The mechanisms by which the geometries of organic structure-directing agents are translated into the product pore architectures in the syntheses of pure-silica and high-silica zeolites and of aluminum-rich zeolites are discussed. Two different mechanisms of structure direction and self-assembly via the formation of extended inorganic-organic composite structures or of purelyinorganic structures are proposed for the two different classes of materials. The primary impetus for developing a mechanistic understanding of zeolite synthesis is the ultimate goal of the rational design and synthesis of novel zeolite pore architectures. By considering issues such as hydrophobic hydration behavior of the structure-directing agent and the optimization of inorganic–organic van der Waals interactions, the successful design of structure-directing agents for the synthesis of new zeolite structures may be possible, particularly for high-silica systems.

The tetrahedral cluster Ge4S104- and the rodlike ligand 4,4′-bipyridine are utilized in addition copolymerization reactions with the metal (II) ions of Mn, Fe, Co, Cu, and Zn in the preparation of 3-D open-framework solids, MxCol-xGe4S10-2(CH3)4N (x = 0.86, M = Mn; x = 1, M = Mn, Fe, Co, and Zn), 1, and Cu(4,4′-bpy)2. PF6, 2, having diamond-like structures. These structures are viewed in terms of the cubic diamond structure, where the carbon atoms have been replaced by either a cluster or a metal ion and the C-C bond by a sulfide or the 4,4′-bpy. These compounds have been fully characterized by single crystal x-ray crystallography and their composition was confirmed by elemental analysis; they contain 3-D channel systems where cations or anions reside to balance the charge on the framework.

Synthesis conditions were identified leading to agglomerates of nearly cylindrical zeolite nanocrystals with dimensions less than 50 nm in the channel direction and approximately 10 nm in diameter (in the direction perpendicular to the zeolite channels). The nanocrystals form agglomerates with approximate particle sizes ranging from 20 to 400 nm as determined by DLS. Washing with repeated centrifugation and sonication results in stable (over long periods of time) colloidal suspensions of the zeolite particles in water (pH ∼ 7) with zeolite concentrations of lOg/l. The average zeolite particle size of the suspension can be as low as 20 nm as determined by DLS. Films free of microcracks were prepared from these suspensions by evaporation of water.

In this work we generate computer models of zeolites, imogolite, and microporous silica and evaluate the pore structure of each. Our purpose is to contrast the diffusional aspects of gases in these different materials with respect to their application as gas separating membranes. The concepts of Knudsen, surface and micropore diffusion will be evaluated for each model. The advantage of modeling these materials and processes with available molecular techniques is clearly demonstrated by testing assumptions of highly regarded theories.

Molecular sieves, are attractive materials for discriminating chemical sensors. These microporous metal oxides offer shape selective adsorption as well as chemical and thermal stability. Molecular sieves have shown promise in SAW devices, however, these sensors rely only on a weight change upon adsorption of target molecules. We have developed a molecular sieve based capacitance type chemical sensor. Such a device should discriminate between molecules of similar size and shape because the signature change depends on the polarity of the adsorbate which in turn affects the dielectric properties of the molecular sieve. In this paper we describe the deposition of AIPO4 and MeAPO molecular sieve thin films on titanium nitride coated silicon wafers by laser ablation. A subsequent hydrothermal treatment followed by a Pd/Au coating and standard microlithography techniques generate the capacitors. The results for capacitance measurements in the presence of CO2, CO, NO, N2, O2, H2O and toluene indicate clear differences in selectivity between small, medium and large pore molecular sieves.

Fly ash was chemically converted into zeolites. The conversion process not only eliminates the disposal problem of coal wastes but more importantly turns the waste material into a useful one. It was shown that fly ash can be converted into two forms of zeolites: P and faujasite, by varying the treatment condition. In addition, zeolite P was found to form earlier with higher treatment temperatures and adding quartz increased the amount of zeolite P formed. Seeding of faujasite was also studied.

The nanoscale structure and synthesis mechanisms of a recently developed class of inorganic mesoporous materials with ordered arrays of uniform mesopores have been investigated by small angle neutron scattering (SANS). SANS measurements with solvents imbibed into the pores to vary the scattering contrast demonstrate that the low angle diffraction peaks from these materials are entirely due to the pore structure and that the pores are fully accessible to both aqueous and organic solvents. SANS measurements on the concentrated cationic surfactant and silicate precursor solutions typically used in the synthesis of the mesopore materials indicate that the existence of preassembled supramolecular arrays that mimic the final pore structure is not essential for the synthesis of these materials.

A new synthesis route to open framework mesostructures based on H-bonding and self-assembly between neutral primary amine surfactants (S°) and neutral inorganic precursors (I°) has been used to prepare hexagonal mesoporous silicas containing site isolated titanium centers. These new titanosilicates, designated Ti-HMS, exhibit exceptional catalytic reactivity for the oxidation of substrates too large to access the pore structure of conventional titanosilicates, such as titanium silicalite, TS-1. The catalytic properties of Ti-HMS materials for the peroxide oxidation of 2,6- di- tert-butylphenol are compared with those of microporous TS-1 and a mesoporous Ti-MCM-41 analog prepared by an electrostatic templating mechanism using a liquid crystal quaternary ammonium cationic surfactant.

A new templating route to ordered mesoporous materials is demonstrated based on hydrogen bonding interactions and self-assembly between neutral primary amine surfactants (S°) and neutral inorganic precursors (1°). The S° I° templating pathway affords ordered mesoporous materials with thicker framework walls, smaller X-ray scattering domain sizes, and substantial textural mesoporosities in comparison to MCM-41 materials templated with quaternary ammonium cations. This synthetic strategy also allows for the facile, environmentally benign recovery of the cost-intensive template by simple solvent extraction methods.

Composites of surfactants with certain transition metal oxides can be arranged into periodic arrays with giant tunnel structures. Transmission electron micrographs of these structures resemble images of mesoporous silicate molecular sieves synthesized in the presence of surfactants. However, data in this study lead to the conclusion that Keggin-ions of the type (H2W12O40)6- are formed during the hydrothermal synthesis of a cetyltrimethylammonium/tungstate composite. These cluster anions are not connected to each other. Removal of the organic template therefore results in the collapse of the tunnel structures.

A strategy has been developed which uses pre-arranged surfactant-salt structures as precursors for microporous and mesoporous framework materials. Transition metal silicates with long-range structural order have been synthesized by reacting surfactant salts of niobotungstate clusters with tetraethylorthosilicate to form a salt-gel. Infrared and solid-state NMR double resonance spectra indicate that, in addition to linkages between silicate tetrahedra, niobium-oxygen-silicon linkages have been formed in this reaction. Removal of the cationic surfactants by acid-extraction has resulted in porous structures with surface areas up to 265 m2/g.

A series of crystalline mesoporous molecular sieves were prepared using alkyl hexadecyl dimethyl ammonium bromide salts (C16H33)(CnH2n + 1)(CH3)2NBr, in which the number of carbon atoms (n) in one alkyl group was varied from 1 to 12. The influence of (n) value on the nature of the final phase obtained and on its pore size was investigated. A hexagonal phase was obtained for n = 1, 3, 5 and 7, while a lamellar phase was obtained for all other templates. Vanadium and titanium modified MCM-41 molecular sieves were also prepared in the presence of C12H25(CH3)3N+ and C16H33(CH3)3N+ ions, respectively. These materials were characterized by XRD, nitrogen physisorption, FTIR, solid state NMR, XPS, UV-Vis and catalytic testing in the oxidation of 1-naphthol, 2,6-di-tert-butylphenol, norbornylene, n-hexane and propylamine. Ti-MCM-41 exhibited considerable catalytic activity only in the oxidation of aromatics, olefins and alcohols. V-MCM-41 was found to be a good catalyst in the oxidation of aromatics and alkanes.

Vanadium containing large pore silica zeolites with ZSM-12 and SSZ-24 structures were synthesized and characterized. Incorporation of V in the zeolite framework was evidenced mainly by EPR and 51V NMR techniques.

The synthesis of silicate/surfactant mesophases is driven by cooperative assembly of organic surfactant and inorganic silicate species, and the resultant mesophase morphology can be controlled by synthesis conditions (i.e., CTAB concentration in precursor solution and SiO2- CTAB mole ratio). The self-assembly process of these mesophases is driven complexation of the polyanionic silicate species with several CTAB cations to form a multi-tailed surfactant. One of these mesophases is a novel rippled lamellar phase in which the ripple wavelength and lamellar spacing are similar to the hexagonal mesophase rod center-to-center spacing; each of these dimensions are consistent with the length of two CTAB molecules.

Mesoporous silica phases of the M41S type were investigated by SiK XANES spectroscopy and the results compared with the information provided by 29Si MAS NMR spectroscopy. The results show that the pore walls are more ordered than in “truly” amorphous silica phases (as, e.g., glass) and indicate a relationship of their structure to layered silicates.

A non-aqueous synthesis route broadens the spectrum of useful precursors and the range of compositions which can be achieved in the synthesis of ordered, mesoporous multicomponent materials. A formamide solution of surfactant (cetyltrimethylammonium chloride/hydroxide) allows for distribution of a water-sensitive metal oxide precursor prior to reaction. Hydrolysis of the metal oxide precursor and phase separation to the pure oxide are controlled by adding limited amounts of water. Subsequent addition of a second metal oxide source as an aqueous solution initiates the reactions leading to a mixed oxide having ordered mesopores. Ordered mesoporous titanium silicates having final Ti/Si mole ratios in excess of 1/20 are synthesized.

Recently we proposed that heterogenous nucleation is an important phenomenon for the preparation of ordered mesoporous materials. In this paper we further investigate the effect of colloidal particles on the nucleation process of mesoporous materials. Based on the change of the electrical mobilities of the particles in the surfactant solution, we suggest that the adsorption and co-adsorption of surfactant and ceramic precursors changes local structural and chemistry on the particle surfaces, and favors the nucleation events within these regions.

We have synthesized metal-sulfide/surfactant nanocomposite materials by cooperative assembly of molecular precursors in an aqueous medium. The template-mediated synthetic approach is applicable to metal sulfides that exhibit aqueous thiometallate chemistry. The products are lamellar and have bilayers or interdigitated layers of surfactant molecules sandwiched between metal sulfide layers. The layers of anionic metal sulfide molecules are not completely condensed in the nanocomposites, which results in a negative charge on the metal sulfide layers. The materials are stable at room temperature in water, methanol, 1 M HCl, 30 wt% NH3, and 1 M NaOH. The materials do not dissolve at 80 °C in water and are stable to at least 180 0C in air. The nanocomposites exhibit ion exchange of smaller surfactants, alkali-metal ions, and divalent metal ions.

A comparative study of chemical and textural properties for materials obtained by three different methods of dealumination of alumina-rich parent Ca-A zeolite showed that the method using ammonium hexafluorosilicate (AFS) resulted in the most interesting developments of mesoporous materials, with much higher void volumes and cation exchange properties than obtained by acid leaching or hydrothermal treatment. AFS treatment on both the Na and Ca forms of zeolite A resulted in materials with 12 nm sized mesopores, whereas smaller mesopores of about 4 nm were obtained when using the higher Si/Al ratio parent zeolite Na-X. Pore size distribution profiles obtained for these new materials are fairly narrow, indicating homogeneous mesopore sized solids.

A new anion exchangeable layered compound with a composition of Ni1-xZn2x(OH)2(OCOCH3)2x·nH2O (0.15 < x < 0.25) was prepared by hydrothermal hydrolysis of Ni-Zn mixed acetate solutions. The structure is related to zinc basic salts such as Zn5(OH)8Cl2·nH2O and Zn5(OH)8Cl2·nH2O; nickel ions form brucite-type hydroxide layers with vacanciesNi1-x(OH)2, and zinc ions occupy the tetrahedral sites above and below the vacant sites outside the hydroxide layers. Acetate ions are weakly bound to the Zn2+ ions, completing the tetrahedra, and easily exchanged with most of inorganic as well as organic anions. The reactions are reversible. Exchange with [Si8O20]8- ions resulted in the formation of two-dimensional silicate layers analogous to those of 2:1 type clay minerals.

A range of layered double hydroxides (LDHs) with Ni/Al and Mg/Al as the M(II)/M(III) cations and containing carbonate as the charge balancing anion have been synthesised. A variation in the M(II)/M(III) ratio between 2 and 6 has been attempted with the influence of the M(II)/M(III) ratio upon the subsequent exchange of carbonate by [V10O28]6- (at pH 4.5) examined. Complete exchange is obtained for all ratios, although the crystallinity of the products varies. For M(II)/M(III) ratios > 4, the product crystallinity is poor. In addition, a second phase is detected for all ratios. In the case of Ni/Al, the amount of vanadium incorporated is found to depend upon the Al content whereas for Mg/Al the amount incorporated is constant. Overall, the replacement of carbonate by decavanadate does not appear to have any significant effect on the textural characteristics (e.g. surface area or porosity) of the pillared products.