Dual-oxide Fe3O4/MnO2 nanocatalysts immobilized in biopolymer-based hydrogels for antibiotic degradation

The development of sustainable, recoverable, and efficient catalysts for the removal of pharmaceutical pollutants from water remains a critical environmental challenge. Herein, we report multifunctional chitosan-agarose hydrogels incorporating Fe 3 O 4 and MnO 2 nanoparticles via sequential in situ precipitation to create a dual-oxide Fenton-like catalytic platform. The synthesis strategy enables homogeneous nanoparticle distribution, controlled Fe 3 O 4 size (via sulfate or chloride precursors), and tunable MnO 2 loading within an interconnected porous biopolymer matrix. Structural analyses confirmed crystalline inverse spinel Fe 3 O 4 and amorphous γ-MnO 2 uniformly embedded in the hydrogel network. The dual-oxide configuration promotes synergistic Fe-Mn redox cycling, enhancing reactive oxygen species generation under mild conditions (pH = 7.4, room temperature). Using rifampicin as a model antibiotic, the optimized hydrogel achieved 94% degradation within 30 min, following pseudo-first-order kinetics (k = 0.194 min⁻¹), outperforming comparable reported systems. The materials exhibited soft magnetic behaviour, enabling facile magnetic recovery without metal leaching, and maintained high catalytic activity over repeated cycles. Additionally, external magnetic fields modulated degradation efficiency through magneto-mechanical effects. This work introduces a sustainable and magnetically recoverable hydrogel-based catalytic system for efficient antibiotic removal from wastewater.