Inorganic nanorings and nanotori: State of the art
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Inorganic nanorings and nanotori: State of the art Oxana V. Kharissova1, Mauricio Garza Castañón1, Boris I. Kharisov2,a) 1
Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, C.P. 66455, México Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, C.P. 66455, México a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 19 September 2019; accepted: 14 November 2019
Toroidal (ring-like) structures are common in organic chemistry, but at the nanoscale level, the inorganic nanorings and nanotori are limited and represented mainly by carbon, several p- and noble metals (Ag, Au, Al, and Au/Co/Au), metal and nonmetal oxides (ZnO, MoO2, Fe2O3, and SiO2), hydroxides (Co(OH)2), and salts (PbI2 and metal selenides), and some combinations of carbon nanotori with fullerenes and carbon chains, as well as doped nanorings, are known. The nanotori are closely related to ball-type nanostructures as nano-onions, nanoballs, and nanospheres. Despite their relative low existence, they possess several useful properties and respective applications as isolators, sensors, optoelectronics, as traps for atoms and ions, and counterparts in lubricants, thus causing a certain interest in their development. The properties of nanotori have been studied mainly by DFT calculations. Several nanorings possess stabilities up to 3000 K before unfolding, multiresonant properties and magneto–optical activity, paramagnetism, and ferromagnetism. The carbon nanorings are studied considerably better, being compared with other compounds. This review summarizes the state of the art of all available inorganic toroidal nanostructures, believing that a considerable higher number of inorganic systems might be prepared in this form, taking into account their unusual properties.
Introduction Toroidal-like nanosize structures, called as nanorings or nanotori, are not frequent among other less-common nanostructures [1], in particular among closely related ball-type nanostructures as nano-onions, nanoballs, and nanospheres. Ring- and torus-like nanostructures are indeed “two sides of the same medal,” whose properties have been studied more theoretically using density functional theory (DFT) calculations than experimentally. However, as it will be shown below, they can possess intriguing properties, e.g., being, in some cases, ferromagnetic [2], which could lead to novel applications. Under self-assembling, the nanorings/nanotori can form a variety of geometries (Fig. 1) on the basis of liquid-crystalline coloidal phases, very useful as storage and adsorption materials [3]. Another practically undeveloped area is their use as dopants for classic oil lubricants, allowing much lesser metal–metal contact and, as a consequence, considerably higher duration of oil service in distinct mechanisms before changing the maintenance oil. As it is known, one of the main losses in metallurgical industries is related with periodic stopping of processes because
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