Construction Of Cd_0.5Zn_0.5S-based Composite Photocatalyst And Its Full-spectrum Hydrogen Production Performance And Mechanism

As a clean energy with high combustion calorific value and low pollution,hydrogen has great potential in today’s energy revolution.Photocatalytic hydrogen production technology is one of the most popular hydrogen production technologies.Nowadays,a large number of semiconductors such as Ti O₂^[1],Zn O^[2]and other metal oxides,Cd S^[3],Zn In₂S₄^[4]and other transition metal sulfides,g-C₃N₄^[5]and other polymers are widely used in optical Catalytic hydrogen production.Among them,the transition metal sulfide Cd_0.5Zn_0.5S is highly valued due to its tunable energy band structure and superior hydrogen production activity,but it still has the disadvantages of low utilization of sunlight and high recombination rate of photogenerated electrons and holes.At the same time,most semiconductors can only use visible light,and near-infrared light is wasted in large quantities,which greatly limits the further improvement of photocatalytic hydrogen production efficiency.Therefore,it is of great significance to develop full-spectrum driven photocatalysts with near-infrared light absorption properties.In this paper,Cd_0.5Zn_0.5S is selected as the main catalyst.From the perspective of expanding the light absorption range and improving the separation rate of photogenerated electrons and holes,three different types of near-infrared light absorption materials are selected to construct heterojunctions with Cd_0.5Zn_0.5S.And the full-spectrum photocatalytic hydrogen production performance and mechanism of the composite system are explored,mainly including the following three works:（1）The Na_xMo O₃ nanorods with localized plasmon resonance effect（LSPR）induced by oxygen vacancies are composited with Cd_0.5Zn_0.5S nanoparticles to construct a Z-type heterojunction,and the full spectrum hydrogen production properties and mechanisms of Na_xMo O₃/Cd_0.5Zn_0.5S composite photocatalyst are studied.Under full-spectrum illumination,the hydrogen production rate of 5wt%Na_xMo O₃/Cd_0.5Zn_0.5S reaches 6.033 mmol g^-1 h^-1,which is 4.08 times higher than that of pure Cd_0.5Zn_0.5S.Through the study of the mechanism,it can be seen that due to the LSPR effect of Na_xMo O₃ and the Z-type heterojunction composed of Na_xMo O₃ and Cd_0.5Zn_0.5S,the light utilization rate of the composite photocatalyst is improved,and the recombination of photogenerated electrons and holes is effectively suppressed.The synergistic effect of the full-spectrum photocatalytic hydrogen production was realized.（2）A new type of narrow bandgap material,RPCN（C/K co-doped red polymeric carbon nitride）nanosheets has the ability to absorb near-infrared light due to the narrowing of the band gap caused by atomic doping.In this chapter,this novel RPCN was composited with spherical Cd_0.5Zn_0.5S for the first time,and the full-spectrum hydrogen production performance and mechanism of the RPCN/Cd_0.5Zn_0.5S composite photocatalyst are investigated.Under full-spectrum illumination,the hydrogen production rate of 15wt%RPCN/Cd_0.5Zn_0.5S is as high as 34.8 mmol g^-1 h^-1,which is 8times higher than that of pure Cd_0.5Zn_0.5S.DRS showes that the composite system exhibited excellent full-spectrum absorption properties under the action of RPCN.After a series of analyses,the RPCN/Cd_0.5Zn_0.5S has excellent carrier separation rate and charge transfer rate,which enables efficient hydrogen production.According to the mechanism analysis and band gap calculation,the improvement of the visible light hydrogen production efficiency of the RPCN/Cd_0.5Zn_0.5S composite photocatalyst mainly relies on the effective separation of photogenerated electrons and holes in the type II heterojunction.In the near-infrared band,the hydrogen production activity of RPCN/Cd_0.5Zn_0.5S mainly relies on the strong near-infrared light trapping caused by the narrow band gap material RPCN,Which enables the RPCN/Cd_0.5Zn_0.5S composite photocatalyst to achieve efficient hydrogen production under the full spectrum.（3）The metalloid material Ti₃C₂ has excellent LSPR effect.In this chapter,Ti₃C₂/Cd_0.5Zn_0.5S composite photocatalyst was successfully prepared,and its full-spectrum hydrogen production performance and mechanism were studied.Under full spectrum irradiation,the hydrogen production rate of 5wt%Ti₃C₂/Cd_0.5Zn_0.5S reaches 23mmol g^-1 h^-1,which is 6 times higher than that of pure Cd_0.5Zn_0.5S.The hydrogen production rate in the near-infrared region is as high as 61μmol g^-1 h^-1.The DRS and electrochemical tests show that due to the effective loading of metalloid Ti₃C₂ with near-infrared light absorption ability,the composite photocatalyst exhibits excellent photogenerated carrier separation rate and strong light absorption characteristics,making Ti₃C₂/Cd_0.5Zn_0.5S successfully achieved high-efficiency hydrogen production under the full spectrum.Under near-infrared light,the LSPR of Ti₃C₂ will generate hot electrons and simultaneously migrate to the conduction band of Cd_0.5Zn_0.5S for hydrogen production.