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.

Synthesis, properties, and applications of magnetic iron oxide nanoparticles

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

The interest in the preparation and application of nanometer size materials is increasing since they can exhibit properties of great industrial interest. Several techniques have been proposed to produce nanomaterials using supercritical fluids. These processes, taking advantage of the specific properties of supercritical fluids, are generally flexible, more simplified and with a reduced enviromental impact. The result is that nanomaterials with potentially better performances have been obtained. We propose a critical review of the supercritical based techniques applied to the production of nanoparticles, nanofibers, nanowires, nanotubes, nanofilms and nanostructured materials. The most relevant characteristics of each process and the kind of nanomaterial that can be produced are highlighted.

Nanomaterials and supercritical fluids

Binary transition metal oxides (BTMOs) possess higher reversible capacity, better structural stability and electronic conductivity, and have been widely studied to be novel electrode materials for supercapacitors. In this review, we present an extensive description of BTMO materials and the most commonly used synthetic methods. Furthermore, we review several notable BTMOs and their composites in application of supercapacitors. With the increasing attention for energy storage, more and more exciting results about BTMO materials will be reported in the future.

Binary metal oxide: advanced energy storage materials in supercapacitors

Ce1 − xZrxO2
solid solutions are produced continuously by hydrolysis of mixtures of cerium
ammonium nitrate and zirconium acetate in near-critical water at ca.
300 °C and 25 MPa using a flow reactor. Rapid hydrothermal
coprecipitation leads to nano-particulate Ce1 − xZrxO2
(x = 0–1),
the composition of which is largely determined by the initial relative concentrations
of Ce4+ and Zr4+ ions in the starting solution.
The freshly prepared materials are crystalline, possess very small particle
sizes, and have high surface areas. The effects of calcining the products
in air at high temperature have been studied. Apart from the 1∶1 Ce∶Zr
solid solution, the phases of Ce1 − xZrxO2
remain stable on calcining to 1000 °C, but the particles sinter
and the surface areas decrease significantly. The materials have been characterised
by Powder X-ray Diffraction (PXD), IR and Raman Spectroscopy,
microanalysis, Thermogravimetric Analysis (TGA), X-ray Fluorescence (XRF)
and BET (surface area measurements). In selected cases, high resolution
Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM)
images were recorded to examine the particle morphology.

Continuous hydrothermal synthesis of inorganic materials in a near-critical water flow reactor; the one-step synthesis of nano-particulate Ce1 − xZrxO2 (x = 0–1) solid solutions

Magnetic spinel type oxides such as magnetite, Fe3O4, cobalt, nickel, and zinc ferrites, MFe2O4
(M = Co, Ni, Zn) and the mixed nickel and cobalt ferrite, NixCo1 − xFe2O4 have been synthesised continuously by the hydrolysis and simultaneous oxidation of mixtures of Fe(II) acetate and different M(II) acetates in near-critical and supercritical water using a flow reactor. The materials have been characterised by powder X-ray diffraction (PXD) and, in selected cases, by transmission electron microscopy (TEM). The bulk composition of the samples was determined by Atomic Absorption analysis (AA). Additionally, Energy-dispersive Detection X-ray analysis (EDX) was carried out on some of the samples. TEM pictures showed a “bimodal” particle
size distribution: small particles of ca. 10 nm and larger particles of up to 100 nm, both of which are highly crystalline. Possible reaction mechanisms are discussed, which may be responsible for the observed morphology. The effects of temperature and residence time on the reaction have been studied.

The continuous hydrothermal synthesis of nano-particulate ferrites in near critical and supercritical water

A continuous and clean one-step synthesis of nano-particulate Ce1−xZrxO2 solid solutions in near-critical water

Gram-scale quantities of microcrystalline powdered 
CeO2–ZrO2 solid solutions can be produced 
continuously in a near-critical water flow reactor at ca. 300 
°C and 25 MPa; rapid hydrothermal co-precipitation leads to 
nano-particulate 
Ce1−xZrxO2
 (x = 0 to 1), the composition of which is merely determined 
by the initial concentrations of Ce4+ and Zr4+ ions 
in the starting solution.

Albertina Cabanas

Papers

Continuous hydrothermal synthesis of inorganic materials in a near-critical water flow reactor; the one-step synthesis of nano-particulate Ce1 − xZrxO2 (x = 0–1) solid solutions

The continuous hydrothermal synthesis of nano-particulate ferrites in near critical and supercritical water

A continuous and clean one-step synthesis of nano-particulate Ce1−xZrxO2 solid solutions in near-critical water

A Continuous and Clean One‐Step Synthesis of Nano‐Particulate Ce1‐xZrxO2 Solid Solutions in Near‐Critical Water.