Design Of Defected TiO₂ Nanomaterials With Photocatalytic Performance Of Ammonia Synthesis

In recent years,the problem of energy shortage is becoming more and more serious,and photocatalytic technology is one of the most potential green means to solve this problem.The photocatalyst is the core of photocatalytic technology,and the research of high-efficient photocatalyst plays a key role on the development of photocatalytic technology.Among many photocatalytic materials,TiO₂ is one of the most promising photocatalysts with the characteristics of non-toxic and harmless,low price and good photochemical tolerance.However,the wide bandgap of TiO₂（3.2 e V for anatase and 3.0 e V for rutile,respectively）and the high carrier recombination probability seriously have hindered its application in the field of photocatalysis.The energy band structure,hydrophilicity and carrier transport properties of TiO₂nanomaterials have been regulated from the introduction of defects and metal element doping.The above two problems can be solved to some extent.The specific research contents include the following two aspects:1.Construction of Surface-hydrophobic Defective TiO₂ Nanomaterials:Firstly,the TiO₂ nanoparticles were prepared by sol-gel method,then TiO₂ oxygen defect layer was formed on the TiO₂ surface by Na BH₄ reduction,and the defective TiO₂（Vo-TiO₂）was obtained.（Vo-TiO₂）.Secondly,the as-prepared Vo-TiO₂ was fluorinated by hydrothermal method to obtain surface hydrophobic defective TiO₂ nanomaterials（F-Vo-TiO₂）.The experimental results show that the photocatalytic performance of the F-Vo-TiO₂ photocatalyst is obviously higher than that of pure TiO₂ without using noble metal cocatalyst.Further in-depth systematic research on the photocatalytic mechanism,this significantly enhanced photocatalytic activity is attributed to the strong hydrophobic and gas-friendly properties of F-Vo-TiO₂ photocatalysts.This work demonstrates that the photocatalytic nitrogen fixation synthesis ammonia performance can be significantly improved by adjusting the hydrophobicity of the photocatalysts.2.Construction of Cu-doped defect TiO₂ and Cu₂S heterojunction:Firstly,the Cu doped TiO₂（Cu:TiO₂）nanoparticles were prepared by sol-gel method and then reduced Cu:TiO₂ nanoparticles by Na BH₄.The metal Cu nanoparticles and oxygen defect layers（R-Cu:TiO₂）were formed on the TiO₂ surface.Secondly,the as-prepared R-Cu:TiO₂ were sulfurated with the surface metal Cu nanoparticles to convert into Cu₂S,to form a doped defect type TiO₂-Cu₂S heterojunction（S-R-Cu:TiO₂）.The experimental results indicate that photocatalytic nitrogen fixation efficiency of ammonia synthesis for S-R-Cu:TiO₂ is 8 times higher than that of pure TiO₂ without the use of noble metal cocatalyst.Further,the in-depth research of photocatalytic mechanism shows that this significantly enhanced photocatalytic activity is attributed to the synergistic effect of multicomponent system.S-R-Cu:TiO₂ can promote the charge separation efficiency and expand the light absorption range.This work demonstrates that the preparation of multicomponent photocatalysts system will significantly improve the photocatalytic nitrogen fixation synthesis ammonia performance.In this paper,we design and construct two high-performance synthetic ammonia photocatalysts,surface-hydrophobic defective TiO₂ nanomaterials and Cu-doped defective TiO₂ and Cu₂S heterojunctions,respectively.These studies indicate that the photocatalytic activity of ammonia synthesis without using noble metals as assistant catalysts can be greatly improved,which will surely lay the foundation for future research on low-cost and high-performance ammonia synthesis catalysts.We believe that in the near future,more photocatalysts with excellent performance of novel,cheap and high performance synthetic ammonia will be developed.