Preparation And Hydrogen Evolution Properties Of Conductive MOF And Organic Polymeric Photocatalyst Composites

As a clean energy,hydrogen energy has many advantages such as high energy density,abundant reserves,green and pollution-free and so on.Therefore,it is an ideal new energy alternative to fossil fuels.The photocatalytic technology for hydrogen production is an ideal way to convert solar into new energy.The key of it is on the development of efficient photocatalysts.Organic photocatalysts,which boast abundant species,freely adjustable molecular structure,excellent visible-light response as well as easy to preparation,have been attracting the attention of many researchers.However,the disadvantages of organic photocatalysts,such as low separation efficiency of photogenerated carriers,easy recombination,and poor active electron transport,limit their catalytic activity.To solve the above problems,the conductive 2D metal-organic framework（Metal Organic Framework,MOF）is compounded with an organic polymeric photocatalyst in this paper.The transfer rate of active electrons in the organic photocatalyst can be improved owing to the excellent charge transfer properties of the MOF material,thus greatly enhancing the activity of photocatalytic hydrogen evolution.The two main aspects of this research are as follows:First,the classical organic photocatalyst g-C₃N₄ was compounded with the conductive MOF Ni-CAT-1.The layered structure of g-C₃N₄ was prepared by high-temperature calcination,and the Ni-CAT-1/g-C₃N₄ composites with different ratios were synthesized in situ.The successful synthesis of Ni-CAT-1/g-C₃N₄ composites was confirmed by X-ray powder diffraction（PXRD）,Fourier transform infrared spectroscopy（FT-IR）,and X-ray photoelectron spectroscopy（XPS）.The images of scanning electron microscopy（SEM）and transmission electron microscopy（TEM）showed that needle-like Ni-CAT-1 grew on the surface of g-C₃N₄ substrate and dispersed uniformly.The positions of band gap,conduction band and valence band of Ni-CAT-1/g-C₃N₄ composites were obtained by the UV-visible diffuse reflectance spectroscopy（DRS）and flat band potential tests,which demonstrated that the catalysts meet the thermodynamic requirements for the photocatalytic water splitting.The photoelectrochemical characterization confirmed that the introduction of Ni-CAT-1can effectively reduce the recombination time of photogenerated electrons and holes.The results of photocatalytic activity test showed that（11%）Ni-CAT-1/g-C₃N₄composites have a high yield of hydrogen with 2.76 mmol·h^-1·g^-1,which is 3.5 times higher than the activity of pure g-C₃N₄(0.77 mmol·h^-1·g^-1).The mechanism of photocatalytic hydrogen production was further put forward.The photocatalytic hydrogen production mechanism was further explored by clarifying the electron transfer of the catalyst:the excited electrons were transferred from g-C₃N₄ to Ni-CAT-1 to participate in the reduction reaction to generate hydrogen.Second,porous crystalline triazine framework（Covalent Triazine Framework,CTF）compounding with conductive MOF were prepared to achieve further improvement of hydrogen evolution performance in visible light.The Ni-CAT-1/CTF composites with different ratios were synthesized in situ.The successful preparation of Ni-CAT-1/CTF composites was confirmed by X-ray powder diffraction（PXRD）,Fourier transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）.The composites were thermodynamically determined by photoelectrochemical characterization to meet the requirements for photocatalytic hydrogen production.The results of photocatalytic activity test showed that the hydrogen yield of（5%）Ni-CAT-1/CTF was 8.029 mmol·h^-1·g^-1,which was four times higher than that of pure CTF(1.958 mmol·h^-1·g^-1).By analyzing,it was confirmed that the introduction of Ni-CAT-1 could effectively promote the separation and transportation of photogenerated electrons and holes in CTF,thus greatly improving its photocatalytic activity.