Nanosystems

Inorganic nanosystems are defined as nanosized chemical objects whose composition is merely inorganic and which exhibit peculiar features due to quantum-size and geometrical effects. Two are the general synthetic pathways by which nano-objects are obtained: the so-called 'top-down' and 'bottom-up' approaches. Mainly in the latter method, chemistry plays a unique role in assembling and building up nanometric units from smaller ones. The nanosystems can be defined and classified according to the hierarchical order of dimensionality. Zero-dimensional systems include pseudospherical objects such as nanoclusters and nanoparticles, supported onto inorganic bulk supports as well as in colloidal solutions, or ceramic nanopowders. One-dimensional systems take into account carbon-based, metal-based or even oxide-based systems in which the extension over one dimension is predominant over the other two, such as solid nanofibers, nanowires or nanorods, as well as hollow nanotubes. As twodimensional nanosystems, the crystalline flat nanometric materials, such as nanodiscs or nanoprisms, and the amorphous nanofilms and nanomembranes are considered. Then, three-dimensional nanosystems consist of both crystalline and amorphous nanostructures, such as nanocrystals and a very large variety of ordered nanoarranged porous materials. Three-dimensional arrangements can be also created from simpler components, as nanoparticles or nanorods, and superstructures or superlattices with improved features are thus obtained. The description, the synthesis, the properties and the main applications in technology and industry of the chemical systems at nanoscale most commonly found in inorganic chemistry are here summarized and reviewed. Finally, few highlights are given on inorganic-organic hybrid nanosystems and on systems with applications in biochemistry, as these subjects are on the borderline with organic chemistry and biology.