【作者】 曹长青；

【导师】 侯惠奇；

【作者基本信息】 复旦大学 ， 环境科学， 2008， 博士

【摘要】 有机锡化合物具有非常广泛的应用,作为农药、防污涂料等杀生剂是其重要的用途之一。部分有机锡化合物,尤其是三苯基锡（TPT）和三丁基锡（TBT）的毒性很大,对自然环境造成较大危害,因而受到了人们的极大关注。人们对这些物质在环境中的迁移、转化、归宿和生态效应等进行了很多研究。然而,对有机锡在环境中发生的化学反应的微观机理研究非常少。本论文以激光闪光光解-瞬态吸收光谱技术为研究手段,以环境中危害最大的有机锡即TPT和TBT为研究对象,研究了水相中·OH自由基与TPTCl和TBTCl的微观反应机理,并在此基础上探讨了自然条件下光解反应（包括直接光解和间接光解）对TPT和TBT在环境中转化的重要程度。利用HNO₂吸收355nm激光解离产生·OH自由基,在研究·OH自由基与HNO₂、Cl^-反应机理和瞬态物种吸收信号的基础上,研究了TPTCl-HNO₂和TBTCl-HNO₂水溶液体系的激光闪光光解反应,主要得出以下结论:（1）三苯基锡阳离子（TPT⁺）能与·OH自由基反应生成TPT⁺·OH加合物,该瞬态物种在260nm-350nm有一定吸收,吸收峰在310nm附近;TPT⁺与·OH自由基的二级反应速率常数为（7.2±1.4）×10⁹ L mol^-1 s^-1;（2）在无氧条件下,TPT⁺·OH加合物的衰减是一级反应,其反应速率常数为（1.15±0.15）×10⁵ s^-1;在氧气饱和条件下,TPT⁺·OH加合物能与O₂发生作用,其二级反应速率常数为（6.0±2.9）×10⁷ L mol^-1 s^-1;（3）三丁基锡阳离子（TBT⁺）亦能与·OH自由基反应生成TBT⁺·OH加合物,它在＜320nm波段有一定吸收,吸收峰应小于250nm;TBT⁺与·OH自由基的二级反应速率常数高达（1.02±0.07）×10¹⁰L mol^-1 s^-1;（4）TBT⁺·OH加合物在无氧条件下的衰减亦是一级反应,其反应速率常数为（3.50±0.32）×10⁵ s^-1;在氧气饱和条件下,TBT⁺·OH加合物能迅速与O₂发生反应,其二级反应速率常数为（6.4±1.3）×10⁸L mol^-1 s^-1。另外,基于253.7nm和365nm紫外灯对TPTCl和TBTCl的直接光解和间接光解的宏观实验,结合微观反应机理研究的结果,可得到如下结论:（1）虽然有机锡化合物中C-Sn键的平均解离能比较低,但由于它们通常不吸收290nm以上的紫外光,因此直接光解对大部分有机锡类化合物（包括TPT和TBT）在自然环境中的降解基本可以忽略,不少文献中关于自然界紫外光能较容易地使TPT类化合物的苯环脱落的提法是缺乏依据的;（2）考虑到苯基锡类物质通常难以被微生物和自然环境下的热、酸或碱等分解,而·OH自由基与TPT反应很快,可推测间接光解对苯基锡在自然环境中的转化非常重要;作为农药使用的TPT,能被水相中（如露水、雨水、河流）各种自由基降解,当水相中存在HNO₂/NO₂^-化合物时,TPT可能是环境中硝基苯类污染物的一个来源;而进入海水中的TPT化合物,由于自由基浓度较低,因此间接光解对其转化也不重要:（3）对于TBT类化合物,虽然它与·OH自由基的反应速率常数很大,但由于通常它存在于海洋水体中,因此间接光解对这一部分TBT的转化并不重要;（4）利用UV/H₂O₂或者相似的手段处理有机锡废水,是一种比较有效的方法。更多还原

【Abstract】 Organotin compounds have been widely used as pesticides,antifouling paints and other biocides and have various other commercial uses.The fate of these compounds constitutes one of today’s public environmental concerns since some organotin compounds,especially triphenyltin（TPT） and tributyltin（TBT） are high toxic to aquatic life even at very low concentrations.Many studies have focused on the transportation,transformation,removal processes and toxic effects of organotin compounds.However,few microscopic researches have investigated the kinetics and mechanisms of related chemical processes.The current study introduces the nanosecond laser flash photolysis - transient absorption spectra technique into the research on the photochemical reaction mechanisms of triphenyltin and tributyltin with hydroxyl radical in the aqueous solution.Based on the results of laser flash photolysis study,the direct and indirect photolysis oftriphenyltin and tributyltin under 365nm and 253.7nm UV lamp were also studied,and the significance of these reactions for the removal of organotin compounds in the natural environment was discussed.In the laser flash photolysis study,Hydroxyl radical was generated by the photolysis of nitrous acid using 355nm laser light.On the basis of the investigation results of the reaction of hydroxyl radical with nitrous acid and CI,the reactions in the TPTCI-HNO₂ and TBTCI-HNO₂ aqueous solution after irradiated by 355nm nanosecond laser light were studied respectively,and the following points could be drawn:（1） Triphenyltin cation（TPT⁺） reacts with hydroxyl radical to form TPT⁺·OH adduct and the rate constant is（7.2±1.4）×10⁹L mol^-1 s^-1.The absorption of TPT⁺·OH adduct lies below 350nm,with a peak absorption at approximately 310nm.（2） TPT⁺·OH adduct decays with a first-order rate constant of（1.15±0.15）×10⁵ s^-1 in the N₂ saturated aqueous solution.When O₂ exists,TPT+·OH adduct can react with O₂ at a rate constant of（6.0±2.9）×10⁷ L mol^-1 s^-1.（3） Tributyltin cation（TBT⁺） can also react with hydroxyl radical to form TBT⁺·OH adduct and the rate constant is（1.02±0.07）×10¹⁰L mol^-1 s^-1.The absorption of TBT⁺.OH adduct lies below 320nm,and the absorption peak which should be below 250nm could not be determined in this study.（4） TBT⁺.OH adduct decays at a first-order rate constant of（3.50±0.32）×10⁵ s^-1 in the N₂ saturated aqueous solution.When O₂ exists,TBT⁺·OH adduct can react with O₂ very fast at a rate constant of（6.4±1.3）×10⁸ L mol^-1 s^-1.Further more,on the basis of the above results and the photolysis experiment under 365nm and 253.7nm UV lamp,the following conclusions could be drawn:（1） Direct photolysis of organotin compounds is of little significance due to their negligible absorption above 290nm,although the mean bond dissociation energy of Sn-C bond is low.Hence,the commonly stated "triphenyltin species are rapidly dealkylated by UV irradiation" is not well founded.（2） The indirect photolysis of TPT may play an important role in the removal process of TPT used as pesticide,since most bacteria lack the ability to biodegrade TPT, and heat,acid and alkali under natural environment conditions could not cleave the Sn-C bond of TPT,either.When the aqueous phase contains HNO₂/NO_2-,TPT can be transformed to nitrobenzene,which is also an important pollutant.As for the TPT entering the oceanic environments,indirect photolysis of TPT is of little significance since the concentration of reactive radicals is low.（3） For TBT compounds,neither direct nor indirect photolysis plays an important role in the removal process of TBT in natural environments since TBT compounds are mostly found in the oceanic environments with low concentration of reactive radicals.However,indirect photolysis may be very important for the removal of BTs entering the atmosphere.（4） The experimental results also implied that UV/H₂O₂ and similar methods may be efficient to treat organotin polluted wastewater.更多还原