Heavy metal recovery from electroplating wastewater by synthesis of mixed-Fe3O4@SiO2/metal oxide magnetite photocatalysts

Abstract

Heavy metal recovery is a promising way to reduce the pollution from electroplating wastewater (EPW), and magnetite photocatalysts of mixed-ferrite (M-Fe₃O₄)@SiO₂/metal oxides have been prepared to reuse heavy metals from simulated-EPW (S-EPW) and real-EPW (R-EPW). In this work, four pure magnetite photocatalysts M-Fe₃O₄@SiO₂/ZnO, M-Fe₃O₄@SiO₂/CuO, M-Fe₃O₄@SiO₂/Fe₂O₃, and M-Fe₃O₄@SiO₂/NiO were synthesized via a simple precipitation reaction, where the M-Fe₃O₄@SiO₂ core–shell nanoparticles served as the magnetic cores and supports for the metal oxides. The structures, morphologies, and magnetic properties of these magnetite photocatalysts were characterized, and then the photocatalytic performances of the pure and complex magnetite photocatalysts (M-Fe₃O₄@SiO₂ supported single and mixed-metal oxides) were tested and compared using methyl orange (MO) degradation experiments. It was found that M-Fe₃O₄@SiO₂/ZnO had the best photocatalytic performance of the pure magnetite photocatalysts, with a MO removal rate of 91.5%, followed by 37.4% for M-Fe₃O₄@SiO₂/NiO, 19.0% for M-Fe₃O₄@SiO₂/Fe₂O₃, and 17.6% for M-Fe₃O₄@SiO₂/CuO. The removal rates were 17.4% and 13.2% for the complex magnetite photocatalysts prepared from S-EPW and R-EPW, respectively. More than 98% of the heavy metals can be recovered from EPW through the simultaneous synthesis of the magnetite photocatalysts.