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A series of new layered inorganic-organic nanocomposites, with organic functionalities directly bonded to an inorganic framework via the Si-C bond, were prepared by a template sol-gel synthesis. These layered Al-and Mg-silsesquioxanes were precipitated at room temperature by addition of aqueous base to an alcohol solution containing a mixture of AlCl 3 or MgCl 2 and a trialkoxysilane with a n-dodecyl, n-octyl, n-pentyl, 3-methacryloxypropyl, isobutyl, or phenyl functionality. The Si/Al and Si/Mg ratios of the reaction mixtures were 2:1 and 4:3, respectively, and were chosen to match the composition of clay mineral pyrophyllite (layered aluminosilicate) and talc (layered magnesiosilicate). X-ray diffraction and electron microscopy show that the products are crystalline with a layered structure. A comparison of basal spacings and length of the organic functionalities is consistent with a ∼10 Å inorganic layer and a bilayer arrangement of R groups for Alsilsesquioxanes and an interpenetrating arrangement of R groups for Mg-silsesquioxanes. FTIR and 13 C NMR spectra indicate that in the products the Si-C bond is intact and silanes are fully hydrolyzed, while the organic functionalities filling the interlayer space are in a solid-like environment. 29 Si NMR spectra reveal that silanes are not fully condensed and that the degree of condensation is higher in Mg-silsesquioxanes than Al-silsesquioxanes. Broad in-plane diffraction peaks and a variety of Al coordination states observed by 27 Al NMR are best explained by the defects in a clay-like inorganic framework caused by trifunctional Si. The most crystalline products were formed from long-chain alkyl-trialkoxysilanes with Al, while trialkoxysilanes with shorter R groups gave less well-organized structures. This dependence on chain length suggests that the formation of the layered structure is due to self-assembly of the hydrolyzed trialkoxysilanes into lamellar micelles. The micelles act as a template for the formation of a clay-like inorganic framework by condensation between the silanols and aqueous metal species attracted by the negatively charged surfactant layers. Although the thermal stability of R group limits high-temperature applications, these materials may find use as sorbents, environmental barriers, polymer fillers, catalytic supports, or chemical sensors.

Reductive dehalogenation, mediated by nonspecific biomimetic Co macrocycles, was studied in aqueous systems using carbon tetrachloride as a model compound. Two water-soluble macrocycles, cobalt t e t r a k i s( Nm e t h y 1-4-p y r i d i n i u my1 ) p or p h y r i n (CoTMPyP) cation and cobalt tetrasulfophthalocyanine (CoPcTs) anion, were used as homogeneous and mineral-supported catalysts. The supported catalysts were prepared by exchanging CoTMPyP on the hectorite, fluorohectorite, and amorphous silica surface and by exchanging CoPcTs on the layered double hydroxide surface. Supported macrocycles were catalytically active in the dechlorination of CC14 and the initial reaction rates followed Michaelis-Menten kinetics. The value of vmax was correlated to the previously reported orientation of macrocycles in the interlayers and to the accessibility and electronic state of the metal center, following the order: CoTMPyPsilica > CoPcTs-layered double hydroxide > CoT-MPyP-fluorohectorite > CoTMPyP-hectorite. In both heterogeneous and homogeneous systems, volatile reaction products accounted for less than 30% of CC14 degraded. In short-term experiments (2 h), homogeneous CoTMPyP was more active than heterogeneous catalysts, while homogeneous CoPcTs was deactivated due to aggregation, and degraded less CC14 than supported CoPcTs. In long-term experiments (3 days), where large CC14/macrocycle ratios were used, silica-supported CoTMPyP was more active than homogeneous CoTMPyP, suggesting that adsorption stabilized the catalyst.

Abstract--Phenol (benzenol) oxidation by three synthetic manganese oxides (buserite, manganite, and feitknechtite) has been studied in aerated, aqueous, acidified suspensions. The rate of reaction was pH dependent. Oxidation was greatly enhanced below pH 4, when diphenoquinone and p-benzoquinone were identified as the first products. Initial reaction rate was correlated with standard reduction potential (E ~ of the oxides following the order: feitknechtite > manganite > buserite. A more gradual process of phenol oxidation after the initial reaction was influenced by electrochemical properties of the solution. High soluble manganese activity and increase in pH adversely affected reaction rates. Thus, the reactivity of the oxides was related to their stability and possibly the ability to readsorb Mn(II), following the order: buserite > manganite > feitknechtite. The results indicate that thermodynamic and electrochemical data for oxides and phenols are useful in predicting under which conditions phenols can be oxidized by a given system.

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