2. 超音波による貴金属微粒子の生成,成長過程の観測

概要

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Noble metal ions, NaAuCl_4 (Au(III)), PdCl_2 (Pd(II)) are reduced to form metallic nanoparticles by the sonication in the presence of surfactants, such as polyethylene glycol monostearate (PEG-MS; nonionic) and sodium dodecylsulfate (SDS; anionic). It is found that colloidal Pd can be isolated from coexisting Pd ions without any morphological change by the treatment of an anion exchange resin. This makes possible TEM observation of the Pd particles at desired reaction time without disturbance of Pd ions during the process of particle formation, which is an important subject for colloid chemistry but has not been so abundantly investigated. In the case of Pd(II)/ SDS, the size of Pd particles in the initial stage of the growing process (1.5 min sonication) is 4.2 nm and the number of the particles is 6.8×10^<14>. In the middle stage (6 min sonication), the size of particles is enlarged to 6.0 nm with the number of 7.7×10^<14>. In the final stage, where ions are completely reduced by 15 min sonication, the size of particles is 7.0 nm and the number of particles is 7.5×10^<14>. The unaltered number of particles at every stage suggest that the nucleation rate of Pd(0) is roughly equal to the coagulation rate of Pd particles in SDS. Smaller size of 4.4 nm is observed in PEG-MS surfactant. In gamma irradiation experiments, the sizes of particles are larger than those formed in sonication both SDS and PEG-MS.
日本ソノケミストリー学会の論文