Construction Of Antimony Compounds/g-C₃N₄ Heterojunction And Study Of Photocatalytic Performance

H₂ has attracted wide attention as clean energy source with high energy density.It is the focus of current research to develop a green way to produce hydrogen.Different from the traditional hydrogen production processes with high energy consumption and high pollution,photocatalytic hydrogen production can be carried out under mild conditions and without secondary pollution.It can directly convert solar energy into hydrogen energy,which is a green hydrogen production technology with great development prospect.Photocatalytic technology can also decompose harmful pollutants into H₂O and CO₂.The key of photocatalytic technology is to develop efficient and stable photocatalyst.g-C₃N₄ is a kind of nonmetal visible light catalyst which is non-toxic,harmless and easy to prepare and has a suitable energy band structure.It can be used in photocatalytic decomposition of water to produce hydrogen and degradation of pollutants.However,its absorption capacity to visible light is still weak,and the recombination rate of photogenerated carriers is fast,so its photocatalytic activity is limited.Studies have shown that the photocatalytic activity can be enhanced by the construction of semiconductor heterojunction,which can reduce the carrier recombination rate and increasing the separation rate of high electrons and holes.So that the photocatalytic activity is enhanced.In this dissertation,g-C₃N₄ was combined with Sb₂MoO₆and Sb VO₄ to construct heterojunctions respectively,which were applied in photocatalytic hydrogen production and organic pollutant degradation.The main research contents are as follows:（1）Firstly,bulk g-C₃N₄ was prepared by calcination of melamine at high temperature of 550 ℃.Sb₂MoO₆ was prepared by solvothermal method.Then Sb₂MoO₆/g-C₃N₄heterojunction photocatalyst was constructed by simple mechanical stirring method.The Sb₂MoO₆/g-C₃N₄ heterojunction has good activity of Rh B degradation and hydrogen production.The rate of Rh B degradation and hydrogen production is significantly higher than that of the two monomers.When the Sb₂MoO₆ loading content was 7.5%,94%Rh B could be degraded in 40 min with a degradation rate constant of 0.0688 min^-1 under visible light,which was 6.6 and 31.3 times higer than that of g-C₃N₄(0.0104 min^-1)and Sb₂MoO₆(0.0022 min^-1),respectively.The optical hydrogen production rate is 908μmol·h^-1·g^-1,which is 3.9 times and 5.4 times higer than that of Sb₂MoO₆(229μmol·h^-1·g^-1)and g-C₃N₄(168μmol·h^-1·g^-1),respectively.The analysis of the optical properties,photoelectric properties and reactive substances of the composites shows that there are two main reasons for the enhancement of photocatalytic activity of the composites:One is the visible light absorption capacity of the composite is enhanced.In addition,S-scheme heterojunction is formed between them.Under the action of internal electric field,band bending and electrostatic attraction,electrons in Sb₂MoO₆ are easily to reunited with the holes on g-C₃N₄,retaining the electrons on g-C₃N₄ and the holes on Sb₂MoO₆ and its strong oxidation and reduction ability.（2）g-C₃N₄ nanosheets were prepared by ultrasonic dispersion of bulk g-C₃N₄.Sb VO₄nanoparticles were synthesized by solvothermal method and ultrasonic dispersion method.Then 0D/2D Sb VO₄/g-C₃N₄ heterojunction was constructed by simple mechanical stirring method.The experimental results show that the heterojunction can be used for Rh B,MB and ceftriaxone sodium degradation,and can also be used for photocatalytic hydrogen production.When the Sb VO₄ loading was 10%content,the degradation rates of Rh B,MB and ceftriaxone sodium by Sb VO₄/g-C₃N₄ under visible light were 0.0587 min^-1,0.0371min^-1 and 0.0159 min^-1 respectively,which are 5.4,2.3 and 4.3 times higher than that of the degradation rates of g-C₃N₄ monomer.The optimum hydrogen production rate is 752μmol·h^-1·g^-1,which is 8.7 and 4.1 times respectively of the monomer Sb VO₄(86μmol·h^-1·g^-1)and g-C₃N₄(182μmol·h^-1·g^-1).After 12 h of cycling test,10%Sb VO₄/g-C₃N₄materials still have good H₂ production activity.After the introduction of Sb VO₄,the visible light absorption of the composites is significantly enhanced and an efficient S-scheme heterojunction is formed between Sb VO₄ and g-C₃N₄.Under the action of internal electric field,band bending and electrostatic force,the electrons located in the Sb VO₄ conduction band recombine with holes on the valence band of g-C₃N₄.Leaving the strong oxidation and reduction ability of the electrons on g-C₃N₄ and the holes on the Sb VO₄,and thus the photocatalytic activity is enhanced.