Synthesis, structure and properties of metal nanoclusters

Abstract

Metal nanoclusters have physical properties differing significantly from their bulk counterparts. Metallic properties such as delocalization of electrons in bulk metals which imbue them with high electrical and thermal conductivity, light reflectivity and mechanical ductility may be wholly or partially absent in metal nanoclusters, while new properties develop. We review modern synthetic methods used to form metal nanoclusters. The focus of this critical review is solution based chemical synthesis methods which produce fully dispersed clusters. Control of cluster size and surface chemistry using inverse micelles is emphasized. Two classes of metals are discussed, transition metals such as Au and Pt, and base metals such as Co, Fe and Ni. The optical and catalytic properties of the former are discussed and the magnetic properties of the latter are given as examples of unexpected new size-dependent properties of nanoclusters. We show how classical surface science methods of characterization augmented by chemical analysis methods such as liquid chromatography can be used to provide feedback for improvements in synthetic protocols. Characterization of metal clusters by their optical, catalytic, or magnetic behavior also provides insights leading to improvements in synthetic methods. The collective physical properties of closely interacting clusters are reviewed followed by speculation on future technical applications of clusters. (125 references).

Experimental Challenges in Studying Hydrogen Absorption in Ultrasmall Metal Nanoparticles

“…Among various methods for the synthesis of supported metal nanoparticles, the most widespread approach is the incipient wetness impregnation method: the porous support (typically carbon and metal organic framework) is impregnated with a solution of metal precursor, which is subsequently reduced using different reducing agents (H2, NaBH4, etc.) (Wilcoxon and Abrams, 2006;Roesler and Fischer, 2015). Another interesting technique is the melt infiltration of low temperature melting metals, such as Mg, into different porous carbon hosts (de Jongh and Eggenhuisen, 2013;Au et al, 2014).…”

The use of preformed nanoparticles in the production of heterogeneous catalysts

“…The nanoparticles have maintained their shape and size during the assemblage and calcination processes. With the development of reliable synthetic procedures 27,28 over the last decade allowing access to a range of transition and noble metal particles useful for catalysis using preformed nanoparticles in supported materials is readily achievable. Using these nanoparticles provides an avenue to more predictable samples than those obtained using traditional methods such as co-precipitation and sol-gel.…”

Photochemistry for the Synthesis of Noble Metal Nanoparticles

“…The fluorescence spectra of single Au m (m > n) revealed that the bulk spectrum of Au m (m > n) was mainly composed of the two spectra peaks at 1.97 and 2.04 eV, which may correspond to Au 21 and Au 19 , respectively ( Figure 3). Taking into account the evolution of the fluorescence spectrum, a domain of Au clusters containing Au n (n, <12 or 17) was generated during irradiation with UV light, and the distribution then slowly shifted to the Au m (m, 19 or 21).…”