Inhibited photocorrosion and improved photocatalytic H2-evolution activity of CdS photocatalyst by molybdate ions

Abstract For CdS photocatalyst as one of the photocatalytic H2-evolution materials, both photocatalytic performance and stability are the main challenge owing to the recombination of photogenerated charge pairs and serious photocorrosion. In this paper, molybdate ions were injected into the CdS suspension in lactic acid solution as sacrificial agent during photocatalytic H2-evolution process (the resultant sample was denoted as CdS(M)). The results indicated that the color of CdS(M) suspension was lighter than that of original CdS suspension after the illumination, namely, molybdate ions can reduce the oxidation of S2− to S0 from the CdS lattice and effectively suppress the photocorrosion of CdS. Simultaneously, the photocatalytic H2-evolution performance of CdS(M) was obviously increased. When the concentration of Na2MoO4 was 22 μmol L−1, the H2-evolution rate of CdS(M-22) reached the highest value (42.49 μmol h−1), which was 2.51 times as high as that of the CdS sample (16.90 μmol h−1). The mechanism of improved photostability and photocatalytic activity of CdS by the injection of molybdate ions is that the molybdate ions can quickly capture H+ ions in solution to form Calvin-cycle-like pathway for interfacial catalysis reactions and promote the ionization of lactic acid to inhibit the oxidation of S2− to S0 on the CdS surface by trapping the photogenerated holes for the stability of CdS. This work may provide a valuable strategy how the photocorrosion of CdS can be overcome with the enhanced photocatalytic H2-evolution performance.