Behavior of Ketyl radical in the micelle solution in the presence of silver ion or silver particle

“光丙酮法”一直被认为是一种制备分散细小的胶体金属(银、金、铂和铜)的简便方法。本研究以芳香酮代替丙酮，考察了酮基自由基在反应中的作用。在十二烷基硫酸钠(十二烷基硫酸钠)胶束和芳香酮(如二苯甲酮和苯乙酮)存在下，高氯酸银水溶液在近紫外光下被光解。近紫外光照射只被芳香酮(敏化光还原)吸收的近紫外光导致银胶体的形成和芳香酮的光漂白。银离子的敏化光还原和芳香酮的光漂白的大体特征可以用一个简单的反应过程来解释，其中包括适当的动力学参数组合。也就是说，在近紫外光的激发下，芳香酮产生芳香酮三重态，它从十二烷基硫酸钠胶束中提取一个H原子，产生一个酮基自由基。一些酮基还原了银离子和银离子簇，并返回芳香酮。其他的酮基则转变为某些副产物，如相应的片呐醇、氢化物和与SDS的偶联化合物。由于颗粒的尺寸效应，早期形成的胶体银的消光系数比通常的值小。激光光解证实了反应混合物中二苯甲酮的酮基自由基的存在，并对不同反应条件下酮自由基的寿命进行了比较。利用光丙酮法独特的反应过程，成功地制备出结构和光谱性质不同于合金胶体的复合贵金属胶体。

"Photo-acetone method" has been known as a tractable method to prepare finely dispersed colloidal metals (Ag, Au, Pt and Cu). In this study, aromatic ketone was used instead of acetone in order to investigate the role of the ketyl radical during the reaction. Aqueous silver percholate solutions were photolyzed with near-UV light in the presence of sodium dodecylsulfate (SDS) micelle and aromatic ketone, such as benzophenone and acetophenone. The formation of finely dispersed colloidal silver and the photobleach of aromatic ketone were caused by irradiation with near-UV light, which was absorbed solely by aromatic ketone (sensitized photoreduction). Gross features of the sensitized photoreduction of silver ion and the photobleach of aromatic ketone were interpreted in term of a simple reaction scheme entailing suitable combinations of the kinetics parameters. Namely, the excitation of aromatic ketone by near-UV light yields an aromatic ketone triplet, which abstracts an H atom from SDS micelle, giving rise to a ketyl radical. Some ketyl radical reduces silver ion and silver ion cluster and goes back to aromatic ketone. Other ketyl radical changes into certain byproducts such as the corresponding pinacol, hydrol and coupling compound with SDS.It was noticed that an extinction coefficient of colloidal silver formed during the early stage was smaller than the usual value because of the size effect of the particles. The existence of the ketyl radical of benzophenone in the reaction mixture was confirmed by laser photolvsis, It was tried to compare the lifetime of the ketyl radical under various reaction conditions. Taking advantage of the unique reaction process of the photo-acetone method, the composite noble metal colloid, whose structure and spectroscopic properties were different from alloy colloid, has been successfully prepared.