Facile construction of double vacancy modified BiOBr/g-C3N4@Bi heterojunctions for effective photochemical CO2 reduction

Three different heterojunctions, BiOBr/g-C3N4, Bi/g-C3N4, and BiOBr/g-C3N4@Bi modified with carbon vacancies and/or oxygen vacancies, were first synthesized via a facile solvothermal approach by adjusting the ratio of Bi(NO3)3 · 5H2O with ethylene glycol (EG). The as-prepared heterojunctions were characterized by various modern analytical instruments, and their visible-light photocatalytic performance for CO2 conversion was evaluated. Our findings demonstrate that the ternary photocatalyst BiOBr/g-C3N4@Bi exhibits better activity toward visible-light-driven CO2 reduction than pristine g-C3N4 and its binary counterparts without hole scavengers, and its maximum CO yield (7.4 μmol · h−1 · g−1) is approximately four 4 times that of pure g-C3N4. This is attributed to the VO and VC defects, which enhance the photon absorption capacity. On the other hand, the g-C3N4 matrix exhibits strong interfacial interactions with BiOBr and metallic Bi, leading to an increase in the separation efficiency of the photoinduced carriers. In other words, the strong interfacial interactions among g-C3N4, BiOBr and metallic Bi, the vacancy defects VO and VC, and the metallic Bi particles cooperate to significantly improve the separation and transportation of the photoexcited charge carriers, thereby augmenting the CO2 photoreduction activity of the BiOBr/g-C3N4@Bi ternary heterojunction in the absence of a sacrificial agent. This approach based on facile solvothermal treatment has promising potential in fabricating highly efficient photocatalysts suitable for visible-light-driven CO2 reduction.