Magnetic ZnO@Fe₃O₄ composite for self-generated H₂O₂ toward photo-Fenton-like oxidation of nitrophenol

Abstract

The present work focuses on the synthesis of a magnetically separable and stable catalyst for self-supplying H₂O₂ in photo-Fenton degradation of p-nitrophenol. Different from the most popular Fe₃O₄@ZnO core-shell structure, ZnO microflower cores were partially wrapped with Fe₃O₄ nanoparticles via a layer-by-layer self-assembly process. Several characterisation techniques were employed to investigate the crystal structure, morphology, surface chemistry and optical properties of the produced composites. The band gaps of the ZnO and Fe₃O₄ were considerably decreased from 3.05 to 2.60 to 2.35 eV after the assembly. The optimum Fe₃O₄ deposition layer number was found to be 5 for achieving 100% p-nitrophenol removal in 60 min. The degradation was triggered with in-situ photocatalytic formation of hydrogen peroxide over Fe₃O₄@ZnO. The exposed Fe₃O₄ nanoparticles provided Fe²⁺ and Fe³⁺ Fenton-active species for stable operation. We explored possible mechanisms of the enhanced photocatalysis by quenching and radical trapping experiments. The magnetic separation was also performed to recover and reuse the spent catalyst.