Efficient Photocatalytic CO ₂ Reduction to Syngas with Tunable Ratios Enabled by an S-Scheme TiO ₂ /CN Heterojunction

Photocatalytic conversion of CO2 and H2O into syngas offers a green and sustainable pathway for the production of chemical feedstocks. However, most high-yield syngas production systems rely on a noble metal photosensitizer or cocatalyst, making it challenging to obtain cost-effective syngas. In this work, we designed and prepared S-scheme TiO2/CN heterojunctions with varying mass ratios by calcining the mixture of NH2-MIL-125(Ti) and pristine carbon nitride (CN). The combination of TiO2 with CN significantly enhances visible light absorption, and the formation of an S-scheme heterojunction effectively improves the separation and migration of photogenerated carriers. In addition, the enlarged specific surface area as well as the enhanced CO2 adsorption capacity also promote the photocatalytic CO2 reduction. Without any noble metal photosensitizer or cocatalyst, the 150TiO2/CN heterojunction demonstrated excellent performance to produce syngas. The production rates of CO and H2 are 6.2 and 1.9 mmol g–1 h–1, respectively, and the syngas production rate was 3.4 and 29.5 times that of pure CN and TiO2, respectively, when high-purity CO2 is used as the feed gas and the ratio of H2O/MeCN in solvent is 1:4. By adjustment of the composition of feed gas and solvent, high yield syngas with widely tunable CO/H2 ratios from 3.3:1 to 1:3.7 was achieved, and the maximum syngas production rate reached 12.1 mmol g–1 h–1. This work provides insights into the design of highly efficient photocatalysts for CO2 conversion to fuels or chemicals.