Solvothermal methods

The solvothermal method is similar to hydrothermal synthesis except for the solvent used. In this procedure, non-aqueous solvents (organic solvents) are used as the reaction medium. The use of organic solvents has been reported to be an effective approach to avoid the oxidation, hydrolysis and volatilization of nano-oxides and their reactants. This method was advantageously exploited to make nanosized ceria-zirconia mixed oxides.  

Fernandez-Gonzalez et al ° synthesized nanostructured praseodymium-doped ceria-titania mixed oxides by the solvothermal method. They used Ce(N03)6(NH4)2, Pr(N03)3 and tetra isopropyl orthotitanate as metal precursors, ethanol as the solvent and acety-lacetone (acac) as the complexing agent. The complexing agent controls the hydrolysis and condensation processes, and helps the stabilization of the heterometallic nanocrystals in organic solvents. The powder obtained was finally calcined. SEM images of the synthesized samples are shown in Fig. 8.7. 

The solvothermal reaction under supercritical conditions is suitable for the synthesis of functional materials, since the reaction rate and equilibrium can be varied by changing the dielectric 

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The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

A very important solvothermal method involves the use of supercritical C02 as an antisolvent that reduces the solvent strength, resulting in the precipitation of the oxide... 

Abstract A colloidal solution of titanium dioxide (TiO ) nanoparticles was prepared by the solvothermal method and dip-coated onto a polypropylene fabric with TMOS binder. The prepared TiO particles, colloidal solution and the coated fabrics were characterized by X-ray diffraction, SEM and TEM. The results showed that the TiO particles prepared by the solvothermal method were composed of anatase which uniformly coated the snbstrate. Photocatalysis induced bactericidal properties of coated fabrics were tested by measuring the viability of Escherichia coli. It was fonnd that solvothermally prepared TiO coatings have the ability to kill E. coli. This nniqne property of TiO makes it an ideal candidate in producing self-sterilizing protective masks and in providing bactericidal and self-cleaning properties to a variety of snrfaces. 

Photocatalysis based on TiO has attracted much attention for enviromnental cleaning and antibacterial applications [1-3], In order to synthesize TiO nanoparticles, various modification of the sol-gel method have been widely used. However, sol-gel prepared TiO requires a post-calcination process for crystallization [4], which limits the applicability of TiO coatings to temperatnre resistant substrates. On the other hand, the solvothermal method, which does not need to be followed... 

Fig. 1.1 Preparation of TiOj nanoparticles by the solvothermal method, and schematic of the...

Crystallization in the anatase structure was reported to occur in the sol-gel processed TiO after calcination between 350°C and 500°C [5]. However, crystallized TiO particles can be produced by using the solvothermal method without any post-treatment. 

TiOj coated fabric filters were prepared in a one-step process by the solvothermal method, and their properties were compared with those electrosprayed with Degussa P25. Filters coated with TiO nanoparticles prepared by the solvothermal method were superior to the commercial TiO powder in terms of particle size and homogeneity. A significant amount of bactericidal activity towards E. coli was successfully implanted into fabric filters by dip coating a solvothermally prepared TiO dispersion. 

Graft polymers can be obtained by reactive extrusion (47). Likewise, the grafting can be performed in solution. In the solvothermal method, the polymer is dissolved in a solvent and the solution is in a vessel. The material can be heated even above the critical point of the solvent (42). In the past, this method was mostly used in inorganic chemistry, however using this method MA could be successfully grafted onto ABS. 

Apart From solvothermal methods, thermolysis of precursors in high boiling solvents, the sol-gel method, hydrolysis and use of micelles have been employed to synthesize the metal oxide nanocryslals. Thus, Park el al.n have used metal-oleales as precursors for the preparation of monodisperse Fe,04, MnO and CoO nanocrystals. 1-Ociadecene, octyl ether and trioclylamine have been used as solven ts. Hexagonal and cubic CoO nanocrystals can be prepared by the decomposition of cobalt acelylacelo-... 

Solvothermal method has been used in synthesis of a series of non-oxide nanomaterials, such as semiconductors [1,2], ceramic materials [3], and in fabricating special nanostructures [4]. It will be an exciting, promising field for designing and preparing advanced materials in the future. This paper focuses on some aspects of recent progress in solvothermal synthesis of non-oxides nanomaterials. 

Cubic boron nitride is an important materia that is widely used in cutting tools and as grinding, abrasive materials. Both Hu et al. [8] and Cui et al. [9] have synthesized cubic BN via this method. By using the solvothermal metathesis reaction of BBrs and LisN, Cui and co-workers obtained better yield of cubic BN, and the TEM image and the XRD pattern are shown in Fig. 3. Some other metastable non-oxides have also been prepared and reported using solvothermal method, e.g. AIN [10-11] and Si3N4 [12]. 

Non-oxide ceramic nanomaterials, such as carbides, nitrides, borides, phosphides and silicides, have received considerable attention due to their potential applications in electronics, optics, catalysis, and magnetic storage. In contrast with the traditional processes, such as solid state reactions, CVD, MOCVD and PVD, which involve using high temperatures, toxic organometallic precursors, or complicated reactions and posttreatments, solvothermal method is a low temperature route to these materials with controlled shapes and sizes. 

Nonaqueous solution methods In addition to the aqueous methods, ceria nanocrystals could also be obtained through a number of nonaqueous solution mefhods, such as the solvothermal methods, ionic liquids routes, polyol routes, as well as reactions in coordinating high-boiling oil solvents. 

Nonaqueous solution methods The syntheses of rare earth phosphate NCs in nonaqueous solutions mainly include the solvothermal method, polyol method, the synthesis in ionic liquids, and the synthesis in high-boiling coordinating solvents like TOPO or OA. 

Haase et al. obtained the monodisperse fluorescent NPs of doped LaP04 through hydrothermal reactions, solvothermal methods, or precipitation in high-boiling solvents (Meyssamy et al., 1999 Riwotzki et al., 2000,2001). Caruso et al. demonstrated biofunctionalization of nano-sized... 

Mixed y-Ga203-Al203 oxides of different stoichiometry were prepared by the solvothermal method from Ga(acac)3 and Al(OPr-i)3 as starting materials and were used as catalysts for selective reduction of NO with methane. The initial formation of gallium oxide nuclei controls the crystal structure of the mixed gallium-aluminum oxides. It is found that the acid density per surface area is independent of the Al Ga feed ratio but depends on the reaction medium (diethylenetriamine, 2-methylaminoethanol, toluene, 1,5-pentanediol etc.), whereby in diethylenetriamine the catalyst had lower densities of acid sites and showed a higher methane efficiency. 

For the preparation of inorganic materials with well-defined morphologies, liquid phase syntheses are preferred. These synthetic reactions proceed at relatively lower temperatures and therefore require lower energies. The sol-gel (alkoxide) method is one of these methods - however, this method usually gives amorphous products, and calcination of the products is required to obtain crystallized products. In this chapter, solvothermal methods are dealt with, which are convenient for the synthesis of a variety of inorganic materials. General considerations for solvothermal reactions are discussed first and then the solvothermal synthesis of metal oxides is reviewed. 

Methods closely connected with solvothermal method... 

Intercalation of organic molecules into layered host lattice produces a variety of organic-inorganic hybrid materials. The solvothermal method provides a reaction system that allows application of high temperatures and therefore is a powerful technique for preparation of intercalation compounds. Exfoliation of layers may occur because of applied high temperatures. For example, exfoliated poly-ethylene/montmoriUonite nanocomposites were reported to be prepared by solvothermal reaction of organophilic montmorillonite with polyethylene in toluene at 170°C for 2... 

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