Defect‐Tailoring Mediated Electron–Hole Separation in Single‐Unit‐Cell Bi3O4Br Nanosheets for Boosting Photocatalytic Hydrogen Evolution and Nitrogen Fixation

Solar photocatalysis is a potential solution to satisfying energy demand and its resulting environmental impact. However, the low electron–hole separation efficiency in semiconductors has slowed the development of this technology. The effect of defects on electron–hole separation is not always clear. A model atomically thin structure of single‐unit‐cell Bi₃O₄Br nanosheets with surface defects is proposed to boost photocatalytic efficiency by simultaneously promoting bulk‐ and surface‐charge separation. Defect‐rich single‐unit‐cell Bi₃O₄Br displays 4.9 and 30.9 times enhanced photocatalytic hydrogen evolution and nitrogen fixation activity, respectively, than bulk Bi₃O₄Br. After the preparation of single‐unit‐cell structure, the bismuth defects are controlled to tune the oxygen defects. Benefiting from the unique single‐unit‐cell architecture and defects, the local atomic arrangement and electronic structure are tuned so as to greatly increase the charge separation efficiency and subsequently boost photocatalytic activity. This strategy provides an accessible pathway for next‐generation photocatalysts.     

Synergy-Compensation Effect of Ferroelectric Polarization and Cationic Vacancy Collaboratively Promoting CO2 Photoreduction

Photocatalytic CO₂ reduction is severely limited by the rapid recombination of photo-generated charges and insufficient reactive sites. Creating electric field and defects are effective strategies to inhibit charge recombination and enrich catalytic sites, respectively. Herein, a coupled strategy of ferroelectric poling and cationic vacancy is developed to achieve high-performance CO₂ photoreduction on ferroelectric Bi₂MoO₆, and their interesting synergy-compensation relationship is first disclosed. Corona poling increases the remnant polarization of Bi₂MoO₆ to enhance the intrinsic electric field for promoting charge separation, while it decreases the CO₂ adsorption. The introduced Mo vacancy (V_Mo) facilitates the adsorption and activation of CO₂, and surface charge separation by creating local electric field. Unfortunately, V_Mo largely reduces the remnant polarization intensity. Coupling poling and V_Mo not only integrate their advantages, resulting in an approximately sevenfold increased surface charge transfer efficiency, but also compensate for their shortcomings, for example, V_Mo largely alleviates the negative effects of ferroelectric poling on CO₂ adsorption. In the absence of co-catalyst or sacrificial agent, the poled Bi₂MoO₆ with V_Mo exhibits a superior CO₂-to-CO evolution rate of 19.75 µmol g⁻¹ h⁻¹, ≈8.4 times higher than the Bi₂MoO₆ nanosheets. This work provides new ideas for exploring the role of polarization and defects in photocatalysis.     

花状空心Sn3O4微球的制备及其光催化性能的研究

通过简易的一步水热法在不同制备温度(120℃、135℃、150℃)下成功合成了花状空心Sn₃O₄微球。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)、表面积分析仪、紫外可见吸收光谱(UV-Vis)和光致发光谱 (PL)等测试手段对其形貌、结构、比表面积和光学性质进行了分析, 并以罗丹明B(RhB)为模型污染物研究了样品的光催化性能。实验结果显示: 中空微球结构不随水热合成温度发生明显改变; 随着水热合成温度的升高, 样品的UV-Vis吸收峰从384 nm蓝移至365 nm, 同时PL发射峰位的峰强逐渐降低。光催化结果显示, 在120℃合成的空心Sn₃O₄微球具备最优的光催化性能。     

Constructing Built‐in Electric Field in Ultrathin Graphitic Carbon Nitride Nanosheets by N and O Codoping for Enhanced Photocatalytic Hydrogen Evolution Activity

Codoping of N and O in ultrathin graphitic carbon nitride (g‐C₃N₄) nanosheets leads to an inner electric field. This field restrains the recombination of photogenerated carriers and, thus, enhances hydrogen evolution. The layered structure of codoped g‐C₃N₄ nanosheets (N‐O‐CNNS) not only provides abundant sites of contact with the reaction medium, but also decreases the distance over which the photogenerated electron–hole pairs are transported to the reaction interface. Quantum confinement in the ultrathin structure results in an increased bandgap and makes the photocatalytic reaction more favorable than bulk g‐C₃N₄. Under visible light irradiation, N‐O‐CNNS with 3 wt% Pt achieves a hydrogen evolution rate of 9.2 mmol g^?1 h^?1 and a value of 46.9 mmol g^?1 h^?1 under AM1.5 with 5 wt% Pt. Thus, this work paves the way for designing efficient nanostructures with increased separation/transfer efficiency of photogenerated carriers and, hence, increased photocatalytic activities.     

Bi4Ti3O12铁电薄膜的MOCVD制备及其物理性质研究

采用常压ＭＯＣＶＤ技术在（１００）硅衬底上生长了具有（１００）及（００１）取各的钛酸铋（Ｂｉ４Ｔｉ３Ｏ１２）薄膜。在适当的生长条件下可获得（１００）取向膜，在７５０－８００℃下退火可获得（００１）择优取向膜。通过观察Ｐ－Ｅ电滞回线可确认膜的铁电性质，测得（１００）取向膜的剩余极化强度为３８μｃ／ｃｍ＾２，矫顽场为４５ＫＶ／ｃｍ。同时测量了钛酸铋薄膜的介电常数及损耗角正切。     

Engineering of Electronic States on Co3O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction

Due to the earth abundance and tunable electronic properties, etc., transition metal oxides (TMOs) show attractive attention in oxygen evolution reaction. O‐vacancies (V_o) play important roles in tailoring the local surface and electronic environment to lower the activation barriers. Herein, an effective strategy is shown to enhance the oxygen evolution reduction (OER) performance on Co₃O₄ ultrathin nanosheets via combined cation substitution and anion vacancies. The oxygen‐deficient Fe‐Co‐O nanosheets (3–4 nm thickness) display an overpotential of 260 mV@10 mA cm^?2 and a Tafel slope of 53 mV dec^?1, outperforming those of the benchmark RuO₂ in 1.0 m KOH. Further calculations demonstrate that the combined introduction of Fe cation and V_o with appropriate location and content finely tune the intermediate absorption, consequently lowering the rate‐limiting activation energy from 0.82 to as low as 0.15 eV. The feasibility is also proved by oxygen‐deficient Ni‐Co‐O nanosheets. This work not only establishes a clear atomic‐level correlation between cation substitution, anion vacancies, and OER performance, but also provides valuable insights for the rational design of highly efficient catalysts for OER.