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

Synthesizing highly efficient photocatalysts for photoreduction of CO 2 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(NO 3 ) 2 to CS(NH 2 ) 2 , and used as photocatalysts for CO 2 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(NO 3 ) 2 to CS(NH 2 ) 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(NO 3 ) 2 to CS(NH 2 ) 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(NO 3 ) 2 to CS(NH 2 ) 2 = 2 : 1 shows the highest performance for photocatalytic reduction of CO 2 to CO (146.3 μmol g −1 ) and H 2 (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(NO 3 ) 2 to CS(NH 2 ) 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. CdS with a self-assembled nanoflower morphology synthesized using Cd(NO 3 ) 2 : CS(NH 2 ) 2 = 2 : 1 in ethylenediamine shows the highest performance for CO 2 photocatalytic reduction.