Spinel Cum <sub> 2 </ Sub> O <sub> 4 </ Sub> (m = Fe, Co, Cr) Preparation And Photocatalytic Production Of Hydrogen Activity

CuFe₂O₄, CuFeCoO₄ and CuCr₂O₄/TiO₂ photocatalysts were successfully synthesized via different methods. The as-obtained photocatalysts were modified by metal ions doping, halogen ions doping, and Ag loading. Thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet visible diffuse reflectance absorption spectra (UV-Vis DRS), and fluorescence spectra (FS) were employed to characterize the as-synthesized nanocrystals. Moreover, the photocatalytic activity of the as-obtained photocatalysts was evaluated based on the photocatalytic H₂ evolution under simulated sunlight irradiation.(1) Copper ferrite (CuFe₂O₄) nanoparticles were successfully fabricated via solid-state reaction, co-precipitation approach, as well as citric acid-assisted sol-gel method, and showed high photocatalytic H₂ evolution activity (solid-state reaction: 0.67 mmol·h^-1·g_cat^-1; co-precipitation approach: 0.80 mmol·h^-1·g_cat^-1; sol-gel method: 1.03 mmol·h^-1·g_cat^-1). The effects of sacrificial reagent types, the concentration of sacrificial reagent, pH value, calcination temperature, the concentration of photocatalyst, and the irradiation time on the photocatalytic H₂ evolution activity were investigated in detail. The best result of the photocatalytic H₂ evolution activity (1.72 mmol·h^-1·g_cat^-1) was obtained over the CuFe₂O₄ prepared through sol-gel approach when oxalic acid was used as the sacrificial reagent, the concentration of oxlic acid was 0.05 M, the concentration of the photocatalyst concentration was 1.0 g·L^-1, and the calcination temperature was 700℃. After irradiated for more than 40 h, the photocatalytic H₂ evolution of the as-obtained CuFe₂O₄ almost showed no decline, indicating that it is of stable catalytic performance, and with long life-span.(2) CuCo_xFe_2-xO₄ photocatalysts were prepared by citric acid-assisted sol-gel method. The influence of the Co content and calcination temperature in the photocatalytic H₂ evolution activity showed that the optimal Co content and calcination temperature were x=l and 800℃, respectively, and the average H₂ evolution rate was 2.46 mmol·h^-1·g_cat^-1 under this conditions. The results showed that appropriate amount of Y and F doping can help to the sepration of photo-excited electron-hole pairs, and enhance the photocatalytic H₂ evolution activity. The best average H₂ evolution rate (2.77 mmol·h^-1·g_cat^-1) was obtained when the Y and F doping concentration was 4% and 7%, respectively.(3) P-n type CuCr₂O₄/TiO₂ heterojunction photocatalyst was obtained via sol-gel approach. The best result of the photocatalytic H₂ evolution activity (449μmol·h^-1) was achieved when n_CuCr2O4:n_TiO2 was 0.7, the calcination temperature was 500℃and the concentration of the photocatalyst concentration was 0.8 g·L^-1. Appropriate amount of Y doping and Ag loading can enhance the photocatalytic H₂ evolution activity of the as-obtained 70mol%CuCr₂O₄/TiO₂, and the best average H₂ evolution rate (506μmol·h^-1) was obtained when the Y doping concentration and the Ag loading content were 7% and 1.3wt%, respectively. Furthermore, the possible photocatalytic mechanism of the Y doped Ag-CuCr₂O₄/TiO₂ heteroj unction photocatalyst was discussed.