CHAPTER 11: Metal Nanoparticle Synthesis in Ionic Liquids¹

An overview is given of the synthesis and stabilization of metal nanoparticles (M-NPs) from metal salts, metal complexes and metal carbonyls in ionic liquids (ILs). The synthesis of M-NPs can proceed by chemical reduction, thermolysis, photochemical, microwave irradiation or sonochemical/ultrasound induced decomposition, electroreduction, gas phase synthesis including sputtering, plasma/glow discharge electrolysis and physical vapor deposition or electron beam and γ-ray irradiation. Commercially available metal carbonyls M_x(CO)_y are elegant precursors as they contain the metal atoms already in the zero-valent oxidation state needed for M-NPs so that no extra reducing agent is necessary. Microwave induced thermal decomposition of metal complexes, including metal carbonyls in ILs, provides an especially rapid and energy-saving access to M-NPs because of the ILs’ significant absorption efficiency for microwave energy due to their high ionic charge, high polarity and high dielectric constant. The electrostatic and steric properties of ionic liquids allow for the stabilization of M-NPs without the need for additional stabilizers, surfactants or capping ligands. Examples of the use of M-NP–IL dispersions in C–C coupling or hydrogenation catalysis are given.