Study On The Generation And Mechanism Of Reactive Oxygen Species In The Photocatalytic Removal Of NO By TiO₂

Nano titanium dioxide(TiO2)is a multi-functional wide band gap semiconductor metal oxide.Since Fujishima et al.found that TiO2 can decompose water to produce hydrogen under illumination,the reduction of hydrogen production by photocatalytic technology and the removal of various atmospheric pollutant molecules has become a hot research topic.However,its poor response to visible light and serious recombination of photogenerated electron-hole pairs limit the application of TiO2 in the field of photocatalysis.Reactive oxygen species(ROS)are important intermediates in photocatalytic reactions.The identification,quantitative determination and activity evaluation of ROS are of great significance for understanding the mechanism of photocatalytic reactions,improving the degradation efficiency of pollutants and the practical application of photocatalytic technology.In this paper,a series of anatase TiO2 materials were prepared by direct hydrolysis and hydrothermal method using tetrabutyl titanate(TBOT)as the main raw material,and applied to simulate the photocatalytic removal of NO under sunlight.The physicochemical properties and catalytic mechanism of the catalysts were characterized in detail and studied in depth.Reactive oxygen species are reactive and have strong oxidation ability,which can directly act on the vast majority of pollutant molecules and eventually degrade into harmless other substances through deep oxidation.Therefore,by improving the activity of photocatalytic ROS production of the catalyst,we can obtain a kind of excellent performance that can be applied to the degradation of a variety of environmental pollutants.The specific contents are as follows:1.Tetra-butyl titanate(TBOT)was selected as the main raw material,and a series of TiO2 catalysts were synthesized by direct hydrolysis,with the hydrolysis time of TBOT as the only variable factor.The crystal structure of the material was studied by X-ray diffraction(XRD),and the defect structure of the material was characterized by paramagnetic resonance(EPR)and fluorescence spectroscopy(PL).The effects of aging time on the specific surface area and chemical structure of the material were also studied.The yields of hydroxyl radical(·OH)and hydrogen peroxide(H2O2)in different samples irradiated by visible light were determined by fluorescence spectroscopy.In a series of samples,we found that 8h-TiO2 had the best catalytic activity,which we believe is related to the structure of oxygen-centered persistent free radicals(EPFRs)found in the EPR characterization.With the help of infrared spectrum(FT-IR)and nuclear magnetic resonance(NMR)technology represents the EPFRs possible structure,ultraviolet-visible absorption spectra(UV-vis DRS)found EPFRs can promote the response in the visible region of the material,according to the result of PL characterization of inference EPFRs can form a built-in electric field on the surface of the material and promote light raw material carrier separation and migration,thus improve its catalytic activity.In addition,the cyclic photocatalytic activity of the material and the removal ability of NO from the gaseous phase were also investigated.It was found that the 8h-TiO2 sample showed good NO degradation activity under the irradiation of monochromatic green light(λ=550 nm),which was attributed to the photosensitization effect of EPFRs.2.A series of TiO2 materials were prepared by hydrothermal method and adding organic reducing agent ethylene glycol(EG)of different qualities.XRD characterization of comparative study the modified TiO2 and traditional TiO2 crystal structure and crystal size differences,using UV-vis DRS,FT-IR and X-ray photoelectron spectroscopy(XPS)characterization methods such as glycol content on the material light absorption properties were analyzed and the influence of molecular structure of key environmental,EPR and Raman spectrum(Micro Raman)to determine the content of the main defects of the material and,PL series,optical current and the impedance test report modification of sample with higher light carrier separation efficiency and produce more photons under visible light irradiation,indicates that the change of Ti-O bond environment is favorable for electron transport.The degradation activity of NO was used to reflect the difference of catalytic performance of the materials.The photocatalytic mechanism of the materials was studied by free radical and hole capture test and ESR test,and the main way of the photocatalytic removal of NO in monochrome red light(λ=650 nm)was explained.The results show that excessive addition of ethylene glycolwill inhibit the hydrolysis growth of TiO2 crystals and introduce large number of defect structures into the crystal lattice.The formation of defects will narrow the band gap width of TiO2 and extend the visible light response range to the near infrared region of the material,which greatly improves the utilization efficiency of photons of different wavelengths.A new way of NO degradation was found in the activity test using monochrome red light.The main species involved in NO degradation were identified by the capture experiment of active species.In ESR-TEMP test with visible light and red light respectively,we determined the signal and intensity of 1O2 generation.Meanwhile,ESR-TEMP test proved that it was impossible to stimulate the material to generate photoelectric electrons under red light.Therefore,the sample catalyzed oxygen to generate 1O2 under red light.The mechanism of NO degradation is worth further discussion.