Nonsiliceous materials

Ti, B, Ni, Cr, Fe, Co, Mn) has been described, as was the synthesis of nonsiliceous materials such as oxides of W, Fe, Pb, Mo, and Sb [18]. Although these materials do not represent tme zeolites, they are highly interesting materials which are commonly covered in the zeolite literature with great potential for shape-selective catalysis of bulky molecules. 

Fusion with anhydrous potassium fluoride in a platinum dish is undoubtedly the simplest, most effective and reliable method available for the complete dissolution of a wide variety of siliceous materials. The potassium fluoride cake can then be transposed in the same container to a pyrosulfate fusion with rapid and complete volatilisation of both hydrogen fluoride and silicon tetrafluoride [54]. Except for a small quantity of barium sulfate, the pyrosulfate cake will dissolve completely in dilute hydrochloric acid. The resulting pyrosulfate fusion is one of the simplest and most effective methods available for rapid, complete and dependable dissolution of nonsiliceous materials, particularly high-fired oxides. This fusion has the distinct advantage that the flux can be obtained by simply adding easily purified alkali metal sulfates to sulfuric acid, and the fusion can be carried out in either borosilicate flasks or platinum vessels with very little contamination from either reagents or containers. 

In this chapter we have tried to show how a rational addition of nentral additives or ligands complexing with either the inorganic or organic reactants, respectively, can be used to control the mesoscopic phase behavior of inorganic-snrfactant composites. The focns has been on siliceous materials, but the approach is applicable also to the synthesis of nonsiliceous materials. The discnssion has been merely qnalitative in natnre, dne to the partial lack of accurate experimental... 

Meanwhile, SDA-mediated syntheses have also been used successfully in the preparation of nonsilica mesoporous metal oxides,54-60 metal sulfides,61 and metal phosphates.62,63 An account devoted to nonsiliceous mesoporous materials and the host-guest chemistry of such systems can be found in a review by Zhao and coworkers.64... 

A combination of several different opaline materials may be found juxtaposed. For example, in fossilized wood both tridymite and crystobalite may be determined in a sample whde adjacent portions of the sample may be composed of opal-A. The silicified wood may be transparent or translucent, clear and colorless, or white, yellow, red, brown, and black, indicating inclusions of other, usually iron-containing, complexes during precipitation of the colloid or gel. The faithfully preserved structures of fossilized wood suggest that the replacement phenomena are molecule-by-molecule processes that take place under low temperamres and pressures, and require concomitant removal of nonsiliceous compounds but do not disrupt the ceUularity of the woody tissues. Alternatively, primary... 

Oxides Compared to silica-based networks, nonsiliceous ordered meso-poious materials have attracted less attention, due to the relative difficulty of applying the same synthesis principles to non-sihcate species and their lower stability (227). Nonsiliceous framework compositions are more susceptible to redox reactions, hydrolysis, or phase transformations to the thermodynamically preferred denser crystalline phases. Template removal has been a major issue and calcination often resulted in the collapse of the mesostracture. This was the case for mesostractured surfactant composites of mngsten oxide, molybdenum oxide, and antimony oxide, and meso-structured materials based on vanadia that were obtained at early stages. Because of their poor thermal stability, none of these mesostructures were obtained as template-free mesoporous solids (85, 228, 229). 

Compared to sihca-based networks, nonsiliceous ordered mesoporous materials have attracted less attention, due to the relative difficulty to apply the principles employed to create mesoporous silica to nonsilica compositions. Other framework compositions are much more sensitive than silica to redox reactions, hydrolysis, or phase transformations. The reactivity of the inorganic precursors is much more difficult to control in the case of transition metal oxides, the reaction kinetics being much faster. Also, crystalline nonsiliceous frameworks are less prone to adapt the curvature of micellar aggregates, whereas the amorphous nature of silica allows for certain flexibility. 

Nonsiliceous Mesoporous Materials via Mediated Coloumbic Interaction (I X S )... 

This elegant methodology can be exploited to synthesize other nonsiliceous mesoporous materials. In fact. Yada et al. observed several similar transformations of lamellar yttrium-based mesophases teinplated by dodecyl sulfate to the corresponding hexagonal phases. In this case, no cubic inesophases were observed, even after long... 

In 1972, this approach for molecular imprinting was modified when Gunter Wulff s research group developed a nonsiliceous cross-linked polymer synthesized around a template molecule. This route was also successfully followed by Shea and Thompson in 1978, who obtained a polymeric material with a predetermined spatial orientation of their functional moieties, a molecularly imprinted polymer (MIP). Both these syntheses were carried out by covalently binding the template to the functional monomei followed by posterior polymerization of the derivatized monomer. Noncovalent approach for imprinted material synthesis was first carried out by Klaus Mosbach e a/, in 1988. This technique of imprinting... 

Silica, Functionalized Silica, Nonsiliceous Metal Oxides, and Sol-Gel-Derived Inorganic and Hybrid Materials... 

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