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Since the beginning of last century, nanotechnology has tried to imitate nature so as to achieve reproducible and multifunctional complex models to replace traditional materials. In 1915, W. Ostwald was the first who realized the interdependence between the nanoparticle’s properties, size and shape. In the last two decades, researchers have attempted to obtain various nanodimensional structures in terms of shape, size or color and compatibility with the function and the environment for which they were created. Managing to obtain a very diversified design from a type of a nanoparticle to another, these need nomenclature and taxonomy.
The use of nanoparticles in practical areas revealed the need to obtain them and their characteristics: to have a high purity and uniform chemical compositions, their size falls within a narrow uniform distribution and are controllable, the shape and morphology of nanoparticles to be identical.
This article aims to expose some aspects on design typology nanoparticles over time and their functionality, based on the method of synthesis, covering several classifications of established nanomaterials.
The methods currently used to obtain synthesis of nanoparticles are generally known under the generic names of “bottom up” and “top-down”.(Fig.1) The method “top-down” – from obtain “high” to “low” (nano) are realized through the mechanical shredding or grinding, heating or repeated toughening, or with lithographic techniques. The “bottom up” procedures or self-assembly are more used in the synthesis of nanoparticles and in the development of many synthetic methods such as homogeneous nucleation of liquid and vapor, heterogeneous nucleation on substrates, etc. The wide variety of nanostructured materials, in terms of shape, size, dimensionality, chemical composition and uses imposed the necessity of their classification.
After their form, nanostructured materials are classified into several groups that are presented below. Quantum dots (Fig.2), quantum well are nanostructures which are represented by crystalline nanoparticles, with spherical or bucilar shape, extremely small (1-100), which represent a new type of semiconductor. The “Quantum dot” (quantum dot) notion was introduced for the first time in nanotechnology by scientists Hirozuki Sakaki and Zauhiho Arakawa, in 1982, with the implementation of the laser that was inspired by innovative technology. Quantum dot and quantum wells are nanostructures found today in integrated circuits (embedded systems). They have forms ranging from pyramids and cylinders (vertical dots) or are free powders, showing a spherical structure, referred to as nanocrystals. Clusters and nanocrystals have sizes of 0,2 – 1 nm, and spherical form and have particular applicability in the field of semiconductors, catalysis and electrocatalysis (in fuel cells). The cluster concept was used for the first time by Robert Boyle in 1661, in his book: The Sceptical Chymist . The term cluster is synonymous with the term “aggregate” which consists of a number N> 3 atoms or molecules, which may be the same, resulting in homo-atomic clusters or homo-molecular, or can be composed of two or more different particles leading to hetero-atomics clusters or hetero-molecular.
Depending on their chemical composition, clusters can be metallic or non-metallic. Nanotubes (Fig.3) - nanostructures that present a lumen of nanometric dimension and variable length, being useful in energy storage devices, sports clothing and shoes, water filters, etc. Nanorods (Fig.4) - nanostructures with form of filaments with nanoscale diameter and relatively higher length being applicable in hyperthermia for cancer treatment, in devices storing and emitting energy, in display technologies (display), etc. Nanowires (Fig.5)-represented in the form of nanofilament nanostructures with semiconductor properties. Nanostructured films – are very thin layers, coating, usually nature oxides, which are performing in the photocatalysts, sensors, biosensors and solar cells.
Richard W. Siegel classified nanomaterials after dimensionality 0D, 1D, 2D and 3D (Fig.6). For example 0D nanomaterials (zero dimensional) are represented by quantum dots, nanocluster, metal nanocrystallites (Pd, Pt, Au, Cu, Zn, Ni, Co, Rh) and semiconductor (ZnS, PbS, CdS) continuous nanostructures of atoms or molecules that possess all sizes in nanoscale; 1D nanomaterials (unidimensionale) are the ones that posses one size in nanoscale and are represented by nanostructures such as: nanofire: Au, Ag, Pt, Sn, Al, etc; nanochains and nanoribbons; nanobelts: ZnO (hexagonal), SnO2 (rutile type), CdO (NaCl type structure), Ga2O3; carbon nanotubes with single wall, type MWCNT – carbon nanotubes with more walls.
Researches in nanotechnology are constantly evolving. The various shapes, sizes and structures of nanoparticles is a testament to modern market of requirements’ materials. The properties exhibited by nanoscale materials include the information that contributes to achieving the goal, this being getting functional performance on a low scale with minimal costs, whether they be semiconductors, hyperthermia agents, magnetic materials, sensors, catalysts or photocatalysts. A number of regulations in this area focuses on environmental policy, toxicity or biocompatibility, elements that contribute to enhance people’s lives.
This work was supported by A.L.P.H.A.-Pupils Comenius Bilateral Project (2013-1-RO1-COM07-296201)
We warmly thank Tamara Slatineanu and other Romanian teachers for their support.