Sol—gel synthesis

The entire spectrum of tools in synthetic inorganic chemistry, including high temperature methods, precipitation, solvothermal synthesis, sol-gel chemistry, chemical vapor deposition (CVD), and soft matter techniques adopted in part from organo-metallic chemistry, have been applied to synthesize the active mass of catalysts. Table 4.2.1 summarizes basic techniques. The preparation methods differ whether... 

In custom-designing materials with tailored properties, it is often necessary to s)m-thesize metastable phases that will be kinetically stable under the temperature and conditions of use. These phases are obtainable only through kinetic (chemical) control. In many cases, kinetic control has been achieved via the soft chemical low-temperature (e.g. electrochemical synthesis, sol-gel method) and/or topochemical routes (e.g. intercalation, ion exchange, dehydration reactions), since these routes use nuld synthetic conditions. It should be noted that not all soft chemical routes are topochemical. A reaction is said to be under topochemical control only if it follows the pathway of minimum atomic or molecular movement (Elizabe et al., 1997). Accordingly, topochemical reactions are those in which the lattice of the solid product shows one or a small number of... 

There exist a variety of methods to synthesize quasi-one-dimensional nanostructured materials, which include but not limited to vapor phase growth, template-assisted synthesis, sol-gel deposition, surfactant-assisted growth, sonochemical method, hydrothermal method, and electrochemical deposition [21], Among the various methods, the electrochemical anodization method is one of the simplest and cheapest methods to synthesize ordered quasi-one-dimensional nanostructure. 

An important topic of research is the introduction of the catalyst in the microreactor. In brief solid catalysts can be incorporated on the interior of micromachined reaction channels, prior to or after closure of the channel, by a variety of strategies anodic oxidation, plasma-chemical oxidation, flame combustion synthesis, sol-gel techniques, impregnation, wash coating, (electro-)plating, aerosols, brushing, chemical vapor deposition, physical vapor deposition and nanoparticle deposition or self-assembly. Some of these methods can be applied in combination with photolithography or shadow masking. 

Many routes for obtaining template particles are known using molten salt synthesis, hydrothermal synthesis, sol—gel processing, as well as hybrid, multistep methods. The TGG method has been widely used for the development and texturing of piezoelectric ceramics [44]. One of the reasons for this widespread use is the cost consideration, since TGG enables the relatively inexpensive fabrication of textured ceramics with single crystal-Uke properties. However, our present discussion pivots around the mechanical properties. 

Wang et al. [140] have studied amorphous CoSn/C alloys decorated with Pt as highly efficient electrocatalysts for ethanol oxidation. The catalysts were prepared using a two-stage chemical synthesis (sol-gel preparation and Steady-state replacement method). XRD results evidenced that the CoSn-base was in the amorphous state, but the characteristic peaks of the Pt fee crystalline structure appeared after Pt deposition. The TEM images confirmed that Pt was deposited onto CoSn/C. The electrochemical measurements showed that the mass activity of the Pt-CoSn/C catalyst was 454.6mA mgp, , which was about 1.71 and 1.74 times those of Pt/C and PtSn/C. The authors attributed this behavior to the possible modification in the Pt electronic structure elicited by the amorphous CoSn alloy. Materials based on amorphous alloys can open new perspectives regarding ethanol electro-oxidation. 

Hybrid organic-inorganic materials synthesis, sol gel formation... 

In term of boehmite synthesis, sol-gel routes, and more specifically precipitation in aqueous medimn of metalUc salts, are favored techniques for syntheses of inorganic particles with accurate size and shape control. Indeed, by adjusting a set of parameters, nanomaterials with finely tuned characteristics and properties can be obtained. We show that the addition of complexing species (polycarboxylates and polyols) in the reacting medimn may play an important role in the shape and size of oxide nanoparticles. 

It has also been found that polymers possessing functional groups such as amines and pyridines are soluble in pregeUed sol solutions, especially, poly(2-vin5ipyridine) and poly(N-vinylpyrroHdinone) (PVP) (49). There, materials were made as part of a study of the synthesis of nonshrinking sol—gel-derived networks (49). 

Sol-Gel Techniques. Sol-gel powders (2,13,15,17) are produced as a suspension or sol of coUoidal particles or polymer molecules mixed with a Hquid that polymerizes to form a gel (see Colloids SoL-GELtechnology). Typically, formation of a sol is foUowed by hydrolysis, polymerization, nucleation, and growth. Drying, low temperature calciaation, and light milling are subsequently required to produce a powder. Sol-gel synthesis yields fine, reactive, pseudo-crystalline powders that can be siatered at temperatures hundreds of degrees below conventionally prepared, crystalline powders. 

The aim of the present work was optimization of synthesis of SG -polymeric cation exchanger composite films by sol-gel technology in the presence of non-ionic surfactants and their application for detenuination of Zn (II) as phenanthrolinate (Phen) complex. 

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-... 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

Various methods are applied to the synthesis of titania particles including sol-gel method, hydrothermal method [2], citrate gel method, flame processing and spray pyrolysis [1]. To utilize titania as a photocatalyst, the formation of ultrafme anatase titania particles with large crystallite size and large surface area by various ways has been studied [4]. 

For many years, research efforts in materials chemistry have focused on the development of new methods for materials synthesis. Traditional areas of interest have included the synthesis of catalytic, electronic, and refractory materials via aqueous methods (sol-gel and impregnation) and high-temperature reactions [1-3]. More recent strategies have focused on the synthesis of materials with tailored properties and structures, including well-defined pores, homogeneously distributed elements, isolated catalytic sites, comphcated stoichiometries, inorganic/organic hybrids, and nanoparticles [4-13]. A feature... 

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