The influence of the precursor molar ratio on the structure of the CdS catalyst during synthesis and visible-light driven CO2 reduction into solar fuel

Abstract

Synthesizing highly efficient photocatalysts for photoreduction of CO₂ into solar fuel is of great significance for solving the energy shortage and environmental pollution. Here, a series of CdS photocatalysts are synthesized via the solvothermal method by tuning the Cd–S precursor molar ratio of Cd(NO₃)₂ to CS(NH₂)₂, and used as photocatalysts for CO₂ reduction into solar fuel. The crystal structure, morphology, optical properties, charge separation, and photocatalytic performance of the CdS photocatalysts are greatly influenced by the Cd–S precursor molar ratio. After changing the molar ratio of Cd(NO₃)₂ to CS(NH₂)₂, the morphology of the synthesized CdS changes from nanorods to self-assembled nanoflowers and floccules with a high proportion of (002) crystal planes. As the molar ratio of Cd(NO₃)₂ to CS(NH₂)₂ increases, the BET specific surface area of the synthesized CdS catalysts increases obviously, the surface sulfur vacancies gradually increase, and the photo-generated charge separation is also enhanced. CdS2-1 synthesized using a molar ratio of Cd(NO₃)₂ to CS(NH₂)₂ = 2 : 1 shows the highest performance for photocatalytic reduction of CO₂ to CO (146.3 μmol g⁻¹) and H₂ (582 μmol g⁻¹) in 6 h under visible light irradiation, which is 11.2 and 4.4 times those over CdS1-3 synthesized using a molar ratio of Cd(NO₃)₂ to CS(NH₂)₂ = 1 : 3, respectively. This research demonstrates that a slight change of the precursor molar ratio in the synthesis of a catalyst can cause big changes in the photochemical properties and the corresponding photocatalytic performance.