Other Synthesis Methods

Recently, the VLS growth method has been extended beyond the gas-phase reaction to synthesis of Si nanowires in Si-containing solvent (Holmes et al, 2000). In this case 2.5-nm Au nanocrystals were dispersed in supercritical hexane with a silicon precursor (e.g., diphenylsilane) under a pressure of 200-270 bar at 500°C, at which temperature the diphenylsilane decomposes to Si atoms. The Au nanocrystals serve as seeds for the Si nanowire growth, because they form an alloy with Si, which is in equilibrium with pure Si. It is suggested that the Si atoms would dissolve in the Au crystals until the saturation point is reached then they are expelled from the particle to form a nanowire with a diameter similar to the catalyst particle. This method has an advantage over the laser-ablated Si nanowire in that the nanowire diameter can be well controlled by the Au particle size, whereas liquid metal droplets produced by the laser ablation process tend to exhibit a much broader size distribution. With this approach, highly crystalline Si nanowires with diameters ranging from 4 nm to 5 nm have been produced by Holmes et al. (2000). The crystal orientation of these Si nanowires can be controlled by the reaction pressure. 

In the context of using these simpler and cost-efficient techniques for device applications, Konenkamp et al. [39] fabricated vertical LEDs using ZnO nanowires grown by electrodeposition from aqueous solutions on fluorine-doped Sn02-coated glass substrates. Because during electrodeposition the growth of ZnO columns 

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Besides the synthesis methods for porous membranes and their modification methods discussed above, other synthesis methods have been reported. These are outlined below. Preparation of dense membranes is discussed in Section 2.2. The other types are the so-called dynamically formed membranes which... 

Synthesis of Polysilanes. The most commonly utilized method is based on the Wurt/ type alkali metal coupling or dichlorosilanes. Other synthesis methods include dehydrogenative coupling, ring-opening polymerization, polymerization of masked disilenes. electrochemical synthesis, and polymer modification. 

A new compound formed during a novel silicothermal synthesis of O-sialon from clay, silica and elemental Si was found to have similar Al and Si NMR spectra to O-sialon. This NMR observation led to its subsequent identification as a low-temperature form which was previously unknown because other synthesis methods require higher temperatures, at which the low-temperature form is unstable, and conversion to the more usual high-temperature form has occurred (Barris et al. 1997). 

Other synthesis methods have also been developed but may not be practiced on a large commercial scale as compared to those indicated above. Examples of syntheses that begin from liquid phase precursors include the sol-gel, hydrothermal, and Pechini methods. In the course of these reaction schemes, polycondensation or precipitation occurs, and the volatile components are removed, often by thermal methods. Other synthesis routes to ceramic materials include the nitridation of metals to form metal nitrides and the carbothermal reduction of oxides to form carbides and borides. 

According to other synthesis methods, 3 can be prepared by coupling of the N - -dialkylated 2-(N-nitroimino)-hexahydro-l,3,5-triazine (21, R = alkyl, ary-lalkyl) with 2-chloro-5-(ffiloro-methyl)-l,3-thiazole (22, CCMT Table 29.2.1.9) at the 3-position and subsequent ring cleavage reaction of the resulting bis-aminal structure within the sbc-membered system of 23 (Scheme 29.2.1.3) [42, 43, 44]. 

Professor DeSimone s group at North Carolina has focused on carrying out polymerization reactions in supercritical fluids (7representative example is shown in Figure 4(b), where a fluorinated monomer which is soluble in CO2 is polymerized via free radical reactions. Control of molecular weight distribution has been achieved and the rates are comparable to other synthesis methods. As a direct result, there is considerable commercial interest in using supercritical CO2 as solvent replacement for fluorinated polymer synthesis. 

Several other synthesis methods such as hydrolysis [20], pyrolysis [21,22], hydrothermal [10,23], and free-drying [24] methods are often used to fabricate ceramic nanoparticles, including calcium phosphates and carbonates, metal oxides, as well as nonoxides such as metal sulfates. Due to space limitations, these methods are not expanded here but it is important to note that the versatility of these methods provides rich opportunities to manufacture, modify, and functionalize complex nanoparticles or other nanoarchitectures. 

Traditionally, anion-exchange resins have been made by a two-stage set of reactions (although other synthesis methods are now being used). The first step is a Friedel-Crafts reaction to attach the chloromethyl group to the benzene rings of styrene-divinylbenzene copolymer. Then the anion exchanger is formed by reaction of the chloromethylated resin with an amine. The most common type of... 

Several methods have been developed for synthesizing the M-N4 macrocycle modified CNTs. The method most widely employed is the impregnation method [129, 134-142, 144], in which the Me-N4 macrocyclic complexes are first impregnated into CNTs in a solution and subsequently the M-N4 macrocycle modified CNT composites are obtained by evaporation of solvent. In some smdies, the acquired composites are further heat-treated in inert gas atmosphere [138, 141, 144]. The other synthesis methods to produce the M-N4 macrocycle modified CNTs include electrochemical deposition [128, 133] direct deposition [131, 132] and chemical vapor deposition [130]. 

In addition to the standard poly-condensation in PPA, other synthesis methods were proposed in literature, e.g. by using novel preparation media containing methane-sulfonic acid and P2O5 [5, 6, 8]. Recently, in our laboratory, we synthesized a series of PBIs via a... 

Pereniguez et al. [101] have prepared LaNiOs as precursor of Ni/La20s for methane reforming reactions upon reduction and compared USS preparation with solution combustion and hydrothermal synthesis. The citric acid-assisted synthesis of LaNiOs, named spray pyrolysis -F combustion, produced a material with intrinsically improved catalytic activity compared to the other synthesis methods. As described above, the combustion of the citric acid induced a larger specific surface area and the smallest LaNiOs crystallites (12 nm, XRD). By comparison, the synthesis in the absence of citric acid produced average crystallites... 

In the view of the above section, it is clearly seen that coupling of hydrothermal method with microwave radiation is widely studied in the literature. In this section, we will shortly discuss some possible combination of microwave heating with other synthesis methods. 

In addition to the classical methods of LDH synthesis, many other synthesis methods are also frequently employed to prepare LDHs salt oxide (or hydroxide) method, non-equilibrium and non-conventional aging method, surface synthesis, electro synthesis, template synthesis, etc. [20]. 

Therefore, the so-called co-precipitation method was introduced by many research groups to obtain greater homogeneity and better electrochemical properties, as can be seen from Figure 5.8 [29-31]. In addition, the modified sol-gel method to prepare macroporous structure also leads to a remarkable increase in cycle life, as shown in Figure 5.9 [32]. Based on this consideration on homogeneity, a lot of other synthesis methods were applied for preparing this kind of material [33-35]. 

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