Bi4O5Br2 nanosheets modified by carbon quantum dots: Efficient BPA degradation induced by enhanced absorption and Z-scheme charge transfer

Constructing semiconductor photocatalysts with enhanced absorption and rapid carrier dynamics is es-sential for applying semiconductor photocatalysis in environmental remediation and energy conversion. In this study, we modified carbon quantum dots (CQDs) onto the surface of Bi4O5Br2 using a one-step hy-drothermal method. The modification enabled the excellent degradation of bisphenol A (BPA) due to the up -conversion luminescence of CQDs and the Z-scheme charge transfer path formed by the unique energy level of the two materials. The CQDs/Bi4O5Br2 composite added with 4 mg of CQDs completely degraded BPA (20 mg/L) within 100 min when the radiation wavelength exceeded 400 nm, and Bi4O5Br2 itself only de-graded BPA by 1.44%. In sharp contrast, if a xenon lamp was directly irradiated without a 400 nm filter to sift the ultraviolet components, the degradation rate of the Bi4O5Br2 monomer could reach 40% under the same conditions. This indicates that introducing CQDs plays a vital role in visible-light-driven degradation. Furthermore, on the basis of the structural characterisation, the successful introduction of CQDs was confirmed in the CQDs/Bi4O5Br2 hybrid system. On this basis, the possibility of Z-scheme charge transfer was proved by X-ray photoelectron spectroscopy and ultraviolet electron spectroscopy measurements. The degradation mechanism of BPA under Z-type charge transfer was proposed through electron paramagnetic resonance, free radical capture and total organic carbon tests. This work is expected to provide a new idea for designing an energy band that matches semiconductor heterojunction photocatalysts, enhancing the unique narrow band gap structure and up-conversion properties of CQDs. In addition, it facilitates the construction of photocatalysts with better performance. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this study, a semiconductor photocatalyst with enhanced absorption and rapid carrier dynamics was constructed by modifying carbon quantum dots onto the surface of Bi4O5Br2. The modified composite exhibited excellent degradation performance of bisphenol A due to the up-conversion luminescence of carbon quantum dots and the unique energy level of the two materials. The introduction of carbon quantum dots played a vital role in visible-light-driven degradation. The successful introduction of carbon quantum dots and the possibility of Z-scheme charge transfer were confirmed by structural characterization and spectroscopy measurements. The degradation mechanism of bisphenol A under Z-type charge transfer was proposed based on various tests. This work provides new insights for designing efficient photocatalysts with narrow band gap and up-conversion properties.