The Construction And Optimization Of Z-scheme Catalyst CdS-RGO-BiVO₄ For Water Splitting

With the continuous progress and development of human society,energy shortages and environmental pollution have become a constraint.The development of sustainable,green clean energy is imminent.Photocatalytic technology is expected to be one of the most potential methods of solving these problems,attracting many researchers' attention.Z-scheme catalyst system,as the forefront of the photocatalyst system in nearly four decades of development,has advantages such as a wide range of visible light absorption,high catalyst activity.In this paper,the controllable synthesis of CdS is carried out,and then CdS-BiVO4Z-scheme catalysis is constructed and optimized with CdS as hydrogen-producing end based on the work done by our team.The influence s of photocatalytic reaction conditions on the catalytic performance of Z-scheme catalysts has also been studied.The controllable synthesis of five different morphology CdS was achieved.CdS with different morphologies(amorphous,spherical,nanoparticle,fishbone,nanorods)were synthesized by different methods(precipitation,hydrothermal method,solvent heat method)and characterized by XRD,SEM,FTIR,UV-vis,BET,PL.The characterization technique was used to analyze and illuminate the photocatalytic activity of hydrogen production.The results show that the crystal morphology?photoelectric-hole separation efficiency and specific surface area of CdS have a significant effect on the photocatalytic activity of hydrogen production.The photocatalytic hydrogen production of nanorods CdS was the best among the five different morphologies CdS,reaching 16 150 ?mol/g·h.The CdS-RGO-BiVO4Z-scheme catalysts with high catalytic activity were constructed and optimized.The Z-sheme catalysts were prepared by precipitation method,hydrothermal method and evaporation & photoreduction and characterized by XRD,SEM,FTIR,UV-vis,BET and PL.The photocatalytic activity and stability were investigated,too.The results show that the Z-scheme catalyst prepared by the precipitation method has the lowest activity because the CdS prepared by this method is the cubic phase which has low hydrogen production activity.The activity of Z-scheme catalysts prepared by hydrothermal method is low because the CdS prepared by this method is a hexagonal phase with high hydrogen production activity,but its CdS can not form good morphology.The activity of Z-scheme catalysts prepared by evaporation & photoreduction is the highest,because the CdS in the Z-scheme produced by this method is the cubic phase with high hydrogen production activity and the regular nanorods ensured its hydrogen production activity,which has a hydrogen production activity of 24 065 ?mol/g·h.The results show that hydrogen production activity of the loading GO to CdS at first was higher than loading GO to Bi VO4 at first.When the content of CdS nanorods was 80%,the a ctivity of Z-scheme catalyst was 74.5% higher than that of pure CdS,reaching 28 185 ?mol/g·h.The hydrogen production activity of CdS decreased by 41% and the hydrogen production activity of Z-scheme catalyst decreased by 23% after 15 h,which indicated that the catalyst could realize the Z-scheme cycle of photo-generated carriers and the Z-scheme system could effectively inhibit CdS light corrosion.The effect of reaction conditions on the photocatalytic activity of optimal Z-scheme catalyst was studied,and solar simulation experiment was carried out.The influences of sacrificial agent,the type of hydrogen evolution promoter,the amount of hydrogen evolution catalyst,p H and temperature on the hydrogen production activity of Z-scheme catalyst were investigated.The experimental results show that when the lactic acid is used as the sacrificial agent,0.4 wt% Pt is used as the hydrogen evolution promoter,the p H is 2.5,the photocatalytic activity can reach 29 580 ?mol/g·h.Z-scheme catalyst has a good hydrogen production activity with sun as the light resource,too.