Effect of two different dopants (Mg2+ and Ca2+) and processing parameters on γ-phase stabilization and conductivity of Bi4V2O11−δ

Mg²⁺ and Ca²⁺ doped Bi₄V₂O_11−δ systems are synthesized by a melt quench technique followed by heat treatment. The Ca²⁺ doped samples show higher density than Mg²⁺ doped samples. All the quenched samples show γ-phase stabilization irrespective of dopants and their concentration. The γ-phase stabilization takes place at lower dopant concentration than earlier reported systems. The conversion of γ-phase to ordered β-phase is observed with heat treatment for Bi₄V_2−xMg_xO_11−δ (x=0.05, 0.10 and 0.20) and Bi₄V_2−xCa_xO_11−δ (x=0.05 and 0.10). Ca²⁺ doped system, particularly high concentration (x=0.15 and 0.20) did not show γ→γ׳ phase transition. The lowest activation energy; E_a is observed for Bi₄Mg_0.15V_1.85O_11−δ sample ~0.74 eV in the temperature range 570–750 °C.     

钒酸盐管饲对STZ糖尿病大鼠OGTT和理糖激素的影响

目的 研究一定剂量的钒酸盐的降糖作用与理糖激素变化的关系。方法 采用管饲法喂饲Wistar 大鼠20 mg·kg^-1·d^-1 正钒酸钠(Va) 共2 w ks, 观察口服葡萄糖耐量(OGTT)、胰岛素释放曲线、胰高血糖素(Glc)、皮质酮(Cor)、体重的变化。结果 Va 不影响正常大鼠的OGTT 和血浆Glc 和Cor 水平, 而抑制体重的增长;Va 显著改善STZ 糖尿病大鼠的OGTT, 并使升高的Glc 和Cor 正常化, 而低体重和低水平的胰岛素释放曲线无明显改善。结论 提示该剂量的Va 可有效地降血糖, 纠正糖尿病糖代谢和激素紊乱, 但对体重仍有较明显的副作用。     

耐高温钒酸铋黄色颜料的制备

为了提高钒酸铋(BiVO4)黄色颜料的耐高温性,利用正硅酸乙酯(TEOS)的水解反应,在BiVO4表面形成SiO2膜,使钒酸铋黄色颜料经过1 000℃的高温煅烧,依然颜色鲜艳。通过实验确定了制备耐高温钒酸铋黄色颜料的适宜工艺条件:在室温下,TEOS浓度为0.14 mol/L,反应2 h并陈化约20 h,十二烷基苯磺酸钠(DBS)质量分数为0.4%,包覆2次SiO2。采用红外光谱仪、X射线衍射仪、差热分析仪对产品进行了表征,并得出结论:复合颗粒红外光谱显示,表面存在SiO2标准谱图中的特征吸收峰;X射线衍射证实SiO2以四方晶相包覆于BiVO4表面;差热分析结果表明,包覆的SiO2起到了防止BiVO4烧结的作用。     

不同结构形貌BiVO4的水热制备及可见光催化性能

采用水热法,无需添加剂,通过调控反应液pH值和反应温度制备了不同结构和形貌的BiVO4可见光催化剂.利用X射线衍射(XRD)、扫描电子显微镜(SEM)、紫外可见漫反射(DRS)和低温氮吸附等手段对样品进行表征,结果显示:水热温度与反应液pH值对晶体结构有很大影响,180℃水热温度和酸性条件有利于单斜相的生成.反应液pH值对形貌也有很大影响,不同条件下得到了片状、立方状、棒状等不同形貌的BiVO4.同时以亚甲基蓝为降解对象,考察了所制备BiVO4的可见光催化活性.其中,pH值为2,反应液中制备的片状单斜相BiVO4具有最高的光催化活性(4 h达92.0%).此外,还考察了光催化剂用量、亚甲基蓝浓度和电子受体的存在对光催化过程的影响,结果表明:当催化剂用量为1.0 g/L,亚甲基蓝浓度为10 mg/L,KBrO3为电子受体时光催化效果最佳.     

Ultra-Thin Protective Coatings for Sustained Photoelectrochemical Water Oxidation with Mo:BiVO4

As global warming caused by the greenhouse effect is becoming one of the major issues of the 21st century, hydrogen as an alternative to fossil-based fuels and other energy carriers has gained importance in current research. One promising approach to produce hydrogen is photoelectrochemical water splitting, which uses solar energy combined with suitable semiconducting photoabsorber electrodes to generate hydrogen and oxygen from water. However, most water splitting applications reported to date suffer from degradation of the photoabsorber, resulting in a loss of activity after just a few seconds or minutes. Here, a new approach using conformal ultra-thin and oxidation-stable protective layers is presented on Mo:BiVO₄ thin films combined with a thin Fe_0.1Ni_0.9O water oxidation co-catalyst, applied by electrochemical deposition, to achieve unprecedented photocurrent densities of up to 5.6 mA cm⁻² under simulated AM1.5G illumination and a neutral pH while providing more stable electrodes for water oxidation.     

Elaborately Modified BiVO4 Photoanodes for Solar Water Splitting

Photoelectrochemical (PEC) cells for solar‐energy conversion have received immense interest as a promising technology for renewable hydrogen production. Their similarity to natural photosynthesis, utilizing sunlight and water, has provoked intense research for over half a century. Among many potential photocatalysts, BiVO₄, with a bandgap of 2.4–2.5 eV, has emerged as a highly promising photoanode material with a good chemical stability, environmental inertness, and low cost. Unfortunately, its charge transport properties are modest, at most a hole diffusion length (L_p) of ≈70 nm. However, recent rapid developments in multiple modification strategies have elevated it to a position as the most promising metal oxide photoanode material. This review summarizes developments in BiVO₄ photoanodes in the past 10 years, in which time it has continuously broken its own performance records for PEC water oxidation. Effective modification techniques are discussed, including synthesis of nanostructures/nanopores, external/internal doping, heterojunction fabrication, surface passivation, and cocatalysts. Tandem systems for unassisted solar water splitting and PEC production of value‐added chemicals are also discussed.     

Additive-free hydrothermal synthesis of novel bismuth vanadium oxide dendritic structures as highly efficient visible-light photocatalysts

A novel bismuth vanadium oxide (BiVO₄) dendritic structure was successfully synthesized via an additive-free hydrothermal route. The crystal structures, morphologies and photophysical properties of the as-obtained BiVO₄ samples were characterized. The photocatalytic activities of the as-synthesized BiVO₄ samples were evaluated by the degradation of rhodamine B (RhB) under visible-light irradiation. BiVO₄ sample synthesized at 140 °C showed the highest photocatalytic degradation efficiency, up to 99.3%, due to its relatively high surface area and high crystallinity.     

Monoclinic Scheelite Bismuth Vanadate Derived Bismuthene Nanosheets with Rapid Kinetics for Electrochemically Reducing Carbon Dioxide to Formate

Electrochemical reduction of CO₂ to high-value chemical feedstocks, such as formate, is one of the most promising ways to alleviate the greenhouse effect. Unfortunately, the exploration of electrocatalysts with high activity and selectivity over a wide potential window (especially low potential for high current density) still remains a grand challenge. In this study, the fabrication of bismuthene nanosheets using an in-situ electrochemical transformation strategy of monoclinic scheelite BiVO₄ flakes is demonstrated. Catalyzing the CO₂ electroreduction in 1 m KHCO₃ aqueous solution, the bismuthene nanosheets exhibit a dramatically high formate Faradaic efficiency (FE) of ≈97.4% and a very large current density of −105.4 mA cm⁻² at −1.0 V versus reversible hydrogen electrode. Significantly, over a record wide potential window of 750 mV from the initial −0.65 V to the applied minimum −1.4 V, the formate FEs of the bismuthene nanosheets are always higher than 90%, outperforming state-of-the-art electrocatalysts. Both experimental and theoretical investigations reveal that, in comparison with ^•COOH and H^• intermediates, the bismuthene nanosheets preferentially promote fast reaction kinetics towards HCOO^•, which eventually accelerates the production of formate.     

Recent trends and outlooks on engineering of BiVO4 photoanodes toward efficient photoelectrochemical water splitting and CO2 reduction: A comprehensive review

Photoelectrochemical (PEC) water splitting, and carbon dioxide (CO₂) utilization devices have attracted immense attention as sustainable technologies for the generation of hydrogen (H₂) fuel and value-added chemicals feedstock. Among numerous semiconductors, bismuth vanadate (BiVO₄) has emerged as a promising photoanode owing to its fascinating features such as high chemical stability, straddling band alignment with water redox levels, eco-friendly, and cost-effectiveness. However, sluggish oxidation kinetics, photo-corrosive nature, low electronic conductivity, and short carrier diffusion length limit its commercialization on the PEC horizon. To mitigate these inadequacies, several strategies have emerged such as novel heterojunctions, doping with unique materials, interface modulation, morphology, facet orientation, co-catalyst loading for surface engineering, etc. to realize the outstanding cost-to-efficiency ratios and long-term stability of PEC devices. The review highlights the recent advancement in BiVO₄-based photoanodes in last five years (2018–2022) and their utilization in the single absorber and unexplored tandem PEC systems towards boosted water splitting and CO₂ reduction. A discussion on theoretical studies of BiVO₄-based PEC systems elucidates the microscopic mechanism of promotion effect of the bulk/interface/surface strategies on surface catalysis as well as interfacial charge transfer in boosting oxidation kinetics. Moreover, this review addresses the versatility of the BiVO₄-based photoanode for the novel yet commercially viable PEC applications. This review will provide a broad avenue in designing highly durable, and scalable BiVO₄-based systems toward various PEC energy conversion devices.     

SnO2 as thin conformal layer over BiVO4 surface for enhanced charge carrier separation towards O2 evolution from water oxidation

Recently, bismuth vanadate (BiVO₄) has attracted substantial attention for photocatalytic applications owing to its many advantages as semiconductor to drive water oxidation. Despite possessing promising characteristics to be applied in photocatalysis, the fast electron-hole pairs recombination is still one of the drawbacks involving this semiconductor. The use of conformal layers to minimize such limitation and to improve charge separation is the aim of this work. Herein, we report on the use of SnO₂ as a conformal coating layer over the BiVO₄ surface for O₂ evolution reaction. The incorporation of SnO₂ over the BiVO₄ surface showed the beneficial effect in O₂ evolution compared to the pristine material, resulting in 490 μmol after 6 h of irradiation. Transient absorption and surface photovoltage spectroscopies indicate enhanced charge carrier separation and transport by passivating BiVO₄ with SnO₂ thin layer. Even though the O₂ evolution tests in this work were carried out without the presence of a co-catalyst, the use of a thin conformal coating of SnO₂ over BiVO₄ showed promising results for further studies.