Highly efficient photocatalytic hydrogen generation by solution-processed ZnO/Pt/CdS, ZnO/Pt/Cd1−xZnxS and ZnO/Pt/CdS1−xSex hybrid nanostructures

Abstract

Photocatalytic generation of hydrogen by using the hybrid nanostructures, ZnO/Pt/CdS, ZnO/Pt/Cd_1−xZn_xS and ZnO/Pt/CdS_1−xSe_x, has been studied under UV-visible and visible irradiation by employing Na₂S and Na₂SO₃ as hole scavengers. Good H₂ evolution rates up to 17.4 mmol h⁻¹ g⁻¹ and an apparent quantum yield (AQY) of 11.1% were obtained with ZnO/Pt/CdS under UV-visible irradiation. With the visible irradiation alone, the rate of H₂ production was slower. With 20% Zn substitution in place of Cd in CdS, the rate of H₂ generation was 31.2 mmol h⁻¹ g⁻¹ and 12.5 mmol h⁻¹ g⁻¹ respectively with UV-visible and visible irradiation, the corresponding AQY values being 23.1% and 18%. With 50% substitution of S by Se in CdS, the rate of hydrogen generation was at 19 mmol h⁻¹ g⁻¹ and 16 mmol h⁻¹ g⁻¹ with UV-visible and visible irradiation respectively, but the AQY values were in the range of 8–9%. Replacing Na₂S and Na₂SO₃ by benzyl alcohol as the scavenger improves the catalytic activity of ZnO/Pt/CdS yielding H₂ at the rate of 31.6 mmol h⁻¹ g⁻¹ and AQY of 34.5% under visible irradiation. The results were even more remarkable with ZnO/Pt/Cd_0.8Zn_0.2S where the rate was 36.5 mmol h⁻¹ g⁻¹ and the AQY reached 50.4% with visible irradiation. A noteworthy feature of the present study is that the hybrid nanostructures were prepared by simple solution processing involving sequential addition of reagents to ZnO nanoparticles in methanol medium.