Centimeter-sized crystals of pyridine dodecasil 3C (all silica zeolite ZSM-39) have been prepared using hydrothermal seeded growth techniques and characterized by differential scanning calorimetry, nuclear magnetic resonance, optical microscopy and powder X-ray diffraction.

Arylene- and alkylene-bridged polysilsesquioxanes were prepared by sol-gel processing of bis(triethoxysilyl)-arylene monomers 1-4, and alkylene monomers 5-9. The arylene polysilsesquioxanes were porous materials with surface areas as high as 830 m2/g (BET). Treatment with an inductively coupled oxygen plasma resulted in the near quantitative removal of the arylene bridging groups and a coarsening of the pore structure. Solid state 29Si NMR was used to confirm the conversion of the sesquioxane silicons (T) to silica (Q). The alkylene-bridged polysilsesquioxanes were non-porous. Oxygen plasma treatment afforded silica gels with mesoporosity. The porosity in the silica gels appears to arise entirely from the oxidation of the alkylene spacers.

Microporous zeolites can be synthesized using organic structure-directing molecules whose function is to organize inorganic species into particular topologies that then spontaneously self-assemble into the final crystalline materials. Extension of the zeolite assembly process to the use of organic molecular aggregates as structure-directing agents yields ordered mesoporous materials like MCM–41 and MCM–48. A unifying picture of the assembly processes ocurring in the syntheses of micro- and mesoporous materials is presented.

It is shown that ceramics derived from polycarbosilane polymers may develop an open nanoporous network after heat treatment to a temperatures between 1300 and 1550°C in argon. The resulting SiC-based ceramics were characterised by N2 gas adsorption analysis and X-ray diffraction. The apparent surface area, and pore volume increase with increasing heat treatment temperature, reaching values of 170 m2g-1 and 0.12 cm3-1 respectively. The pore network develops as the SiC crystals grow and as carbon is ejected from the structure. It is thought that the porosity may reside within the carbon phase, but this remains to be confirmed.

The use of lyotropic liquid crystal phases is a promising tool in tailoring the porous structure of inorganic gels. In this work, we examine the effect of hexagonal liquid crystal phases produced with quaternary ammonium surfactants on the textural ordering of silica gels.

The sol-gel polymerization of the silicon alkoxide precursor (tetramethoxysilane) is followed by 29Si NMR and rheological measurements. The structural evolution of the material from the starting sol to the thermally treated gel is studied using low angle X-ray diffraction. The textural characteristics of the gels are correlated with the nature of the surfactant molecules.

Microporous silica gels have been synthesized through a nano-particulate sol-gel route. These gels have uniformly distributed and extremely small pores(< 15Â in diameter). Hydrolysis and condensation reactions leading to these gels were carried out in an alkyl silicate-water (ammonia) two phase system. These reactions took place at the alkyl silicate droplet-water interfacial boundary. No alcohol was added. A clear, stable and uniformly distributed colloidal silica suspension having an average particle size less than 6 nm was prepared by this method. Fast hydrolysis, slow condensation and low solubility all contribute to a high supersaturation level and result in the formation of small particles. This process is consistent with classic nucleation theory. When the particles are produced under acidic rather than under basic reaction conditions, smaller particles are formed due to the slower condensation rate and lower solubility of these silica particles in acidic conditions. At the same pH, alkylsilicates having smaller alkyl groups react faster with water leading to smaller primary particles. Homogeneous nucleation conditions are achieved when the water/alkylsilicate ratio is high.

In view of the outstanding role that silicic acids (sa.) play in inorganic materials a survey will be presented regarding the possibilities of the integration of sa. in organic matrices via chemical reactions. The objective is to combine the advantageous properties of the silicic acid with those of the organic compounds in order to generate novel materials. The reactions of silicic acids with organic molecules, as studied by 29Si NMR spectroscopy, are described using the silicic acid H8Si8O20 with a defined double four-ring structure as an example. By silylation of the hydrophilic H8Si8O20 its functional organophilic derivatives were synthesized. The s.a. derivatives with epoxy-, alkoxy-, HSi-, ketoester or unsaturated groups are capable of condensation, polymerization, complexation or additive reactions leading to reactive inorganic-organic precursors or polymers with the defined silicic acid unit. The synthesis and structure of the following s.a. containing precursors and polymers will be reported, (a) inorganic-organic polymers with a high content of silanol groups, (b) microporous polymers free of silanol groups and (c) metal (Al, Zr) alkoxide complexes attached to defined silicic acid units. The model reactions of the double four-ring silicic acid derivatives can be transferred to technical silicic acid solutions prepared from water glass. The presented reaction pathways are a basis for the preparation of a great variety of new inorganic-organic compounds with tailor-made structures and properties which can be used for highly homogeneous and stoichiometric materials.

A novel synthetic methodology has been developed for preparing monodisperse colloidal silica-cadmium sulfide nanocomposite spheres in the 50 – 300 nm size regime. This methodology uses water-in-oil microemulsions as the reaction medium. Monosize silica colloids are first produced by the controlled hydrolysis of tetraethyl orthosilicate in the micro water droplets of the microemulsion. Cadmium sulfide quantum dots are incorporated into the silica colloids during synthesis by the introductions of Cd2+ and S2- microemulsions. Various morphologies of the nanocomposite are fabricated by controlling the heterogeneous coagulation of CdS and SiO2. Unique high surface area silica particles can be prepared when nitric acid etches out the CdS and leaves behind topologically defined voids. The CdS nanocomposites are new materials useful for non-linear optics, while the high surface area silica particles should have novel applications in areas such as catalysis.

Monosized and anisotropically capped CdS nanocrystals have the property to self-connect into a polymeric material. The viscosity of this fibrous material can be adjusted to fabricate texturized and homogeneous coatings. These films can be thermally converted into pure CdS films. Based on the size dependent band gap of this semiconductor, the absorbance of the film can be fine-tuned through the size of the particle-precursor or by controlling the film heat treatment. The evolution of the film nanostructure with temperature was investigated by optical absorption, DTA, SEM and X-ray diffraction techniques.

Semiconductor nanoparticulates are important materials bridging the gap in size and electronic properties between molecular species and bulk materials. Synthetic approaches to producing controlled sized clusters of this sort will be described, covering physical encapsulation in zeolites or porous glass and extending to discrete syntheses using surface terminating reagents. The optical properties of the resultant materials will be described in detail and the structural topology of the clusters elucidated by combined powder and single crystal diffraction. Thermal transformations of these clusters into bulk materials will be tracked and the processing possibilities explored for the production of polycrystalline films and polymer/semiconductor composites. Photoconductivity in the latter composites will be described.

A new route for preparing CdX (X = S, Se, Te, S+Se) nanocrystallites dispersed in a sodium borosilicate glass matrix from a hydrogel is proposed. Chalcogenizing complexing molecules - for instance a mixture of NH4SCN + H2SeO3 - introduced in the starting solution allowed an in situ crystallite preparation concomitant to gel densification. Prevention of crystallite oxidation is thus obtained. Moreover, coalescence is minimized because of the low gel-glass transition temperature. Low temperature absorption spectra have been interpreted in terms of exciton and electron-hole confinements, accounting for both an intrinsic broadening of energy states inside each nanocrystal and a Gaussian size distribution. Crystallite sizes and size dispersion can be adjusted by changing the initial Cd concentration. The crystallinity of the nanoparticles without change in dispersion is strongly improved by thermal treatment above the Tg of the glass matrix.

Pillaring of highly basic layered double hydroxides (MgnAl(OH)2n+2Cl, n=2–5) with octameric polysilicate (Si8O208-) has been achieved via a direct ion exchange route.

A new type of sol-gel-based transparent inorganic-organic nano composites has been developed by increasing the inorganic phase dimension to values just below the point, where scattering can be neglected. For this purpose, nanosized boehmite particles ≤ 50 nm are homogeneously incorporated in a sol based on tetraethoxysilane and an epoxysilane. The nano-scale boehmite particles act as catalysts for the polymerization of the epoxy silane to polyethylene oxide, as proved by 13C NMR, and are linked to the matrix by Si-O-Al bridges, as proven by 27Al-NMR spectroscopy. The synthesized sols can be applied by standard coating techniques on transparent polymers and are cured thermally. The mechanical properties (scratch resistance, hardness) have been substantially improved compared to systems with molecular dimensions of the inorganic phase. The effect is attributed to the special structure of flexibly suspended nano-scale boehmite particles in an inorganic-organic network by a tailored interface.

An overview of several NMR studies of liquids in confined geometries is presented. First, the NMR relaxation rates, 1/T1, 1/T1ρ , and 1/T2 were measured for several molecular liquids confined to porous silica glasses with pore radii in the range from 12 Å to 100 Å as a function of temperature, pore size, and frequency. The experimental relaxation data were interpreted in terms of bulk, surface, and topological contributions using the following expression:

where 1/Tib and 1/Tis are the bulk and the surface layer relaxation rates, ε is the thickness of the surface layer, R is the pore radius, and Ai(ω) represents the pure topological effect.

Second, the pressure effects on the dynamics of the confined liquid of acetonitrile-d3 were also investigated. Third, the natural abundance of 13C spin lattice relaxation rates for CS2 confined to porous silica glasses provided information about confinement effects on the angular momentum behavior of this simple liquid.

The dynamical properties of hybrid materials obtained from mixtures of silicon alkoxides and polyethers are studied. Different techniques are used to analyze the mobility of the different parts of the material: thermal analysis (DSC, DTMA) and NMR to probe the collective motion modes and EPR to probe the local scale. The motions are dependent on the organic ratio in the blend and the covalent grafting between the two phases. Some structural models of these blends are proposed.

Diffusion coefficients of water and cyclohexane in porous sol-gel glass of average pore diameter 2.9 nm were obtained using a radioactive tracer technique. This information was applied to calibrate the membrane in the diaphragm cell which was subsequently used to measure the diffusion coefficients for cyclohexane, acetone, toluene, acetonitrile, and chloroform. Results for cyclohexane were compared with computer simulation of molecular motion of cyclohexane in a model cylindrical pore of diameter 2.9 nm. Translational motion of polar liquids inside the pores was found to be faster than that of neutral, not wetting solvents.

Sol-gel derived siloxane oxide materials are an entirely new family of hybrid systems at the frontier between silicones and glasses or ceramics, with a large variety of potential applications. Better control of the chemistry involved in their preparation should lead to an improvement in their properties, and this requires an investigation of the whole process, from the solution to the final materials. Nuclear Magnetic Resonance is a very suitable technique for this purpose, and this paper will give some illustrations on model systems (CH3)2SiO/TiO2, (CH3)2SiO/ZrO2, prepared from dimethyldiethoxysilane and titanium or zirconium alkoxides. It will be focused mainly on the use of 170 solution NMR which clearly shows the formation of Si-O-Ti or Si-O-Zr bonds, but also their disappearance during the aging process. 29Si MAS-NMR spectra of dried gels confirm that the difunctional units are mainly in polydimethylsiloxane chains, and that the system is phase separated. However, the use of cross-polarization techniques involving lK and 29Si nuclei will allow the detection of small number of units in a more constrained environment, certainly close to oxide-based particles.

As shown in another communication to Symposium V, nano-sized aluminas enriched in pentacoordinated aluminum (Alv) are obtained through the limited hydrolysis of aluminum alkoxides. Here the surface properties of these aluminas are investigated from the catalytic point of view. The goal is to obtain geometrical information on the Lewis acid sites. 1H→27A1 (cross-polarization) high resolution MAS NMR, using chemisorbed NH3 which acts as a XH spin reservoir, allows the direct observation of surface Al involved in the catalytic site. The polarization transfer from these protons to surface Al is remarkably efficient because of the relatively short A1:N-H distance. It is observed that the main Lewis acid sites are located on distorted tetrahedral aluminum and pentacoordinated Al. These results are compared to low temperature infrared data of adsorbed CO.

Fe(II)C2H5PO3. H2O has been prepared via prolonged reaction between iron oxychloride and ethylphosphonic acid in acetone, in a sealed tube. The lamellar structure is very similar to that of previously reported divalent metal phosphonates M(II)(RPO3). H2O (M= Mg, Mn, Ni, Zn). The compound shows sign of 2D antiferromagnetic correlations above the Néel temperature Tn=24K and a weak ferromagnetic behavior is observed below TN. We also report on the preparation methods and the crystal structures of two new anhydrous copper phosphonates a-Cu(II)(C2H5PO3), and β-Cu(II)(CH3PO3) which exhibits an original tubular three-dimensional structure. The reactivity of bulky phosphonic acids is also described, with the case of Co(II)(t-C4H9PO3).H2O.

Thin films of crystalline titania with different grain sizes and porosities were prepared by dip-coating on Si (100) substrates starting from a sol-gel process. Three synthesis procedures were developed and compared, using acetylacetone (acac, with HCI) and acetic acid (HOAc) as modifying agents or directly using hydrochloric acid as catalyst. The structural evolution of the films was characterized by Glazing Angle X-ray Diffraction (XRD), Spectroscopic Ellipsometry and Atomic Force Microscopy (AFM). Anatase phase was observed on all of the films calcined at 440° C. The grain sizes and crystallinity generally increased with calcination temperature. Thin films obtained from acac- and HOAc-modified titanium sols had fine grains (50–80 nm) and less porosity (<10%) after calcination at 1000° C. Thin films derived from the sol catalyzed directly with acid had the largest grains (90–130 nm), higher crystallinity and greater porosity (17%).