Synthesis of SiO2/ZnO/Fe2O3/ZnFe2O4 from Spent Alkaline Batteries and Mining Tailings Applied as a Photocatalyst and Pseudocapacitor

Abstract

In this study, a mixed oxide (SiO2/ZnO/Fe2O3/ZnFe2O4) was prepared using the anode recycled from alkaline batteries and the silt fraction of mining tailings and applied as a photocatalyst under solar irradiation and as a pseudocapacitor. The structure and morphology of the mixed oxide revealed clusters of nanometric particles with rhombic and octahedral shapes. A 23 full factorial design was performed to determine the effect of pH, hydrogen peroxide (H2O2), and photocatalyst on methylene blue (MB) decolorization. The maximum efficiency was 96%, obtained using 2.35 × 10−5 mol H2O2 and 20 mg of photocatalyst at pH 3 for 30 min under solar irradiation. This efficiency remained even after four successive decolorization cycles. Pseudocapacitive properties showed that the mixed oxide exhibited favorable characteristics for application as electrochemical pseudocapacitors due to its high capacitance (87.16 F g-1), energy density (27.24 Wh kg-1) at 524.41 W kg-1 of power density, and reversibility (93%). The studied mixed oxide has excellent potential for use in photocatalytic reactions and electrochemical devices, contributing to environmental sustainability and circular economy.