The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

In this feature article, syntheses of nanosized particles by using colloidal assemblies as a template are described We asked ourselves the following question:  What parameters play a role in the control of the size, shape, and polydispersity? We know that parameters such as the shape of colloidal assemblies, the hydration of the head polar group, the water molecules bounded to the interface, etc play a major role However, there are a number of exceptions preventing any generalization It is shown that the chemical mechanism in nanoparticles production in colloidal assemblies can differ from those usually observed in homogeneous solution This shows that the solution chemistry cannot always be transferred to colloidal systems It is possible to select the size and markedly reduce the polydispersity by a surface treatment of the nanoparticles This favors formation of mono- and multilayers made of nanoparticles, and it is found that these particles form crystals organized in a three-dimensional face-cent

Nanosized Particles Made in Colloidal Assemblies

Nanotechnology has spurred efforts to design and produce nanoscale components for incorporation into devices. Magnetic nanoparticles are an important class of functional materials, possessing unique magnetic properties due to their reduced size (below 100 nm) with potential for use in devices with reduced dimensions. Recent advances in processing by chemical synthesis and the characterisation of magnetic nanoparticles are the focus of this review. Emphasis has been placed on the various solution chemistry techniques used to synthesise particles, including: precipitation, borohydride reduction, hydrothermal, reverse micelles, polyol, sol–gel, thermolysis, photolysis, sonolysis, multisynthesis processing and electrochemical techniques. The challenges and methods for examining the structural, morphological, and magnetic properties of these materials are described.

Chemically prepared magnetic nanoparticles

The paper presents a critical overview on magnetic nanoparticles and microspheres used as separation media in different fields of chemistry, biochemistry, biology, and environment protection. The preparation of most widely used magnetic iron oxides in appropriate form, their coating or encapsulation in polymer microspheres, and functionalization is discussed in the first part. In the second part, new developments in the main application areas of magnetic composite particles for separation and catalytical purposes are briefly described. They cover separations and isolations of toxic inorganic and organic ions, proteins, and other biopolymers, cells, and microorganisms. Only selected number of relevant papers could be included due to the restricted extent of the review.

Preparation and properties of magnetic nano-and microsized particles for biological and environmental separations

Functionalized reverse micelles are used to control the size and the polydispersity of the metallic and semiconductor particles. The size of the particles can be controlled, either by the amount of water solubilized in the droplets, or by the solvent used to form reverse micelles, or by adding macrocyle molecules.

Synthesis “in situ” of nanoparticles in reverse micelles

Micellar factors which play a role in the control of the nanosize particles of cobalt ferrite

The use of dispersed media to synthetize microparticles in “situ” has made considerable progress in the last few years: Reverse micelles[1], Langmuir-Blodgett films[2], zeolites[3], vesicles[4], glass matrices and sol-gel methods[5].Semiconductor nanocrystals present quantum confinement effects, called Q-dots[6]. To control the size and the shape of nanoparticles reverse and normal micelles, bicontinuous and lamellar solutions have been used.

N. Moumen

Papers

Synthesis “in situ” of nanoparticles in reverse micelles

Micellar factors which play a role in the control of the nanosize particles of cobalt ferrite

Control of the Size and Shape of Nanoparticles

Nanosized Particles: Self-Assemblies, Control of Size and Shape