Showing papers by "Galen D. Stucky published in 1997"

Hydrothermal syntheses and structural characterization of zeolite analogue compounds based on cobalt phosphate

Abstract: Zeolite analogues containing transition metals are highly desirable for industrial processes. A generalized synthesis method has been developed and demonstrated to have the potential to generate many transition-metal-rich zeolite-type structures. The method has been used to make zeolite analogues based on cobalt phosphate with diverse chemical compositions and structure types, including some analogues never previously synthesized and some zeolite-like structures only previously known theoretically. The concentrations of transition-metal atoms in the frameworks can be controlled by varying the charge and geometry of the structure-directing amine molecules.

Does Abalone Nacre Form by Heteroepitaxial Nucleation or by Growth through Mineral Bridges

Abstract: We present experimental support for a model of abalone nacre growth that is based on mineral bridges between successive aragonite tablets rather than on heteroepitaxial nucleation. Interlamellar sheets of organic polymers delineate the aragonite tablets but allow the tablets to grow mineral bridges through pores in the sheets. Atomic force microscope images of interlamellar organic sheets from flat pearls made by Haliotis rufescens (red abalone; marine gastropod mollusk) reveal a fibrous core and holes of 5−50 nm in diameter. Scanning ion conductance microscopy shows that these holes are actually pores through the interlamellar sheets. With the help of statistical analysis we can associate the pore-to-pore spacings in the interlamellar sheets with the observed offsets of successive nacre tablets. These results, supplemented by AFM, SEM, and TEM images, support and extend the model of biofabrication of gastropod nacre which is based on mineral bridges between the aragonite tablets.

Preparation of Hard Mesoporous Silica Spheres

Abstract: Large, hard, transparent, mesoporous silica spheres are synthesized in one step by using oil-in-water emulsion chemistry under basic conditions with cationic surfactants and (n-BuO)4Si. The pores are shown by TEM and nitrogen absorption studies to be monodispersed in size, with total surface area over 1000 m2/g.

Magnetic Field Alignment of Ordered Silicate-Surfactant Composites and Mesoporous Silica

Abstract: Macroscopic orientational ordering of the pores of condensed hexagonal mesostructured silica (MCM-41) was achieved through alignment of an unpolymerized, hexagonal, lyotropic silicate-surfactant liquid crystal in a high magnetic field. This alignment was preserved after polymerization of the silicate species by acid treatment. Subsequent calcination to remove the surfactant yielded a mesoporous silica solid that retained both macroscopic pore alignment and mesoscale periodicity. Potential applications of such liquid crystal processing strategies range from the formation of anisotropic silica-based bulk ceramics to the production of oriented mesoporous thin films for chemical sensors, separations, catalysis, or host-guest applications.

Large-Cage Zeolite Structures with Multidimensional 12-Ring Channels

Abstract: Zeolite type structures with large cages interconnected by multidimensional 12-ring (rings of 12 tetrahedrally coordinated atoms) channels have been synthesized; more than a dozen large-pore materials were created in three different topologies with aluminum (or gallium), cobalt (or manganese, magnesium, or zinc), and phosphorus at the tetrahedral coordination sites. Tetragonal UCSB-8 has an unusually large cage built from 64 tetrahedral atoms and connected by an orthogonal channel system with 12-ring apertures in two dimensions and 8-ring apertures in the third. Rhombohedral UCSB-10 and hexagonal UCSB-6 are structurally related to faujasite and its hexagonal polymorph, respectively, and have large cages connected by 12-ring channels in all three dimensions.

Alkaline Lyotropic Silicate−Surfactant Liquid Crystals

Abstract: Multinuclear (2H, 13C, 29Si, 81Br) magnetic resonance spectroscopy, small-angle X-ray scattering, and polarized optical microscopy techniques have been used to investigate molecular and mesoscopic organization in silicate−surfactant lyotropic liquid crystals with hexagonal and lamellar morphologies under highly alkaline conditions. Such systems cooperatively self-assemble following the addition of a basic aqueous solution containing anionic silicate oligomers (e.g., double-four-ring species) to an isotropic micellar solution of cationic surfactant molecules (e.g., cetyltrimethylammonium bromide). Important similarities and differences are shown to exist between multicomponent silicate−surfactant and conventional binary lyotropic liquid crystals. Under highly alkaline conditions, the silicate−surfactant systems possess the characteristics of ordinary lyotropic liquid crystalline systems, though the balance of forces underlying their self-assembly is complicated by the richness of the aqueous silicate chemi...

Gemini Surfactants at Solid−Liquid Interfaces: Control of Interfacial Aggregate Geometry

Abstract: Recent work has shown that conventional surfactants form ordered aggregates of well-defined shape and size at solid−liquid interfaces.1,2 Here we report interfacial aggregate structures as a function of surfactant geometry by using gemini surfactants with varying tail and spacer lengths. On the anionic cleavage plane of mica, aggregates tend to favor a lower curvature than in solution but follow the same general variation with surfactant geometry (i.e., with larger headgroup areas resulting in greater curvature). These morphologies on mica correlate well with those observed in surfactant−silicate mesophases, where electrostatic binding of headgroups also plays a dominant role. In addition, interfacial sphere-to-rod transitions are induced on mica (as in free solution) by binding with a headgroup-specific counterion. In contrast to mica, the hydrophobic cleavage plane of graphite interacts with surfactant tailgroups, giving rise to interfacial aggregates that are surface-controlled and relatively independe...

Syntheses and Characterizations of Chiral Tetrahedral Cobalt Phosphates with Zeolite ABW and Related Frameworks

Abstract: The hydrothermal syntheses, X-ray crystal structures, and magnetic properties of a family of 3-D chiral framework cobalt phosphates are presented. Two different types of framework structures are described: one has the same topology as the well-known zeolite ABW framework and represents the only pure cobalt phosphate framework with a known zeolite topology; the other exhibits a framework connectivity which can be considered as a hybrid of tridymite and ABW frameworks. These new chiral materials were obtained by systematic chemical variation, accurate control of solution pH values, and use of non-aqueous solvents. Synthesis conditions were found which favored the crystallization of Co2+ oxygen tetrahedra in strict alternation with P5+ oxygen tetrahedra from cobalt phosphate solutions in the presence of Na+, K+, NH4+, or Rb+ ions. The transition from one framework type to the other is affected by the size of these extra-framework cations. The two ABW structures (NH4CoPO4-ABW, RbCoPO4) have eight-ring channe...

A New Phase of Oriented Mesoporous Silicate Thin Films

Abstract: The syntheses and characterization of silicate/surfactant thin films with the structure P63/mmc is presented. The films are synthesized using a novel double-headed quaternary amine surfactant and c...

Magnetic-Field-Induced Orientational Ordering of Alkaline Lyotropic Silicate−Surfactant Liquid Crystals

Abstract: Macroscopically oriented silicate−surfactant liquid crystals are produced by slow cooling of lamellar and hexagonal mesophases through their isotropic−anisotropic phase transition in an 11.7 T magn...

Directed synthesis of organic/inorganic composite structures

Abstract: Publisher Summary The impact of the discovery of the synthesis of periodic mesoporous material using amphiphilic surfactants is apparent from the demographics of papers that have appeared in this area. In addition to providing for the first time access to high surface area, monodispersed mesopores (1nm to > 10nm), the research has provided, in a more generic sense, a new synthesis paradigm on the ways in which to bring together spatially distinct, nanostructured organic, and inorganic arrays into two- and three-dimensional periodic, composite structures. Designed materials synthesis and properties based on the molecular level interplay of the kinetics and energetics of organic and inorganic domain and interface assembly are of vital interest to many areas including biomineralization, conducting and optical display polymer composites, chemical sensors, fine chemical and bio-catalysis, and the creation of composite phases with useful mechanical and thermal properties for insulation and packaging applications. It is clear that this discovery is a major entry not only in the “breakthrough” library of zeolite and molecular sieve syntheses, but also in advancing the field of materials syntheses in general. This chapter focuses on some observations concerning this composite synthesis paradigm. The presentation is admittedly only a selected sampling, with some brief excursions into implications related to biomineralization and porous materials design at longer (10 nm to 1000nm) length scales.

Comparative Study of XPS and DFT with Reference to the Distributions of Al in Tetrahedral and Octahedral Sheets of Phyllosilicates

Abstract: Five phyllosilicate samples of dioctahedral smectite, mica, magnesium chlorite, saponite, and hectorite were studied using X-ray photoelectron spectroscopy (XPS) to determine the distribution of Al in the tetrahedral and octahedral sheets. The binding energies of the Al(2p) peaks in all the samples were obtained at 74.5 and 73.7 eV for octahedral and tetrahedral Al, respectively. The ratio of the peak areas follows the same trend as that of octahedral Al present in the phyllosilicate lattice. To confirm the experimental result, localized cluster models were generated from the pyrophyllite structure to calculate their density of states by the density functional theory (DFT). The DFT results match very well with XPS results with respect to the difference of binding energies of Al in the tetrahedral and octahedral sheet of phyllosilicates; so this method is a useful tool to measure the qualitative distribution of Al in the phyllosilicates.

Cooperative structure direction in the synthesis of microporous materials : Preparation and crystal structure of TREN-GaPO

Abstract: A unique, large-pore gallium oxyfluorophosphates has been synthesized by using a combination of two structure-directing amines: tris(2-aminoethyl)amine (TREN) and pyridine. TREN−GaPO has two parallel channel systems delineated by 12- and 8-membered rings, and the organic amines are found to be ordered in these two channels.

Control of Inorganic Layer Thickness in Self-Assembled Iron Oxide/Surfactant Composites

Abstract: The synthesis and characterization of ordered, lamellar, iron oxide/surfactant composites in which the iron oxide layer thickness is selectively varied are presented. These new materials are prepared by the controlled precipitation and hydrolysis of aqueous iron cations into self-assembled iron/surfactant arrays. The use of redox chemistry to alter the solubility of iron oxide and thus control hydrolysis, solubility, and inorganic layer thickness is a key feature of the synthesis procedure. The composites show a layered structure as determined by X-ray diffraction and can be produced with approximately 3 to nearly 20 A of iron oxide in alternation with surfactant bilayers. For samples with 10 A or thicker iron oxide layers, magnetic susceptibility measurements and Mossbauer spectroscopy indicate the presence of superantiferromagnetic domain structures with smaller domains observed in samples with thinner layers. The results are a first step toward the simple design of hierarchical nanostructured magnetic ...

Morphology definition by disclinations and dislocations in a mesostructured silicate crystal

Abstract: Curved surface morphologies resulting from disclinations are unusual in inorganic phases because the relatively large lattice energies generally permit only translational dislocations. In this letter, we show, however, that disclinations can be readily observed and identified in composite organic/inorganic phases. Disclinations and dislocations in MCM-41, a two-dimensional hexagonal (p6mm) mesophase crystal synthesized using silicate and surfactant precursors, were investigated by using transmission electron microscopy. We observed two types of dislocations and two types of disclinations. All dislocations observed are of the smallest Burgers vector a (the basis vector). Dislocation dipoles and disclination quadrupoles appear more frequently than isolated ones.

Single-crystal structures and optical properties of the nonlinear optical KTiOPO4-Type materials K0.55Li0.45TiOPO4 and K0.54Li0.46TiOAsO4 prepared by molten salt ion-exchange

Abstract: Single crystals of the KTiOPO4 (KTP) type phases K0.55Li0.45TiOPO4 and K0.54Li0.46TiOAsO4 have been prepared by molten salt ion-exchange reactions from their potassium-containing precursors. After ion-exchange, both phases maintain the distinctive distorted TiO6 octahedra seen in KTiOPO4 and KTiOAsO4. The pattern of lithium-ion substitution differs for these two phases: In K0.55Li0.45TiOPO4, Li substitutes for both of the two crystallographically distinct potassium cations to roughly equal extent, whereas in K0.54Li0.46TiOAsO4, the 9-coordinate K(2) atom is preferentially replaced by Li. The lithium cations occupy six-rings of TiO6 and PO4 polyhedra and adopt approximate square-planar coordination in both these materials. Second harmonic generation at 1064 nm is not significantly affected by lithium substitution in either of these phases. Crystal data: K0.55Li0.45TiOPO4: Mr = 183.55, orthorhombic, space group Pna21 (No. 33), a = 12.741(2) A, b = 6.357(1) A, c = 10.535(2) A, V = 853(2) A3, Z = 8, R(F) =...

Synthesis and Characterization of Mesostructured Aluminophosphates Using the Fluoride Route.

Abstract: The room-temperature synthesis of the hexagonal mesostructured aluminophosphate and its phase transition into the lamellar phase are reported.