Search

V-doped SBA-16 catalysts (V-SBA-16) with 3D nanocage mesopores have been successfully synthesized by a modified one-pot method under weak acid condition. The obtained materials were characterized by means of small angle XRD, N 2 adsorption–desorption, TEM, UV–Vis and UV-Raman spectroscopy. These characterization results indicated that well-order mesoporous structures were maintained even at higher vanadium loadings and high concentration of VO x species were incorporated into the framework of SBA-16 support. The catalytic performances of V-SBA-16, V/SBA-16 and V/SiO 2 catalysts were comparatively investigated for the oxidative dehydrogenation of ethane to ethylene. The highest selectivity to ethylene of 63.3% and ethylene yield of 25.6% were obtained over 1.0V-SBA-16 catalyst. The superior catalytic performance of V-SBA-16 catalysts could be attributed to the presence of isolated framework VO x species, the unique structure of SBA-16 support and weak acidity. Moreover, V/SiO 2 catalyst exhibited relatively poor catalytic activity duo to the formation of V 2 O 5 nanoparticles on the surface of SiO 2 support and the low dispersion of VO x species. These results indicated that the catalytic performances of the studied catalysts were strongly dependent on the vanadium loading, the nature and neighboring environment of VO x species and the structure of support.

A series of highly dispersed Mo-incorporated mesoporous SBA-16 catalysts (Mo-SBA-16) were successfully synthesized by one-step hydrothermal method. The effects of different Mo loadings and MoOx structure of the Mo-SBA-16 catalysts for the oxidative dehydrogenation of ethane (ODHE) were investigated. Framework-incorporation promotes a better dispersion of molybdenum oxo species. Different kinds of MoOx species are related to the activity and selectivity of ethylene for ODH of ethane. A small amount of Mo species was incorporated into the framework of SBA-16, which greatly increased the selectivity of ethylene, but the C2H6 conversion was slightly greater than that of Mo/SBA-16 catalysts. Meanwhile, for both Mo-SBA-16 and Mo/SBA-16 catalysts the selectivity of ethylene was significantly enhanced with the increasing of reaction temperature. Moreover, Mo-SBA-16 catalysts showed much higher selectivities of ethylene than Mo/SBA-16 ones, mainly due to the presence of isolated MoOx species in the framework of SBA-16. And the maximal selectivity to C2H4 of 75.7% was obtained over 0.05Mo-SBA-16 catalyst. The three-dimensional mesoporous channels of Mo-SBA-16 allowed a better diffusion of ethane and produced ethylene to improve the catalytic performance.

The effects of surface treatment of polypropylene (PP) fiber on the mechanical and microstructure of fiber-reinforced cementitious (FRC) composites are investigated. Surface treatment of the PP fiber was performed with 3-aminopropyltrimethoxy silane (APS) and methyltriethoxy silane (MTES) in order to improve interaction between PP fiber and matrix. The effects of APS and MTES on the surface of PP fiber are studied by scanning electron microscopy, energy dispersive spectrometer, and Fourier transform infrared spectroscopy. The experiment results indicated that the treatment of PP fiber with APS and MTES can effectively increase the adhesion between fiber and matrix, and an improvement in the flexure and compressive strength of the cementitious composites was found in the samples containing treated PP fiber compared to the samples containing untreated PP fiber. The optimized mechanical properties could be obtained using 1.0% APS (by weight) and 1.0% MTES (by weight)-treated PP fiber at studied conditions, r...

The synthesis and characterization of a new class of cementitious composites filled with polymer emulsions were investigated, and their superior mechanical strength and durability properties compared to composites devoid of fillers were reported. Polymer emulsions were utilized to mechanically reinforce the composite and bridge the cement, fly ash, aggregate and fibers. The results reveal that the epoxy emulsion and poly (ethylene-co-vinyl acetate) emulsion markedly enhance the mechanical and durability properties of cemetitious composites. The fibers can be pulled out in the form of slip-hardening and the abrasion phenomenon can be observed clearly on the surface of the fibers. The hydration extent of cement is higher than that of the pristine composites. The polymer modified cementitious composites designed on micromechanics, have flexibility and plasticity which could be applied for a novel form of multifunctional materials with a range of pipeline coatings applications.

An engineered cementitious composite (ECC) is a micromechanically based designed high-performance fiber-reinforced cementitious composite with high ductility and durability, represented by strain-hardening behavior in uniaxial tension. However, the setting time of ECC is retarded and early strength is decreased due to the presence of high volume of fly ash (HVFA). Therefore, shortening the setting time and increasing flexural strength of HVFA-ECC will be of obvious economic importance. The experimental study on setting time and flexural strength of HVFA-ECC proved that the setting time can be shortened by adding alkali accelerator and the optimum content is 4.0%, while the flexural strength of HVFA-ECC can be increased by applying fine particles fly ash, modified fly ash or adding exciting agent of fly ash.

Herein, we report the direct synthesis of micro–mesoporous silicas using unsaturated anionic surfactant α-linolenic acid as mesophase template. The self-assembly of α-linolenic acid, which could transform to a rigid mesophase template via inner-micellar polymerization when heated, was successfully leveraged to fabricate hydrothermally stable mesoporous silicas at high temperature, which retained a BET surface area of 678 m2 g−1 after hydrothermal treatment in boiling water for 5 days. Different analysis methods, e.g. X-ray diffraction, nitrogen physisorption, the non-local density functional theory (NLDFT) analysis and transmission electron microscopy, were employed to investigate the mesostructure of as-synthesized samples, which revealed a micro- and mesopores hybrid in one phase. 1H NMR was applied to characterize the α-linolenic acid micellar structure and confirmed that C C bonds have been opened up and polymerization occurred within micelles. The 29Si MAS NMR spectra indicated Q4 silicon is the dominating species, which explains well the high hydrothermal stability of the materials.

In this paper, we systemically studied the evolution rules of morphologies of the extraordinary patterns including the flowerlike patterns of nanostructured cuprous oxide, which were synthesized by electrochemical deposition from a mixed solution of surfactant sodium dodecyl sulfate and copper sulfate, as well as that of the mesostructure along with the variation of the content of the SDS surfactant. The evolution of morphology was observed as follows: with the increment of surfactant, the morphologies of the deposited cuprous oxide were evolved from that with crystalline to noncrystalline characteristics. Concretely, as the surfactant increases, the crystalline face of the deposited crystal was initially sunken and then vanished. Consequently, the crystalline angles vanished; and finally the orientation of crystalline axis vanished too. Also, the rotational symmetry of patterns was replaced by the radial symmetry., Moreover, the templating effect of surfactant additives was employed to acquire different mesoscopic structured growth units that also affect the macroscopic shape and microscopic order of the cuprous oxide. On the basis of the combination of self-assembly analysis and interfacial dynamics, the reason for formatting interesting and unusual patterns, such as flower patterns of nanostructured cuprous oxide, was explained. In particular, the formation can be rationalized by the modulation of electric field as an immaterial template which determins the macroscopic shape along with the assistance of surfactant self-assembly in molding the nanoscale structures.

Using diethyl ether as a co-solvent, a non-stable interface of biphasic oil-water system (the so-called oil-water two-phase (OWTP) system) was employed in the preparation of mesostructured silicas with diversified particle morphologies. By adjusting the molar ratios of H2O:C2H5OC2H5:NH3 center dot H2O and the alkalinity of the OWTP system, several product morphologies could be obtained under different reaction conditions. On the other hand, different product morphologies with distinct structural properties could be obtained at a specific reaction condition, indicating that product morphology varied upon intrinsic characteristics of non-equilibrium processes in the system as well. There are six kinds of product morphologies in our results. In the biphasic region the morphotypes such as vesicles, slices, and spheres were widely distributed. Multi-lamellar fragments were formed under relatively strong alkaline conditions and at a high proportion of diethyl ether (>41%). bi-continuously phased fragments were observed in the weak alkaline conditions and medium proportion between diethyl ether and water. In the single-phase region, hexagonally ordered MCM-41, plain sheets of MCM-48, as well as smooth and plain slices with worm-like pore structures were formed with bi-modal pore-size distribution structure. Based on HRTEM analysis, these structural features were rationalized being derived from fragments that originated from the oil/water interface. Apparently, the product morphosynthesis resulted from a combination of fluid theological distortions and reconstructive reaction fields. With a systematic approach we have established the reaction phase diagram of the system, which enabled us to define the structural properties and to classify the morphology of the products for nomenclatural purposes in studying OWTP systems. (c) 2007 Elsevier Inc. All rights reserved.

The self-organization behavior of an amphiphilic sexithiophene bearing amide functionalities is studied and compared to that of a deriv. bearing an ester group at the same position. The introduction of hydrogen-bond interactions in assemblies of these pi-conjugated oligomers is found to affect the mol. organization both in protic media and in thin deposits on mica. The amphiphilic 2,2';5',2'';5'',2''';5''',2''''; 5'''',2'''''-sexithiophene-5,5'''''-dicarboxylic acid bis[(4,7,10,13,16-pentaoxaheptadecyl)amide] forms assemblies in n-butanol and water and partially aggregates in toluene. Spectroscopy reveals that the presence of a hydrogen-bonding moiety increases the thermal stability of the assemblies in n-butanol and even more in water soln. On mica surfaces, the formation of rod-like one-dimensional nano-structures is obsd. after deposition from toluene solns. In addn., transmission electron microscopy in combination with selected area electron diffraction shows that in water plate-like structures are formed built from parallel oriented stacks, with a pi-pi distance of 3.5 .ANG.. Comparison of these data to mol. modeling and quantum chem. calcns. is used to better understand the influence of the amide group on the stacking of these compds. The introduction of these H-bonding interactions leads to denser and more stable stacks. Furthermore, we show that a deriv. of the amide compd., bearing terminal ammonium groups, forms a complex with chiral polyanions in aq. media such that the sexithiophene segments are stacked in a meta-stable helical fashion with preferred handedness. We obsd. that poly(glutamate) and DNA generate a chiral sexithiophene assembly. In time the induced chirality disappears, which is explained by the meta-stability of the kinetically formed adduct. This constitutes one step forward towards the controlled formation of functional multi-component systems in aq. soln. [on SciFinder (R)]

A series of meso-microporous Cu-SAPO-34 catalysts were successfully synthesized by a one-pot hydrothermal crystallization method, and these catalysts exhibited excellent NH3-SCR performance at low temperature. Their structure and physic chemical properties were characterized by means of X-ray diffraction patterns (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), N2 sorption-desorption, nuclear magnetic resonance (NMR), Inductively Coupled Plasma-Atomic Emission spectrometer (ICP-AES), X-ray absorption spectroscopy (XPS), Temperature-programmed desorption of ammonia (NH3-TPD), Ultraviolet visible diffuse reflectance spectroscopy (UV-Vis DRS) and Temperature programmed reduction (TPR). The analysis results indicate that the high activities of Cu-SAPO-34 catalysts could be attributed to the enhancement of redox property, the formation of mesopores and the more acid sites. Furthermore, the kinetic results verify that the formation of mesopores remarkably reduces diffusion resistance and then improves the accessibility of reactants to catalytically active sites. The 1.0-Cu-SAPO-34 catalyst exhibited the high NO conversion (>90%) among the wide activity temperature window in the range of 150-425°C.

Herein we report the synthesis and characterization of hollow silica spheres with a narrow size distribution, uniform wall thickness, and a worm-like pore structure. The formation of these spheres was monitored by confocal laser scanning microscopy and dynamic light scattering. A model for the molecular build-up of these silica hollow spheres is derived from these data in combination with studies of the as-made particles by transmission electron microscopy, scanning electron microscopy, pore size analysis, thermogravimetric analysis, and solid-state nuclear magnetic resonance. We further demonstrate that these spheres can be used for the encapsulation and subsequent release of different dye molecules.

Zeolite fibers have attracted growing interest for a range of new applications because of their structural particularity while maintaining the intrinsic performances of the building blocks of zeolites. The fabrication of uniform zeolite fibers with tunable hierarchical porosity and further exploration of their catalytic potential are of great importance. Here, we present a versatile and facile method for the fabrication of hierarchical ZSM-5 zeolite fibers with macro-meso-microporosity by coaxial electrospinning. Due to the synergistic integration of the suitable acidity and the hierarchical porosity, high yield of propylene and excellent anti-coking stability were demonstrated on the as-prepared ZSM-5 hollow fibers in the catalytic cracking reaction of iso-butane. This work may also provide good model catalysts with uniform wall thickness and tunable porosity for studying a series of important catalytic reactions.

Silica becomes increasingly used in chemical, pharmaceutical, and (nano)technological processes', resulting in an increased demand for well-defined silicas and silica-based materials. The production of highly structured silica from cheap starting materials and under ambient conditions, which is a target for many researchers, is already realized in the formation of diatom biosilica, producing highly hierarchical ordered meso- and macropores silica structures. This notion formed the starting point in our integrative biomolecular and biomimetic study on diatom silicon biomineralization in which we have analyzed silica transformations and structure-direction in polymer-mediated silica syntheses using a combination of (ultra)small-angle X-ray scattering and (cryo)electron microscopy. Using bio-analogous reaction conditions and reagents, such as waterglass and (combinations of) polyethylene oxide (PEO) based polymers, we demonstrate in this review the synthesis of tailormade mesoporous silicas in which we can, as in biosilica synthesis, control the morphological features of the resulting materials on the nanometer level as well as on the micrometer level.

Gigantic hollow silica spheres with a hierarchical intra- and inter-particle porosity were obtained from an EO76–PO29–EO76/butanol/ethanol/H2O quaternary system, which is unique in its extremely rapid silica condensation and in the resulting hierarchical morphology.

Freshly prepared acid-cleaned biosilica of 21 different diatom species was studied using a combination of wide, small, and ultrasmall angle X-ray scattering analysis (WAXS, SAXS, and USAXS) in order to determine whether the structural and fractal properties from the subnanometer level up to dimensions of several microns are species-specific, and if so to quantify them. WAXS data are in line with the amorphous nature of this kind of biosilica: no Bragg reflections were observed at the level below 1 nm. Straight domains in the scattering spectra ( in both SAXS and USAXS) revealed the presence of different fractal regions with highly species-specific transition points, as part of the surface structure. All silica specimens had four of these fractal regions, but with a length scale per region characteristic for each specimen except for the region (Region I) covering the WAXS domain (d 396 nm), revealed the roughest surface. Transition points between straight regions in the scattering spectra did relate to the dimension of meso- and macro-pores that are known to be present in diatom biosilica; the pore sizes determined from the spectra agreed with estimates made from electron micrographs. Interestingly, dominant scattering peaks were observed in USAXS, as if we were dealing with crystals as in highly ordered MCM-type silicas. This crystallinity was only apparent, not real; it is most probably due to the high regularity in pore distributions in diatom biosilica in the size range of 100 to similar to500 nm. Our data show that diatom biosilica has quantifiable species-specific fractal surface properties, next to the well known species-specific pore architecture that is well beyond those of other well-ordered artificial silica materials. Consequently, it is likely that each also has its own surface pattern of reactive sites and in view of these large variations each diatom species potentially can be the source for the design of a different silica-based material.

Hollow mesoporous silica spheres that are highly defined in shape and size are prepd. using a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) [PEO-PPO-PEO] block copolymer based emulsion as the template, and sodium silicate as the silica source. The wall structure of the particles depends on the reaction temp. and can be monitored using small-angle X-ray scattering, solid-state NMR spectroscopy, and cryo-transmission electron microscopy.

Poly(ethylene glycol) (PEG) was employed as templating agent for the synthesis of porous silica. The effect of PEG chain length and of the PFG/silica ratio on textural properties (fractality, pore size, and pore distribution) were investigated by monitoring the development of silica-PEG intermediates using ultrasmall and small-angle X-ray scattering analysis with high-brilliance synchrotron radiation to obtain sufficient radiation intensity for dynamic results at the subminute scale. We show that even a simple structure-directing polymer, such as PEG, results in silicas with pores of diameters spanning a range of less than 2 nm up to 20 nm, depending on polymer molecule length and polymer/silica ratio. Flocculation may well be the most important distinction between silicas prepared with small and large PEG. In this view, small PEG600 gets encapsulated by silica and forms pools within the silica framework, whereas large PEG20,000 is entangled in a mass of silica spheres, making enclosure by silica or phase separation impossible. Both polymer chain length and the polymer/silica ratio govern the relative importance of flocculation, phase separation, and hydrophobic silica-PEG interactions steering the silica polymerization. Increase in hydrophobicity results in a larger surface area and a more uniform pore size distribution, art effect confirmed by scanning electron microscopy (SEM) and observations of physical adsorption of nitrogen gas (BET). Polymers, such as PEG, may well be an inexpensive and versatile substitute and model for polypeptides known as structure-directing agents in biomineralization if silicas resembling natural ones, notably the ones present in such a huge diversity in algae of the group of diatoms, are the focus of scientific attention, e.g., for biomimicking with a view on industrial applications.

The role of external ionic strength in diatom biosilica formation was assessed by monitoring the nanostructural changes in the biosilica of the two marine diatom species Thalassiosira punctigera and Thalassiosira weissflogii that was obtained from cultures grown at two distinct salinities. Using physicochemical methods, we found that at lower salinity the specific surface area, the fractal dimensions, and the size of mesopores present in the biosilica decreased. Diatom biosilica appears to be denser at the lower salinity that was applied. This phenomenon can be explained by assuming aggregation of smaller coalescing silica particles inside the silica deposition vesicle, which would be in line with principles in silica chemistry. Apparently, external ionic strength has an important effect on diatom biosilica formation, making it tempting to propose that uptake of silicic acid and other external ions may take place simultaneously. Uptake and transport of reactants in the proximity of the expanding silica deposition vesicle, by (macro)pinocytosis, are more likely than intracellular stabilization and transport of silica precursors at the high concentrations that are necessary for the formation of the siliceous frustule components.

Silica becomes increasingly used in chemical, pharmaceutical, and (nano)technological processes, resulting in an increased demand for well-defined silicas and silica-based materials. The production of highly structured silica from cheap starting materials and under ambient conditions, which is a target for many researchers, is already realized in the formation of diatom biosilica, producing highly hierarchical ordered meso- and macropores silica structures. This notion formed the starting point in our integrative biomolecular and biomimetic study on diatom silicon biomineralization in which we have analyzed silica transformations and structure-direction in polymer-mediated silica syntheses using a combination of (ultra)small-angle X-ray scattering and (cryo)electron microscopy. Using bio-analogous reaction conditions and reagents, such as waterglass and (combinations of) polyethylene oxide (PEO) based polymers, we demonstrate in this review the synthesis of tailor-made mesoporous silicas in which we can, as in biosilica synthesis, control the morphological features of the resulting materials on the nanometer level as well as on the micrometer level.

Recent years have witnessed rapid growth in the number of new investigations at the interface of materials chemistry and biology. This review highlights the recent developments in the studies of protein-mediated silica biomineralization in diatoms and the "downscaling" and "upscaling" models derived thereof, as well as the recent progress in the fabrication of artificial silicas with novel pore structures and morphologies at different length scales based on these new insights into biosilica formation. (C) 2004 Elsevier Ltd. All rights reserved.

Silica is by far the most abundant compound in the earthi¯s crust. It serves various functions in nature: organisms ranging from lower eukaryotes to plants use it as one of the biominerals that provide support, protection, strength, or tools in various functions. Biogenic silica is the least studied of the biominerals. The best-studied ones (Hunter 1996) are composed of calcium (apatite, enamel, calcite); these are present in the bone tissue and teeth of mammals and in the shells of shellfish. In contrast to calcium minerals, relatively little is known about the formation of biogenic silica. The most likely function of biogenic silica in unicellular organisms seems to be giving strength to the living cell; good examples from the aquatic environment are siliceous (exo)skeletons or cell casings of the microalgal groups of diatoms (Fig.1) and silicoflagellates, and of Radiolaria (Simpson and Volcani 1981; Pickett-Heaps et al. 1990; Round et al. 1990).