Mesoporous silicas were modified with titanium alkoxide precursors. Results are consistent with a model that describes the resultant silica surface as a mixture of Si–OH groups, isolated Si–O–Ti type species, and oligomeric (-Ti-O-)n ensembles. Decreasing the rate of hydrolysis of the precursor by using chelated Ti-alkoxides increases the fraction of isolated Ti.

Computer modeling of fluids in zeolites can provide a detailed molecular level understanding of the process of adsorption and diffusion under the influence of the 3-D potential field and the confinement offered by the crystal structure. We have shown that there is a strong link between the location, geometry and energetics of sites and the observed thermodynamics and spectroscopy of the adsorbates. Here we report on the modeling of Xe in zeolite Y, which is of interest both because it is commercially important and because it offers two distinct adsorption sites.

The coadsorption of acetonitrile (ACN) or deuterated acetonitrile (dACN) with CO at Cu-ZSM-5 reveals several interesting features concerning the partial valency of Cu. Specifically, CO binds at Cu+1 and Cu° centers (in the absence of preadsorbed ACN) and exhibits C-O stretching frequencies of 2157 cm−1 and 2112 cm−1, respectively. Carbon monoxide readily adsorbs at an ACN (or dACN) saturated Cu-ZSM-5 and exhibits a C-O stretch of 2122 cm−1, a value more consistent with a partially reduced Cu+1 center. Furthermore, the IR cross section for the CN stretch in a number of nitriles (ACN, dACN, and benzonitrile) coadsorbed with CO displays interesting effects attributed to rehybridization and changes in CN dipole moment.

Addition of surfactants in TEOS derived sols leads to micro- or mesoporous materials whose porous texture can be varied by changing the surfactant quantity and/or chain length. This series of materials, with a relatively narrow pore size distribution, is well adapted to study the potentialities of an innovative characterization technique like 129Xe Nuclear Magnetic Resonance in comparison with Small Angle X-ray Scattering and N2 adsorption. SAXS revealed a high surface rugosity of the materials and a good correlation with pore hydraulic radius distributions measured by N2 adsorption. Using 129Xe NMR, we have studied the Xe chemical shifts (δXe,) as a function of pXe, and have pointed out several original results showing the importance, for microporous materials, of the NMR line shapes and of the slope of the lines δXe.=f(pXe).

The electronic and vibrational spectroscopy of one family of metal germanium sulfide open-framework materials, designated Cat2FeGe4S10 (Cat = (CH 3)4N, Cs), along with their precursor Cat4Ge4S10 germanium sulfide clusters have been studied. Ultraviolet-visible and midinfrared reflectance spectroscopy has been used to study the electronic states. The reflectance spectroscopy of the frameworks is dominated by the d-d transitions of the Fe(II) in a S4 symmetry site. The vibrational spectroscopy has been analyzed by Fourier transform Raman. The frameworks are weakly vibrationally coupled. Their spectra contain vibrational modes that are nearly identical in frequency to those of the isolated cluster. There is a fortuitous window in the cluster vibrations in which framework modes of the Fe(II) center can be observed. In addition computational methods have been used to model the experimental results.

We performed in-situ photoluminescence and Raman measurements on an anodized silicon surface in the HF/ethanol solution used for anodization. The porous silicon thereby produced, while resident in HF/ethanol, does not immediately exhibit intense photoluminescence. Intense photoluminescence develops spontaneously in HF/ethanol after 18–24 hours or with replacement of the HF/ethanol with water. These results support a quantum confinement mechanism in which exciton migration to traps and nonradiative recombination dominates the de-excitation pathways until silicon nanocrystals are physically separated and energetically decoupled by hydrofluoric acid etching or surface oxidation. The porous silicon surface, as produced by anodization, shows large differences in photoluminescence intensity and peak wavelength over millimeter distances. Parallel Raman measurements implicate nanometer-size silicon particles in the photoluminescence mechanism.

23Na and 23Na/19F double resonance MAS NMR methods have been used to study the binding of hydrofluorocarbon-134 (CF2HCF2H) in zeolites NaY and CsY. The interaction of HFC- 134 with the sodium cations is so strong that the sodium cations in the sodalite cages (site I') migrate into the supercages to bind to the hydrofluorocarbon molecules.

We have used a novel technique, measurement of stress isotherms in microporous thin films, as a means of characterizing porosity. The stress measurement was carried out by applying sol-gel thin films on a thin silicon substrate and monitoring the curvature of the substrate under a controlled atmosphere of various vapors. The magnitude of macroscopic bending stress developed in microporous films depends on the relative pressure and molar volume of the adsorbate and reaches a value of 180 MPa for a relative vapor pressure, P/Po = 0.001, of methanol. By using a series of molecules, and observing both the magnitude and the kinetics of stress development while changing the relative pressure, we have determined the pore size of microporous thin films. FTIR measurements were used to acquire adsorption isotherms and to compare pore emptying to stress development, about 80% of the change in stress takes place with no measurable change in the amount adsorbed. We show that for sol-gel films, pore diameters can be controlled in the range of 5 – 8 Å by “solvent templating”.

Recent NMR studies by Nakayama et al. on sodium zeolite A saturated with potassium metal have implied the presence of the anionic Na− species. This, if confirmed, would represent the first observation in a zeolite and opens up a wide range of possibilities for mixed metal zeolitic systems. We report the results of a number of metal combinations, using both sodium and potassium forms of zeolite A as hosts, studied by ESR, solid state MAS-NMR and powder neutron diffraction.

Continuum and stochastic mathematical models are introduced describing zeolite nucleation and crystal growth from precursor gels. Model predictions are in agreement with existing experimental results. For example, the maximum in the nucleation rate profile under constant supersaturation is observed well before substantial crystallization occurs. Moreover, simulations indicate a strong influence of the gel microstructure on apparent crystallization kinetics, as well as particle size and morphology.

Heteropolyacid hydrates of the general form H3PM12O40. nH2O are of interest to researchers in areas such as proton conductivity and catalysis. The water molecules in these hydrated acids reside in the interstitial volume between the large Keggin anions and can, under certain conditions, complex with the acidic protons to form stable cations such as the “dioxonium” ion (H5O2+). We have used incoherent inelastic neutron scattering (IINS) measurements of dodecatungstophosphoric acid hexahydrate (H3PW12O40 · 6H2O) to obtain the vibrational density of states spectrum of H5O2+ stabilized by the PW12O403− Keggin anions. Spectra were measure for fully hydrogenated and fully deuterated ions in order to determine the relative merit of previous assignments of the normal mode vibrations.

Developing very thin molecular sieve films (<lμm), required by many zeolite filmbased applications, has been found continually to be a technical challenge. The synthesis strategy of this work is to elucidate some of the parameters that influence the morphology, orientation, surface coverage density and thickness of Si-ZSM-5 films on supported substrates. Three different methods to grow zeolite coatings on fused silica have be studied and compared. The zeolite films have been characterized by field emission-SEM, XRD, sorption study and transmitting spectroscopy. At the early stage of crystal growth, the gel layer spontaneously condensed on the substrate surface may have a large porosity of 15%. The strong affinity to grow the (010) faces along the substrate surface is possibly responsible for the preferred orientation of the films. The conditions for synthesis of closely packed coatings, consisting of sub-micron crystals with preferred orientation, are also identified. Engineering issues for fabrication of low optical scattering zeolitic films will also be discussed for designing molecular sieve optical devices.

We have synthesized periodic mesoporous silica thin films (PMSTF) from homogeneous solutions. To synthesize the films a thin layer of a pH = 7 micellar coating solution that contains TMOS is dip- or spin-coated onto silicon wafers, borosilicate glass, or quartz substrates. Ammonia gas is diffused into the solution and causes rapid hydrolysis and condensation of the TMOS and the formation of periodic mesoporous thin films within ∼10 seconds. The combination of homogeneous solutions and rapid product formation maximizes the concentration of desired product and provides a controlled, predictable microstructure. The films have been made continuous and crack-free by optimizing initial silica concentration and film thickness.

The influence of microstructure on the properties of zeolite films and means of controlling the former (film thickness, crystal orientation) are the theme of this report. Firstly, the formation of thin silicalite films from regrowth of nanocrystalline silicalite/alumina composite films is presented. The crystallites at the intergrown top layer are oriented with their straight channels parallel to the substrate film. The membranes show H2/N2 selectivities of about 60 at 150 °C.This high selectivity is attributed to the orientation of the separating layer. Secondly, the formation of oriented multilayers of zeolite L crystallites by alternating dippjpg of a glass substrate in a bohemite and a “plate-like” zeolite L suspensions is illustrated. Finally, continuous films of zeolite NaA are prepared on various substrates (glass, porous and nonporous alumina) using in situ growth from homogeneous solutions. The films exhibit good adhesion to the substrates. The films prepared on porous alumina disks show He/N2 and O2/N2 selectivities of 10 and 0.4 respectively at 120 °C.

Zeolite films are sought as components of molecular sieve membranes. Different routes used to prepare zeolite composite membranes include growing zeolite layers from gels on porous supports, depositing oriented zeolites on supports, and dispersing zeolites in polymeric membranes. In most cases, it is very difficult to control and avoid the formation of cracks and/or pinholes. Our approach to membrane synthesis is based on hydrothermally converting films of layered aluminosilicates into zeolite films. We have demonstrated this concept by preparing zeolite A membranes on alumina supports from kaolin films. We have optimized the process parameters not only for desired bulk properties, but also for preparing thin (ca. 5 μm), continuous zeolite A films. Scanning electron microscopy shows highly intergrown zeolite A crystals over most of the surface area of the membrane, but gas permeation experiments indicate existence of mesoporous defects and/or intercrystalline gaps. It has been demonstrated that the thickness of the final zeolite A membrane can be controlled by limiting the amount of precursor kaolin present in the membrane.

High quality, continuous mesoporous films are prepared on both porous and dense substrates. An interfacial reaction mechanism is used to grow mesoporous films within the pores of porous supports using a diffusion cell reactor. The porous support was placed between two compartments containing a silicate solution in one compartment and a surfactant solution in the other. The silicate and surfactant solutions diffused into the support to form a mesoporous film at the liquid-liquid interface. This method produces a transparent film free from large defects. Spincoating technique is also used to prepare mesoporous films on dense substrates. These films have uniform thickness and show well-defined interference depending on the film thickness.

Model pore structures were prepared from dispersions of submicron monodispersed silica particles by a sedimentation process. Ordered dense sphere packing structures were observedwith scanning electron microscopy. Nitrogen sorption- as well as Hg-porosimetry measurements confirmed the calculated values of the pore openings in those structures. In Hgporosimetry measurements a two step extrusion curve was observed, when the pore system was only partially filled during the intrusion process. This two step curve was not observed in case the pore system was filled with mercury to more than 95% during the intrusion run. The mercury porosimetry results can be interpreted in terms of the coexistence of octahedral and tetrahedral voids (pores) in the examined sphere packing structure and their special arrangement within the structure (connectivity). Two models will be described to explain thegeneral occurrence of hysteresis in Hg-porosimetry. The actual pore geometry is shown to have a profound influence on the hysteresis shape as well as a change in the contact angle (constant within each measurement) can result in totally different hysteresis curves. Nitrogen adsorption and desorption measurements on the same powders did not reveal any fine structure within the hysteresis range.

Thin porous silicon (PS) layers (30–1000 nm) have been produced by electrochemical anodization of highly p-doped silicon in a hydrofluoric acid electrolyte at constant current density. Variable angle spectroscopic ellipsometry was used for characterization in the spectral range 1.24–5.00 eV. Four multilayer models were developed for the PS layers. Ellipsometric spectra were fitted for three of these models by utilizing an effective medium approximation for each sublayer containing crystalline silicon and voids. A third constituent, amorphous silicon, was added in the fourth model. Excellent fits to experimental data were obtained in the entire spectral range and thickness and composition of each individual sublayer in the models were determined. The analyses revealed a compositional gradient normal to the surface. The porosity and the fraction of amorphous silicon decreased with film depth, whereas the fraction of crystalline silicon increased. The mean porosity of a PS layer was obtained as the thickness weighted average of the porosities of the sublayers. The proposed multilayer models allow a more detailed analysis of PS layers compared to single layer models.

Luminescent porous poly-Si films with large areas or micron-sized patterns have been obtained by anodization or stain etching of phosphorus-doped poly-Si films deposited by low pressure chemical vapor deposition onto Si, thermal oxide or CVD nitride. The anodized film is composed of spherical Si grains with nano-pores formed around the surface. However, the stainetched film has large rectangular Si grains, and no nano-pores can be observed. The intensity of photoluminescence is enhanced after nitric acid boiling or stain etching, and is found to be closely related to the crystallinity of the porous Si layers.

Solid state metal phosphonates (M(O3P-R-PO3) or M(O3P-R)2 (M = metal)) have layered structures where the metal atoms lie in planar sheets and the intervening R groups take up the interlamellar space. Microporous metal phosphonates can be prepared by reaction of the metal with a mixture of large and small phosphonates (M(O3P-LARGE)x(O3P-SMALL)2-x. The larger group acts as a pillar that holds the layers apart. Void spaces result from the presence of the smaller groups. The porous nature of these solids make them potential candidates for applications as sensors, size- and shape- selective catalysts, and chromatographic materials. Metal diphosphonates (M(O3P-R-PO3) can also be prepared one layer at a time on a surface, resulting in the construction of interesting superstructures that are not accessible through the solid state synthesis. For example, these superstructures can contain different components in sequential layers and may have applications in energy conversion, vectorial electron transport, and NLO devices. The preparation of microporous thin films would combine the desirable potential applications of the porous solids with the interesting parallel superstructures that can be prepared from the thin film assemblies. We report our progress toward the construction of microporous metal phosphonate thin films. The two methods that are currently being developed include: 1) phosphonate exchange of pre-assembled films, and 2) co-deposition of different large and small phosphonates during film assembly.