Shaonan Gu

In-built Tb4+/Tb3+ redox centers in terbium-doped bismuth molybdate nanograss for enhanced photocatalytic activity

A series of terbium-doped Bi2MoO6 with different Tb contents were synthesized using a hydrothermal method. The crystalline structure, surface area, morphology, chemical state and optical properties were analyzed in detail. The photocatalytic activity of the samples was evaluated by degradation of organics under visible light irradiation. The results indicated that doping of terbium ions could obviously improve the photocatalytic activity of Bi2MoO6, which was attributed to the generation of Tb4+/Tb3+ redox centers in terbium-doped Bi2MoO6. The photoluminescence (PL) spectroscopy, photocurrent measurement and active species trapping experiments suggest that the recombination of photo-generated electron–hole pairs was efficiently restrained by a trapping–releasing process between the Tb4+ and Tb3+ ions.

Novel In2S3/ZnWO4 heterojunction photocatalysts: facile synthesis and high-efficiency visible-light-driven photocatalytic activity

Novel heterojunction photocatalysts In2S3/ZnWO4 were prepared by a hydrothermal and surface-functionalized method, and the optimized In2S3/ZnWO4 ratio was tuned to explore their visible-light photocatalytic activity for rhodamine B (RhB) degradation. The heterojunction structure formed by the In2S3 nanoparticles grew on the primary ZnWO4 nanorods. Remarkably, In2S3/ZnWO4 composites exhibited much higher photocatalytic activity than that of the individual In2S3 and ZnWO4. The enhanced activity could be attributed to the strong visible-light absorption and the effective separation and transportance of the photogenerated charges. Moreover, the main active species for the degradation of RhB were also investigated. Then, a possible reaction mechanism for the excellent photocatalytic activity of the In2S3/ZnWO4 composites was proposed.

Samarium and Nitrogen Co‐Doped Bi2WO6 Photocatalysts: Synergistic Effect of Sm3+/Sm2+ Redox Centers and N‐Doped Level for Enhancing Visible‐Light Photocatalytic Activity

Samarium and nitrogen co-doped Bi2 WO6 nanosheets were successfully synthesized by using a hydrothermal method. The crystal structures, morphology, elemental compositions, and optical properties of the prepared samples were investigated. The incorporation of samarium and nitrogen ions into Bi2 WO6 was proved by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. UV/Vis diffuse reflectance spectroscopy indicated that the samarium and nitrogen co-doped Bi2 WO6 possessed strong visible-light absorption. Remarkably, the samarium and nitrogen co-doped Bi2 WO6 exhibited higher photocatalytic activity than single-doped and pure Bi2 WO6 under visible-light irradiation. Radical trapping experiments indicated that holes (h(+) ) and superoxide radicals ((.) O2 (-) ) were the main active species. The results of photoluminescence spectroscopy and photocurrent measurements demonstrated that the recombination rate of the photogenerated electrons and holes pairs was greatly depressed. The enhanced activity was attributed to the synergistic effect of the in-built Sm(3+) /Sm(2+) redox pair centers and the N-doped level. The mechanism of the excellent photocatalytic activity of Sm-N-Bi2 WO6 is also discussed.

Substitution of Ce(III,IV) ions for Bi in BiVO4 and its enhanced impact on visible light-driven photocatalytic activities

Bi1−xCexVO4+δ (0 ≤ x ≤ 0.3) solid solution photocatalysts were synthesized by substitution of Ce for Bi in the BiVO4 lattice using the hydrothermal method. X-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy revealed that the crystal phase transformed from the monoclinic phase to the tetragonal phase, probably due to the substitution of cerium ions in the Bi3+ positions. UV-vis diffuse reflectance spectroscopy was used to investigate the absorption range and band gap of the photocatalysts. The photocatalytic activities of the prepared samples were examined by studying the degradation of MB and phenol under visible-light irradiation and the best performance was attained for the sample with a cerium content of 20 at% (Bi0.8Ce0.2VO4+δ). The results of photoluminescence spectroscopy and photocurrent measurement demonstrated that the recombination of photogenerated charges was greatly depressed and the photocatalytic activity was improved by the substitution of Ce for Bi in BiVO4. Furthermore, the proposed mechanism of the enhanced photocatalytic activity was discussed.

In situ preparation of novel heterojunction BiOBr/BiVO4 photocatalysts with enhanced visible light photocatalytic activity

Heterojunction photocatalysts BiOBr/BiVO4 were in situ synthesized through acid etching coupled with a hydrothermal process, and the optimized BiOBr/BiVO4 ratio was tuned to explore their visible-light photocatalytic activity for MB degradation. Remarkably, BiOBr/BiVO4 composites exhibited higher visible-light photocatalytic ability compared with single BiVO4 and BiOBr alone. The charge-separation process was interpreted based on the energy band structure. The heterojunction formed between BiVO4 and BiOBr, that effectively promotes the separation of photo-induced electrons and holes, is responsible for the improved photocatalytic activity.

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.

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.