CdS/WO3 S-scheme heterojunction with improved photocatalytic CO2 reduction activity

WO3/BiOBr S-Scheme Heterojunction Photocatalyst for Enhanced Photocatalytic CO2 Reduction

The photocatalytic CO2 reduction strategy driven by visible light is a practical way to solve the energy crisis. However, limited by the fast recombination of photogenerated electrons and holes in photocatalysts, photocatalytic efficiency is still low. Herein, a WO3/BiOBr S-scheme heterojunction was formed by combining WO3 with BiOBr, which facilitated the transfer and separation of photoinduced electrons and holes and enhanced the photocatalytic CO2 reaction. The optimized WO3/BiOBr heterostructures exhibited best activity for photocatalytic CO2 reduction without any sacrificial reagents, and the CO yield reached 17.14 μmol g-1 after reaction for 4 h, which was 1.56 times greater than that of BiOBr. The photocatalytic stability of WO3/BiOBr was also improved.

Construction of bismuth oxide iodide (BiOI)/zinc titanium oxide (Zn2TiO4) p-n heterojunction nanofibers with abundant oxygen vacancies for improving photocatalytic carbon dioxide reduction

The conversion of carbon dioxide (CO2) into value-added syngas represents an effective approach for addressing both environmental issues and carbon neutrality issue. However, the slow charge dynamics and low CO2 affinity severely limit the photocatalytic CO2 reduction reaction. In this study, bismuth oxide iodide (BiOI)/zinc titanium oxide (Zn2TiO4) composite nanofibers were successfully prepared by immobilizing BiOI nanosheets on Zn2TiO4 electrospun nanofibers through a solvothermal reaction method. The results of photocatalytic research indicate that the BiOI/Zn2TiO4 composite nanofibers exhibit improved photocatalytic activity in CO2 reduction compared to pristine BiOI nanosheets and Zn2TiO4 nanofibers. The highest carbon monoxide (CO) release rate of BiOI/Zn2TiO4 nanofibers could reach 9.10 µmol‧g-1‧h-1, which is 18.6 times and 6.6 times higher than that of pristine BiOI nanosheets and Zn2TiO4 nanofibers, respectively. The enhanced photocatalytic activity can be credited to the formed BiOI/Zn2TiO4 p-n heterojunction, which can boost electron separation, reduce charge recombination at the interface, and promote the reaction process. The presence of oxygen vacancies in BiOI/Zn2TiO4 nanofibers can not only provide active site to facilitate the adsorption and activation of CO2 molecules, but also adjust the energy band structure of the catalyst to accelerate carriers transfer. After four cycles of testing, the CO release rate of BiOI/Zn2TiO4 nanofibers remains nearly constant, demonstrating its excellent stability. This work develops a feasible strategy to improve the efficiency of photoreduction of CO2 through energy band engineering and surface defect technology.

Three-dimensional S-scheme heterojunction by integration of purple tungsten oxide nanowires and cadmium sulfide nanospheres for effective photocatalytic hydrogen generation

The practical photocatalytic application of cadmium sulfide (CdS) has been significantly constrained by fast carrier recombination and significant photocorrosion. Therefore, we developed a three-dimensional (3D) step-by-step (S-scheme) heterojunction using the coupling interface between purple tungsten oxide (W₁₈O₄₉) nanowires and CdS nanospheres. The photocatalytic hydrogen evolution rate of optimized W₁₈O₄₉/CdS 3D S-scheme heterojunction can reach 9.7 mmol·h^-1·g^-1, 7.5 and 16.2 times greater than pure CdS (1.3 mmol·h^-1·g^-1) and 10 wt%-W₁₈O₄₉/CdS (mechanical mixing, 0.6 mmol·h^-1·g^-1), proving that the tight S-scheme heterojunction constructed by the hydrothermal method can efficiently enhance the carrier separation. Notably, the apparent quantum efficiency (AQE) of W₁₈O₄₉/CdS 3D S-scheme heterojunction approaches 7.5% and 3.5% at 370 nm and 456 nm, respectively, which is 7.5 and 8.8 times than pure CdS (1.0% and 0.4%). The produced W₁₈O₄₉/CdS catalyst also has relative stability of structure and hydrogen production. Additionally, the H₂ evolution rate of W₁₈O₄₉/CdS 3D S-scheme heterojunction is 1.2 times greater than 1 wt%-platinum (Pt)/CdS (8.2 mmol·h^-1·g^-1), which indicates that the W₁₈O₄₉ can effectively replace the precious metal for boosting the hydrogen production rate.

Recent Progress in Metal Oxide-Based Photocatalysts for CO2 Reduction to Solar Fuels: A Review

One of the challenges in developing practical CO₂ photoconversion catalysts is the design of materials with a low cost, high activity and good stability. In this paper, excellent photocatalysts based on TiO₂, WO₃, ZnO, Cu₂O and CeO₂ metal oxide materials, which are cost-effective, long-lasting, and easy to fabricate, are evaluated. The characteristics of the nanohybrid catalysts depend greatly on their architecture and design. Thus, we focus on outstanding materials that offer effective and practical solutions. Strategies to improve CO₂ conversion efficiency are summarized, including heterojunction, ion doping, defects, sensitization and morphology control, which can inspire the future improvement in photochemistry. The capacity of CO₂ adsorption is also pivotal, which varies with the morphological and electronic structures. Forms of 0D, 1D, 2D and 3DOM (zero/one/two-dimensional- and three-dimensional-ordered macroporous, respectively) are involved. Particularly, the several advantages of the 3DOM material make it an excellent candidate material for CO₂ conversion. Hence, we explain its preparation method. Based on the discussion, new insights and prospects for designing high-efficient metallic oxide photocatalysts to reduce CO₂ emissions are presented.