Preparation And Photocatalytic H₂ Evolution Performance Of Polyoxometalates/CdS Composite Photocatalysts

Cd S is a promising visible-light-driven photocatalyst due to its relatively narrow band gap(2.4 e V) as well as a more negative conduction band edge than the reduction potential of H2O/H2. But its catalytic activity is limited because of the recombination of photo-generated carriers on its surface and the phenomenon of corrosion. Previous studies have proved that co-catalysts loaded onto the surface of semiconductors can enhance its catalytic hydrogen production rate by accelerating free electron-hole pairs. POMs can capture electrons of CB, or can provide the active site for the reaction between photo-generated holes and sacrificial reagents.In this work, the Mo S2–graphene/Cd S composite photocatalyst was synthesized using a facile two-step hydrothermal process. The composite photocatalyst were evaluated under visible light irradiation(λ>400 nm) with lactic acid as a sacrificial reagent. The H2 evolution rate of M–G/Cd S(NP–NR) achieved the highest amount of 2.32 mmol/h. The H2 evolution rate is 12.4 times that of Cd S.Loading Na6 Si W11O39Co on the surface of Mo S2–graphene/Cd S composite photocatalyst was synthesized using a facile two-step hydrothermal process. When 1wt% Si W11 Co is loaded on M/G-Cd S, the H2 evolution rate is further increased to 1.70 mmol h-1, which is about 21.3 times that of pure Cd S and 2.7 times that of M/G-Cd S. Meanwhile, the affecting factors of the activity hydrogen production were explored, such as the sacrificial reagent concentration, the temperature and time of synthesis, the POMs contents.The results show that the POMs can greatly increase the photocatalytic activity of Cd S semiconductor catalyst.