Synthesis of silver and gold nanoparticles using methods of green chemistry

Introduction Nanotechnology is a ield of science being still under development and has a big inluence on the industry from several years. Investment in its development values annually several billion dollars worldwide being equally supported by the governments and the corporations [1]. Amongst variable nanomaterials and ields of their application metal nanoparticles can be distinguished as the most popular in biology and medicine with gold (AuNPs) and silver (AgNPs) nanoparticles playing prominent role. They were already used as far as in fourth century for dyeing ceramics and stained glass. At the time their sources were mostly of natural origin [2]. Nowadays many methods of their synthesis have been elaborated in dependence on their shape and size to be obtained. However, most of them have been developed on the basis of two simple methods. First and the most popular of them were described by Turkevich [3]. It consists of reduction of Au3+ ions to Au with citric acid, which also stabilizes forming nanoparticles and could be exchanged to other ligand. In Shiffrin – Brust method [4] sodium borhydride is used as reducer and the acid is immediately replaced by selected mercaptan. In the irst method water can be used as a solvent whereas in the second the choice of a solvent is dependent on the hydrophobicity of the used mercaptan, which acts as stabilizer. Both methods can be also used in order to obtain silver nanoparticles. Their advantage is that monodispersed nanoparticles are formed, with size depending on ratio of the reducing agent to the substrate. Unfortunately, those techniques are not lawless. For example, the second one frequently uses toxic mercaptans and organic solvents. Together with the development of various ields of industry it started to pay attention to environmental degradation by-products formed as a result of technological processes. This resulted in studies on minimizing the use of toxic substances and replace them with natural ones in various sectors of the enterprise – in this way, the trend called “green chemistry” was created [5] with the main priorities being: lower energy consumption, and hence costs by lowering the • temperature of the reactions use of catalysts, which preferably are possible to be regenerated • elimination of toxic solvents and organic substrates, and repla• cement of them with natural ones or exchange for the less toxic ones (e.g. replacement of benzene – toluene) reduction or elimination by-products requiring disposal. •