Constructing 2D/2D BiOI/Bi2O2CO3 S-scheme heterojunction for boosted CO2 photoreduction

The BiOI/Bi₂O₂CO₃ heterojunction photocatalysts were fabricated through a hydrothermal process for the reduction of carbon dioxide (CO₂) to carbon monoxide (CO). The acquired results confirmed that the BiOI/Bi₂O₂CO₃ has an S-scheme heterojunction structure and presents a two-dimensional (2D) lamellar nanostructure, which enhances the mobility of photoinduced carriers and suppresses the recombination of carriers. XPS and EPR data demonstrate the existence of abundant oxygen vacancies in the BOC4 heterojunction. These vacancies can effectively reduce the reaction energy barrier during catalysis. In the BiOI/Bi₂O₂CO₃ S-scheme heterojunctions, the BOC4 shows an excellent photocatalytic CO₂ reduction performance. Under simulated light irradiation, the rate of CO₂ reduction to CO for the BiOI/Bi₂O₂CO₃ reaches 8.11 μmol·g⁻¹·h⁻¹, which is 3.54- and 2.33-fold greater compared to those of pure BiOI and Bi₂O₂CO₃, respectively. It is considered that the improvement of photocatalytic carbon dioxide reduction performance for the BiOI/Bi₂O₂CO₃ heterojunction is attributed to the synergistic effect of the heterojunction and oxygen vacancies. The BOC4 heterojunction with 2D/2D morphology provides shorter charge transport pathways and more interfacial channels, while the oxygen vacancies accelerate the separation of photon-generated carriers and inhibit electron-hole pair recombination. This work proposes that the synergistic effects of the S-scheme heterojunction and oxygen vacancies are critical factors for optimizing photocatalytic CO₂ reduction, offering a novel strategy for designing bismuth oxyhalide-based heterojunction photocatalysts.