WO2002083994A1 - Synthese de materiaux a mesophase presentant des cadres ordonnes de maniere moleculaire - Google Patents

Synthese de materiaux a mesophase presentant des cadres ordonnes de maniere moleculaire Download PDF

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WO2002083994A1
WO2002083994A1 PCT/US2002/011684 US0211684W WO02083994A1 WO 2002083994 A1 WO2002083994 A1 WO 2002083994A1 US 0211684 W US0211684 W US 0211684W WO 02083994 A1 WO02083994 A1 WO 02083994A1
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framework
inorganic
ordered
mesoscopically structured
silica
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Sean C. Christiansen
Dongyuah Zhao
Michael T. Janicke
Christopher C. Landry
Galen D. Stucky
Bradley F. Chmelka
Dipika Kumar
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The Regents Of The University Of California
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
    • C01B37/02—Crystalline silica-polymorphs, e.g. silicalites dealuminated aluminosilicate zeolites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G1/00—Methods of preparing compounds of metals not covered by subclasses C01B, C01C, C01D, or C01F, in general
    • C01G1/02—Oxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/78—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by stacking-plane distances or stacking sequences
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/86—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by NMR- or ESR-data

Definitions

  • the field of the invention is mesoscopically structured materials exhibiting molecularly ordered frameworks.
  • Crystalline nanoporous materials such as zeolites [5] by comparison, exliibit superior mechanical and thermal stabilities, compared to disordered materials, and also possess strong acid sites that are desirable for catalysis.
  • Previous attempts to synthesize mesophase or mesoporous materials with molecularly ordered inorganic frameworks have proven unsuccessful. [6-9] Several efforts to use elevated temperature mesophase syntheses have resulted in the decomposition of the surfactant and subsequent formation of nanoporous zeolite materials.
  • Such clay-surfactant materials are non-templated, typically non-uniform mineral structures that are prepared with no control over framework composition or structure. 14 These attempts demonstrate both the strong interest and the inherent difficulty in producing mesophase materials with molecularly ordered inorganic frameworks.
  • the present invention provides a method of preparing mesoscopically structured materials with molecularly ordered frameworks, which are made by combining a self-assembling agent and a network-forming precursor.
  • a self-assembled inorganic-surfactant mesophase can be prepared with crystal-like ordering of sites in the inorganic framework. This can be achieved by converting, during a hydrothermal annealing step, an initially amorphous inorganic framework of a mesoscopically structured composite into a product with a molecularly ordered inorganic framework.
  • the method produces a crystal-like inorganic framework having long range molecular order of greater than one nanometer.
  • the mesoscopically structured composite formed during initial self- assembly may have hexagonal, cubic, or lamellar mesostructural ordering, which separately transforms during hydrothermal treatment (the annealing step) into generally lamellar inorganic-surfactant composites that possess molecularly ordered inorganic frameworks.
  • Preferred self-assembly agents are amphiphilic surfactants, with a hydrophobic tail and a charged head group. Strong electrostatic interactions between structure-directing species and crystallizing precursors favor the nucleation and growth of molecular order in the resultant framework. Consequently, for negatively charged frameworks, cationic head groups, such as trialkylammonium moieties, are preferred, while for positively charged frameworks, anionic head groups are preferred.
  • the hydrophobic tail is preferably comprised of C 6 -C 20 linear and branched alkyl, alkene, alkyne, phenyl, alkylphenyl, ether, or azide groups or mixtures thereof.
  • the inorganic network precursors can be polymerizable species, for example, silicon alkoxides, metal alkoxides, mixed metal alkoxides, organosiliconalkoxides, organometalalkoxides, hydrolyzable and condensable metal salts, and mixtures thereof.
  • the inorganic species is a silica precursor, such as tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), or tetrapropoxysilane (TPOS).
  • the method is preferably conducted under alkaline conditions.
  • the pH is in the range of pH 10 to pH 14.
  • the annealing step is preferably conducted under hydrothermal conditions for between two to forty days, depending on the choice of surfactant and solution conditions (e.g., temperature and pH).
  • surfactant and solution conditions e.g., temperature and pH.
  • the rates of formation of the locally-ordered silicate structures depend on the composition, charge density, hydrophilicity, and symmetry of the charged surfactant head groups.
  • the annealing step for producing a molecularly ordered silicate framework takes about one to two days; for a dimethylethylammonium head group, it takes about three to seven days; for a diethylmethylammonium head group, it takes about ten to 20 days; while for a triethylammonium head group about thirteen to 25 days are required.
  • two-dimensional (2D) heteronuclear correlation (HETCOR) 29 Si ⁇ 1 H ⁇ NMR measurements show that a substantial fraction of silicon species in the molecularly ordered regions of the silicate framework regions are located within about one nanometer of the charged head groups of the structure-directing surfactant species.
  • Mesostructurally ordered mesophases with molecularly ordered silicate networks can be produced by the present method that have amorphous silica contents that are low, i.e., below ca. 10% as estimated from the detection limits of one-dimensional (ID) 29 Si magic-angle-spinning (MAS) NMR. [15] Accordingly, these materials are expected to exhibit superior mechanical and hydrothermal stabilities compared to the prior art, namely mesostructurally ordered mesophases with disordered silicate frameworks.
  • Figure 1 A series of (a) X-ray powder diffraction patterns, (b) CP/MAS 29 Si NMR spectra, and (c) FTIR spectra for silica-surfactant mesophases synthesized using cetyldimethylethylammonium bromide (C 16 NMe 2 EtBr) and annealed at 135 °C under hydrothermal conditions for different lengths of time.
  • FIG. 1 2D 29 Si ⁇ 1 H ⁇ HETCOR NMR spectrum acquired for the same ordered silica-C 16 NMe 2 Et + mesophase characterized in Figure 1 (7 Days). Separate single- pulse 29 Si MAS and 1H MAS spectra accompany the HETCOR contour plot along the horizontal and vertical axes, respectively. The correlations observed in the 2D HETCOR spectrum establish that all five silicon site moieties are interacting strongly with the methyl and ethyl protons of the surfactant head group. 512 acquisitions were recorded at 11.7 T for each of the 108 t ⁇ increments using a 3-s repetition delay.
  • Figure 3 2D homonuclear J-coupling-correlated 29 Si ⁇ 29 Si ⁇ NMR spectrum acquired for the same ordered silica-C 16 NMe 2 Et + mesophase characterized in Figure 1 (7 Days) and Figure 2.
  • a single-pulse Si MAS spectrum accompanies the contour plot along the horizontal axis, while the double quantum dimension lies along the vertical axis.
  • the atomic connectivities between pairs of J-coupled Si atoms can be established from the correlated intensities at identical double-quantum frequencies. 2048 acquisitions were recorded for each of the 96 increments using a 2-s repetition delay.
  • Figure 4 A series of CP/MAS 29 Si NMR spectra acquired on lamellar silica-surfactant mesophase composites synthesized using surfactants with different cationic cetyltrialkylammonium head groups under otherwise identical hydrothermal conditions at 135 °C until molecularly ordered silicate frameworks were obtained. The times required for such ordering to occur depend strongly on the charge densities of the cationic surfactant head groups, with higher charge densities promoting more rapid formation of ordered frameworks.
  • Figure 5 (a) X-ray powder diffraction patterns and (b) 29 Si CP/MAS NMR spectra obtained from silica-C 1 6NMe 2 Et + mesophases after hydrothermal synthesis at 130 °C for 5, 1, and 12 days under otherwise identical conditions.
  • FIG. 6 High-resolution transmission electron micrograph of the ordered lamellar si!ica-C 16 NMe 2 Et + mesophase product synthesized for 12 Days at 130 °C (see Figure 5, bottom).
  • the corresponding, and correctly oriented, electron diffraction (ED) pattern is shown in the upper-right-hand corner.
  • the numbered reflections in the ED pattern correlate with corresponding planar distances observed in the TEM image, which have been enlarged.
  • FIG. 7 Plots of the integrated intensities of Q 2 , Q 3 , and Q 4 29 Si framework species in the silica-C 16 NMe 2 Et + mesophases as functions of the duration of hydrothermal synthesis.
  • the shaded area represents the period when the initially hexagonal mesophase with its amorphous silicate framework transforms into a lamellar mesophase with a locally ordered silicate framework.
  • Figure 8 Comparison of materials made according Inagaki et al [16] versus the materials shown in Figure 1 (7 days).
  • the XRD of Inagaki et al. (A) shows no apparent diffraction from the silica framework as well as narrow and intense XRD peaks at high scattering angles.
  • B derived from Figure 1
  • the 29 Si NMR data of Inagaki, et al. (C) exhibits broad 29 Si NMR peaks ( ⁇ 10 ppm)
  • corresponding data from Figure 1 (D) exhibits narrow 29 Si NMR peaks ( ⁇ l ppm) indicating a high degree of molecular ordering throughout the sample.
  • Inorganic-organic mesophases with crystalline inorganic frameworks hold great promise for applications as coatings, films and barriers, in catalysis, adsorption and separation, as optical host materials, in electronic devices, and as structural materials.
  • inorganic-organic mesophases and mesoporous solids have been synthesized with frameworks that lack long range (> 1 nm) molecular order.
  • the often harsh conditions to which many coatings, films, catalysts, separation agents, optical, electronic, and structural materials are exposed require robust materials that do not degrade under mechanical wear or hydrothermal conditions.
  • the present application is directed to an improved preparation of self- assembled inorganic/organic composites, in which an inorganic framework assumes crystallike molecular ordering.
  • These materials are prepared by combining a self-assembling organic species, such as an amphiphilic surfactant (preferably, but not necessarily a cationic surfactant) with a network-forming inorganic precursor species, (preferably, but not necessarily silica precursors).
  • a self-assembling organic species such as an amphiphilic surfactant (preferably, but not necessarily a cationic surfactant)
  • a network-forming inorganic precursor species preferably, but not necessarily silica precursors.
  • Self-assembly refers to a process in which molecular moieties segregate according to thermodynamic partitioning criteria (e.g., lyotropic liquid crystals or as defined by the Flory-Huggins ⁇ parameter for block copolymers) or the packing of macroscopic components (e.g., the organization of densely assembled latex spheres).
  • the surfactant species act as structure-directing agents for the inorganic precursor species, which polymerize initially into a typically amorphous inorganic network with initially hexagonal, cubic, or lamellar mesoscopic order cooperatively imparted by interactions among the self-assembled surfactant and inorganic species.
  • XRD X-ray diffraction
  • the composite Upon annealing under hydrothermal conditions, the composite transforms into a lamellar mesophase with a molecularly ordered inorganic framework structure.
  • High degrees of molecular order in the inorganic framework are established by narrow peaks ( ⁇ 2 ppm) in solid-state magic-angle spinning 29 Si NMR spectra of siliceous silicate/surfactant materials [16] and high-angle (>20°) reflections in X-ray or electron diffraction patterns (see accompanying Figures).
  • An inorganic network precursor-surfactant composite can typically be prepared at room temperature using the following molar compositions: 1.0 M inorganic precursor, 0.01 - 10.0 M surfactant, and sufficient base compound to give an alkaline pH.
  • a typical synthesis procedure involves dissolving an appropriate amount of surfactant in water, after which the base compound, and optionally a water-miscible organic solvent, is added. After stirring the solution for about 30 min, the inorganic precursor is then added and the solution stirred for another 30 min, after which time the pH may be lowered to about 11 to 11.5 with concentrated acid. After about 2 h of stirring, each mixture is transferred into reaction vessels, sealed, and placed in an oven at about 130-135 °C.
  • the inorganic framework precursors can include silicon alkoxides, metal alkoxides, mixed-metal alkoxides, organosiliconalkoxides, metal salts, organometalalkoxides and mixtures thereof.
  • Preferred inorganic precursor species include tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), tetrapropoxysilane (TPOS), or organically modified derivatives, which are suitable sources of silica for the preparation of silica structures.
  • the metal-containing precursors may include any of the main group, transition metals, rare-earth metals and mixtures thereof.
  • Transition metal refers to an element designated in the Periodic Table as belonging to Group IIIB (e.g., scandium and yttrium), Group IVB (e.g., titanium, zirconium and hafnium), Group VB (e.g., chromium, molybdenum and tungsten), Group VIIB (e.g., manganese, technetium and rhenium), Group VIIIB (e.g., iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum), Group IB (e.g., copper, gold and silver) and Group IIB (zinc, cadmium and mercury).
  • Group IIIB e.g., scandium and yttrium
  • Group IVB e.g., titanium, zirconium and hafnium
  • Group VB e.g., chromium, molybdenum and tungsten
  • Group VIIB e.g.,
  • the precursors of inorganic frameworks such as Nb O 5 , TiO 2 , ZrO 2 , WO 3 , AlSiO 3 . 5 , AlSiO 5 . 5, SiTiO 4, Al 2 O 3 , Ta 2 O 5 , SiO 2 , SnO 2 , HfO 2 , ZrTiO 4 , and Al 2 TiO 5 , rare earth oxides, metal oxynitrides, metal oxychalcogenides, metal nitrides, or metal chalcogenides are considered to be within the scope of the present invention.
  • a preferred surfactant is comprised of a charged head group and a hydrophobic tail.
  • the charged head group will be a cationic head group, such as trialkyammonium, trispyrrolidinium.
  • the hydrophobic tail is preferably C 8 - C 20 linear and/or branched alkyl, alkene, alkyne, phenyl, alkylphenyl, ether, or azide groups, and mixtures thereof.
  • a most preferred surfactant is a cetyltrialkylammonium bromide.
  • the surfactant can be an amphiphilic block copolymer, anionic and nonionic detergents, and mixtures of the foregoing.
  • a base compound is typically included in an amount sufficient to give an alkaline pH and/or to adjust the ionic strength of the mixture.
  • Preferred base compounds include alkylammonium hydroxides, ammonium hydroxide, and alkali metal hydroxides, such as NaOH, KOH, etc.
  • an acid such as HBr, may be utilized to lower the pH to within a preferred range.
  • the pH of the mixture will be about pH 10-14. Most preferably, the pH range is about pH 11-11.5.
  • the mixture may also include one or more organic solvents, preferably a water-miscible alcohol, such as methanol or ethanol, or a partially water-miscible or water-immiscible organic solvent, such as benzene, trimethylbenzene, hexanol, or hexane, as a hydrophobic swelling agent.
  • organic solvents preferably a water-miscible alcohol, such as methanol or ethanol, or a partially water-miscible or water-immiscible organic solvent, such as benzene, trimethylbenzene, hexanol, or hexane, as a hydrophobic swelling agent.
  • the annealing step is conducted by hydrothermal treatment at about 100 to 140 degrees Celsius, preferably about 130-135 degrees Celsius.
  • the length of the hydrothermal treatment required to form a highly ordered inorganic framework will depend on the choice of surfactants. For example, when annealing a silica/cetyltrialkylammonium bromide composite, the length of the annealing step will depend on the combination of alkyl groups present in the head group of the surfactant as follows: trimethyl ⁇ dimethylethyl ⁇ diethylmethyl ⁇ triethyl ⁇ tripropyl.
  • the annealing temperature should be below the temperature at which significant thermal decomposition of the structure- directing surfactant species occurs. For more thermally stable surfactants, higher annealing temperatures would be possible. III. Example I
  • cationic surfactants cetyltrimethylammonium bromide (C 16 NMe 3 Br) and cetyldimethylethylammonium bromide (C 16 NMe 2 EtBr), were purchased and required no further preparation.
  • the reactants were refluxed for 3-5 days in an ethanolic solution and recrystallized from ethanol/ethyl acetate (3x).
  • TMAOH Tetramethylammonium hydroxide
  • HBr hydrobromic acid
  • CH 3 OH methanol
  • TMOS tetramethylorthosilicate
  • Lamellar silica-surfactant composites were prepared at room temperature using the following molar compositions: 1.0 SiO 2 : 0.7 surfactant : 0.7 TMAOH : 113.4 H 2 O : 9.9 CH 3 OH.
  • a typical synthesis procedure involved dissolving an appropriate amount of surfactant in water, after which TMAOH and CH 3 OH were added and the solution stirred for 30 min.
  • TMOS Teflon-lined Parr reaction vessels
  • pH 11.5 with concentrated HBr
  • each mixture was aliquoted into a number of identical Teflon-lined Parr reaction vessels, sealed, and placed in an oven at 135 °C.
  • the reaction vessels were individually removed from the oven after specified intervals of time and then allowed to cool to room temperature.
  • the mesophase precipitates were subsequently washed with deionized water to remove any excess surfactant and/or solvents.
  • Figure 1 presents structural characterization data of silica-C 1 NMe 2 Et + composites monitored as a function of time to follow the process of framework ordering.
  • the X-ray diffraction (XRD) pattern and broad 29 Si MAS NMR peaks in Figures l(a,b) show that the sample is initially a lamellar mesophase with a locally disordered silica framework. Longer hydrothermal treatment of this composite leads to improved resolution in the 29 Si MAS spectrum ( Figure 1(b), 7 Days), with the 29 Si peak linewidths narrowing to 1 ppm or less.
  • the novel framework structure has been characterized and shown to be a single phase material.
  • the different 29 Si sites are interconnected via bridging oxygen atoms and are molecularly proximate to the structure-directing surfactant species. This is unambiguously established by using solid-state 2D NMR methods.
  • 2D 29 Si ⁇ 1H ⁇ heteronuclear correlation (HETCOR) NMR measurements provide detailed insight on interfacial molecular interactions between different 29 Si sites and the proton-containing amphiphilic surfactant species.
  • the ordered framework of the silica-C 16 NMe 2 Et + composite is shown to be a highly interconnected silicate network, with intimately mixed Q 3 and Q 4 species that are not separated into distinct domains.
  • Figures 4a and 4b show the Si MAS spectra of mesoscopically ordered materials with different molecularly ordered inorganic frameworks obtained using C 16 NMe + and C 16 NMe 2 Et + , respectively.
  • the trialkylammonium head group of the cationic surfactant was modified to include a single methyl and two ethyl group moieties, C 16 NMeEt 2 + , a lamellar composite with an amorphous silica framework again resulted after hydrothermal
  • silica-C 16 NMeEt + composite similarly transformed into a product with a highly ordered silicate framework. This process began after approximately 10 days under hydrothermal conditions and was completed after 19 days, as evidenced by the 29 Si MAS spectrum in Figure 4c, which contains no discernible signal from amorphous silica.
  • the lengthened hydrothermal treatment is consistent with the lower charge density of this cationic surfactant head group, which is expected to interact more weakly with the anionic silicate framework.
  • 2D crystallization of the inorganic framework is shown to promote mesoscopic phase transitions, in this case, from an initial hexagonal mesostructure to a lamellar architecture.
  • two-dimensional (2D) crystallization of an initially amorphous silica framework in a hexagonal mesophase composite induces a transition to a stable lamellar material with a molecularly ordered silicate lattice.
  • the silica-surfactant mesophase samples were all prepared using a molar composition and conditions that favor the initial formation of hexagonally ordered mesophase composites: 1.0 C 16 NMe 2 EtBr : 0.5 NaOH : 1.0 TEOS : 150 H 2 O. They were synthesized by combining appropriate amounts of C 16 NMe 2 EtBr, H 2 O, and NaOH and stirring until the surfactant dissolved, after which TEOS was added and the solution stirred for 30 min. The pH of the solution was then adjusted to 11.0 using 2M NaOH and the solution stirred for an additional 30 min. The mixture was transferred into separate stainless steel autoclaves (Parr) and placed in a temperature controlled oven at 130 °C. These reaction vessels were individually removed from the oven after specified intervals of time and then allowed to cool to room temperature. The mesophase precipitates were subsequently washed with deionized water to remove excess surfactant and/or solvents.
  • X-ray powder diffraction (XRD) data were acquired on a Scintag PAD X diffractometer using Cu-K « radiation and a liquid-nitrogen-cooled germanium solid-state detector. The data were collected from 1° to 35° (2 ⁇ ), with a resolution of 0.02° and a count time of 5 s at each point.
  • HREM High-resolution electron microscopy
  • Figure 5 displays the results for a series of silica- surfactant (cetyldimethylethylammonium, C 16 NMe 2 Et + ) mesophases prepared under identical hydrothermal conditions at 130 °C for various lengths of time. Initially, a hexagonally ordered material (MCM-41) is obtained, as evidenced by XRD reflections at 4.46 (100), 2.59 (110), 2.24 (200) and 1.69 nm (210) shown in Figure 5(a), 5 Days.
  • silica- surfactant cetyldimethylethylammonium, C 16 NMe 2 Et +
  • the silica framework although mesoscopically ordered, however, is locally amorphous, as evidenced by the broad 29 Si NMR linewidths (Figure 5(b), 5 Days) and the absence of high-angle XRD reflections.
  • the broad 29 Si linewidths reflect locally heterogeneous environments arising from a distribution of bond lengths and/or bond angles that are common to locally amorphous silica networks.
  • 29si NMR spectra showed no significant changes in signal-to-noise (concentration) or in the resonant signals present (speciation) during the course of the synthesis.
  • Predominant 2 ⁇ i signals were observed at -71.6 ppm from dilute monomeric species and much weaker signals from dimer species in the vicinity of -80 ppm.
  • the hexagonal mesophase begins to transform into a lamellar phase with a substantially higher degree of molecular ordering in the silica framework.
  • This phase transformation is evident in the powder XRD pattern ( Figure 5(a), 7 Days), which shows hkO reflections at 4.64 (100), 2.70 (110), 2.34 (200), and 1.78 nm (210) that are characteristic of hexagonally ordered MCM-41, along with hOO reflections at 3.76 nm (100) and 1.85 nm (200) corresponding to the appearance of a lamellar mesophase.
  • the 29 Si CP/MAS NMR spectrum for this sample ( Figure 5(b), 7 Days), furthermore, displays five resolvable peaks at -96.9, -100.7, -103.5, -108.9, and -114.4 ppm, as well as a broad distribution of resonances over the range -90 to -115 ppm.
  • These five distinct 29 Si resonances are identical to those previously observed in the locally-ordered lamellar mesophase materials of Example 1, which have been assigned to distinct ⁇ 3 (-96.9 and -100.7 ppm) and ⁇ 4 (-103.5, -108.9, and -114.4 ppm) 29 Si framework species.
  • the relative fraction of molecularly ordered silica is approximately 15% of the total silica present, consistent with estimates from the XRD measurements.
  • the 29 Si NMR results thus indicate the presence of both amorphous and molecularly-ordered 29 Si species, which appear to be associated separately with the hexagonal and emerging lamellar phase, respectively.
  • Si CP/MAS NMR spectrum for this sample contains the same five distinct and narrow (0.8-1.2 ppm FWHM) resonances previously observed after 7 days of hydrothermal treatment, reflecting crystal-like molecular ordering of the 2D silicate sheet framework. There is no evidence of an amorphous silica fraction nor hexagonal mesophase remaining.
  • TEM High resolution transmission electron microscopy
  • ED electron diffraction
  • Figure 6 shows a TEM image and the corresponding electron diffraction (ED) pattern of the final lamellar silica-C 16 NMe 2 Et + product ( Figure 5, 12 days), revealing for the first time imaging evidence of molecularly ordered framework atoms in synthetic inorganic-organic mesophase composites.
  • Three different planar distances are clearly observed in the TEM image and the ED pattern, manifested by the three characteristic lengths and spotty arcs labeled "1", "2", and "3" in Figure 6.
  • the planar distances calculated from the ED pattern and the TEM image at locations "1", “2", and “3" are 2.6, 1.3, and 0.9 nm, respectively.
  • the scattering intensities at 2.6 and 1.3 nm are likely the 100 and 200 reflections resulting from the lamellar organization of the material. These distances are somewhat smaller than the corresponding distances derived from powder XRD ( Figure 5(a), 12 Days), which may be attributable to reduced interlayer spacing due to partial decomposition of the organic species in the intense electron beam or from the partial extraction of surfactant molecules during the preparation of the TEM sample with ethanol.
  • the scattering intensity at 0.9 nm (“3") cannot be assigned to the 300 reflection, because in the 2D ED pattern it appears in a different diffraction plane than that common to the "1" and "2" reflections.
  • the reflection at 0.9 nm is substantially sharper and agrees well with the narrow powder XRD reflection at 0.85 nm ( Figure 5(a), 12 Days) that is attributed to intra-framework order.
  • the TEM, electron diffraction, and XRD results thus corroborate ordering over mesoscopic and molecular length scales in the lamellar silica-C 16 NMe Et + composites.
  • the molecular organization of the inorganic silica in these materials is dependent upon the organic template species used, the pH/ionic strength of the synthesis mixture, as well as the temperature and pressure employed.
  • a key aspect is the strength of the interactions, particularly electrostatic, between the inorganic framework and surfactant head group species, which can be controlled by adjusting the pH or ionic strength of the synthesis solution, along with mixture composition. Strong interactions promote the formation of ordered inorganic frameworks. For a given pH, the charge-density of the head groups exert a strong influence on the rate at which molecular framework order develops: higher head group charge-densities result in more rapid formation of molecularly ordered inorganic networks.
  • Synthesis temperature also plays a crucial role in the formation of these ordered networks.
  • elevated temperatures facilitate the rate at which the ordered networks form, although excessively high temperatures (>140 °C) can lead to the decomposition of the surfactant, causing a subsequent degradation of framework order.
  • excessively high temperatures >140 °C
  • the remnants of the structure-directing surfactant species exert a weak influence on the inorganic architecture, resulting in materials that are mesoscopically and locally disordered.
  • semiconductor compounds synthesized as surfactant-organized nanocrystals should be preparable as continuous 2D and/or 3D mesophases with molecularly ordered frameworks.
  • this art is expected to apply to wholly organic mesophase systems [29], in which strongly interacting self-assembling species interact with and may direct the nucleation and growth of molecularly ordered organic frameworks from charged organic precursor species.
  • this invention applies to self-assembling agents generally, provided sufficiently strong interactions exist between the framework and self-assembling agent across their common interface.
  • surfactants cationic, anionic, non-ionic
  • block-copolymers emulsions
  • monodispersed macroscopic objects such as polymer or silica spheres, rods, disks, or other shapes.
  • Mesoporous materials have been synthesized with block copolymers, many varieties of surfactants, and even biological macromolecules, which could be used to produce mesophase composites with molecularly ordered inorganic frameworks.
  • the key requirement is that the inorganic and organic species must interact with sufficient strength that molecular ordering is promoted in the inorganic framework along with mesoscopic ordering.
  • Different structure-directing moieties e.g., all those used for synthesizing crystalline zeolites and molecular sieves
  • anionic moieties e.g., phosphates, sulfates
  • non-ionic moieties e.g., amines
  • amino acids l,4-diazabicyclo[2,2,2]octane (DABCO) derivatives, and mixtures thereof
  • DABCO diazabicyclo[2,2,2]octane
  • These species can be incorporated as oligomers, as pendant groups on copolymer blocks or on the surfaces of macroscopic objects, such as surface-functionalized polystyrene or silica spheres.
  • Such template-functionalized meso- or macroscale self-assembly agents would allow molecularly ordered nanoporosity to be combined with meso- or macroporosity in these materials.
  • the techniques described herein may thus aid in inducing local crystallization within the framework of meso- or macroporous materials, while preserving porosity.
  • Such procedures could also be applied on a variety of other porous substrates with the goal of inducing local order.
  • mesophase materials can be prepared with structure-directing surfactants or agents that yield local and/or long range crystal-like ordering in their frameworks by using suitable annealing treatment.

Abstract

L'invention concerne des composites à mésophase laminaires auto-assemblés comprenant des tensio-actifs de silice ordonnés de manière cristalline dans les cadres de silice à l'aide de diverses espèces de tensio-actifs cationiques dans des conditions hydrothermiques (T>100°C). La cristallisation de la silice est obtenue à partir d'interactions locales entre des agents de surface organiques et de la silice inorganique. Les taux de formation des structures de silice ordonnées localement dépend de la composition, de la densité de la charge, et de la symétrie des têtes polaires des tensio-actifs chargés. De plus, différentes têtes polaires de tensio-actifs chargés favorisent la formation de différentes configurations locales dans le cadre inorganique ordonné de manière moléculaire, et peuvent se révéler précieuses pour la personnalisation de l'organisation locale d'architectures inorganiques de divers matériaux.
PCT/US2002/011684 2001-04-13 2002-04-12 Synthese de materiaux a mesophase presentant des cadres ordonnes de maniere moleculaire WO2002083994A1 (fr)

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US8408216B2 (en) 2004-12-22 2013-04-02 Philip Morris Usa Inc. Flavor carrier for use in smoking articles

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005061105A1 (fr) * 2003-12-22 2005-07-07 Basf Aktiengesellschaft Catalyseur heterogene a base de ruthenium, ethers diglycidyliques a noyau hydrogene des bisphenols a et f et procede pour leur production
US8408216B2 (en) 2004-12-22 2013-04-02 Philip Morris Usa Inc. Flavor carrier for use in smoking articles

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