Preparation Of Red Phosphorus/black Phosphorene Composite Photocatalyst And Its Catalytic Performance

Hydrogen energy has been widely recognized as one of the ideal energy resources with the most potential to solve energy crisis and environmental issues.Among various approaches to hydrogen energy development,hydrogen production from water by photocatalytic water splitting is one of the most ideal and promising development methods that considers energy consumption,resources and the environment.Currently,the development of highly efficient and stable semiconductor photocatalysts with visible light response is the core of photocatalytic water splitting research.Phosphorus is a relatively abundant nonmetallic element in the earth’s crust,mainly composed of phosphate-based materials of red phosphorus and black phosphorus.With the advantages of wide range of light response and suitable band structure,phosphorus has gained much more attention in the exploration of highly efficient photocatalyst.This paper takes red phosphorus and black phosphenes as the research objects to study the problems such as the easy compound annihilation of red phosphorus photogenerated electron-hole and it’s low surface reaction efficiency,and the poor stability of black phosphorene and the fast recombination of photocarriers.In this study,various methods such as the combination of red phosphorus or black phosphorene with wide bandgap semiconductor Sr Ti O₃（3.2 e V）,supported heterojunction structure is adopted to promote the transfer and separation of photon-generated carrier,thereby improving the photocatalytic efficiency.The main work of the study could be summarized as follows:（1）The typeⅡheterojunction of RP/STO was constructed by the one-step hydrothermal method,and the RP/STO series samples were prepared by adjusting the molar ratio and hydrothermal temperature.By means of XRD,XPS and SEM,the physicochemical property of the composite photocatalyst was analyzed.In the full band and visible light（λ>420 nm）and under the condition of 0.25 M Na₂S and 0.35M Na₂SO₃ mixture as sacrifice reagent,RP_1.0/STO exhibited excellent photolysis performance of hydrogen aquatic products with hydrogen production rates of 217.11μmol·g^-1·h^-1 and 196.76μmol·g^-1·h^-1,which were 4.09 and 6.16 times higher than RP,respectively.Based on the results of RP_1.0/STO complex characterization and photocatalytic activity test,the possible reaction mechanism of RP/STO type II heterojunction was proposed from the perspective of energy band structure.Under visible light irradiation,the electrons generated in the conduction band of RP are excited to migrate to the conduction band of Sr Ti O₃,accumulate on the surface of Sr Ti O₃ and reduce H⁺to H₂.However,the photogenerated holes are transferred in the opposite direction,accumulate on the valence band of RP and consumed by the added sacrificial agent(S^2-/SO₃^2-),thus preventing the combination of e^-and h⁺.（2）To solve the problems of complex process,high cost and scale production in the preparation of black phosphorus nanosheets,this study explored the influence of reaction temperature and reaction time with low-cost and high-purity red phosphorus as raw material and ethylenediamine as the reaction solvent,and successfully prepared black phosphorus nanosheets by one-step hydrothermal method.The prepared black phosphorus nanosheets were proved to have high purity,large size and good crystallinity through a series of XRD,TEM and AFM tests.（3）To further solve the problem,such as the instability of black phosphorene and the fast recombination of photogenerated carriers,the typeⅡheterojunction of BRP/STO was constructed by hydrothermal method to further improve the photocatalytic hydrogen production capacity of the composite based on solvothermal one-step preparation of black phosphorus nanosheets.And the BRP/STO series samples were prepared by adjusting the molar ratio and hydrothermal temperature.By means of XRD,XPS and SEM,the physicochemical property of the composite photocatalyst was analyzed,and it is proved that black phosphorus nanosheets form a compact heterojunction with Sr Ti O₃ nanosheets.In the full band and visible light（λ>420 nm）and under the condition of 0.25 M Na₂S and 0.35 M Na₂SO₃ mixture as sacrifice reagent,BRP_0.5/STO showed the fastest hydrogen production rate of 300.91μmol·g^-1·h^-1 and 139.11μmol·g^-1·h^-1,which were 4.85 and 3.75 times higher than BRP,respectively.Based on the results of BRP_0.5/STO complex characterization and photocatalytic activity test,the possible reaction mechanism of BRP/STO type II heterojunction was proposed from the perspective of energy band structure.Under visible light irradiation,the electrons generated in the conduction band of BRP are excited to migrate to the conduction band of Sr Ti O₃,accumulate on the surface of Sr Ti O₃ and reduce H⁺to H₂.However,the photogenerated holes are transferred in the opposite direction,accumulate on the valence band of BRP and consumed by the added sacrificial agent(S^2-/SO₃^2-).The charge transfer path is consistent with a type II heterojunction.In this paper,red phosphorus and black phosphorene were used as research objects,and the red phosphorus/strontium titanate（RP/STO）type II heterojunction and black phosphorene/strontium titanate（BRP/STO）type II heterojunction were constructed by hydrothermal method separately,which significantly improved the efficiency of photogenerated electron-hole separation,solved the problems of easy composite annihilation and low surface reaction efficiency of red phosphorus photogenerated electron-hole pairs,and compensated the shortcomings of black phosphorene such as poor stability and improve the separation efficiency of photogenerated electron-hole.While broaden visible light response range of strontium titanate and improve the photocatalytic activity and stability.