Abstract:

Catalytic reduction of CO₂ to CO has been considered promising for converting the greenhouse gas into chemical intermediates. Compared to other catalytic methods, photocatalytic CO₂ reduction, which uses solar energy as the energy input, has attracted significant attention because it is a clean and inexhaustible resource. Therefore, using high-performance photocatalysts for effective CO₂ reduction under mild reaction conditions is an active research hotspot. However, several current photocatalysts suffer from low solar energy conversion efficiency due to the extensive charge recombination and few active sites, leading to low CO₂ reduction efficiency. Generally, constructing an S-scheme heterojunction can not only promote charge separation but also help maintain strong redox ability. Therefore, the S-scheme heterojunction is expected to help in achieving high conversion activity and CO₂ reduction efficiency. Here, 2D tetragonal BiOBr_0.5Cl_0.5 nanosheets and hexagonal WO₃ nanorods were prepared using a simple hydrothermal synthesis method, and the 2D/1D BiOBr_0.5Cl_0.5 nanosheets/WO₃ nanorods (BiOBr_0.5Cl_0.5/WO₃) S-scheme heterojunction with near infrared (NIR) light (> 780 nm) response were prepared via the electrostatic self-assembly method for the photocatalytic CO₂ reduction. Following characterization and analysis, including diffuse reflectance spectra (DRS), Mott-Schottky plots, transient photocurrent response, time-resolution photoluminescence spectrum (TRPL), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and electron spin resonance (ESR) measurements, it can be demonstrated that an S-scheme carrier transfer route was formed between the 2D BiOBr_0.5Cl_0.5 nanosheets and 1D WO₃ nanorods. Driven by the internal electric field, which was formed between the two semiconductors, electron migration was boosted, thus inhibiting the recombination of photogenerated carriers, while the stronger redox ability was maintained, thus providing good reduction efficiency over BiOBr_0.5Cl_0.5/WO₃ composite in CO₂ reduction. In addition, the 2D/1D nanosheet/nanorod structure allowed for enhanced interface contact with abundant active sites, which favored charge separation and increased photocatalytic activity. Furthermore, the amount of WO₃ nanorods added during the preparation of the composites was altered, which led to the optimal amount of 5% (w, mass fraction) for the photocatalytic CO₂ reduction. As a result, the BiOBr_0.5Cl_0.5/WO₃ composite exhibited superior photocatalytic reduction performance with a CO yield of 16.68 μmol·g^-1·h^-1 in the presence of any precious metal cocatalyst or sacrificial agent, which was 1.7 and 9.8 times that of pure BiOBr_0.5Cl_0.5 and WO₃, respectively. In addition, the BiOBr_0.5Cl_0.5/WO₃ composite provided continuously increased CO yields with excellent selectivity under full-spectrum light irradiation, suggesting good photocatalytic stability. This work describes a novel idea for the construction of 2D/1D S-scheme heterojunction photocatalysts for efficient CO₂ reduction.

Key words: 2D/1D heterostructure, BiOBr_0.5Cl_0.5 nanosheets, WO₃ nanorods, CO₂ reduction, S-scheme