Construction Of Transition Metal Phosphide/carbon Nitride System And Performance Study On Photocatalytic Hydrogen Production

The rapid development of global economy has caused serious energy and environmental crisis.It is an effective solution to make good use of solar energy for photocatalytic hydrogen production.The development of efficient,stable and green visible-light-driven photocatalytic material is the key point in the industrialization of photocatalytic hydrogen production.As a kind of nonmetallic photocatalyst,graphite phase nitride(g-C₃N₄),has become one of the research hotspots in the photocatalytic field due to the suitable band gap and stable physical and chemical properties.However,since the rapid recombination of photocarriers result in low photocatalytic activity,the practical application was hampered.The construction of g-C₃N₄-based semiconductor materials can improve the absorption performance of visible light and inhibit the recombination of photogenerated carriers effectively.Although Pt and other noble metals can greatly promote the activity of photocatalytic H₂ production when combined with g-C₃N₄,the high price limits the practical application.In recent years,transition metal phosphides(TMPs)have been confirmed as a kind of non-precious metal catalytic materials with strong catalytic activity,which had become one of the focuses of photocatalysis research.In this paper,four highly effective visible light catalytic systems of TMPs/g-C₃N₄ were constructed by one-step in-situ solvothermal method with red phosphorus as the phosphorus source,in order to study their photocatalytic performance and enhancement mechanism.The specific research contents are as follows:(1)Firstly,nano-layered g-C₃N₄ was prepared from urea by high-temperature thermal condensation and ultrasonic stripping.Using red phosphorus as P source,Cu SO₄·5H₂O and Ni Cl₂·6H₂O as Cu and Ni source,respectively,four TMPs/g-C₃N₄ heterojunctions of Cu₃P/g-C₃N₄,Ni₂P/g-C₃N₄,Cu₃P-Ni₂P/g-C₃N₄,Ni₁₂P₅/g-C₃N₄ were contructed by one-step in-situ solvothermal method for photocatalytic hydrogen production.(2)Take ethanol as solvent,the p-type semiconductor Cu₃P and n-type semiconductor g-C₃N₄ were combined to form nanometer Cu₃P/g-C₃N₄ p-n heterojunction.Cu₃P,as a narrow band gap semiconductor,improves the visible light utilization of the system.At the same time,the built-in electric field between p-n junction facilitates the separation of carriers thus enhancing the efficiency of hydrogen production.(3)Ni₂P was supported on the surface of g-C₃N₄ using deionized water as solvent.The study shows that the introduction of Ni₂P increased active sites for hydrogen production and reduced the hydrogen evolution overpotential.In particular,the in-situ loading of Ni₂P formed close interface contact with g-C₃N₄,which greatly promotes the transfer of photogenerated electron-holes.(4)Cu₃P-Ni₂P/g-C₃N₄ ternary heterojunction photocatalyst was synthesized using ethanol as solvent.The study found that when Cu²⁺presented in the reacted solution,Cu₃P-Ni₂P can be synthesized simultaneously,while no Ni₂P can be obtained without Cu²⁺in the system,indicating that the presence of Cu²⁺is conducive to the formation of Ni₂P.On the one hand,Cu₃P,as a p-type semiconductor,formed p-n type nano-heterojunction with g-C₃N₄,which promotes the separation of photogenerated carriers.On the other hand,Ni₂P provides more active sites for the reaction and its metal-like properties can easily capture eletrons so that enhance the ability of carriers separation.The synergistic effect between Cu₃P-Ni₂P and g-C₃N₄ enables the ternary system have efficiently activity of hydrogen production.(5)Ni₁₂P₅/g-C₃N₄ photocatalyst was preapared by simple and easy solvothermal method using water as solvent.By avoiding the harsh preparation conditions such as toxic raw materials,corrosion by high temperature and harmful gas emission,Ni₁₂P₅/g-C₃N₄ can be obtained with close interface contact under mild conditions by taking red phosphorus as P source.As an electron capture agent,Ni₁₂P₅ improved the photocatalytic hydrogen production efficiency of g-C₃N₄ significantly by inhibiting charge recombination and increasing the active sites on the surface of g-C₃N₄.