Synthesis And Modification Of TiO₂ Hollow Spheres And Its Photocatalytic Degradation Of Gaseous Toluene

Volatile organic compounds（VOCs）are considered to be the main cause of environmental pollution,and they can also directly harm human health.Toluene,a typical VOCs,should be carefully concerned for its high motility,toxicity,carcinogenicity and teratogenicity among these VOCs.Though photocatalysis can degrade a variety of VOCs,the degradation efficiency is low and the photocatalyst is easily deactivated,resulting in its poor performance in practical applications.185 nm vacuum ultraviolet（VUV）photocatalysis can achieve better removal efficiency on the degradation of VOCs,but it will generate ozone by-products.In this study,TiO₂ hollow spheres was synthesized and doped with Mn to degrade the residual ozone as well as promote degradation of toluene under vacuum ultraviolet irradiation.In this study,carbon spheres were first prepared by hydrothermal method,which was used as templates.TiO₂ hollow spheres was successfully synthesized at different calcined temperature（250℃,450℃,650℃）,and evaluate their photocatalytic activity.The TiO₂hollow spheres calcined at 450℃exhibit the best photocatalytic activity,the removal efficiency of toluene reaches 94%.Meanwhile,the residual ozone concentration was relatively low,but by-product ozone was still generated.Therefore,it is necessary to modify the TiO₂hollow spheres to achieve the purpose of reducing the ozone concentration generated during the vacuum ultraviolet photocatalytic oxidation.TiO₂ hollow spheres with different manganese contents（1%wt-12%wt）were prepared.The photocatalytic activity was evaluated and the optimal Mn doping amount was screened.When the doping amount of Mn is 5%wt,the removal efficiency of toluene reaches 98%,and the mineralization rate exceeds 75%,which indicates that the doping of Mn promotes the catalytic oxidation of toluene,which leads to more sufficient degradation of toluene,and more toluene converted into carbon dioxide and water.At the same time,the ozone concentration was effectively reduced to a maximum of 0.01 ppm,which means the purpose of reducing the residual ozone concentration was achieved.In order to investigate how Mn doping promotes the photocatalytic activity of TiO₂ hollow spheres,a series of characterization analysis were performed.It is found that the doping of Mn promotes the dispersion of nanocrystals,resulting in a significant reduction in the crystallite size,thereby increasing the specific surface area.XPS analysis found that after manganese was doped into the TiO₂ lattice,the charge become unbalanced,more oxygen vacancies appeared,and more active species generated,which is conducive to the vacuum ultraviolet photocatalytic oxidation.In addition,Uv-vis DRS analysis shows that the band gap of TiO₂ hollow spheres decreases after Mn doping,which improves the light absorption capacity and extends the light response region,thereby improving the photocatalytic activity of the photocatalyst.Finally,for the purpose to figure out the reaction pathways of toluene and mechanism under vacuum ultraviolet irradiation,the intermediates were identified by GC-MS,and the possible pathway of toluene degradation in the vacuum ultraviolet photocatalytic oxidation was proposed.Through a series of process such as splitting of toluene,hydrogenation,and H abstraction by OH radicals,toluene was degraded into ketones,aldehydes,acids,esters,anhydrides and so on,which are easy to be further degraded and mineralized into CO₂ and H₂O.In addition,the mechanism of the vacuum ultraviolet photocatalytic oxidation was explored,and it was speculated that volatile organic compounds abatement in the vacuum ultraviolet photocatalytic oxidation process was not only ascribed to the photocatalytic oxidation and photolysis,but also to catalytic ozonation.