Mechanistic insight into the photocatalytic hydrogenation of 4-nitroaniline over band-gap-tunable CdS photocatalysts.

CdS photocatalysts with tunable band gaps (2.17-2.32 eV) were successfully prepared by a solvothermal method. Photocatalytic hydrogenation of 4-nitroaniline over the obtained samples was evaluated in the presence of HCO2NH4 as a hole scavenger upon purging with N2 under visible light irradiation (λ ≥ 420 nm). The CdS sample prepared by CdCl2 and sulfur powder in ethylenediamine showed excellent catalytic activity, giving 100% of 4-nitroaniline conversion and 95% of p-phenylenediamine selectivity after 35 min of visible light irradiation. The results of electron spin resonance revealed that its photoexcited holes could efficiently react with HCO2(-) ions within HCO2NH4 molecules to produce ˙CO2(-) radicals with strong reductive abilities. Furthermore, photoexcited electrons of the obtained sample exhibited relatively strong reductive abilities as compared to other CdS samples. Therefore, this sample showed the highest catalytic activity among the CdS samples for the photocatalytic hydrogenation of 4-nitroaniline.