Xintong Liu

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.

In-situ synthesis of novel Z-scheme SnS2/BiOBr photocatalysts with superior photocatalytic efficiency under visible light

In this study, a novel SnS2/BiOBr heterojunction photocatalyst was synthesized via a facile in-situ growth strategy. The heterojunction interface was formed by loading BiOBr nanosheets on the surface of ultrathin hexagonal SnS2 nanoplates. UV/Vis diffuse reflectance spectroscopy (DRS) indicated that SnS2/BiOBr composites possessed stronger visible-light absorption. The as-fabricated SnS2/BiOBr heterojunction nanoplates exhibited considerable improvement in terms of photocatalytic activity for the degradation of rhodamine B (RhB) under visible light irradiation as compared with BiOBr and SnS2. The enhanced photocatalytic activity was attributed to the closely contacted interface between BiOBr and SnS2, thereby resulting in faster transfer of the photoinduced electron-hole pairs through their interface, as shown by the results of photoluminescence spectroscopy (PL) and photocurrent measurements. Radical trapping experiments demonstrated that holes (h+) and superoxide anion radicals (O2-) were the main active species in the photocatalytic oxidation process. The mechanism of the excellent photocatalytic activity of SnS2/BiOBr heterojunction composite was also discussed.

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.

Systematic evaluation of petroleum sulfonate: polarity separation and the relationship between its structure and oil recovery properties

Petroleum sulfonate is one of the most important surfactants in the tertiary oil recovery process. However, its complex composition significantly impedes its evaluation, and the relationship between its structure and oil recovery properties is still unclear. In this study, the actives of petroleum sulfonate are subdivided into seven components, a–g, with different polarities via column chromatography. The structural information of each component is fully characterized. Moreover, the relationship between the oil recovery properties and the structure of the separated components is systematically studied. The results reveal the average relative molecular mass in the range of 560–626, average alkyl side chain containing 36–40 carbon atoms and alkyl chain containing an average of 6 branched chains is the ideal structure for enhancing oil recovery properties. Furthermore, this study provides a reliable evaluation method and reveals the relationship between the structure and oil recovery properties of petroleum sulfonate.