A mechanistic study of molecular CO₂ interaction and adsorption on carbon implanted SnS₂ thin film for photocatalytic CO₂ reduction activity

Gas-phase photocatalytic reactions to convert carbon dioxide and water into oxygen and hydrocarbons are the foundation of life on earth. However, the efficiency of photosynthesis is relatively low (~1%), which leaves much room for artificial photosynthesis to reach the benchmark of the solar cells (>15%). In this work, carbon implanted SnS₂ thin films (C–SnS₂) were prepared to study photocatalytic activity and adsorbate-catalyst surface interactions during CO₂ photoreduction. The electron density distribution in C–SnS₂ and its contribution toward the photogenerated charge transfer process has been analyzed by the angle-dependent X-ray absorption near-edge structure (XANES) study. The C–SnS₂ surface affinity toward the CO₂ molecule was monitored by in-situ dark current and Raman spectroscopy measurements. By optimizing the dose during ion implantation, SnS₂ thin film with 1 wt% carbon incorporation shows 108 times enhancement in the CO₂ conversion efficiency and more than 89% product selectivity toward CH₄ formation compared with the as-grown SnS₂ without carbon incorporation. The improved photocatalytic activity can be ascribed to enhanced light harvesting, pronounced charge-transfer between SnS₂ and carbon with improved carrier separation and the availability of highly active carbon sites that serve as favorable CO₂ adsorption sites.