二苯乙烯在CdS胶体界面和醇溶液中光氧化反应的ESR研究

ESR STUDY ON THE PHOTOOXIDATION PROCESSES OF STILBENE ON CdS COLLOID SURFACE AND IN ALCOHOL SOLUTION

采用ESR方法研究了二苯乙烯在硫化镉超微纳米粒子界面光氧化过程产生的中间体及转化机理，并与均相直接光氧化和在甲基紫精存在下的光氧化进行了比较．结果表明，二苯乙烯的界面光氧化经历了超氧阴离子基和二苯乙烯正离子基的生成过程，而且在CdS胶粒表面有H原子的生成；羟基在H原子产生过程中起着重要的作用．二苯乙烯于甲基紫精存在时的光氧化中可直接观察到超氧阴离子基的ESR信号；值得注意得是，当仅有微量水存在时则产生OOH基，而水量较多时可生成OH基及较大量的碳中心自由基；直接光氧化的反应速度较慢．对几种不同过程的机理进行了分析讨论．

The radical intermediates and reaction mechanism in the photooxidation of cis-and trans-stilbeneson the CdS colloid surface as well as in ethyl alcohol solution have been studied by spin-trapping ESRmethod. Results indicated that superoxide anion radical O_2 and stilbene cation radical were gelleratedin photooxidation processes, and atomic H were also formed on the surface of CdS colloid particles; thehydroxyl free radical played an important role in the formation of atomic H; ESR signal of O_2 radicalwas observed in the presence of methyl viologen; OOH radical was produced in the presence of smallamount of water; OH and carbon-centered radicals were formed in the presence of rather large amountof water; reaction rate was very slow for direct photooxidation processes. Reaction mechanisms fordifferent processes were discussed.