Synthesis And Photocatalytic Performance Of Black TiO₂

Since the novel visible light photocatalyst black titanium dioxide（black TiO₂）was successfully synthesized in 2011,it has been widely applied in energy sources such as visible light photocatalytic water splitting into hydrogen,photocatalytic CO₂ reduction and visible light photocatalytic degradation of organic pollutants and sterilization because it has excellent light utilization,low electron-hole recombination rate,outstanding chemical stability,special crystal structure and electronic structure.In many methods of modifying TiO₂ nanomaterials,converting ordinary TiO₂ into black TiO₂ is the most direct,simple and efficient method to improve the visible light utilization efficiency and visible light photocatalytic activity of TiO₂.Although the black TiO₂ can be successfully synthesized by the hydrogenation method,the reduction methods,or the oxidation methods and its visible light photocatalytic activity also has been improved significantly.However,these methods have many disadvantages,such as high cost,high risk,and unsuitable for mass production.Therefore,it is very important to seek a simple,low-cost method for the preparation of black TiO₂.In this thesis,we mainly explored several new methods for preparing black titanium dioxide and also studied its formation mechanism and visible light photocatalytic activity in detail by different characterization techniques.This thesis introduces a method for successfully obtaining black TiO₂ nanoparticles.The procedure combines the ultraviolet light irradiation and low-temperature annealing（300℃）with continuous N₂ flow under atmospheric pressure.The prepared black TiO₂ nanoparticles have a uniform morphology and particle size as well as excellent visible light responsiveness.The characterization of structural and theoretical calculations show that the black TiO₂nanoparticles are able to absorb a high amount of photon energy in the visible light region can be attributed to H-doped TiO₂.The hydrogen atoms doped into the crystals can cause a local or intermediate state in a band gap of about 1.1 eV below the conduction band,thereby the band gap is narrowed.In addition,according to the test results of visible light photocatalytic degradation of RhB,the photocatalytic degradation activity of black TiO₂nanoparticles is greatly improved,comparing with TiO₂ nanoparticles.The oxygen vacancies were successfully introduced into the black TiO₂ nanoparticle crystals by low temperature annealing.The preparation method of the black TiO₂nanoparticles is more simpler,efficient and environmentally friendly.Using XRD,Raman and EPR structural characterization techniques,it was confirmed that oxygen vacancies were successfully introduced into TiO₂ nanoparticle crystals.Combined with XPS spectroscopy and UV-Vis absorption spectroscopy,it can be concluded that the introduced oxygen vacancies can change the crystal structure and electronic structure of black TiO₂nanoparticles,thus broadening the response of light to visible light.At the same time,oxygen vacancies can greatly reduce the recombination rate of electrons-holes.The photocatalytic degradation of RhB and MB organic dyes showed that the visible light photocatalytic activity of the black TiO₂ nanoparticles was also improved.A solvent quenching method was developed to modify the surface of TiO₂ nanocrystals.The black TiO₂ nanocrystals were successfully obtained by heating the ordinary TiO₂nanocrystals to 700℃and immediately immersing the high temperature TiO₂ nanocrystals in ethanol.We confirmed that after solvent quenching,the oxygen vacancies and-OH groups were introduced into the surface of black TiO₂ nanocrystals,and the surface oxygen vacancies played a key role in enhancing visible light absorption and visible light-driven water splitting into hydrogen.The visible light catalyzed hydrogen production rate of black TiO₂ nanocrystals is 180.5μmol g^-1·h^-1,and the photocatalytic hydrogen production rate is as high as 360μmol g^-1·h^-11 under simulated sunlight.