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Metal halide perovskites with suitable energy band structures and excellent visible-light responses have emerged as promising photocatalysts for CO2 reduction to valuable chemicals and fuels. However, the efficiency of CO2 photocatalytic reduction often suffers from inefficient separation and sluggish transfer. Herein, a step-scheme (S-scheme) CsPbBr3/BiOBr photocatalyst with oxygen vacancies possessing intimate interfacial contact was fabricated by anchoring CsPbBr3 QDs on BiOBr-Ov nanosheets using a mild anti-precipitation method. The results showed that CsPbBr3/BiOBr-Ov-2 with an internal electric field (IEF) heterojunction exhibited a boosted evolution rate of 27.4 μmol g−1 h−1 (CO: 23.8 μmol g−1 h−1 and CH4: 3.6 μmol g−1 h−1) with an electron consumption rate (Relectron) of 76.4 μmol g−1 h−1, which was 5.9 and 3.2 times that of single CsPbBr3 and BiOBr-Ov, respectively. Density functional theory (DFT) calculations revealed that BiOBr with oxygen vacancies can effectively enhance the adsorption and activation of CO2 molecules. More importantly, in situ infrared Fourier transform spectroscopy (DRIFTS) spectra show the transformation process of the surface species, while the femtosecond transient absorption spectrum (fs-TA) reveals the charge transfer kinetics of the CsPbBr3/BiOBr-Ov. Overall, this work provides some guidance for the rational design of S-scheme heterojunctions and vacancy-engineered photocatalysts, which are expected to have potential applications in the fields of photocatalysis and solar energy conversion. [ABSTRACT FROM AUTHOR]

The superiority of fluorescence-based methods in the metal ion detection is well established; however, the quantum dot (QD) fluorescent probes currently used for mercury ions (Hg2+) have many limitations, such as a narrow detection range and environmental toxicity. In this work, environment-friendly tin oxide (SnO2) quantum dots were prepared and applied as a fluorescent sensor for the selective determination of Hg2+. The synthesized SnO2 QDs showed excellent performance in Hg2+ ion detection, with a broad linear range of 10−2–105 μM and a low detection limit of 5 nM. Remarkably, SnO2 QDs illustrated high selectivity to Hg2+ ions without interference from other metal ions. Furthermore, the mechanism of fluorescence enhancement in SnO2 QDs was based on the ratio of non-radiative electrons, and the density of active Sn vacancies was further explained. A mathematical model is proposed to interpret the mechanism of the adsorptive process during Hg2+ detection, thereby providing a quantitative understanding of the fluorescence sensing principle of semiconductor QDs. This work demonstrates the promising application of SnO2 QDs for convenient, highly sensitive and low-cost determination of Hg2+ ions in experimental and actual conditions. [ABSTRACT FROM AUTHOR]

Metal halide perovskites with suitable energy band structures and excellent visible-light responses have emerged as promising photocatalysts for CO 2 reduction to valuable chemicals and fuels. However, the efficiency of CO 2 photocatalytic reduction often suffers from inefficient separation and sluggish transfer. Herein, a step-scheme (S-scheme) CsPbBr 3 /BiOBr photocatalyst with oxygen vacancies possessing intimate interfacial contact was fabricated by anchoring CsPbBr 3 QDs on BiOBr-Ov nanosheets using a mild anti-precipitation method. The results showed that CsPbBr 3 /BiOBr-Ov-2 with an internal electric field (IEF) heterojunction exhibited a boosted evolution rate of 27.4 μmol g -1 h -1 (CO: 23.8 μmol g -1 h -1 and CH 4 : 3.6 μmol g -1 h -1 ) with an electron consumption rate ( R electron ) of 76.4 μmol g -1 h -1 , which was 5.9 and 3.2 times that of single CsPbBr 3 and BiOBr-Ov, respectively. Density functional theory (DFT) calculations revealed that BiOBr with oxygen vacancies can effectively enhance the adsorption and activation of CO 2 molecules. More importantly, in situ infrared Fourier transform spectroscopy (DRIFTS) spectra show the transformation process of the surface species, while the femtosecond transient absorption spectrum (fs-TA) reveals the charge transfer kinetics of the CsPbBr 3 /BiOBr-Ov. Overall, this work provides some guidance for the rational design of S-scheme heterojunctions and vacancy-engineered photocatalysts, which are expected to have potential applications in the fields of photocatalysis and solar energy conversion.