Process solvothermal

To increase the crystallization rate and to alter the product phase, an alkaline mineralizer is sometimes added to the solvothermal reaction. Some researchers believe that, compared with the hydrothermal process, solvothermal synthesis allows the product to be free from foreign ions because the organic solution, having a low relative permittivity, is free from ionic species. When precursor gels are prepared from alkoxide, one can prepare products free of foreign ions. However, when the precursor gel is prepared by precipitation from salt solutions, or when alkali/acid mineralizer or ionic surfactant is added to the solvothermal crystallization system, the above statement is a myth. In fact, ions are easily adsorbed or occluded in the product particles because of the low dielectric constant of the organic solvent. 

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-... 

Fig. 1.4 SEM images of caved cuboctahedral hexagonal copper sulfide (CuS covellite) crystals, synthesized by a solvothermal process in ethylene glycol, at 140 °C. (Reprinted in gray scale with permission from [52], Copyright 2009, American Chemical Society)...

Lu Q, Hu J, Tang K, Qian Y, Zhou G, Liu X (2000) Synthesis of nanocrystaUine CuMS2 (M = In or Ga) through a solvothermal process. Inorg Chem 39 1606-1607 Wu C, Yu S-H, Antoniette M (2006) Complex concaved cuboctahedrons of copper sulfide crystals with highly geometrical symmetry created by a solution process. Chem Mater 18 3599-3601... 

The presence of triethylenetetramine in the hydrothermal synthesis of open-framework zinc phosphates results in a number of frameworks with one- to three-dimensional structures. The structures include one-dimensional ladders, two-dimensional layer structures, and one structure where the tetramine is bound to the zinc center. The structural type was highly sensitive to the relative concentration of the amine and phosphoric acid.411 Piperazine and 2-methylpiperazine can be used as templating molecules in solvothermal syntheses of zinc phosphates. The crystallization processes of the zinc compounds were investigated by real time in situ measurements of synchrotron X-ray powder diffraction patterns.412... 

Li, F. Zhang, Z. 2005. Synthesis of high quality CdS nanorods by solvothermal process, and their photoluminescence./. Nanoparticle Research 7 685-689. 

Aita Y, Komatsu M, Yin S, Sato T (2004) Phase-composihonal control and visible light photocatalyhc achvity of nitrogen-doped htania via solvothermal process. J Solid state Chem 177 3235-3238. 

It seems useful to understand the mechanisms involved in the chemistry and in the electrochemistry of sulfur and polysulfides. During the last 10 years, more than 90 papers deahng with solvothermal synthesis of chalcogenides MxE or binary chalcogenides MxM Ez (E = S, Se, or Te) have been published. In a typical process, a metal and/or a metallic salt is heated in a solvent (benzene, toluene, pyridine, ethylenediamine, water, etc.) at 100-200 ° C in the presence of an excess of chalcogen (see for instance Ref. 125). These empirical syntheses would benefit from a sound understanding of the involved mechanisms. 

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... 

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. 

Jiang, L. and Gao, L., Carbon nanotubes-magnetite nanocomposites from solvothermal processes formation, characterization, and enhanced electrical properties , Chemistry of Materials, 2003, 15, 2848-2853. 

In this chapter we discuss preparative routes for inorganic materials in three basic types of systems involving the presence of a distinct solid-liquid interface those in which the liquid and solid phases are of the same chemical identity (solidification and vitrification processes), those in which the liquid and solid phases are not of the same chemical identity (crystallization, precipitation), and the special case in which the liquid phase is a pure ionic liquid or molten salt. Ionic liquids can serve as the solvent as well as a templating agent, and the liquid components may or may not become incorporated into the final solid product. We also discuss two areas where the distinct solid-liquid interface becomes somewhat blurred namely, sol-gel and solvothermal processes. 

A solvothermal process is one in which a material is either recrystallized or chemically synthesized from solution in a sealed container above ambient temperature and pressure. The recrystallization process was discussed in Section 1.5.1. In the present chapter we consider synthesis. The first solvothermal syntheses were carried out by Robert Wilhelm Bunsen (1811-1899) in 1839 at the University of Marburg. Bunsen grew barium carbonate and strontium carbonate at temperatures above 200°C and pressures above 100 bar (Laudise, 1987). In 1845, C. E. Shafhautl observed tiny quartz crystals upon transformation of freshly precipitated silicic acid in a Papin s digester or pressure cooker (Rabenau, 1985). Often, the name solvothermal is replaced with a term to more closely refer to the solvent used. For example, solvothermal becomes hydrothermal if an aqueous solution is used as the solvent, or ammothermal if ammonia is used. In extreme cases, solvothermal synthesis takes place at or over the supercritical point of the solvent. But in most cases, the pressures and temperatures are in the subcritical realm, where the physical properties of the solvent (e.g., density, viscosity, dielectric constant) can be controlled as a function of temperature and pressure. By far, most syntheses have taken place in the subcritical realm of water. Therefore, we focus our discussion of the materials synthesis on the hydrothermal process. 

Solvothermal process is now becoming a powerful technique for preparing nanomaterials. It is analogous to hydrothermal synthesis, except that non-aqueous solvents replace water as reaction medium. From the chemical reaction point of view, solvents in supercritical conditions play a significant role in reaction and crystallization. New materials, especially those having metastable phases and special nanostructures, can be obtained under mild conditions. By sealing the reaction system in an autoclave, the reactants and products prevent effectively from oxidation, hydrolysis and volatilization, and the reaction and crystallization can be realized synchronously. 

We have developed solvothermal synthesis as an important method in research of metastable structures. In the benzene-thermal synthesis of nanocrystalline GaN at 280°C through the metathesis reaction of GaClj and U3N, the ultrahigh pressure rocksalt type GaN metastable phase, which was previously prepared at 37 GPa, was obtained at ambient condition [5]. Diamond crystallites were prepared from catalytic reduction of CCI4 by metallic sodium in an autoclave at 700°C (Fig.l) [6]. In our recent studies, diamond was also prepared via the solvothermal process. In the solvothermal catalytic metathesis reaction of carbides of transition metals and CX4 (X = F, Cl, Br) at 600-700°C, Raman spectrum of the prepared sample shows a sharp peak at 1330 cm" (Fig. 1), indicating existence of diamond. In another process, multiwalled carbon nanotubes were synthesized at 350°C by the solvothermal catalytic reaction of CgCle with metallic potassium (Fig. 2) [7]. 

Figure 1. Raman spectra of the sample prepared by solvothermal process through the catalytic reduction [6] (left) and the catalytic metathesis reaction (right).

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. 

In addition to the catalytic solvothermal synthesis of carbon nanotubes (Fig. 2) [7], SiC nanowires and tubular structures (Fig. 8) were prepared through a solvothermal reduction-carburization route using silicon powders and CCI4 as Si and carbon sources [20], Si3N4 nanorods were also prepared with a similar process [12]. 

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