Synergistic redox and adsorption for enhanced Roxarsone removal: Heterogeneous Fenton-Like reaction with a novel composite of nanoscale zero-valent iron supported on γ-aluminum oxide

Roxarsone (ROX), a livestock growth enhancer, poses environmental and health hazards due to its remarkable stability, making traditional degradation methods ineffective. To tackle this issue, a novel Fenton-like composite, composed of nanoscale zero-valent iron supported on γ-aluminum oxide (nZVI/γ-Al2O3), was synthesized to boost ROX degradation. Results demonstrated nearly complete mineralization of the ROX organic matrix within just 180 min, facilitated by the Lewis acidity sites of γ-Al2O3. Significantly, this composite exhibited selective adsorption of released AsO43− ions on its surface, forming FeAsO4 and Fe-As-Al complexes. It also established an internal redox cycle involving Fe(0), Fe(II), and Fe(III), ensuring a continuous and efficient generation of primary reactive oxygen species (·OH and O2·−). Thus, a simultaneous redox process occurred on the composite surface can be attributed to the synergy of the reducibility of nZVI and the oxidation catalyzed by ·OH and O2·−. Initially, the nitro group of ROX was reduced by nZVI, forming more hydrophilic o-aminophenol, favoring subsequent oxidation and mineralization. Simultaneously, the As-C bonds in ROX were oxidized, yielding AsO43−, which was subsequently adsorbed over extended reaction times. This innovative approach offers a potential solution for treating wastewater contaminated with metalloid-organic composite pollutants, addressing the environmental and health concerns associated with ROX residues.