Novel strategy for enhanced visible light-responsive photoactivity of ZnFe2O4 with a single-mode microwave combustion process: Primary parameters

Abstract

To date, the inferior physicochemical properties of nanomaterials synthesized with a household microwave (MW) oven have been attributed to a large extent to the non-uniform electromagnetic field. Herein, we developed a single-mode MW combustion process (MCP) considering criteria of green chemistry and further annealled the amorphous ZnFe2O4-based sol–gel precursors. The preferred single-mode MCP-based parameters mainly include 7 g : 2 g of the mass ratio (w/w) of SiC : sol–gel precursors, 1 : 1.5 of initial molar ratio of citric acid : metal ions (CA : M), 300 ℃ ∼ 600 ℃ range of the calcination temperature, N2 atmosphere of 3 L/min as well as the washing pretreatment of precursors. Moreover, based on Mössbauer spectroscopy, we infer that the reduction of structural ferric ions into ferrous ions in the lattice resulted in excellent magnetic separation of multiphase heterojunctions ZnO@ZnFe2O4 during a single-mode MCP. Furthermore, the ζ potentials of ZnO@ZnFe2O4 and ZnFe2O4 indicate that cationic dyes could be spontaneously adsorbed onto the negatively charged surface of ZnO@ZnFe2O4. Thus, the visible-light-driven catalytic mechanism of ZnO@ZnFe2O4 was also proposed. Additionally, the aforementioned single-mode MCP strategy could also endow P25-based TiO2 with excellent visible light-responsive photo-activities for effective degradation of estradiol. To our best knowledge, this is the first report associated with a novel single-mode MCP method to endow ZnO@ZnFe2O4 or P25-based TiO2 with an enhanced visible light-responsive (λ ≥ 420 nm) photoactivity.