Construction Of SnNb₂O₆ Composite Photocatalysts And Study On Their Visible-light Driven Photocatalytic Hydrogen Evolution Performance

Hydrogen energy is an ideal pollution-free and clean energy,which is expected to alleviate the increasingly severe environmental pollution and energy crisis,and is of great significance to the promotion of sustainable social development.The main sources of hydrogen energy are fossil fuel hydrogen production,biomass hydrogen production,electrocatalytic hydrogen production,and photocatalytic hydrogen production.Among them,photocatalytic hydrogen production is considered to be the most promising hydrogen production technology due to its advantages of low energy consumption,mild reaction conditions,and recyclability of catalysts.In particular,semiconductor photocatalysts play a vital role in the development of solar-hydrogen-production systems due to their excellent catalytic performance and wide light absorption range.As a typical niobate semiconductor material,tin niobate（SnNb₂O₆）has a unique crystal structure,narrow bandgap,proper valence band position,and excellent chemical stability,which is widely used in solar hydrogen production.However,due to the rapid photo-generated charge recombination and low charge utilization efficiency of SnNb₂O₆,its application in the field of photocatalysis is limited.To solve its shortcomings in the field of photocatalysis,improve its photocatalytic decomposition of aquatic H₂ efficiency.In this paper,SnNb₂O₆was combined with other semiconductor materials and non-noble metal Ni S to construct a composite photocatalytic system to expand the visible light assimilate range and improve the separation efficiency of photogenerated charge hole,thus enhance the photocatalytic performance of SnNb₂O₆.At the same time,a series of characterization and calculation methods were used to explore the optical properties,structural characteristics,photocatalytic activity,and the mechanism of photocatalytic decomposition of water for hydrogen production of the prepared SnNb₂O₆ composite photocatalyst.The main research contents of this paper are as follows:（1）The Covalent organic framework（COF）/SnNb₂O₆ heterojunction photocatalyst was prepared by the hydrothermal method.The morphology,chemical morphology,and optical absorption properties of the samples were investigated by XRD,TEM,SEM,HRTEM,XPS and FT-IR.The photocatalytic activity of Tp Pa-2-COF/SnNb₂O₆heterojunction photocatalyst was investigated by simulating the solar light decomposition of H₂.The results show that Tp Pa-2-COF/SnNb₂O₆heterojunction photocatalyst has better photocatalytic activity than Tp Pa-2-COF and SnNb₂O₆nanosheets.Among them,Tp Pa-2-COF/SnNb₂O₆ heterojunction photocatalyst with 10wt%Tp Pa-2-COF exhibited a photocatalytic activity of 7.66μmol·h^-1,which was 3.5and 5.8 times higher than Tp Pa-2-COF and SnNb₂O₆,respectively,and had good stability.The mechanism of Tp Pa-2-COF/SnNb₂O₆ heterostructure is studied,the results show that the carrier separation efficiency and photocatalytic activity of Tp Pa-2-COF/SnNb₂O₆ heterostructure are enhanced.（2）The SnNb₂O₆/NH₂-Ui O-66 heterojunction photocatalyst was prepared by in situ growth method.The XRD,SEM,TEM,HRTEM,DRS,and other detection and analysis methods are prescribed to explore the crystal structure,morphology,and light absorption properties of the prepared samples.The photocatalytic hydrogen evolution activity and stability of SnNb₂O₆/NH₂-Ui O-66 were investigated through the experiment of simulating sunlight to decompose aquatic H₂.The experimental results show that the SnNb₂O₆/NH₂-Ui O-66-5 complex has the highest H₂ evolution rate of41.85μmol·h^-1,which was 16.7 and 8.1 times higher than SnNb₂O₆ and NH₂-Ui O-66,respectively.The catalytic activity of the heterojunction is greatly improved compared with that of the monomer,and the heterojunction has good stability.The experimental results show that the introduction of NH₂-Ui O-66 into the photocatalyst can effectively improve the transfer and separation efficiency of photogenerated carriers,thus enhancing the photocatalytic activity.（3）The Ni S/SnNb₂O₆ composite photocatalyst was prepared by the hydrothermal method.The XRD,SEM,TEM,HRTEM,DRS,and other detection and analysis methods are used to investigate the crystal structure,morphology,and light absorption properties of Ni S,SnNb₂O_6,and Ni S/SnNb₂O₆ samples.The photocatalytic activity and stability of the samples were tested by simulating the experiment of decomposing aquatic H₂ by sunlight.The results show that the 3%-Ni S/SnNb₂O₆ composite photocatalyst has the highest photocatalytic activity,which is greatly improved compared to the catalytic activity of the monomer SnNb₂O₆.Cycling experiment results show that the photocatalyst has good stability.Through mechanism study,it is concluded that the non-noble metal Ni S as a promoter may accelerate the separation of photogenerated electron-hole pairs,and enhance the light absorption of SnNb₂O₆,thus enhancing the photocatalytic activity.