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Showing papers in "Chemistry of Materials in 1997"


Journal ArticleDOI
TL;DR: A substantial amount of work has been carried out in the area of nanocomposite materials for optical applications as discussed by the authors, which are typically constructed by embedding an optically functional phase into a processable, transparent matrix material.
Abstract: A substantial amount of work has been carried out in the area of nanocomposite materials for optical applications. Composites are typically constructed by embedding an optically functional phase into a processable, transparent matrix material. By doing so, the optical properties can be utilized in more technologically important forms such as films and fibers. This review covers many areas of optical composite research to date. Composites with second- and third-order nonlinearities and laser amplification properties are discussed with examples from the recent literature. Other composites, including transparent magnets, may be made using similar structures. The principles used to construct these composites may have important technological applications soon and are therefore summarized in this review.

942 citations


Journal ArticleDOI
TL;DR: The template method for synthesizing nanostructures involves the synthesis of the desired material within the pores of a nanoporous membrane or other solid as discussed by the authors, which involves using porous alumina and polymeric filter membranes as the templates.
Abstract: The template method for synthesizing nanostructures involves the synthesis of the desired material within the pores of a nanoporous membrane or other solid. Our work has involved using porous alumina and polymeric filter membranes as the templates. Fibrils or tubules of the desired material are formed within each pore of the template membrane. A number of synthetic methods have been used to synthesize these nanostructures. This paper reviews sol−gel template synthesis: the use of sol−gel chemistry to synthesize semiconductor oxide micro- and nanostructures within the pores of micro- and nanoporous membranes. For example, TiO2 nanotubules and nanofibers of the anatase form have been synthesized. The high surface area offered by these TiO2 nanostructures has been used for photodecomposition of salicylic acid in sunlight. Enzyme immobilization by stannous bridges inside the TiO2 tubes has also been studied. In addition, V2O5 fibrous electrode materials have been prepared by this method and Li intercalation ...

680 citations


Journal ArticleDOI
TL;DR: In this paper, the first use of sol−gel chemistry to prepare semiconductor nanofibrils and tubules within the pores of an alumina template membrane was described, and 200 nm diameter TiO2 fibrils were used as photocatalysts for the decomposition of salicylic acid.
Abstract: The template method for preparing nanostructures entails synthesis of the desired material within the pores of a nanoporous membrane or other solid. A nanofibril or tubule of the desired material is obtained within each pore. Methods used previously to deposit materials within the pores of such membranes include electrochemical and electroless deposition and in situ polymerization. This paper describes the first use of sol−gel chemistry to prepare semiconductor nanofibrils and tubules within the pores of an alumina template membrane. TiO2, WO3, and ZnO nanostructures have been prepared. TiO2 nanofibrils with diameters of 22 nm were found to be single crystals of anatase with the c-axis oriented along the fibril axis. Bundles of these fibrils were also found to be single crystalline, suggesting that the indiviual fibrils are arranged in a highly organized fashion within the bundle. Finally, 200 nm diameter TiO2 fibrils were used as photocatalysts for the decomposition of salicylic acid.

597 citations


Journal ArticleDOI
TL;DR: In this article, a printed field effect transistor (FET) is reported, which has a polyimide dielectric layer, a regioregular poly(3-alkythiophene) semiconducting layer, and two silver electrodes, all of which are printed on an ITO-coated plastic substrate.
Abstract: A printed field-effect transistor (FET) is reported, in which all the essential components are screen-printed for the first time. This transistor has a polyimide dielectric layer, a regioregular poly(3-alkythiophene) semiconducting layer, and two silver electrodes, all of which are printed on an ITO-coated plastic substrate.

584 citations


Journal ArticleDOI
TL;DR: In this paper, a simple method is used to prepare highly monodispersed silver nanoparticles in the liquid phase, which starts from an initial synthesis in functionalized AOT reverse micelles.
Abstract: A simple method is used to prepare highly monodispersed silver nanoparticles in the liquid phase, which starts from an initial synthesis in functionalized AOT reverse micelles. To narrow the particle size distribution from 43% to 12.5% in dispersion, the particles are extracted from the micellar solution. The size-selected precipitation method is used. The decrease in polydispersity of the silver nanoparticles is followed by transmission electron microscopy, by UV−vis spectroscopy, and by small-angle X-ray scattering. The nanocrystallites dispersed in hexane are deposited on a support. A monolayer made of nanoparticles with spontaneous hexagonal organization is observed. The immersion of the support on the solution yields to the formation of organized multilayers arranged as microcrystal in a face-centered cubic structure.

533 citations


Journal ArticleDOI
TL;DR: In this paper, an attempt was made to prepare porous carbon by using the channels of Y zeolite as a template, where poly(acrylonitrile) and poly(furfuryl alcohol) were carbonized in the channels and the resultant carbon/zeolite complexes were subjected to acid treatment in order to extract carbon from the ZO framework.
Abstract: An attempt was made to prepare porous carbon by using the channels of Y zeolite as a template. Poly(acrylonitrile) and poly(furfuryl alcohol) were carbonized in the zeolite channels and the resultant carbon/zeolite complexes were subjected to acid treatment in order to extract carbon from the zeolite framework. In addition, pyrolytic carbon deposition in the channels was carried out by exposing the zeolite to propylene at high temperature, and then the carbon was liberated in the same manner as above. The morphology and structure of the carbon prepared in the channels were characterized, and the results were discussed in relation to the morphology and structure of the original zeolite template. It was found that the microscopic morphology of the resultant carbons reflects that of the corresponding zeolites. All of these carbons are highly porous, and some of the CVD carbons have BET surface areas as high as >2000 m2/g.

516 citations


Journal ArticleDOI
TL;DR: The use of chemical solution deposition for the fabrication of perovskite thin films is reviewed in this paper, where a variety of approaches including sol−gel, chelate, and metalloorganic decomposition have all been employed with success in the preparation of these materials.
Abstract: The use of chemical solution deposition for the fabrication of perovskite thin films is reviewed. A variety of approaches including sol−gel, chelate, and metalloorganic decomposition have all been employed with success in the preparation of these materials. For a number of perovskite compounds, thin-film properties that equal those of the bulk materials have been obtained. Various aspects of the solution chemistries for the three different routes are discussed, and the effects of solution precursor properties on the conversion of the as-deposited film to the desired perovskite phase are discussed. The roles that thermodynamic and kinetic factors have on this transformation process are also reviewed. Finally, some of the applications for solution-derived thin films currently under development are reviewed, and the inherent limitations of the deposition technique for device manufacture are considered.

499 citations


Journal ArticleDOI
TL;DR: In this paper, high-resolution electron microscope (HREM) observations revealed that nanometer-sized cerium(IV) oxide ultrafine particles were formed using a reaction within reversed micelles, which was known as a microemulsion method.
Abstract: Cerium(IV) oxide ultrafine particles were prepared using a reaction within reversed micelles, which was known as a microemulsion method. The ultrafine particles, which were obtained by mixing the water-in-oil microemulsions containing cerium nitrate solution with those of ammonium hydroxide, were characterized by high-resolution electron microscope (HREM) observations. HREM micrographs revealed that nanometer-sized CeO2 particles were formed, and their shapes were uniform. Selected-area electron diffraction patterns of the particles were completely indexed as those of cerium(IV) oxide with the cubic fluorite structure, and the lattice constant calculated from radii of Debye−Sherrer rings was 0.541 nm. Most of the particles were distributed between 2 and 6 nm, and the mean particle size obtained in this method was between 2.6 and 4.1 nm. The size of 2.6 nm is the smallest among the values ever reported for CeO2 particles. Both direct and indirect optical energy gaps of the particles were independent of the...

461 citations


Journal ArticleDOI
TL;DR: In this paper, the chemistry of various non-hydrolytic sol−gel processes including hydroxylation in nonaqueous systems and aprotic condensation reactions are surveyed.
Abstract: This review surveys the chemistry of various nonhydrolytic sol−gel processes including hydroxylation in nonaqueous systems and aprotic condensation reactions. Some examples of applications in the field of single and multicomponent oxides demonstrate the interest of these approaches as alternatives to the usual hydrolytic routes. More particularly nonhydrolytic methods lead to improved control over the molecular level homogeneity and stoichiometry of multicomponent oxides.

440 citations


Journal ArticleDOI
TL;DR: In this article, the thermal stability, mechanical strength, conductivity, electrochemical stability window, and Li/electrolyte interface stability of poly(vinylidene fluoride)−hexafluoropropene (PVdF−HFP) copolymer plasticized with a solution of LiSO3CF3, LiN(SO2CF3)2, or LiPF6 in oligomeric poly(ethylene glycol) dimethyl ethers (PEGDME, Mw = 250, 400, and 500).
Abstract: Polymer electrolyte membranes comprising poly(vinylidene fluoride)−hexafluoropropene (PVdF−HFP) copolymer plasticized with a solution of LiSO3CF3, LiN(SO2CF3)2, or LiPF6 in oligomeric poly(ethylene glycol) dimethyl ethers (PEGDME, Mw = 250, 400, and 500) were prepared by hot-melt-rolling or solvent-casting techniques. Since the electrolytes containing PEGDME400 and PEGDME500 are “dry” with essentially no volatile components up to 150 °C, we have dubbed them PEO-like. Their thermal stability, mechanical strength, conductivity, electrochemical stability window, and Li/electrolyte interface stability were characterized. Plasticizing PVdF−HFP with the PEGDME/LiX solutions disordered the polymer structure leading to polymer electrolytes having lower crystallinity than the polymer host itself. The mechanical strength of the electrolyte membranes varied depending on the PVdF content. Tensile strength (stress) as high as 420 psi at an elongation-at-break value (strain) of 75% was observed. The conductivities of t...

423 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe four approaches to the materials synthesis of organized inorganic matter, including self-assembled organic templates (transcriptive synthesis), cooperative assemblies of templates and building blocks (synergistic synthesis), spatially restricted reaction fields (morphosynthesis), and combinations of these approaches (integrative synthesis) in the area of sol−gel chemistry.
Abstract: In this review, we describe four approaches to the materials synthesis of organized inorganic matter. These include the use of self-assembled organic templates (transcriptive synthesis), cooperative assemblies of templates and building blocks (synergistic synthesis), spatially restricted reaction fields (morphosynthesis), and combinations of these approaches (integrative synthesis) in the area of sol−gel chemistry. We illustrate these strategies, respectively, by describing recent work on the formation of silica-based organized materials, viz. the preparation of ordered silica macrostructures using bacterial templates, template-directed synthesis of ordered hybrid mesophases and organoclays, synthesis of microskeletal frameworks of silica and other metal oxides in compartmentalized liquids, and use of bacterial superstructures in the fabrication of hierarchical macrostructures of mesoscopically ordered silica.

Journal ArticleDOI
TL;DR: In this paper, the authors 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.
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.

Journal ArticleDOI
TL;DR: In this article, simple synthesis methods for mesoporous fibers and powders by rapid evaporation of hydrolyzed silicon alkoxide−surfactant solutions are described, and pore sizes of calcined fibers were 20 A and surface areas as high as 1770 m2/g.
Abstract: Simple synthesis methods for mesoporous fibers and powders by rapid evaporation of hydrolyzed silicon alkoxide−surfactant solutions are described. Mesoporous fibers are prepared by dry spinning, and mesoporous powders by spray drying of alkoxide−surfactant solutions. Precursor solutions, containing fully hydrolyzed tetraethoxysilane, cetyltrimethylammonium chloride surfactant, and, in the case of the fibers, a fiber-forming polymer, in an acidic alcohol/water mixture, are drawn into continuous filaments or atomized into droplets in a heated air stream. During solvent drying, silica and surfactant self-assemble to form the hexagonally ordered mesophase structure, and all of the nonvolatile components (silica, polymer, and surfactant) are incorporated into the mesophase. The pore diameter and surface area of calcined fibers were 20 A and 1100 m2/g, respectively. For the powders, pore sizes of 25 A and surface areas as high as 1770 m2/g were measured. Spray-dried powders consisting of hollow spherical partic...

Journal ArticleDOI
TL;DR: In this article, 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.
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.

Journal ArticleDOI
TL;DR: The subject of sol−gel electrochemistry is introduced in this article, starting with a brief account of milestones in its evolution, followed by a description of recent advances in the various fields of sol −gel electro chemistry.
Abstract: The subject of sol−gel electrochemistry is introduced, starting with a brief account of milestones in its evolution. Then, the types of sol−gel materials that are useful for electrochemistry are presented, followed by a description of recent advances in the various fields of sol−gel electrochemistry. Modified electrodes, solid electrolytes, electrochromic devices, and corrosion protection coatings are described. Emerging fields such as RuO2 supercapacitors and electrochemical synthesis of sol−gel precursors are also addressed.

Journal ArticleDOI
TL;DR: In this paper, a series of ion exchangeable layered perovskite type oxides, A2-xLa2Ti3-xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0), were found to be highly efficient photocatalysts for overall water splitting when a small amount of Ni was loaded.
Abstract: A series of ion-exchangeable layered perovskite type oxides, A2-xLa2Ti3-xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0), were found to be highly efficient photocatalysts for overall water splitting when a small amount of Ni was loaded. These compounds are spontaneously hydrated even in an aqueous alkaline solution and decompose intercalated H2O molecules into H2 and O2 under the bandgap irradiation.

Journal ArticleDOI
TL;DR: In this paper, the pore size enlargement was accompanied by a significant improvement of pore sizes, a gradual decrease of the specific surface area, and a pore wall thickening.
Abstract: MCM-41 periodic mesoporous silicates were synthesized using cetyltrimethylammonium bromide, and their pore sizes were tailored by postsynthesis hydrothermal treatment method of Khushalani et al., allowing us to obtain large-pore MCM-41 samples with a high degree of structural ordering. It was shown that the pore size enlargement was accompanied by a significant improvement of pore size uniformity, a gradual decrease of the specific surface area, and the pore wall thickening. After a certain upper limit of pore size (i.e., about 6.5 nm) was reached, a further hydrothermal treatment led to samples of diminished quality. The structural uniformity decreases dramatically, i.e., the pore size distribution becomes broader and a small but noticeable amount of micropores develops. Moreover, the appearance of pore blocking effects (as inferred from the irreversibility of nitrogen adsorption−desorption isotherms) indicates that the pore geometry deviates significantly from its initial cylindrical shape characteristi...

Journal ArticleDOI
TL;DR: In this article, the authors synthesized five new emitter molecules having an oxadiazole group as an electron transport unit and a triphenylamine group as a hole transport unit.
Abstract: We synthesized five new emitter molecules having an oxadiazole group as an electron transport unit and a triphenylamine group as a hole transport unit. We investigated the electroluminescent (EL) properties of these molecules as an emitter layer. The deposited films of all compounds were found to be amorphous and showed strong blue-green fluorescence, ranging from 450 to 490 nm. With the best device using these emitters, the maximum luminance exceeded 19 000 cd/m2. We observed that external EL quantum efficiencies (φEL) were drastically influenced by combinations of hole-transport materials. Formation of exciplexes between the emitters and hole-transport materials was found to greatly influence φEL. We observed that the hole-transport layers (HTLs) having a low ionization potential (Ip) value tended to form exciplexes with the emitter layers, resulting in a low φEL. On the other hand, the HTLs having a large Ip formed no exciplexes with emitter layers and showed a high φEL. In the best device, a φEL∼4% wa...

Journal ArticleDOI
TL;DR: In this article, a sealed stainless steel tube at 600−800 °C from Ga using a Na flux and N2 from the thermal decomposition of sodium azide, NaN3.
Abstract: GaN single crystals were prepared in a sealed stainless steel tube at 600−800 °C from Ga using a Na flux and N2 from the thermal decomposition of sodium azide, NaN3. The maximum size of the crystals obtained was 2 mm. Oxygen and other impurity elements were not detected in the crystals by AES and EDX. When scaled up, this method may provide large GaN crystals for use as substrates for nitride based lasers.

Journal ArticleDOI
TL;DR: In this article, the synthesis of CdS and CdSe nanocrystallites using the thermolysis of several dithio- or diselenocarbamato complexes of cadmium in trioctylphosphine oxide (TOPO) is reported.
Abstract: The synthesis of CdS and CdSe nanocrystallites using the thermolysis of several dithio- or diselenocarbamato complexes of cadmium in trioctylphosphine oxide (TOPO) is reported. The nanodispersed materials obtained show quantum size effects in their optical spectra and exhibit near band-edge luminescence. The influence of experimental parameters on the properties of the nanocrystallites is discussed. HRTEM images of these materials show well-defined, crystalline nanosized particles. Standard size fractionation procedures can be performed in order to narrow the size dispersion of the samples. The TOPO-capped CdS and CdSe nanocrystallites and simple organic bridging ligands, such as 2,2‘-bipyrimidine, are used as the starting materials for the preparation of novel nanocomposites. The optical properties shown by these new nanocomposites are compared with those of the starting nanodispersed materials.

Journal ArticleDOI
TL;DR: In this article, the synthesis, characterization, and catalytic activity of titania−silica mixed oxides are described, and important structure/property relationships for these materials are emphasized.
Abstract: Titania−silica mixed oxides are intriguing catalysts and catalyst supports since their surface reactivities depend strongly on composition and homogeneity of mixing. In this review, the synthesis, characterization, and catalytic activity of titania−silica are described, and important structure/property relationships for these materials are emphasized.

Journal ArticleDOI
TL;DR: Very highly conductive Au films on glass substrates have been prepared by stepwise, layer-by-layer immobilization of 11-nm diameter colloidal Au particles and a short organic crosslinker Particle.
Abstract: Very highly conductive Au films on glass substrates have been prepared by stepwise, layer-by-layer immobilization of 11-nm diameter colloidal Au particles and a short organic cross-linker Particle

Journal ArticleDOI
TL;DR: In this article, a multilayer thin film consisting of anionic α-zirconium phosphate (α-ZrP) sheets and polycations (poly(allylamine hydrochloride) (PAH), cytochrome c) were characterized by transmission electron microscopy (TEM), ellipsometry, UV−visible absorbance spectroscopy, reflectance FT-IR, XPS, and X-ray diffraction.
Abstract: Monolayer and multilayer thin films consisting of anionic α-zirconium phosphate (α-ZrP) sheets and polycations (poly(allylamine hydrochloride) (PAH), cytochrome c) were characterized by transmission electron microscopy (TEM), ellipsometry, UV−visible absorbance spectroscopy, reflectance FT-IR, XPS, and X-ray diffraction. Titration and powder X-ray diffraction experiments confirm that exfoliation of α-ZrP begins to occur when enough tetra(n-butylammonium) hydroxide (TBA+OH-) has been added to exceed single-layer packing of TBA+ ions (x ≈ 0.50) in the intercalation compound Zr(HPO4)2-x(TBA+PO4-)x·nH2O. The identical contrast of many sheets in TEM micrographs suggests that the suspension is unilamellar. Alternately dipping cationic substrates into α-ZrP-containing suspensions and aqueous PAH gives a multilayer film that resembles the corresponding bulk intercalation compound. X-ray photoelectron spectra of multilayer films show that they are Zr-rich, relative to α-ZrP, consistent with some corrosion during t...

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate that a surfa... demonstrates that a polygonal metal oxide thin film with thickness control of nanometer precision is an important technology that leads to wide practical applications.
Abstract: Fabrication of metal oxide thin films with thickness control of nanometer precision is an important technology that leads to wide practical applications. The present study demonstrates that a surfa...

Journal ArticleDOI
TL;DR: In this article, the surface area of sensitizer for different types of anchoring is estimated on the basis of single-crystal X-ray diffraction studies of the esterified form of the complex.
Abstract: Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray powder diffraction (XRD) studies on nanocrystalline TiO2 powders and thin films are presented The size, shape (mostly exposed faces), and ordering of the TiO2 anatase particles in the nanocrystalline films are discussed The use of the topochemical approach, which considers the properties of (nanocrystalline) solids in terms of crystallographic features of (nano)crystals is suggested The surface area of sensitizer [bis(4,4‘-dicarboxy-2,2‘-bipyridine)bis(thiocyanato)]ruthenium(II) [abbreviated as (cis-Ru(dcbpy)2(NCS)2] on the semiconductor surface for the different types of anchoring is estimated on the basis of single-crystal X-ray diffraction studies of the esterified form of the complex

Journal ArticleDOI
TL;DR: In this paper, highly elongated filaments of crystalline barium sulfate, with lengths up to 100 μm and aspect ratios of 1000, were formed in BaNaAOT microemulsions.
Abstract: Supersaturated reverse micelles and microemulsions containing either AOT (sodium bis(2-ethylhexylsulfosuccinate)), C12EO4 (poly(oxyethylene-4-dodecyl ether)), or DDAB (didodecyldimethylammonium bromide) surfactants have been used as organized reaction microenvironments for barium sulfate precipitation. Nanoclusters of amorphous barium sulfate, 2−4 nm in size, were formed in association with BaNaAOT reverse micelles. In contrast, highly elongated filaments of crystalline barium sulfate, with lengths up to 100 μm and aspect ratios of 1000, were formed in BaNaAOT microemulsions. The individual filaments were single crystals of barite elongated predominantly along the [010] axis and in some instances consisted of coaligned nanofilaments, 20−50 nm in width. Similar reactions in C12EO4 reverse micelles and microemulsions afforded barite nanocrystals, 5−7 nm in dimension and tabular-shaped barite crystals, up to 400 nm in size, respectively. Rhombic crystals of barite, approximatety 200 nm in size, were deposite...

Journal ArticleDOI
TL;DR: Water:ethanol solvent mixtures of differing polarity have been used to tailor the framework and textural mesopores of HMS molecular sieve silicas through an electrically neutral assembly pathway as discussed by the authors.
Abstract: Water:ethanol solvent mixtures of differing polarity have been used to tailor the framework and textural mesopores of HMS molecular sieve silicas through an electrically neutral (S°I°) assembly pathway (S° = dodecyl- or tetradecylamine; I° = tetraethyl orthosilicate). Mesostructure assembly from a water-rich solvent mixture, water:ethanol = 90:10 (v/v), afforded wormhole-like framework structures with a complementary textural pore volume equal in magnitude to the framework pore volume. An ethanol-rich mixture, water:ethanol = 35:65 (v/v), also formed wormhole-like frameworks, but the textural porosity was less than 20% of the framework pore volume. HMS derivatives with high textural porosity were composed of mesoscale fundamental particles that aggregate into larger particles. In contrast, HMS mesostructures with low textural porosity were assembled into much larger aggregates of macroscale spheroid to disk-shaped fundamental particles. The differences in particle textures were attributed to differences i...

Journal ArticleDOI
TL;DR: Titanium dioxide has been grafted onto the pore surface of MCM-41 and FSM-16 by reacting TiCl4 in hexanes with the as-synthesized mesostructured silicate as mentioned in this paper.
Abstract: Titanium dioxide, a large-bandgap semiconductor and versatile photocatalyst, has been grafted onto the pore surface of MCM-41 and FSM-16 (a mesoporous material derived from kanemite) by reacting TiCl4 in hexanes with the as-synthesized mesostructured silicate. The products have been extensively characterized by powder XRD, TEM, SEM, EDS, XPS, N2 adsorption, SANS contrast matching, solid-state 1H MAS NMR, IR, and UV−vis spectroscopies. It was found that titania forms well-dispersed isolated (TiO2)n clusters (n ∼ 30−70) within the channel structure. These are attached to the silicate walls via Si−O−Ti bonds. A minor second phase consisting of anatase crystallites ca. 100−250 A in diameter on the external surface of the mesoporous silicate crystals was sometimes obtained. It is concluded that an organic moiety, such as the surfactant present in the pores, or a physical constraint, such as the pore walls, is necessary to prevent the creation of large TiO2 agglomerates and enable the formation of nanosized TiO...

Journal ArticleDOI
TL;DR: In this article, a protonic oxide of HxTi2-x/4□ x/4O4·H2O (x ∼ 0.7; □, vacancy) was delaminated into colloidal single sheets (thickness 0.75 nm) by being interacted with a bulky organic amine.
Abstract: Thin flakes of titanium dioxide have been synthesized through a novel route via exfoliation of a layered precursor. A protonic oxide of HxTi2-x/4□ x/4O4·H2O (x ∼ 0.7; □, vacancy) was delaminated into colloidal single sheets (thickness 0.75 nm) by being interacted with a bulky organic amine, (C4H9)4NOH. The resulting titania sol was freeze-dried to produce a gel in a thin filmlike texture. The gelation took place by reassembling 10−20 titanate sheets and consequently yielding lamellar aggregates. Upon heating above 400 °C, the gel was transformed into titanium dioxide (anatase) in thin flaky morphology (20−30 nm in thickness versus ∼μm in the lateral dimension). Intermediates at various stages of the synthetic process as well as the final product were examined by applying various characterization techniques such as X-ray diffraction (XRD), scanning and transmission electron microscopes (SEM, TEM), FT-IR and Raman spectroscopies, thermogravimetry, and elemental analysis. The flaky particulates were aggregat...

Journal ArticleDOI
TL;DR: In this article, the authors used zeolites as templates to prepare microporous polymer replicas and showed that the microporosity of the template is reflected in the replica polymer.
Abstract: Zeolites were used as templates to prepare microporous polymer replicas. Phenol−formaldehyde polymers were synthesized and cured within the channel networks of zeolites Y, β, and L. Dissolution of the aluminosilicate framework in aqueous HF yields an organic replica that contains <2% aluminosilicate. The zeolite template exerts important topological effects on the structure and physical properties of the replica. Using zeolites Y and β, which have three-dimensionally interconnected channel structures, the microporosity of the template is reflected in the replica polymer. Pore size distributions are consistent with the predominance of 5−6 A walls in the parent zeolite. In contrast, complete collapse of the replica, to a give nonporous material, occurs upon removal of the zeolite L template, since the latter has a one-dimensional channel structure. TEM and SEM micrographs also show evidence of collapse in the latter case. Pyrolysis of the zeolite−resin composites at 900 °C, and subsequent etching, produces ...