Defective CQDs modified Bi4O5Br2 to construct S-scheme heterostructure for efficient photocatalytic CO2 reduction and pollutant degradation

Designing highly efficient photocatalysts capable of photoreducing CO₂ and degrading organic dyes is of practical importance. Nevertheless, obstacles remain, including the challenges in CO₂ adsorption, low efficiency of carrier separation, and unsatisfactory performance in photocatalytic processes. This work presents a straightforward hydrothermal method for incorporating coal-derived carbon quantum dots (CQDs) onto Bi₄O₅Br₂ nanosheets. The synergy between CQDs and Bi₄O₅Br₂ enhances the visible light absorption properties of the CQDs/Bi₄O₅Br₂ heterostructure and improves the migration efficiency of photogenerated electron holes. The design of vacancy defects plays a crucial role in promoting light absorption, charge separation, and transport of materials. The introduction of carbon vacancies in the CQDs not only creates surface active sites but also significantly enhances the charge transport capability of the CQDs/Bi₄O₅Br₂ heterostructure. Due to the synergistic effects of the S-scheme heterostructure and vacancy engineering, the optimal sample BOB-2 achieved the highest CO yield of 307.73 μL g⁻¹ in 3 h without any sacrificial agent, along with a Rhodamine B (RhB) degradation efficiency of up to 99.1 % within 15 min, markedly surpassing the performance of Bi₄O₅Br₂. The reaction mechanism of CO₂ reduction and RhB degradation was thoroughly analyzed. This study provides a novel perspective on the utilization of coal-based carbon materials and outlines a pathway for the design of efficient photocatalysts.