What Is Nanoparticles?

Nanoparticles
Nanoparticles are defined as the microscopic particles with at least one dimension less than 100 nm. Nanoparticles are of immense scientific interest because of their vast potential applications in biomedicines, computer, electronics, and defense industries. Nanoparticles are of great scientific and technological interests because they can effectively act as bridge between the bulk form and atomic or molecular structures of the materials. Bulk materials possess constant physical and chemical properties regardless their sizes while nano-scaled materials possess varying properties depending on their sizes [Marignier, J.L., Belloni, J., Delcourt, M.O., Chevalier, J.P. Microaggregates of nonnoble metals and bimetallic alloys prepared

Cobalt ferrite nanoparticles are of utmost importance that can be used for biological applications due to their magnetic properties, stability in physiological conditions, low cytotoxicity, as well as biocompatibility [Schwertmann, U., Cornell, R.M. Iron oxides in the laboratory: Preparation and characterization 2nd ed.Willey-VCH, Weinheim: New York, 1991]. Cobalt ferrite is a cubic ferrite with inverse spinel structure, where Co+2 ions are located in B sites and Fe+3 ions are both located at A and B sites. The unit cell is characterized by a length of 8.38 Å and the interaction distances are b = 2.963 Å, u = 0.2714 Å, p = 2.963 Å, q = 0.3106 Å, r =38.336 Å and s = 3.127 Å [A. Goldman, “Modern Ferrite Technology”, New York: Van Nostrand Reinhold, (1990)]. Cobalt ferrite is characterized by high anisotropy values than the normal ferrites such as magnetite and maghemite. The anisotropy constant of bulk cobalt ferrite is in the range 1.8-3.0 x 106 erg/cm3 and the saturation magnetization is 80.8 emu/g at room temperature and 93.9 emu/g at 5 K [L.D. Tung, V. Kolesnichenko, D. Caruntu, N.H. Chou, C. T. O Connor, L. Spinu, “Magnetic properties of ultra fine cobalt ferrite nanoparticles,” J. Appl. Phys., Vol. 93 (2003) 7486-7488]. In cobalt ferrite, as

For synthesis of cobalt ferrite nanoparticles different techniques such as coprecipitation, hydrothermal, thermal decomposition, and microemulsion have been adopted so far. Among these techniques, hydrothermal synthesis is an easy and cost effective technique which can be carried out at the laboratory scale. This process is carried out using aqueous solutions of the reactant which are in the sealed container called autoclaves at high temperature (130-250 °C) and high pressures (0.3-4 MPa). Temperature, time, and solvent used in reaction are important parameters affecting the final product of the synthesized nanoparticles. Usually the nanoparticles size increases with increasing temperature and reaction time. An important and generalized method of hydrothermal synthesis for crystalline ferrite and iron oxide nanoparticles was recently given by Li et al. [Wang, X., Zhuang, J., Peng, Q., Li, Y. A general strategy for nanocrystal synthesis. Nature 2005, 437:121-124]. They used solid-liquidsolution reaction to prepare different nanocrystals under different reaction temperatures. Using this technique also prepared monodispersed single crystalline ferrite microspheres [Deng, H., Li, X., Peng, Q., Wang, X., Chen, J., Li, Y. Angew.