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

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.