The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

Much progress has been made over the past ten years on the synthesis of monodisperse spherical nanocrystals. Mechanistic studies have shown that monodisperse nanocrystals are produced when the burst of nucleation that enables separation of the nucleation and growth processes is combined with the subsequent diffusion-controlled growth process through which the crystal size is determined. Several chemical methods have been used to synthesize uniform nanocrystals of metals, metal oxides, and metal chalcogenides. Monodisperse nanocrystals of CdSe, Co, and other materials have been generated in surfactant solution by nucleation induced at high temperature, and subsequent aging and size selection. Monodisperse nanocrystals of many metals and metal oxides, including magnetic ferrites, have been synthesized directly by thermal decomposition of metal-surfactant complexes prepared from the metal precursors and surfactants. Nonhydrolytic sol-gel reactions have been used to synthesize various transition-metal-oxide nanocrystals. Monodisperse gold nanocrystals have been obtained from polydisperse samples by digestive-ripening processes. Uniform-sized nanocrystals of gold, silver, platinum, and palladium have been synthesized by polyol processes in which metal salts are reduced by alcohols in the presence of appropriate surfactants.

Synthesis of monodisperse spherical nanocrystals.

The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.

/pdf/towards-a-definition-of-inorganic-nanoparticles-from-an-4qpaj5a6q5.pdf

Towards a definition of inorganic nanoparticles from an environmental, health and safety perspective

Understanding the correlation between magnetic properties and nanostructure involves collaborative efforts between chemists, physicists, and materials scientists to study both fundamental properties and potential applications. This article introduces a classification of nanostructure morphology according to the mechanism responsible for the magnetic properties. The fundamental magnetic properties of interest and the theoretical frameworks developed to model these properties are summarized. Common chemical and physical techniques for the fabrication of magnetic nanostructures are surveyed, followed by some examples of recent investigations of magnetic systems with structure on the nanometer scale. The article concludes with a brief discussion of some promising experimental techniques in synthesis and measurements.

Magnetic Properties of Nanostructured Materials

An overview of the structure and magnetism of spinel ferrite nanoparticles and their synthesis in microemulsions

We have determined the Curie temperature ${\mathit{T}}_{\mathit{c}}$ of ferrimagnetic ${\mathrm{MnFe}}_{2}$${\mathrm{O}}_{4}$ nanoscale particles by means of direct measurement of the magnetization. A considerable enhancement in ${\mathit{T}}_{\mathit{c}}$ compared to the bulk was observed for particles in the size range 7.5 to 24.4 nm. At d=7.5 nm, ${\mathit{T}}_{\mathit{c}}$ is 97 K higher than for the bulk material. The shift in Curie temperature is well described by the finite-size-scaling formula [${\mathit{T}}_{\mathit{c}}$(d)-${\mathit{T}}_{\mathit{c}}$(\ensuremath{\infty})]/${\mathit{T}}_{\mathit{c}}$(\ensuremath{\infty})=(d/${\mathit{d}}_{0}$${)}^{\mathrm{\ensuremath{-}}1/\ensuremath{\nu}}$ with \ensuremath{\nu}=0.71\ifmmode\pm\else\textpm\fi{}0.07 and ${\mathit{d}}_{0}$=2.0 nm.

Size-dependent Curie temperature in nanoscale MnFe2O4 particles.

Preparation of manganese ferrite fine particles from aqueous solution

Magnetic properties of aerosol synthesized iron oxide particles

Barium ferrite fine particles have been synthesized from ferric nitrate and barium nitrate aqueous solution by an aerosol technique. The as-received particles showed a spin-glass behavior with a history-dependent low-field magnetization below 180 K. An exothermic peak with an initial crystallization temperature of 687 degrees C was found by DSC (differential scanning calorimetry) analysis. Heat treatments above this temperature greatly changed the magnetic properties and morphologies without changing the Ba/Fe atomic ratio, which was 1/12. Heat-treated samples had coercivities and saturation magnetizations as high as 5360 Oe and 70.6 emu/g, respectively. >

Z.X. Tang

Papers

Size-dependent Curie temperature in nanoscale MnFe2O4 particles.

Preparation of manganese ferrite fine particles from aqueous solution

Magnetic properties of aerosol synthesized iron oxide particles

Magnetic properties of aerosol synthesized barium ferrite particles

Magnetization reversal in ferrite magnets