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

“光丙酮法”是制备分散的银、金、铂、铜等胶体金属的一种简便易行的方法。本研究以芳香酮代替丙酮，考察了酮自由基在反应中的作用。高胆酸银水溶液在十二烷基硫酸钠（SDS）胶束和芳香酮（如二苯甲酮和苯乙酮）存在下用近紫外光进行了光解反应。在近紫外光照射下形成分散的胶体银，并对芳酮进行光漂白，而芳酮完全吸收了近紫外光（感光光还原）。用一个简单的反应方案解释了银离子敏化光还原和芳酮光漂白的总体特征，该反应方案需要适当的动力学参数组合。即，近紫外光激发芳酮产生芳酮三重态，它从SDS胶团中提取一个H原子，产生一个酮基自由基。一些基自由基还原银离子和银离子簇，生成芳酮。其他的酮基自由基转变为某些副产物，如相应的酚、氢和与SDS偶联的化合物。结果表明，由于颗粒的尺寸效应，早期形成的胶体银的消光系数小于通常值。用激光光解法证实了二苯甲酮的基自由基在反应混合物中的存在，并对不同反应条件下基自由基的寿命进行了比较。利用光丙酮法独特的反应工艺，成功制备了结构和光谱性质都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.