Showing papers by "Galen D. Stucky published in 1996"
TL;DR: In this article, the molecular shapes of covalent organosilanes, quaternary ammonium surfactants, and mixed surfactant in various reaction conditions can be used to synthesize silica-based mesophase configurations.
Abstract: The low-temperature formation of liquid-crystal-like arrays made up of molecular complexes formed between molecular inorganic species and amphiphilic organic molecules is a convenient approach for the synthesis of mesostructure materials. This paper examines how the molecular shapes of covalent organosilanes, quaternary ammonium surfactants, and mixed surfactants in various reaction conditions can be used to synthesize silica-based mesophase configurations, MCM-41 (2d hexagonal, p6m), MCM-48 (cubic Ia3d), MCM-50 (lamellar), SBA-1 (cubic Pm3n), SBA-2 (3d hexagonal P63/mmc), and SBA-3 (hexagonal p6m from acidic synthesis media). The structural function of surfactants in mesophase formation can to a first approximation be related to that of classical surfactants in water or other solvents with parallel roles for organic additives. The effective surfactant ion pair packing parameter, g = V/a0l, remains a useful molecular structure-directing index to characterize the geometry of the mesophase products, and pha...
1,428 citations
TL;DR: In this paper, the authors showed that soluble polyanionic proteins alone are sufficient to control the crystal phase of calcite and calcite without the need for deposition of an intervening protein sheet.
Abstract: IN the initial stages of the biomineralization of abalone shells, a primer layer of oriented calcite crystals grows on a nucleating protein sheet1,2. The deposition of this primer is followed by an abrupt transition to c-axis-oriented crystals of aragonite, another crystalline form of calcium carbonate. The formation of each of the two crystal types is accompanied by the synthesis of specific polyanionic proteins1–3, suggesting that cooperative interactions between these proteins and the inorganic ions during crystal nucleation and growth control the phase of the deposited mineral and that differential expression of the proteins allows the organism to induce phase changes. It is known that soluble shell proteins can control crystal morphology4–10, but it has been suspected that the switch in phase—from calcite to aragonite—might require the deposition of a new nucleating protein sheet. Here we describe in vitro studies of the crystallization of calcium carbonate in the presence of soluble polyanionic proteins extracted from abalone shell. We find that these proteins alone are sufficient to control the crystal phase, allowing us to switch abruptly and sequentially between aragonite and calcite without the need for deposition of an intervening protein sheet. These results show that soluble organic components can exert greater control over hierarchical biomineral growth than hitherto suspected, offering the prospect of similar phase control in materials chemistry.
1,112 citations
TL;DR: Ordered mesostructured porous silicas that are also macroscopically structured were created by control of the interface on two different length scales simultaneously, and might have implications for technical applications, such as slow drug-release systems or membranes, and in biomineralization, where many processes are also interface-controlled.
Abstract: Ordered mesostructured porous silicas that are also macroscopically structured were created by control of the interface on two different length scales simultaneously. Micellar arrays controlled the nanometer-scale assembly, and at the static boundary between an aqueous phase and an organic phase, control was achieved on the micrometer to centimeter scale. Acid-prepared mesostructures of silica were made with the p6, Pm3n, and the P63/mmc structures in the form of porous fibers 50 to 1000 micrometers in length, hollow spheres with diameters of 1 to 100 micrometers, and thin sheets up to 10 centimeters in diameter and about 10 to 500 micrometers in thickness. These results might have implications for technical applications, such as slow drug-release systems or membranes, and in biomineralization, where many processes are also interface-controlled.
755 citations
371 citations
TL;DR: In this paper, three different samples corresponding to atomic V/Si ratio of 0.01, 0.05, and 0.10 have been prepared by reacting a silica-based mesoporous matrix of the cubic MCM-48 structure, with dry hexane solutions of OV(OiPr)3.
Abstract: The high hydroxyl content of mesoporous silicates makes it possible to use them as anchors for the attachment of transition-metal species. In the present study, three different samples corresponding to atomic V/Si ratio of 0.01, 0.05, and 0.10 have been prepared by reacting a silica-based mesoporous matrix of the cubic MCM-48 structure, with dry hexane solutions of OV(OiPr)3. Bulk structural characterization (X-ray diffraction and BET) shows that the cubic structure is maintained during the impregnation process. In the presence of V centers, a noticeable decrease of the main-pore diameter and of the a unit-cell parameter is observed. Thus, a strong interaction between the mesoporous walls and the V centers is suggested. The microstructural configuration of V centers has been investigated further by 51V NMR and UV−vis spectroscopies. Both techniques reveal that, in the absence of water, pseudotetrahedral O3/2VO centers, probably coordinated by three (Si−O−V) bridges, are grafted to the mesoporous walls. Th...
233 citations
TL;DR: In this paper, X-ray diffraction and scanning electron microscopy analyses of the growth of these flat pearl composites reveal that biomineralization is initiated by the deposition of an organic sheet on the implanted substrate, followed by growth of a calcite layer with preferred {10.4}.
Abstract: Analyses of biopolymer/calcium carbonate composites grown on inorganic abiotic substrates implanted between the shell and the shell-secreting epithelium of live red abalones (Haliotis rufescens) provide detailed spatial and temporal data on the in vivo assembly process that generates the shell. X-ray diffraction and scanning electron microscopy analyses of the growth of these flat pearl composites reveal that biomineralization is initiated by the deposition of an organic sheet on the implanted substrate, followed by the growth of a calcite layer with preferred {10.4} orientation and, finally, by the growth of nacreous aragonite. The calcite layer is structurally similar to the green organic/calcite heterolayer of native shell nacre. It comprises 0.2−2.0-μm-diameter elongated crystallites of typical geological habits in various aggregate arrangements. The shell also contains an external layer of (00.1)-oriented prismatic calcite, which is deposited on one edge of a flat pearl and has a morphology similar t...
225 citations
TL;DR: Two approaches to the synthesis and structure determination of NaZnPO4·H2O, a new open-framework, chiral, hydrated sodium zincophosphate phase, are reported in this article.
Abstract: Two approaches to the synthesis and structure determination of NaZnPO4·H2O, a new open-framework, chiral, hydrated sodium zincophosphate phase, are reported. The ordered, alternating, vertex-sharing ZnO4 and PO4 groups in NaZnPO4·H2O form a new framework topology, which includes novel 4-ring “squares” and edge-sharing helixes of 4-rings. The disordered extra-framework species (Na+, H2O) are located in pear-shaped cavities (12-ring diameter), interconnected through 8-rings and 6-rings. Crystal data: NaZnPO4·H2O (I), Mr = 201.36, hexagonal, space group P6122 (No. 178), a = 10.4797(8) A, c = 15.089(2) A, V = 1435 A3, Z = 12, R = 5.99%, Rw = 5.29% (709 observed reflections with I > 3σ(I). NaZnPO4·H2O (II), Mr = 201.36, hexagonal, space group P6522 (No. 179), a = 10.412(2) A, c = 15.184(2) A, V = 1426 A3, Z = 12, R = 6.90%, Rw = 8.10% (687 observed reflections with I > 4σ(I).
148 citations
TL;DR: A mesoporous material containing Ti and Si atoms in the walls, which is isomorphous to the cubic MCM-48 silicate structure has been synthesized by using a gemini surfactant.
92 citations
TL;DR: It is found that the combined TappingMode atomic force microscope and scanning ion conductance microscope provided higher contrast and less apparent sample damage in the topographic and ionic conductance images in the tapping mode.
85 citations
TL;DR: The M3Zn4O(XO4)3·nH2O network as discussed by the authors is based on a flexible, anionic ZnO4O (XO 4)3 network built up from vertex-linked tetrahedral XO4 and OO4 units.
Abstract: The syntheses, representative crystal structures, and some properties of a new family of microporous zincophosphate/arsenate materials, denoted M3Zn4O(XO4)3·nH2O (M = Li, Na, K, Rb, Cs, ...; X = P, As; n = ∼3.5−6), are reported. All these materials are based on a flexible, anionic Zn4O(XO4)3 network built up from vertex-linked tetrahedral ZnO4 and XO4 units. Four ZnO4 units share a vertex, resulting in novel OZn4 centers. The use of mixed four-coordinate anion types (XO43-, O2-) results in a number of interesting structural and stability properties. The M3Zn4O(XO4)3·nH2O network contains only pairs of 3-rings (a spiro-5 unit) and 8-rings, and no 4-rings or 6-rings: it encloses roughly spherical cavities connected by a three-dimensional network of 8-ring channels propagating in the orthogonal [100], [010], and [001] directions (cubic unit-cell axes). Extraframework cations and water molecules occupy these cavities and channels. These phases display typical “zeolitic” dehydration/rehydration and ion-exchang...
56 citations
TL;DR: Two zinc phosphates materials (ZnPO-W and ZnPO TMA) have been prepared by hydrothermal methods and characterized by single-crystal X-ray diffraction.
TL;DR: In this article, the role of silicon in human tissues and of silica in bioactive-glass bone implants has been investigated, and laboratory silica syntheses have increasingly featured biomineralization techniques, mild reaction conditions, biogenic and biomolecule-like organic dopants, and biosilicate starting materials.
Abstract: Biopolymers containing anionic and hydrogen-bonding functionalities have recently been found in biosilicates. An improved understanding of the role of silicon in human tissues and of silica in bioactive-glass bone implants has also been realized. Laboratory silica syntheses have increasingly featured biomineralization techniques, mild reaction conditions, biogenic and biomolecule-like organic dopants, and biosilicate starting materials.
TL;DR: In this paper, a series of analogs of the non-aluminosilicate RHO framework were characterized and synthesized in the space group I23, ranging from a = 13.584 to 14.224.
Abstract: This is an extensive study of the non-aluminosilicate analogs of the zeolite RHO. This molecular sieve is of great interest commercially because of its catalytic properties. In the absence of rigid supporting structural subunits (smaller cages or channels), the aluminosilicate RHO exhibits atypical framework flexibility with large displacive rearrangements. The beryllophosphate and berylloarsenate analogs are easily synthesized under very mild reaction conditions and therefore may be of interest for inexpensive and rapid commercial production. However, they have decreased thermal stability. In an effort to increase thermal stability and explore framework flexibility, we have synthesized and characterized a series of analogs of the non-aluminosilicate RHO framework. All materials crystallize in the space group I23, ranging from a = 13.584(2) A for Li-BePO RHO to a = 14.224(4) A for Ba-RbBeAsO RHO for hydrated phases. The extra framework cations are distributed over the double 8-ring, single 8-ring, and two...
TL;DR: In this article, the absorption coefficient of the black sodalite for photon energies between 0 and 3 eV was measured and interpreted by performing one-electron band structure calculations for a fully loaded compound.
Abstract: Prolonged exposure of colorless dry sodalite to alkali vapor causes the material to gradually turn blue, dark blue, and finally black. The blue color observed at low sodium uptake appears because the absorbed sodium atoms are spontaneously ionized. The electron produced by ionization is shared by the four sodium ions present in the sodalite cage (three initially there and the fourth originating from the absorbed atom). The color center created in this way is represented by the formula (Na+)4eF3−. Here, e stands for the electron and F3− for the negatively charged frame surrounding a zeolite cage. At the highest loading, when each cage contains an absorbed alkali atom, the color centers are arranged in a body‐centered cubic lattice, allowing the electrons associated with the centers to form bands. This may explain the black color observed at high concentration. In this paper we present measurements of the absorption coefficient of the black sodalite for photon energies between 0 and 3 eV, and interpret them by performing one‐electron band structure calculations for a fully loaded compound. These calculations deal only with the ‘‘solvated’’ electrons. The effect of the other electrons is taken into account through an empirical potential energy representing the interaction of a solvated electron with the zeolite frame. Because of this we study only the bands formed by the electrons of the color centers. Since the gap in the electron energy bands of the dry sodalite is over 6 eV, the color of the black sodalite is controlled by the solvated‐electron bands formed in this gap. The measured spectrum has a threshold of about 0.6 eV which seems to suggest that the system has a gap in the electronic structure and is therefore a semiconductor. The calculations indicate, however, that, if the one‐electron picture is valid, the fully doped black sodalite is a narrow‐band metal. The threshold in the spectrum appears because the transition matrix element is zero for transitions responsible for photon absorption, and not because of a gap in the density of states. The calculated spectrum is in reasonable agreement with the measured one. Conclusions based on one‐electron calculations can be altered by electron–electron interactions, which could turn a metal into an insulator. Two simple criteria, proposed by Mott and Hubbard, were used to test whether this transition might occur in our system. Unfortunately the results indicate that the system is close to the transition region which means that predictions made by these simple criteria are not reliable.
TL;DR: The nanoscale structure and synthesis mechanisms of the MCM-41 class of inorganic mesoporous materials have been investigated by small angle neutron scattering (SANS) measurements with solvents imbibed in the pores to vary the scattering contrast as discussed by the authors.
Abstract: The nanoscale structure and synthesis mechanisms of the MCM-41 class of inorganic mesoporous materials have been investigated by small angle neutron scattering (SANS). SANS measurements with solvents imbibed in 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. Static and shear flow 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.
TL;DR: The composition-dependent optical and electronic tunability of the sodalite analogues with stoichiometries Zn8X2[BO2]12 (X = O, S, Se) and [CdyZn(1-y)]8x2[BeSixGe( 1-x)O4]6 as mentioned in this paper have been demonstrated.
Abstract: The composition-dependent optical and electronic tunability of the sodalite analogues with stoichiometries Zn8X2[BO2]12 (X = O, S, Se) and [CdyZn(1-y)]8X2[BeSixGe(1-x)O4]6 (X = S, Se and Te) have been demonstrated. The materials strongly photoluminesce, and a comparison of the photoluminescence behavior of the single crystals with the as-synthesized powder analogues shows that the visible emission is intrinsic to the sodalite analogue and not due to impurities such as bulk semiconductor. The emission maxima of these materials can be varied by as much as 100 nm with subtle modifications in the host sodalite framework composition and excitation energies can be stored over, at minimum, several minutes. The materials can be prepared either hydrothermally or by high-temperature solid-state reactions. The local and average long-range structures of composition Zn8X2[BO2]12 (X = O, S, Se) and M8X2[BeSixGe1-xO4]6 (M = Zn, Cd; X = S, Se, Te) are described based on the results of polycrystalline X-ray diffraction, m...
TL;DR: In this article, the authors have substituted aliovalent transition-metal (M = Cr, Fe, Ni, Cu, Co) and lanthanide (Ln = Er) ions that absorb visible light onto the titanium sites of the nonlinear optical materials KTiOPO4 and RbTiOAsO4 (RTA).
Abstract: We have substituted aliovalent transition-metal (M = Cr, Fe, Ni, Cu, Co) and lanthanide (Ln = Er) ions that absorb visible light onto the titanium sites of the nonlinear optical materials KTiOPO4 (KTP) and RbTiOAsO4 (RTA). The substitution formally creates a charge deficiency on the Ti site. To compensate for this, we have substituted aliovalent counterions on the titanium (Nb), phosphorus (S, Se, Cr, Mo, W, Re), oxygen (F), or potassium (Ca, Sr, Ba, Pb) sites. The resulting new materials expand the KTiOPO4 structure field for partial replacement of one or more ions. The M and Ln ions alter the optical absorption and second harmonic properties of the materials. The ions reduce the second harmonic intensities of the isomorphs (measured at 532 nm) but improve their phase-matching capabilities, allowing fundamental and second harmonic radiation to be phase matched at slightly shorter wavelengths than in the undoped host.
TL;DR: The first NMR evidence for hyperfine interactions between unpaired electrons and the framework atoms in alkali-metal doped zeolites by the 27Al and 29Si MAS NMR spectra of aluminosilicate sodalites loaded with paramagnetic Na43+ cluster was presented in this paper.
01 Jan 1996