Preparation And Photocatalytic Hydrogen Evolution Performance Of Polyoxometalates/Semiconductor Composite Photocatalysts

TiO₂and CdS, as excellent semiconductor materials,have a wide range of applications inphotocatalytic water splitting.However,limited by a high electron hole recombination rate,issues regarding to the low quantum efficiency of single TiO₂and CdS cannot be ignored.Polyoxometalates （POMs） can act as a widely used electron acceptor to capturephotogenerated electrons and enhance the photocatalytic hydrogen production.In this work, K₈Nb₆O₁₉·16H₂O was successfully doped into CdS by using one-steppreparation method.NiS nanoparticles has been performed to replace the noble metals to actas co-catalyst. A aqueous solution containing Na₂SO₃and Na₂S plays the role of sacrificialreagents.Moreover, a300W Xe lamp equipped with a cutoff filter （≥400nm） was used as thelighted source. The reaction cell was connected to a closed gas circulation system and theamount of H₂was analyzed by a gas chromatograph.As a result, NiS-K₈Nb₆O₁₉-CdS catalystwas more active than than K₈Nb₆O₁₉-CdS. Comparing with the lactic acid solution, thehydrogen production of mixed solution of Na₂S and Na₂SO₃is better.Considering that Nb and Ta belong to the same main group, there are a lot of similaritiesin the nature. Researching the hydrogen production performance of K₈Ta₆O₁₉·17H₂O and CdScomposite catalyst. By analyzing the experimental results, we find the hydrogen productionrate of NiS-K₈Ta₆O₁₉-CdS is higher than that of NiS-CdS. Therefore, K₈Ta₆O₁₉couldpromote the photocatalytic hydrogen production reaction.We also prepare K₈Nb₆O₁₉-TiO₂catalyst. Pt acts at co-catalyst, methanol solutions act asthe sacrificial reagents.Under the UV irradiation, we found the K₈Nb₆O₁₉can improve thehydrogen production activity of TiO₂.These results suggest that the polyoxometalate could impove the activity of CdS andTiO₂by effectively retarding electron hole recombination. The results also show that thecombination of semiconductors with the appropriate POMs is a promising strategy forimproving photoelectrochemical performance of semiconductors.