Toshima Naoki, Kanemaru Masao, Shiraishi Yukihide, Koga Yoshikata
Department of Materials Science and Environmental Engineering, Tokyo University of Science, Yamaguchi, Onoda-shi, Yamaguchi, 756-0884, Japan.
J Phys Chem B. 2005 Sep 1;109(34):16326-31. doi: 10.1021/jp051400h.
We showed recently that low entropy core/shell structured nanoparticles form spontaneously from the physical mixture of a dispersion of Ag nanoparticles and that of another noble metal (Rh, Pd, or Pt) at room temperature. Here we use isothermal titration calorimetry (ITC) and show that the initial step of such a spontaneous process is strongly exothermic. When the alcohol dispersion of poly(N-vinyl-2-pyrrolidone) (PVP)-protected Rh nanoparticles (average diameter 2.3 nm) was titrated into the alcoholic dispersion of PVP-protected Ag nanoparticles, a strong exothermic enthalpy change, DeltaH, was observed: DeltaH = -908 kJ/mol for Ag(S) nanoparticle (average diameter 10.8 nm) and -963 kJ/mol for Ag(L) nanoparticles (average diameter 22.5 nm). The strength of interaction increases in the order of Rh/Ag > Pd/Ag > Pt/Ag. This strong exothermic interaction is considered as a driving force to from low entropy bimetallic nanoparticles by simple mixing of two kinds of monometallic nanoparticles. We show also that exothermic interactions occur between a pair of noble metal nanoparticles themselves by using ITC.
我们最近发现，在室温下，由银纳米颗粒分散体与另一种贵金属（铑、钯或铂）的物理混合物可自发形成低熵核/壳结构纳米颗粒。在此，我们使用等温滴定量热法（ITC），结果表明这种自发过程的初始步骤是强烈放热的。当将聚（N-乙烯基-2-吡咯烷酮）（PVP）保护的铑纳米颗粒（平均直径2.3 nm）的醇分散液滴定到PVP保护的银纳米颗粒的醇分散液中时，观察到强烈的放热焓变ΔH：对于银（S）纳米颗粒（平均直径10.8 nm），ΔH = -908 kJ/mol；对于银（L）纳米颗粒（平均直径22.5 nm），ΔH = -963 kJ/mol。相互作用强度按Rh/Ag > Pd/Ag > Pt/Ag的顺序增加。这种强烈的放热相互作用被认为是通过简单混合两种单金属纳米颗粒形成低熵双金属纳米颗粒的驱动力。我们还通过ITC表明，一对贵金属纳米颗粒自身之间会发生放热相互作用。
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