Metal Nanoparticle Synthesis in Ionic Liquids

Abstract

The synthesis of metal nanoparticles (M-NPs) in ionic liquids (ILs) can start from metals, metal salts, metal complexes, and in particular metal carbonyls and can be carried out by chemical reduction, thermolysis, photochemical, microwave irradiation, sonochemical/ultrasound-induced decomposition, electroreduction, or gas-phase synthesis, including sputtering, plasma/glow-discharge electrolysis, physical vapor deposition, or electron beam and γ-irradiation. Metal carbonyls, M x (CO) y , are commercially available and elegant precursors because the metal atoms are already in the zerovalent oxidation state for M-NPs so that no reduction is necessary. The thermal decomposition of metal complexes, including metal carbonyls in ILs by microwave irradiation, provides a fast and low-energy access to M-NPs. The reason is an excellent absorption efficiency of ILs for microwave energy due to their high ionic charge, high polarity, and high dielectric constant. Ionic liquids allow for the stabilization of M-NPs without the need of additional stabilizers, surfactants, or capping ligands because of the electrostatic and steric properties inherent to ILs. From the IL dispersion, the M-NPs can be deposited on various surfaces, including graphene derivatives and nanotubes. The formation of intermetallic MM′-nanoalloys in ILs has just begun to be explored. Examples for M(M′)-NP/IL dispersions in catalytic reactions (C–C coupling, methanol synthesis, hydrogenation) are noted.