Design And Photocatalytic Properties Of Transition Metal Nitride Based Composite Materials For Hydrogen Production

With the acceleration of industrialization,the consumption of energy is increasing day by day,and fossil fuels still occupy a dominant position in China’s energy system,which brings serious environmental pollution and energy shortage problems.For this reason,based on the responsibility of promoting the construction of a community with a shared future for mankind and the internal requirements of achieving sustainable development,China has proposed the“double carbon”important decision of“carbon peaking”and“carbon neutrality”.The application of semiconductor based photocatalysis technology in energy and environment has very broad application prospects for achieving the“double carbon”goal.However,currently,the photocatalytic activity of a single semiconductor is constrained by the rapid recombination of photo generated charge carriers,and the catalytic activity is still difficult to meet actual production need.Therefore,the modification of existing photocatalysts and the development of new catalysts are the key to overcome this challenge.This article synthesized a series of transition metal nitrides（TMNs）（Ni₃N,W₂N,and Mo₂N）with metal like properties through high-temperature nitridation and mixed pyrolysis methods.TMNs were combined with traditional sulfur based photocatalysts(Cd_0.9Zn_0.1S,CdS,and ZnIn₂S₄)to construct a series of highly active photocatalytic systems.A detailed study was conducted on the photocatalytic hydrogen evolution activity of the designed composite catalyst,and the mechanism of enhancing the hydrogen evolution activity of TMNs as co-catalysts was elucidated,providing a research foundation for the application of TMNs in the field of photocatalysis.The detailed research content and conclusions of this article are as follows:（1）Mo₂N nanoparticles with excellent conductivity were synthesized by mixed pyrolysis method and self-assembled with ZnIn₂S₄ nanosheets prepared by hydrothermal method,successfully preparing Mo₂N/ZnIn₂S₄ composite catalyst.The photocatalytic hydrogen evolution activity of the catalyst was tested and it was found that under 420 nm LED illumination,the loading of Mo₂N can enhance the hydrogen evolution activity of ZnIn₂S₄.The composite catalyst with the optimal Mo₂N loading showed a hydrogen evolution rate of 117.81 mmol h^-1 g^-1,which was about 4.5 times that of pure ZnIn₂S₄(26.36 mmol h^-1 g^-1).It was found that Mo₂N not only enhanced the light absorption of the composite catalyst,but also promoted the separation and transfer of photo generated carriers,thereby inhibiting the recombination of electrons and holes and achieving a significant increase in photocatalytic hydrogen production activity.（2）Tungsten and molybdenum are chemical elements of the same group,and W₂N has better conductivity compared to Mo₂N.Therefore,we also synthesized W₂N nanoparticles using a mixed pyrolysis method.In addition,W₂N was loaded onto the surface of CdS/SiO₂ core-shell structure through self-assembly.The results of hydrogen evolution activity test showed that the composite catalyst with the optimal W₂N loading showed a high hydrogen evolution rate of 26.04 mmol h^-1 g^-1,which was 10 times higher than that of CdS/SiO₂(2.58 mmol h^-1 g^-1).And after loading W₂N,the light response of the composite can be extended to 550 nm.Through a series of characterization tests and analysis,it can be concluded that W₂N mainly enhanced the catalytic activity of CdS/SiO₂ from two aspects:firstly,expanding the light response range of the catalyst and enhancing light absorption;The second was the promotion of the separation and transfer of photo generated charge carriers,thereby inhibiting the recombination of photo generated electrons and holes,and improving the utilization rate of photo generated electrons.（3）To further broaden the photoresponse range and also to investigate the effect of photothermal effect of TMNs on the photocatalytic reaction.The 2D/1D Ni₃N/Cd_0.9Zn_0.1S heterostructures were prepared by compounding the high-temperature nitrided Ni₃N nanosheets with Cd_0.9Zn_0.1S nanorods.The results showed that the composite catalyst with the optimal Ni₃N ratio showed both H₂ production rate of 35.08mmol h^-1 g^-1 and benzaldehyde production rate of 16.44 mmol h^-1 g^-1 under visible light excitation,and still exhibited 0.18 mmol h^-1 g^-1 under light irradiation at 700 nm.The high H₂ production rate was also observed under 700 nm light irradiation.In addition,Ni₃N/Cd_0.9Zn_0.1S also showed excellent sterilization ability,with the inactivation rate of E.coli up to 99.7%after 2 h of light irradiation.The reason for this was that Ni₃N as a co-catalyst can act as an excellent light absorption“antenna”,electron acceptor and active site as well as a hot electron provider,which can effectively enhance light absorption,promote carrier separation,improve surface carrier utilization efficiency and realize NIR driving.In addition,Ni₃N had excellent photothermal effect,which can convert light energy into heat energy and help to optimize the reaction kinetics.