This paper reports the synthesis of technologically important ferrites such as ZnFe 2 O 4 , NiFe 2 O 4 , MnFe 2 O 4 , and CoFe 2 O 4 by using novel microwave-hydrothermal processing. Nanophase ferrites with high surface areas, in the range of 72-247m 2 /g, have been synthesized in a matter of a few minutes at temperatures as low as 164°C. The rapid synthesis of nanophase ferrites via an acceleration of reaction rates under microwave-hydrothermal conditions is expected to lead to energy savings.

While there are many techniques for the production of nanophase materials, we have been using a hydrothermal process because it is a low-temperature method that can lead to energy savings. A recent innovation is the introduction of microwaves in the hydrothermal system, and we named this process the microwave-hydrothermal (M-H) process. M-H synthesis is a novel processing technology for the production of a variety of nanophase ceramic oxide and metal powders under closed-system conditions. This closed-system technology not only prevents pollution at its source, but also saves energy and, thus, could substantially reduce the cost of producing nanophase powders of all kinds. With several examples, the value of this technique is reviewed here. The M-H technique leads to (a) rapid heating to temperature of treatment, which can save energy and time; (b) increased reaction kinetics by one to two orders of magnitude, which also saves time and energy; (c) formation of novel phases; and (d) selective crystallization.

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A peroxo titanic acid (PTA) solution has been prepared by mixing titanic acid wet gel and hydrogen peroxide solution. The PTA solution was a neutral, transparent, stable liquid. The PTA crystallized to form an anatase phase after calcination at a temperature above 250. When the PTA solution was autoclaved at a temperature above 100 for 6h, it changed to a sol containing anatase crystals less than 20nm in diameter. Aggregation occurred after autoclaving at a temperature above 120. When the PTA solution was heated to 100, it was translucent and stable in spite of containing ultrafine anatase crystals (9nm in diameter). It was deduced that the surfaces of anatase crystals are modified by the peroxo groups.

Synthesis of monodispersed nanophase ␣-Fe 2 O 3 (hematite) powder to be used as a red pigment in porcelains was investigated using microwave-hydrothermal and conventionalhydrothermal reactions using 0.018M FeCl 3 ⅐6H 2 O and 0.01M HCl solutions at 100°-160°C. Acicular and yellow ␤-FeOOH (akaganite) particles 300 nm in length and 40 nm in thickness were dominantly formed at 100°C after 2-3 h, while spherical ␣-Fe 2 O 3 particles 100 -180 nm in diameter were preferentially formed after 13 h using a conventional-hydrothermal reaction. However, a microwave-hydrothermal reaction at 100°C led to monodispersed and red ␣-Fe 2 O 3 particles 30 -66 nm in diameter after 2 h without the formation of ␤-FeOOH particles. In this paper, the effect of microwave radiation during hydrothermal treatment at 100°-160°C on the formation yield, kinetics, morphology, phase type, and color of ␣-Fe 2 O 3 was investigated.

One-dimensional structures such as nanowires, nanofibers, and nanoribbons with high aspect ratios have attracted much attention lately due to their high potential for applications in fabricating electronic devices, sensors, etc. These structures are expected to have their unusual characteristics amplified through quantum size effects, and marked shape-specific effects.[1±3] To obtain one-dimensional materials, organic molecules are often used as a medium or template. The use of sodium bis(2-ethylhexyl)sulfosuccinate (NaAOT) represents an especially powerful tool to synthesize nanowires of materials such as CaSO 4 , [4] BaSO 4 , [5] Cu, [6] BaCrO 4 , [7] BaWO 4 , [8] and CdS. [9] Less-ordered hexagonal mesostructured SnO 2 , templated by NaAOT has also been reported. [10] Ceria (CeO 2 ) and ceria-based materials have been extensively used as solid electrolytes in solid oxide fuel cells; as automotive catalysts, utilizing their oxygen storage capacity; as absorbents for fluoride ion or arsenic-based compounds; and as substances to filter out ultraviolet rays. Ceria and ceria-based compounds obtained in nanostructured forms are thus expected to be promising as materials that show interesting properties through shape-specific and/or quantum size effects. Nanostructured ceria, synthesized using organic molecules, has been previously reported in the literature. Masui et al. reported the synthesis of monodisperse ceria nanoparticles with diameters of 2.6 nm in reverse micelles composed of AOT (bis(2-ethylhexyl)sulfosuccinate) anions.[11] Less-ordered mesoporous ceria was synthesized using alkyltrimethylammonium bromide as a template.[12] Ordered mesoporous ceria templated by hexadecylamine has also been reported.[13]Macroporous ceria was obtained by a nanotectonic approach based on the template-directed assembly of organically functionalized ceria crystalline particles by poly(c-benzyl-L-glutamate). [14] In this paper, we report for the first time the synthesis of cerium compound nanowires and nanorings templated by AOT anions and alkyl alcohols. We also demonstrate nanostructural control of the cerium compound nanostructures by the carbon number of the incorporated alkyl alcohol. Figure 1a shows the transmission electron microscopy (TEM) image of a solid synthesized in the presence of NaAOT after a reaction time of 5 h. Nanowires were obtained with widths of several tens of nanometers and lengths of the order of micrometers. The sulfur to cerium, or AOT to cerium molar ratio, determined by energy dispersive X-ray (EDX) analysis was 0.37, indicating that AOT molecules were incorporated in the solid. Figure 1b is an enlarged image of the nanowire and shows stripes, suggesting the formation of a layered structure composed of a cationic cerium-based inorganic sheet with a thickness of 2.0 nm, and an anionic AOT bilayer with a thickness of 1.0 nm, as shown in the schematic representation of Figure 2. When the synthesis was performed in the presence of both butyl alcohol and NaAOT, instead of only NaAOT, similar but more ...