Preparation Of TiO₂-based Nanocomposites And Study Of Their Photocatalytic Properties

Photocatalysis is one of the most effective ways of solving the problems of energy shortage and environmental pollution.As an environmentally friendly semiconductor photocatalyst,TiO₂has a very strong ability to adsorb and degrade most organic compounds and is also photostable and chemically resistant,but it still has the disadvantages of only absorbing UV light（due to its energy band structure Eg=3.2 e V）,being difficult to use visible light to drive photocatalysis,and being prone to compounding of photogenerated electron holes.Therefore,this thesis modifies TiO₂with non-metallic and metallic elements doping to reduce the forbidden band width of TiO₂,improve its photocatalytic efficiency,expand the spectral absorption range and achieve visible light degradation of organic pollutants.The main research contents and results of the project are as follows:（1）The effect of doping with different levels of N on the physicochemical properties and photocatalytic performance of TiO₂was investigated using a sol-solvothermal method.The XRD and Raman characterisation results show that the crystalline form of the prepared TiO₂is anatase at the N doping concentration chosen in this paper.SEM and BET results show that the TiO₂particles have a spherical mesoporous structure and that the specific surface area increases with the addition of N.EDS results show that N is successfully doped into the TiO₂material.XPS and ESR results show that N-TiO₂contains more OVs,·O₂^-and·OH than pure TiO₂,which can effectively increase the efficiency of photocatalytic reactions.The FTIR spectrum detected the characteristic peaks of N-H stretching vibrations,again verifying that N has been successfully doped into TiO₂.The UV-Vis DRS test results illustrate that the absorption edge of N-TiO₂is red-shifted and the band gap energy is reduced to 3.17 e V,which helps to improve the efficiency of electron-hole pair separation and enhance the catalytic activity of the photocatalyst.The photocatalytic test showed that the visible light catalytic performance of doped N element TiO₂samples had varying degrees of change compared to pure TiO₂,with 3-N-TiO₂samples having the strongest photocatalytic performance.After 90 minutes of visible light degradation of methyl orange（MO）,the decolorization rate and mineralization rate reached 99.03%and 63.21%,respectively,which were about 40%and 28%higher than pure TiO₂.Finally,TG analysis and cycling experiments show that 3-N-TiO₂has good thermal and chemical stability.（2）TiO₂nanoparticles doped with Cu,Fe,Ag,Cr,Co and Zn elements were prepared by a sol-solvothermal method.The results of XRD and Raman tests revealed that the crystalline form of the metal doped samples were all anatase type.SEM and BET results show that the TiO₂particles have a spherical mesoporous structure.The doping of metallic elements increases the specific surface area of the photocatalyst,especially the addition of Ag elements can lead to a specific surface area of 116.8 m²/g,which is approximately twice that of pure TiO₂.The EDS results show that the metal elements are successfully doped on the TiO₂.The XPS and ESR results show that 1-Ag-TiO₂contains more OVs,·O₂^-and·OH,which is beneficial for improving the activity of the catalyst.UV-Vis DRS showed that the metal-doped samples showed enhanced light absorption in the visible wavelength band.The band gap energies of the individual metal-doped samples were calculated,with 1-Ag-TiO₂having the smallest band gap width（3.00 e V）.Photocatalytic experiments found that the catalytic performance of TiO₂doped with different metallic elements varied greatly,with 1-Ag-TiO₂showing the highest decolourisation rate,reaching 100%within 70 min,much higher than the 29.68%decolourisation rate of pure TiO₂at the same time,which reached 75.43%mineralisation within 90 min.The doping of Ag significantly enhances the photocatalytic activity of TiO₂.TG analysis and cycling experiments show that 1-Ag-TiO₂also has excellent thermal and chemical stability.