Heterogeneous Photochemical Reaction Of Benz[a]anthracene And CS₂ On The Surfaces Of TiO₂ Particles

Aerosol is a mixture of various components.Semiconductor oxide TiO₂,which are present in troposphere aerosols in comparatively middle amounts,can absorb solar radiation excited into activity status in the troposphere,then participate in the atmospheric photochemical reaction.It is one of the most active components of aerosols.Benz[a]anthracene,one of the sixteen PAHs classified by US EPA as priority pollutants,possessing of mutagenic,carcinogenic,and teratogenic properties,have greater impact on human health.Carbon disulfide(CS₂) is the the major sulfur-containing gaseous pollutants in the atmosphere,playing an significant role in acid deposition and the formation of sulfate aerosols.At the same time Carbon disulfide is also an important source of carbonyl sulfide(COS) in the atmosphere,and the stratospheric carbonyl sulfide has an important influence on solar radiation and stratospheric ozone depletion.Thus it is of significant importance to have a detail study on the heterogeneous photochemical reaction of benz[a]anthracene,CS₂ on the surfaces of TiO₂ particles.It is an effective way to investigate the conversion process of these pollutants,and to assess the contribution of heterogeneous photochemical reaction on atmospheric chemical composition.In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy(DRIFTS), Gas Chromatography-Mass Spectrometry(GC-MS) and Gas Chromatography(GC) were used to characterize surface-bound species and gas-phase product during heterogeneous photochemical reaction of benz[a]anthracene,CS₂ on TiO₂ particles. Combined X-ray Photoelectron Spectroscopy(XPS) and Ion Chromatogram(IC) were used to detect the products and provide evidence for the proposed mechanism.Firstly,it was confirmed that the main photoproduct of photocatalytic oxidation benz[a]anthracene on the surface of TiO₂ particles was benz[a]anthracene-7,12-dione. The surface hydroxyl and oxygen played a key role.Under the simulated sun light irradiation,the process of benz[a]anthracene photodegradation on TiO₂ particles matches the exponential decay equation,and the half-life time is 6.8 min.It is detected much intermediate products by GC-MS such as phthalate esters,straight alkanes and acid,and these products may through complex R·radical reactions.Secondly,the heterogeneous photochemical reaction of CS₂ on TiO₂ particles was studied.CS₂ first reacted with light generated·OH,generating activity species (SCS-OH)^*,then oxidized into COS,SO₂,H₂S,and SO₄^2- by active adsorbed O atoms.The experimental indicated that the high concentration oxygen greatly enhanced the photochemical reaction rate.In a simulated natural conditions,the process of CS₂ photodegradation on TiO₂ particles matches apparent first-order reaction,and the BET absorption coefficient is 5.36×10^-8.