Metal-doped ZnFe2O4 nanoparticles derived from Fe-bearing slag with enhanced visible-light photoactivity

M-ZnFe2O4 (M = Al, Zn, Cu, Mn) nanoparticles, which are potential photocatalysts, were prepared from Fe-bearing solid waste, namely Waelz slag. The valuable elements, namely Fe, Al, Zn, Cu, and Mn, were extracted from the slag simultaneously through sulfuric acid leaching. The extracted elements were converted into sediments in a controlled fashion by manipulating the pH of the lixivium and subsequently transformed into metal-doped ZnFe2O4 nanoparticles using the sol-gel method. The as-synthesised products were characterised using X-ray diffraction, Brunauer-Emmett-Teller analysis, field emission scanning electron microscopy, energy dispersive spectroscopy, UV-vis spectroscopy, and photoluminescence spectroscopy. The photocatalytic performances of the slag-derived M-ZnFe2O4 nanoparticles in photocatalytic methyl orange degradation under visible light were compared with that of undoped ZnFe2O4 nanoparticles. The results indicated that the slag-derived nanoparticles gave better photocatalytic performances than did the undoped sample, with the M-ZnFe2O4 (M = Al, Zn, Cu) sample, which was prepared with precipitates obtained at pH 7, exhibiting the best photocatalytic activity. The enhancement can be attributed to grain refinement and doping.