The Design,Preparation And Hydrogen Production Performance Of CdS-Based Composite Semiconductor Photocatalysts

Photocatalytic hydrogen production from water splitting is one of the ideal ways to solve the problems of energy crisis and environmental pollution and the key is to design and synthesize efficient,stable and low-cost photocatalysts.At present,many semiconductor materials have been investigated and developed for photocatalytic hydrogen production.Among them,cadmium sulfide(CdS)has attracted extensive attention for photocatalytic H2 production due to its narrow bandgap(2.4 eV),suitable energy band position,strong visible light absorption,and tunable morphology.However,CdS has disadvantages such as high photoelectron-hole pair recombination rate,serious photo-corrosion,which seriously affect the photocatalytic hydrogen production performance and stability.Consequently,in this work,on the one hand,SiO2 nanospheres were used as templates to construct spherical structures,and CdS quantum dots(QDs)were combined with g-C3N4 to form heterojunction composites to improve the hydrogen production performance of photocatalysts;On the other hand,an appropriate amount of Co was doped into CdS nanorods,combined with morphology regulation to prepare photocatalysts with excellent hydrogen production performance,and the photocatalytic mechanism was studied in depth combined with theoretical calculation.The main research contents are as follows:(1)A new composite photocatalyst of SiO2@C3N4-CdS QDs was designed and synthesized.Under simulated solar irradiation,the H2 production rate of the photocatalyst is 225.1 μmmol/g/h,which is about 80 times that of pure g-C3N4 and 2.1 times that of CdS.In this system,the g-C3N4 thin film was uniformly and compactly coated on the surface of the nanosphere with SiO2 as supporting template,which shortened the distance from the electron to the surface and shorten the migration time of photogenerated carriers and reduce the recombination probability.Furthermore,the heterojunction formed by g-C3N4 and CdS QDs has a narrower band gap,and can recover the scattered light near field of SiO2 nanospheres,which significantly enhances the light-trapping ability and generate more photogenerated carriers.A series of tests showed that the synergistic effect of SiO2,g-C3N4 and CdS QDs plays a key role in significantly improving the hydrogen production performance of nanocomposite photocatalysts.(2)The Co-doped CdS faceted prismatic nanorod photocatalysts were designed and synthesized by a one-step solvothermal method.The Cd0.9Co0.1S NRs with a large aspect ratio and good polycrystalline plane structure can significantly shorten the radial transfer path of charge and achieve rapid separation.An appropriate amount of Co doping can narrow the band gap of photocatalysts and enhance its light absorption ability significantly.Furthermore,the generation of the photothermal effect and the formation of the internal electric field further enhances the surface reaction kinetics on the catalyst surface,accelerate the separation and migration of photogenerated carriers,so as to effectively inhibit their recombination.As a result,the optimized Cd0.9Co0.1S NRs yield a remarkable H2 evolution rate of 8.01 mmol/g/h,which is about 7.2 times higher than pure CdS.In this work,the internal electric field formed and the photothermal synergistic effect by element doping,which significantly enhances the hydrogen evolution performance and stability of the photocatalyst.