Top-down synthesis of metal nanoparticles by surface disaggregation in a stirred tank [Sintesi top-down di nanoparticelle di metallo ferromagnetico in un serbatoio agitato sigillato]

The choice of a production route ifor metal nanoparticles s generally related to the physico-chemical properties of the materials which the nanoparticles are made of. For example, inorganic NPs are manufactured according to processes which are generally very different from the ones adopted for the synthesis of organic NPs, owing to an intrinsic thermal instability of the latter. Physical and chemical synthesis methods are usually considered as the first choice and a huge literature focused on such techniques proves this statement. The former often require expensive apparatuses and instrumentation and they pose some problems in matter of scalability of the final product. On the opposite, chemical processes are more economical and they allow a satisfactory controllability of shape and dimensions of the as-produced NPs. One of the most crucial drawback related to a chemical synthesis method is the use of reagents having noxious properties for man and environment. This negative aspect of chemical synthesis method is perhaps the main reason leading to an increasing interest towards biological processes, where cells of bacteria, yeasts and fungi act as living nanofactories for the synthesis of NPs. Such processes proved to be useful for the production of zerovalent nanostructures of noble metals like gold, platinum, palladium and silver, owing to the weak electropositive character of the corresponding element. However, biochemical methods proved to be somewhat inefficient when non-noble metal NPs are to be synthesized, as the electron-donors in biochemical processes are considrably weaker than the typical inorganic reductants like hydrazonium compounds or alkali borohydrides. In the present work, a purely physical synthesis method relying upon a mechanical friction between bulk copper spheres and zirconia (ZrO2) balls in a liquid medium is described. The process is carried out at room temperature and it proved to be successful for the synthesis of very fine Cu-NPs.