Tetraethylorthosilicate , mesoporous

Figure 1. Scheme for the liquid crystalline templating mechanism proposed by Kresge et al 1 for synthesis of mesoporous silica MCM-41. Formation of a hexagonal array of cylindrical micelles possibly mediated by silicate anions followed by condensation of the silicate anions from the silicate source (tetraethylorthosilicate) leads to templated framework structure. Calcination or extraction of the template produces hexagonally ordered mesoporous silica. 

The variety of finely divided silica known as hexagonal mesoporous silica (HMS) [6,34] is generally prepared by the copolymerization of a silica precursor such as tetraethylorthosilicate (TEOS), in presence of a suitable template. This acid or base catalyzed reaction follows the sol-gel route and it has been found [28] that during silica preparation by this technique, it is also possible to add an organotriethoxysilane [RSi(OEt)3] that would... 

PCH materials offer new opportunities for the rational design of heterogeneous catalyst systems, because the pore size distributions are in the supermicropore to small mesopore range (14-25A) and chemical functionality (e.g., acidity) can be introduced by adjusting the composition of the layered silicate host. The approach to designing PCH materials is based on the use of intercalated quaternary ammonium cations and neutral amines as co-surfactants to direct the interlamellar hydrolysis and condensation polymerization of neutral inorganic precursor (for example, tetraethylorthosilicate, TEOS) within the galleries of an ionic lamellar solid. 

Synthesis of Acid-Prepared Mesoporous Spheres (APMS).3 Tetraethylorthosilicate (TEOS, 5.65 g, 27.1 mmol) was added to a solution of cetyltrimethylammonium bromide (CTAB, 1.20 g, 3.30 mmol) in aqueous acid (4.40 g cone. HC1, 55.5 g H20). This mixture was stirred for 1 hour and then transferred to a teflon-lined Parr autoclave and heated at 150 °C for 40 minutes. The mixture was cooled and filtered to recover a white powder. APMS could also be prepared at temperatures between 80 and 230 °C by adjusting the heating time (lower temperatures, longer times). 

Various mesoporous silica materials were synthesized using a non-ionic surfactant as template in the presence of different platinum salts in the synthetic gel. The salts were found to influence the structure and porosity of the solids obtained. Thus, our results show that platinum salts promote the hydrolysis of tetraethylorthosilicate (TEOS) and the presence of (NH4)2PtCl4 or H2PtCl6 leads to the formation of materials with smaller pore sizes and less condensed than those obtained in the absence of platinum salts or in the presence of (NH3)4PtCl2. 

This builds on the key research carried out on titanium-doped mesoporous solids and their use in selective oxidations using hydrogen peroxide. Catechol and hydroquinone are now manufactured commerdally using the Enichem catalyst TS-1 (prepared from tetraethylorthosilicate and tetraethylorthotita-nate71) and hydrogen peroxide.72 Traditional methods of manufacture have low atom efficiency and the successful exploitation of new greener catalytic methods in such processes is very important.73,74... 

The Mo-MCM-41 mesoporous molecular sieves (0.5, 1.0, 2.0, 4.0 Mo wt%) were synthesized using tetraethylorthosilicate (TEOS) and (NH4)6Mo7024 4H20 as the starting... 

The influence of alkali/silica molar ratio in the synthesis of mesoporous molecular sieve materials was studied in a simple synthesis system containing tetraethylorthosilicate, water, alkali and the cetyltrimethylammonium bromide at room temperature. The resulting silicate materials were characterized by XRD, Si MAS NMR, TEM and N2 adsorption-desorption isotherms. The results suggest that the formation of different surfactant-silicate aggregation array morphology not only relies on an interaction between silicate ions and the surfactant, but also on a proportion of the silicate species to surfactant. 

PbS hollow nanospheres with diameters of 80-250 nm have been synthesized by a surfactant-assisted sonochemical route from Pb(CH3COO)2, thioacetamide, and sodium dodecylbenzenesulfonate [3]. 200-400 nm hollow silica spheres with mesoporous walls were prepared by the application of ultrasound to a mixture of nonionic polyoxyethylene surfactant and tetraethylorthosilicate. The presence of surface-active agents during ultrasonic synthesis was proved to be effective because surfactants can act as soft templates as well as structure directing agents for the assembly and subsequent... 

A final example of the influence of microwave treatment on adsorption materials involves the synthesis of mesoporous silica materials known as FUD-1. Preparations of FUD-1 used microwave heating both with and without humic acid treatment. The materials were synthesized with a poly(ethylene oxide)-poly-(butylene oxide)-poly(ethylene oxide) triblock copolymer as a template and tetraethylorthosilicate (TEOS) as the source of silica. In addition to being well characterized, the resultant materials were also tested for their ability to adsorb Cd ions from solution at a fixed pH of 6. The incorporation of humic acid into FUD-1 led to significantly higher adsorption capacity of Cd + ions than materials without humic acid. As a result, these materials seem to be promising adsorbents for removal of cadmium and related heavy metal ions from aqueous waste streams. 

Functionalization within the mesopores can also affect the pore size. MCM-41 samples contain a large concentration of silanols which can be functionalized via simple elimination reactions. For example, reaction of silanol groups with tetraethylorthosilicate results in the liberation of ethanol and the... 

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