Construction of oxygen defective ZnO/ZnFe2O4 yolk-shell composite with photothermal effect for tetracycline degradation: Performance and mechanism insight

Oxygen vacancy induced photothermal effect is of great significant but lack of adequate attentions for environmental remediation. In this paper, green recyclable ZnO/ZnFe2O4 with oxygen vacancy was prepared by a solvothermal-calcination method. The UV-vis light capture ability of ZnO/ZnFe2O4 microspheres is improved with the multiple light reflections due to the yolk-shell structure, and the oxygen vacancy expands the absorption range of photocatalyst and enhances photothermal conversion. The optimized photocatalyst can heat the solution from room temperature to 70 °C within 60 min of visible light illumination, and the light to heat conversion efficiency is achieved by 61.3%. Compared with the degradation efficiency at 20 °C, photothermal catalysis achieves a stable degradation in 80 min, and the degradation efficiency is increased by 41.5%. This can be attributed to the fact that light induced thermal energy accelerates the migration of electrons and holes, and promotes the diffusion of free radicals by heating active centers in situ. The active species contributing to the degradation, in order of importance, are the superoxide radical, hydroxyl radical, hole and electron. The light-to-thermal assisted photocatalysis with ZnO/ZnFe2O4 provides a new sight for the pollution control in the future practical applications.