Effect of S vacancy in Cu3SnS4 on high selectivity and activity of photocatalytic CO2 reduction

Cu3SnS4 with S vacancy and different ratios of Cu(I/II) and Sn(II/IV) was designed for photocatalytic CO2 reduction with high selectivity and activity in this study. The conduction band (CB) position dominated by the Sn (II) 5p orbital of Cu3SnS4 could be regulated via controlling the content of Sn(II). Cu(I) and Sn(IV) in crystal lattice acted as the adsorption sites of CO2 and H2O as demonstrated by Density Functional Theory (DFT) calculations, meanwhile Cu(I) had a strong adsorption ability to CO, which was conducive to further protonation for CH4 generation (CO2 -> COOH*-> CO*-> CHO*-> CH2O*-> CH3O*-> CH4). S vacancy could result in the appearance of Cu(I) and Sn(II), which could successfully inhibit the electron-hole recombination and improve the reactivity (CH4 with yield of 22.65 mu mol/g/h) and selectivity (CH4 similar to 83.10 %). This work can shed some light on the synthetic method by controlling vacancy and elements to adjust CB position to increase reduction capability and selectivity.