via a two-step cross-linking process. Fe₃O₄ nanoparticles were synthesized by co-precipitation, followed by water bath growth of Fe₃O₄@VO₂ and in situ PDA deposition to improve interfacial stability and charge transfer. The resulting Fe₃O₄@VO₂-PDA-SA/H hydrogel exhibited excellent magnetic recoverability, high photocatalytic efficiency, and structural robustness. Malachite green (MG) and tetracycline hydrochloride (TCH), representative contaminants from aquaculture wastewater, were employed as target pollutants. The composite achieved maximum photodegradation efficiencies of 98.39 % for MG and 87.03 % for TCH, with only moderate efficiency loss after five consecutive cycles (retaining 88.38 % and 61.03 % removal, respectively). Radical quenching experiments revealed that •OH and •O₂ − played dominant roles in pollutant degradation, confirming a synergistic photocatalytic mechanism. These findings demonstrate that Fe₃O₄@VO₂-PDA-SA/H not only ensures efficient and stable photocatalysis in complex aqueous environments but also offers facile recyclability, highlighting its potential as a practical material for advanced wastewater remediation.