Metal Nanoparticles, Synthesis of

Abstract

The successful synthesis of metal nanoparticles decisively depends on sufficient stabilisation by protecting materials. This can be reached either by electrostatic repulsion of charged species or by covering the surface atoms with polymers, surfactants, or especially ligand molecules binding to the particles via covalent bonds. Noble metals are in focus, since their salts or complexes can easily be reduced to the oxidation state 0 and the sensitivity towards oxygen is reduced or even avoided like in the case of gold. Nevertheless, nanoparticles of less noble metals can be prepared. Above all, there is an increasing need to get monodispersed particles, since their properties depend on size and shape. There exist so‐called physical methods to generate metal atoms from bulk metals that are then allowed to coalesce to nanoparticles. High temperatures or laser ablations are examples. Chemically based procedures use in any case stabilizing agencies. Among numerous methods, salt reduction dominates. Thermal decomposition of appropriate precursor complexes and soft ligand removal from organometallics have become known as alternative routes. Photolytic and radiolytic techniques exist, but do not play important roles. The synthesis of magnetic metal nanoparticles is of increasing interest with respect to applications. The syntheses mainly follow recipes known from noble metals. Fe, Co, Ni as well as magnetic bimetallic alloy‐like nanoparticles are available. The magnetic characteristics of nanoparticles again depend decisively on size, structure, and shape, even more than in case of the nonmagnetic species. Therefore, synthetic procedures resulting in uniform particles are of great importance.

Plasma Synthesis of Coated Metal Nanoparticles with Surface Properties Tailored for Dispersion

“…This is mainly a result of the large proportion of unbound atoms located at the surface of materials in the nanometer size range 4. Methods for large‐scale generation of nanoparticles with uniform chemical composition involve the use of thermal plasma sources, evaporation‐condensation processes, chemical vapor deposition (CVD) or chemical synthesis 5, 6. Nanoparticles of various chemical compositions including metal oxides (Al 2 O 3 , CeO 2 ), nitrides (TiN, Si 3 N 4 ) or carbides (SiC, WC) are routinely produced using such processing approaches.…”