Multiple-metal-doped Fe3O4@Fe2O3 nanoparticles with enhanced photocatalytic performance for methyl orange degradation under UV/solar light irradiation

Waelz slag, which is a Fe-bearing hazardous waste, was applied as the raw material in the synthesis of M-Fe3O4@Fe2O3 (M = Al, Zn, Cu, and Mn) nanoparticles, which are potential photocatalysts. Through acidolysis, 97.23% of Fe and most of the valuable metals were extracted from this slag. Using sol-gel processes, designed Fe3O4@Fe2O3 nanoparticles doped with multiple elements were systematically synthesised and characterised using X-ray diffraction, field emission scanning electron microscopy, electron diffraction spectroscopy, transmission electron microscopy, and Brunauer-Emmett-Teller analysis. The photocatalytic activities of the synthesised particles and undoped Fe2O3 nanoparticles were compared through photocatalytic methyl orange degradation experiments under UV and simulated solar light. The results indicated that all of the slag-derived nanoparticles gave improved photocatalytic performances compared to the undoped sample, and the M-Fe3O4@Fe2O3 (M = Al, Zn, and Cu) sample exhibited the best photocatalytic activity. The enhancement can be attributed to grain refinement, doping, and the formation of a typical Fe3O4@Fe2O3 core-shell structure.