Alkoxide method

Kato, K. 1998. Low-temperature synthesis of SrBi2Ta209 ferroelectric thin films through the complex alkoxide method Effects of functional group, hydrolysis and water vapor treatment. Jpn. J. Appl. Phys. 37 5178-5184. 

Taramasso et al. (5) had originally reported two methods for the hydrothermal synthesis of TS-1. The first method (mixed alkoxide method) involves the preparation of a solution of mixed alkoxides of titanium and silica (preferably ethoxides) followed by hydrolysis with alkali-free solution of tetrapropylammonium hydroxide (TPAOH), distillation of the alcohol and crystallization of the resulting gel at 448 K. In the second method (dissolved or hydrolyzed titanium method) a soluble tetrapropylammonium peroxo-titanate species was prepared initially and then colloidal SiC>2 (Ludox AS-40) was added. This entire operation had to be carried out at 278 K. The TS-1 samples obtained by these two synthesis routes differed, particularly because of the presence of impurities such as Al3+ usually present in colloidal silica (33). 

Similar procedures adopted for the synthesis of TS-1 (the mixed alkoxide method, dissolved titanium method, pre-hydrolysis method, wetness impregnation method, and promoter induced synthesis method) were also used for the synthesis of TS-2. Tetrabutylammonium hydroxide (TBAOH) instead of TPAOH was used as the template (6,7,305-308). 

Mixed alkoxide method. Synthesis using TPAOH and HF and wetness-impregnation method using TPABr and NH4F... 

Co-precipitation in Aqueous Medium - Despite its effectiveness, the alkoxide method presents some drawbacks for industrial scale-up the high cost of the starting reactants and the requirement for water-free and oxygen-free environment for the alkoxide solutions. 

C) Alkoxide method (5-7) in which an extremely facile hydrolysis of the metal alkoxides readily leads to the formation of the corresponding metal hydroxides. 

Hydrated Ti02, the intermediate product in the alkoxide method, exhibits negligible activity. Usually, the number of crystal defects, which act as, recombination center of e -h+, is reduced by thermal treatment (annealing). 

The reaction of berylliumorganic compounds with alcohols (method 4) or ketones (method 7) yields RBeOR, which usually are stable to further alcoholysis, but the action of the excess of alcohols on BeR2 (R = Me, Et, Pr ) at low temperatures gave Be(OR)2 (R = Me, Bu CEt3) [399], The dimeric Me-BeOMe easily disproportionates with the formation of BeMe2 and insoluble Be(OMe)2 [399], The metathesis of BeCl2 with lithium alkoxides (method 5) was proposed for the preparation of polymeric Be(ORn)2 and Be(OPri)2 [65] however, the IR spectra of the products presented in this publication indicate the presence of considerable amounts of admixtures. 

The metatheis of acetates with the alkali alkoxides (method 5) can be used for the preparation of the methoxides and ethoxides of all three elements and is the only reaction leading to Hg(OR)2 [1623]. The trans-esterification of Zn(OMe)2 (method 6), according to [1121], can be carried out only in the presence of LiOR (forming soluble bimetallic complexes). The direct electrochemical synthesis on the anodic oxidation of metals in alcohols has been described for Zn(OEt)2 and a series of cadmium derivatives (Cd(OR)2 — obtained in the presence of such donor ligands as Dipy, Phen, and Dmso [98]) (method 2). 

The metathesis reaction of metal chloride with alkali alkoxides (method 5) was historically the first approach applied, and it remains the main route to both mono- and bimetallic derivatives of Mn(H). The most efficient approach to Mn(II) derivatives is, however, provided by the alcoholysis of the corresponding silylamide (method 4). The derivatives of Mn(IH) and mixed-valence Mn(H,IH) were obtained by alcoholysis ofMn(III) acetate by polyatomic phenols in the presence of 2,2 -dipyridil accompanied by reduction in the latter case (methods 4 and 4+7). 

The most usual synthetic routes to the derivatives of platinum group metals are the exchange reactions of the complexes containing halide ligands with alkali metal alkoxides (method 5), alcoholysis of the same kind derivatives (usually by phenols, method 4), alcoholysis of hydroxide complexes (method 3), and redox reactions — reduction of chlorides or 0s04 in alcohol media (method 7) (Table 12.25). 

Mixed alkoxide method. Hydrothermal synthesis using tetraethylorthosilicate (TEOS) as the source of Si, tetraethyltitanate (TEOT) as the source of Ti, tetrapropylammonium hydroxide (TPAOH) as structure directing agent (template), base and distilled water... 

Taramasso and others first prepared TS-1 at the end of the 1970s, using two different methods for the preparation of the crystallization gel [10]. In the most commonly used mixed alkoxide method, this was obtained by the controlled hydrolysis of tetraethyltitanate and tetraethylsiUcate in the presence of tetrapropylammonium hydroxide. Crystallization under hydrothermal conditions produced crystalline TS-1. In the preparation of the gel, it is crucial to prevent segregation of Ti phases by the correct choice of procedure and control of the conditions. The maximum Ti content, expressed as the atomic ratio Ti/(Ti-i-Si), was reported to be ca 0.025 [11]. Other information is available in Refs. [6-9] and references therein. 

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. 

M. Kogure, T. Sato, T. Tanaka, S. Yasujima, T. Suzuki and H. Ohya, Preparation of antimony acid cation exchange membranes by using metal alkoxide-gel method, Bull. Chem. Soc. Jpn., 1991, 1991, 1618 H. Ohya, R. Paterson, T. Nomura, S. McFadzean, T. Suzuki and M. Kogure, Properties of new inorganic membranes prepared by metal alkoxide methods. Part I A new permselective cation exchange membrane based on Si/Ta oxides, J. Membr. Sci., 1995, 105, 103-112. 

H. Ohya, K. Masaoka, M. Aihara and Y. Negishi, Properties of new inorganic membranes prepared by metal alkoxide methods. Part III. New inorganic lithium permselective ion exchange membrane, J. Membr. Sci., 1998,146, 9-13. 

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