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.

Use of CeO2-based oxides in the three-way catalysis

Applications Rosaria Ciriminna,† Alexandra Fidalgo,‡ Valerica Pandarus, Franco̧is Beĺand, Laura M. Ilharco,*,‡ and Mario Pagliaro*,† †Istituto per lo Studio dei Materiali Nanostrutturati, CNR, via U. La Malfa 153, 90146 Palermo, Italy ‡Centro de Química-Física Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tećnico, Complexo I, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal SiliCycle Inc., 2500, Parc-Technologique Boulevard, Quebec City, Quebec G1P 4S6, Canada

The Sol–Gel Route to Advanced Silica-Based Materials and Recent Applications

The use of nanocomposites in materials processing can lead to monophasic or multiphasic ceramics, glasses or porous materials, with tailored and improved properties. This review deals with a variety of nanocomposites such as sol–gel, intercalation, entrapment, electroceramic and structural ceramic types, which exhibit superior properties when compared to the monophasic or microcomposite alternatives. The utilization of nanocomposites in materials processing is forecasted to have a major impact in catalytic, sensor, optical, electroceramic and structural ceramic materials.

Feature article. Nanocomposites

On the basis of the analysis of key engineering factors predominating in a reactive precipitation process, a new method called high-gravity reactive precipitation (HGRP), which means that reactive precipitation takes place in high-gravity conditions, is presented here for the massive production of nanoparticles. A rotating packed-bed reactor was designed to generate acceleration higher than the gravitational acceleration on Earth. The syntheses of nanoparticles of CaCO3, aluminum hydroxide, and SrCO3 were employed to demonstrate the advantages and industrial potentials of this technology, where the typical gas−liquid−solid, gas−liquid, and liquid−liquid multiphase reaction systems were involved. Experimental results show that the mean size of CaCO3 particles can be controlled and adjusted in the range of 17−36 nm through the change of operation conditions such as high-gravity levels, fluid flow rates, and reactant concentrations. Nanofibrils of aluminum hydroxide of 1−10 nm in diameter and 50−300 nm in le...

Synthesis of Nanoparticles with Novel Technology: High-Gravity Reactive Precipitation

Synthesis of nanocrystalline nickel-zinc ferrite by the sol-gel method

Glass-metal nanocomposites incorporating ultrafine particles of iron, nickel, cobalt and manganese, respectively, in a silica glass matrix have been prepared by heat treatment of a gel derived from a sol containing silicon tetraethoxide and a suitable metal organic compound. Metal particles in all the nanocomposites are isolated and spherical-shaped with diameters ranging from 3 to 10 nm. Films of these nanocomposites with thickness of the order of a few micrometres have been prepared on glass slides by a simple dip-and-pull technique. Optical absorption spectra of the nanocomposite films have been measured over the wavelength range 200 to 2000 nm. Effective medium theories of Maxwell-Garnett and Bruggeman, respectively, have been used to calculate theoretically the optical absorption of these materials. The Maxwell-Garnett theory gives results which are in better agreement with experimental data than those obtained from Bruggeman formalism. The filling factor f as estimated from the least-squares fit of the experimental results with the Maxwell-Garnett theory has a value in the range 1 to 4%.

https://iopscience.iop.org/article/10.1088/0022-3727/22/9/025/pdf

Glass-metal nanocomposite synthesis by metal organic route

Stable cubic ZrO2 up to a temperature of 1173 K has been synthesized by a chemical precipitation technique. Such a stability appears to be driven by particle size. The critical value below which cubic ZrO2 has been found to be stable is 17 nm. The x-ray diffraction pattern of such ultrafine cubic particles is similar to that obtained by stabilization of ZrO2 by the addition of 20 mole % CaO.

Stability of cubic phase in nanocrystalline ZrO2

Ultrafine iron particles prepared by a sol‐gel route are characterized by Mossbauer spectroscopy and transmission electron microscopy. The Mossbauer absorption patterns consist of a ferromagnetic component superposed on a superparamagnetic doublet. The intensity of the superparamagnetic doublet is found to be larger for particles having smaller average diameter. For very fine particles a diffused electron diffraction pattern is observed. It is also shown that the sol‐gel technique could be used to prepare fine particles of a Fe‐Cr alloy.

Mössbauer spectra of nanocrystalline Fe and Fe‐Cr particles in sol‐gel‐derived SiO2 glass

Glass-metal nanocomposites involving iron, nickel and copper in a silica glass matrix have been prepared as films on glass substrates by the sol-gel route. The metal phase is introduced as chloride and silicon tetraethoxide is used as the glass precursor. DC electrical resistivity of these nanocomposites has been measured over the temperature range 100 to 350 K. Resistivities varying from 10 Omega m to 106 Omega m have been obtained by controlling the volume fraction of the different metal phases within the silica glass. Low-temperature resistivities of the samples are controlled by a simple activation with energies in the range 0.01-0.1 eV. At temperatures above 150 K some of the nanocomposites exhibit another activated mechanism. The latter is believed to arise due to hopping of electrons between the localised states formed by the distributed metal atoms within the silica glass matrix.

http://iopscience.iop.org/article/10.1088/0022-3727/23/8/016/pdf

A. Chatterjee

Papers

Synthesis of nanocrystalline nickel-zinc ferrite by the sol-gel method

Glass-metal nanocomposite synthesis by metal organic route

Stability of cubic phase in nanocrystalline ZrO2

Mössbauer spectra of nanocrystalline Fe and Fe‐Cr particles in sol‐gel‐derived SiO2 glass

Electrical conduction in sol-gel derived glass-metal nanocomposites