P 2 Reparation And Photocatalytic H₂ Evolution Study Of NiS/CdS Composite Photocatalyst

CdS is an attractive candidate for hydrogen evolution by visible-light-driven photocatalytic water splitting. However, the use of CdS for photocatalytic water splitting suffers from low hydrogen evolution rate and serious photocorrosion under a long-term light irradiation. Cocatalyst and sacrificial reagent are often used to enhance the photocatalytic activity of CdS.Generally, mainly noble metals or their oxides are used as the cocatalysts. The photocatalytic activity of CdS could be greatly enhanced by loading NiS as cocatalyst and using Na₂S/Na₂SO₃ as sacrificial reagents. Meanwhile, the aging process of CdS is crucial to the rate of hydrogen evolution. Aging 6 days leads to excellent rate of hydrogen evolution.We studied the rate of hydrogen evolution on NiS/CdS with Na₂S + Na₂SO₃ and CH₃CH(OH)COOH as sacrificial reagents respectively. ES^2-/S is lower than ECH₃CH(OH)COOH/CH₃COCOOH and S^2- can stabilize the sulfur defects of CdS surface. While CH₃CH(OH)COOH is acid, which could accelerate the dissolvability of CdS with introduction of H+. Hence, CH₃CH(OH)COOH contributes to more sulfur defects of CdS surface. Therefore, the rate of hydrogen evolution is higher when Na₂S + Na₂SO₃ are used as sacrificial reagents.We investigate the rate of hydrogen evolution on CdS prepared at different temperatures. In our experiment we found that CdS with cubic phase has relatively high photocatalytic activity. The photocatalyst has good crystallinity and different phase when temperature is elevated, meanwhile, the size of it increased. Hence the separation rate of photogenerated carriers is changed and meantime the rate of hydrogen evolution is altered. Consisdering the above factors, the photocatalytic activity of NiS/CdS decreased in the order of NiS/CdS-400℃> NiS/CdS-70℃> NiS/CdS-200℃> NiS/CdS-500℃> NiS/CdS-300℃. The high photocatalytic activity of NiS/CdS when NiS was used as cocatalyst attributes to the heterogeneous juncture between NiS and CdS and the superior property of NiS.