【作者】 沈建东；

【导师】 陈建民； 张士成；

【作者基本信息】 复旦大学 ， 环境科学， 2008， 硕士

【摘要】 大气气溶胶是多种组分的混合物,TiO₂在对流层大气气溶胶颗粒中含量中等,而且在对流层太阳辐射下即表现一定活性,参与大气化学变化,是大气多相反应最活跃的气溶胶粒子之一。苯并[a]蒽是美国环保局制定的129种优先控制污染物中的PAHs中的一种,具有较强的致癌、致突变及致畸性,对人体健康具有较大影响;CS₂是大气中主要的含硫气体污染物,对酸沉降和硫酸盐气溶胶的形成有重要贡献,同时它也是大气中COS的重要来源,而平流层COS对太阳辐射及平流层臭氧损耗具有重要影响。因此,研究苯并[a]蒽及CS₂与矿尘气溶胶粒子中的典型氧化物TiO₂的多相光化学反应对揭示这些物种的多相光化学反应的转化过程,评估多相光化学在大气化学转化中的贡献有着重要的意义。本文以傅立叶红外光谱和漫反射附件为测定基础的原位观测反应体系,并利用GC-MS,GC以及XPS、IC等分析手段研究了在模拟太阳光照射下苯并[a]蒽和CS₂在TiO₂表面的多相光化学反应过程,主要结论如下:1.苯并[a]蒽可在TiO₂半导体颗粒表面发生光催化氧化反应的主要产物为苯并蒽-7,12-二醌。反应过程中,表面羟基和表面氧起了关键作用。在模拟太阳光照射下,苯并[a]蒽在TiO₂颗粒表面的光降解过程符合指数衰减方程,半衰期为6.8min。利用GC-MS分析方法,检测到比较多的邻苯二甲酸酯类以及直链烷烃和酸类中间产物,它们都可能是通过复杂的R·自由基反应而生成的。2.在氙灯照射下,CS₂在TiO₂表面发生多相光化学反。CS₂首先和光照下生成的·OH反应,生成活性物种（SCS-OH）^*,进而在表面活性氧物种的作用下,生成气态产物COS,SO₂,H₂S,在TiO₂表面生成硫酸盐。增大氧气浓度可提高多相光化学反应速率。在模拟自然条件下,CS₂在TiO₂表面的多相光化学反应符合表观一级动力学反应,表观反应速率常数K=0.0037 min^-1,BET吸附系数为5.36×10^-8。更多还原

【Abstract】 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.更多还原