Chaojun Ren

Enhancement of photocatalytic activity in Tb/Eu co-doped Bi2MoO6: the synergistic effect of Tb–Eu redox cycles

Tb/Eu co-doped Bi2MoO6 photocatalysts were successfully synthesized by a hydrothermal method, and their photocatalytic activity for the degradation of Rhodamine B (RhB) under visible light irradiation was researched. An obvious red-shift of the optical absorption edge for the co-doped samples was observed as compared to the single or non-doped Bi2MoO6. Raman spectra displayed the influence of Tb and Eu ions in the material structure, and the mixed valence states of Tb and Eu ions in the lattice of Bi2MoO6 were verified by XPS. The results of photoluminescence spectroscopy and photocurrent measurement demonstrated that the recombination of photogenerated electron–hole pairs was tremendously depressed by the synergistic effect of Tb–Eu redox cycles in the Tb/Eu co-doped Bi2MoO6 photocatalyst and the photocatalytic activity was improved. Furthermore, the proposed mechanism of the enhanced photocatalytic activity was discussed.

Double Z-scheme system of silver bromide@bismuth tungstate/tungsten trioxide ternary heterojunction with enhanced visible-light photocatalytic activity.

The ternary heterojunction of silver bromide@bismuth tungstate/tungsten trioxide (AgBr@Bi2WO6/WO3) was designed and synthesised by hydrothermal and deposition-precipitation approaches. The composites were characterised by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The photoabsorption range and bandgaps of the photocatalysts were analysed by ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). Compared with Bi2WO6/WO3 or AgBr alone, the AgBr@Bi2WO6/WO3 composites displayed higher visible-light photocatalytic performance for degrading rhodamine B (RhB). AgBr@Bi2WO6/WO3 with 40% AgBr concentration was optimum for photocatalytic activity. Radical-trapping experiments revealed that superoxide anion radicals (O2-) and holes (h+) were the active species during photocatalytic degradation and that O2- was the dominant active species. Therefore, the increased photocatalytic activity of AgBr@Bi2WO6/WO3 was attributed to the atypical double Z-scheme system, which effectively improved the transfer and separation of electron-hole pairs in ternary heterojunction structures.

Synthesis of BiVO4–TiO2–BiVO4 three-layer composite photocatalyst: effect of layered heterojunction structure on the enhancement of photocatalytic activity

BiVO4–TiO2–BiVO4 three-layer heterostructure photocatalyst was successfully synthesized by a simple sol–gel method with a glass substrate. The structural and optical properties of the as-prepared samples were relatively characterized. UV-vis diffuse reflectance spectroscopy indicated that the BiVO4–TiO2–BiVO4 three-layer composite possessed strong visible-light absorption. Compared to pure TiO2, BiVO4 and BiVO4–TiO2 bilayer composites, the BiVO4–TiO2–BiVO4 three-layer composite photocatalyst exhibited much higher photocatalytic activity in decomposition of methylene blue and rhodamine B under visible light irradiation. The results of photoluminescence spectroscopy and photocurrent measurement indicated that three-layer structure could distinctly improve the separation and transmission of the photogenerated charges, which led to the enhanced activity. Moreover, the active species trapping experiments demonstrated holes (h+) and superoxide radicals (˙O2−) were major active species in the degradation process. Then, a possible reaction mechanism accounting for the excellent photocatalytic activity was proposed on the basis of the energy band structure of the composites.