No abstract

Oxygen vacancies in semiconductor photocatalysts play several competing roles, serving to both enhance light absorption and charge separation of photoexcited carriers as well as act as recombination centers for their deactivation. In this Letter, we show that single-molecule fluorescence imaging of a chemically activated fluorogenic probe can be used to monitor changes in the photocatalytic activity of bismuth oxybromide (BiOBr) nanoplates in situ during the light-induced formation of oxygen vacancies. We observe that the specific activities of individual nanoplates for the photocatalytic reduction of resazurin first increase and then progressively decrease under continuous laser irradiation. Ensemble structural characterization, supported by electronic-structure calculations, shows that irradiation increases the concentration of surface oxygen vacancies in the nanoplates, reduces Bi ions, and creates donor defect levels within the band gap of the semiconductor particles. These combined changes first enhance photocatalytic activity by increasing light absorption at visible wavelengths. However, high concentrations of oxygen vacancies lower the photocatalytic activity both by introducing new relaxation pathways that promote charge recombination before photoexcited electrons can be extracted and by weakening binding of resazurin to the surface of the nanoplates.

A new kind of metallic Cu‐loaded brookite TiO2 composite, in which Cu nanoclusters with a small size of 1–3 nm are decorated on brookite TiO2 quasi nanocube (BTN) surfaces (hereafter referred to as Cu‐BTN), is synthesized via a one‐pot hydrothermal process and then used as photocatalyst for CO2 reduction. It was found that the decoration of Cu nanoclusters on BTN surfaces can improve the activity and selectivity of CO2 photoreduction to CH4, and 1.5 % Cu‐BTN gives a maximum overall photocatalytic activity (150.9 μmol g−1 h−1) for CO/CH4 production, which is ≈11.4 and ≈3.3 times higher than those of pristine BTN (13.2 μmol g−1 h−1) and Ag‐BTN (45.2 μmol g−1 h−1). Moreover, the resultant Cu‐BTN products can promote the selective generation of CH4 as compared to CO due to the number of surface oxygen vacancies and the CO2/H2O adsorption behavior, which differs from that of the pristine BTN. The present results demonstrate that brookite TiO2 would be a potential effective photocatalyst for CO2 photoreduction, and that Cu nanoclusters can act as an inexpensive and efficient co‐catalyst alternative to the commonly used noble metals to improve the photoactivity and selectivity for CO2 reduction to CH4.

The synthesis of substituted pyridines has drawn the attention of many chemists due to their importance as building blocks for biologically active compounds and materials. This mini-review focuses on recent developments relating to the synthesis of substituted pyridines from pyridine N-oxides, along with their interesting mechanism aspects. New developments including alkenylation, alkynylation, alkylation, arylation, amination and cyanation are discussed.

MnxCd1−xS solid solutions are obtained, and Mn0.5Cd0.5S exhibits the best H2 production activity, which was further boosted by MoS2-loading.