Introduction Of Oxygen Vacancy And Single Atom On The Surface Of TiO₂ Hollow Microsphere For Efficient Photocatalytic Air Purification

The rapid development of economy has caused serious environmental pollution problems.Especially,although the concentrations of the pollutants in air such as volatile organic pollutants（VOCs）and NO are very low,they are diffusive in large scale,which makes it difficult to control.Recently,semiconductor photocatalysis has attracted much attention as it can oxidize hazardous pollutants under the irradiation of sunlight using air as oxidant.However,as the photoreactivity of Ti O₂,the most typical semiconductor photocatalyst,is not high enough for practical applications due to limited visible light response and quick recombination of photo-generated carriers.In this thesis,high photoactive Ti O₂ hollow microspheres（Ti O₂-HMSs）used for air purification were fabrication by introduction of surface oxyben vacancy（OV）and modification with single atom.The main contents of the study are as follows:Section I:Ti O₂-HMSs with Oxygen Vacancy.Hollow-structured Ti O₂ has attracted much attention owing to its low density,good light-reflecting ability,and excellent permeability.However,the wide bandgap（about 3.2?e V for anatase Ti O₂）and fast recombination of photo-generated carriers hamper its practical application.Herein,OV was introduced onto the surface of Ti O₂ hollow microspheres（Ti O₂-HMSs）by a facile method through calcination of the mixture of（Ti O₂-HMSs）precursor and urea.It was found that the visible photoreactivity of the optimized Ti O₂-HMSs with surface OV（OV/Ti O₂-HMSs）exhibited enhanced photoreactivity with NO removal efficiency of 53.0%,which is 1.94 and 2.12 times higher thant that of pristine Ti O₂-HMSs and pure g-C₃N₄.DFT calculation results showed that the introduction of OV facilitates the adsorption and activation of NO and O₂ on the surface of Ti O₂-HMSs and stimulates the production of reactive oxygen species（ROSs）such as superoxide radicals（·O^-₂）and hydroxyl radicals（·OH）which are responsible for the dramatic promotion of visible-light photocatalytic activity of OV/Ti O₂-HMSs.Section II:Single-atom Au Anchored Ti O₂-HMSs.The study of single-atom catalyst（SAC）has attracted much attention due to the unique catalytic activity and selectivity.However,it remains a major challenge to prepare SAC with excellent stability because of the isolated atoms prefer to aggregate during synthetic and catalytic reaction processes.Here OV was used to anchor and stabilize single atomic Au on the surfaces of Ti O₂-HMSs（Au-SA/DT）.DFT calculation results showed that the formation of Ti-Au-Ti bonds facilitate the electron transfer from Ti to Au,resulting in an increased adsorption and activation of acetone.The photocatalytic activity of Au-SA/DT hollow microspheres is much higher than that of perfect Ti O₂-HMSs（PT）,defective Ti O₂-HMSs（DT）and even Au nanoparticle deposited perfect Ti O₂-HMSs（Au-NP/PT）.Au-SA/DT hollow microspheres exhibited enhanced photoreactivity towards acetone oxidation with a removal rate of 214.2 ppm h^-1,which is 2.8 times as high as the activity of Au-NP/PT(75.6 ppm h^-1)and much higher than that of PT(67.8 ppm h^-1)and the DT(47.6 ppm h^-1).According to DFT theoretical calculations,Ti-Au-Ti bonds are formed on the surface of Ti O₂-HMSs,which facilitates the adsorption and activation of acetone and O₂.The introduction of single atomic Au resulted in an expanded visible light responsive range,promoting the separation of photogenerated electron-hole pairs.By combining in-situ infrared and DFT calculations,a reaction mechanism for acetone oxidation over the Au-SA/DT is proposed.The adsorbed acetone was firstly oxidized into acetic acid and formaldehyde.Decarboxylation of acetic acid results in the formation of methyl radicals,which can also be converted into formaldehyde.Under the attacking of ROSs,formaldehyde is further oxidized to formic acid,and finally completely mineralized into CO₂.Section III:Single-atom Fe anchored Ti O₂-HMSs.In this part,we reported the fabrication of single atomic site Fe supported on OV/Ti O₂-HMSs（Fe₁/DT）by calcining the mixture of dicarbonylcyclopentadiene iron and DT.The photoreactivity of optimized Fe₁/DT photocatalyst（TF50）sharply increased with a NO removal rate of 50.1%,which is 2.0 times high than that of pristine Ti O₂-HMSs.DFT theoretical calculations showed that the atomically dispersed Fe on the surface of Ti O₂ caused the formation of Ti-Fe bonds,resulting in the electron transfer from atomic Fe to the surrounding Ti atoms,thereby facilitating the adsorption and activation of NO and O₂.The impurity energy levels are formed,which are mainly composed of Fe 3d orbitals and Ti 3d orbitals,increasing the visible light harvesting ability.The anchored single atomic Fe can stimulate the separation of photo-generated carriers,beneficial to the oxidation of NO.By combining the results from DRIFTs,a proposed photocatalytic oxidation pathway for the photocatalytic oxidation of NO over Fe₁/DT is put forward.