Synthesis of composite ZnO rods@mixed metal oxides derived from Zn–Fe-LDHs for the photocatalytic degradation of methylene blue

Abstract

ZnO rods/mixed metal oxides, derived from a layered double hydroxide (ZO@ZFO), were effectively synthesised using a simple and efficient coprecipitation method. XRD, FT-IR, SEM, XPS, DRS and EDX were used to investigate the synthesised materials. ZFO consists of two phases, ZnO and ZnFe₂O₄, uniformly distributed on ZnO rods. The photocatalytic efficacy of ZO@ZFO was assessed by decomposing methylene blue (MB) under visible-light conditions. The ZO@ZFO heterojunction, with a ZnO/ZFO mass ratio of 10%, achieved a MB removal efficiency of 95.8%, markedly surpassing those of ZO (54.73%) and ZFO (77.48%) under identical conditions: a catalyst loading of 1.0 g L⁻¹, 40 ppm of MB concentration, pH of 8, and 150 minutes of halogen lamp irradiation. The first-order kinetic simulation for the photocatalytic process yielded optimal results with k₁ = 0.01854 min⁻¹ and r₁² = 0.94314–0.9977. The effectiveness of photodegradation was evaluated under various conditions, including catalyst loading, initial MB concentration, and pH. The traditional type II mechanism for degrading MB via the ZO@ZFO heterojunction was presented. These findings underscore the significant potential of LDH-derived mixed-oxide heterojunctions for photocatalysis.