Search

Abstract: The low-temperature synthesis (90°C) of nanoparticle forms of a pure phase smectic clay (saponite) and zeolite (cancrinite) is reported, along with phase mixtures thereof. A synthesis gel corresponding to the Si:Al:Mg unit cell composition of saponite (3.6:0.40:3.0) and a NaOH/Si ratio of 1.39 affords the pure phase clay with disordered nanolayer stacking. Progressive increases in the NaOH/Si ratio up to a value of 8.33 results in the co-crystallization of first garronite and then cancrinite zeolites with nanolath morphology. The resulting phase mixtures exhibit a compound particulate structure of intertwined saponite nanolayers and cancrinite nanolaths that cannot be formed through physical mixing of the pure phase end members. Under magnesium-free conditions, pure-phase cancrinite nanocrystals are formed. The Si/Al ratio of the reaction mixture affects the particle morphology as well as the chemical composition of the cancrinite zeolite. Ordinarily, cancrinite crystallizes with a Si/Al ratio of 1.0, but a silicon-rich form of the zeolite (Si/Al=1.25) is crystallized at low temperature from a silica-rich synthesis gel, as evidenced by 29Si NMR spectroscopy and XEDS-TEM. Owing to the exceptionally high external surface areas of the pure phase clay (875m2/g) and zeolite end members (8.9–40m2/g), as well as their unique mixed phase composites (124–329m2/g), these synthetic derivatives are promising model nanoparticles for studies of the bioavailability of poly-aromatic hydrocarbons immobilized in silicate bearing sediments and soils. [Copyright &y& Elsevier]

Abstract: The synthesis of saponite in the presence of bis(triethoxysilyl)methane (BTESM) as an organosilicon reagent results in the replacement of up to 33.3% of the oxygen atoms in the tetrahedral sheet by bridging methylene groups. The methylene-functionalized saponites represent a new form of covalently bonded organoclay that truly is isomorphic with purely inorganic saponite made under equivalent reaction conditions from sodium silicate as the silicon source. The isoelectronic and isolobal relationship between methylene and bridging oxygen centers is essential for methylene saponite formation. Bridging ethylene groups are not incorporated into the Kagome net of the basal surfaces due to a mismatch in bridging group size. The textural properties of the methylene saponites are similar to those for purely inorganic magnesium saponite made under equivalent synthetic conditions in the absence of BTESM. Layer stacking disorders afford large surface areas (∼550 to 650m2/g), making the methylene saponites attractive candidates for use as adsorbents and functional fillers for polymer composites. [Copyright &y& Elsevier]

Abstract: Large-pore mesoporous silica with 3D wormhole framework structures (denoted MSU-J) are prepared through a supramolecular hydrogen-bonding assembly pathway from low-cost sodium silicate as the silica source and commercially available mono- and tri-amine Jeffamine and Surfonamine surfactants as structure-directing porogens. The calcined mesostructures exhibit large pore sizes (up to 8.2nm), surface areas (632–1030m2/g) and pore volumes (0.5–2.0cm3/g), depending on the surfactant chain length and synthesis temperature (25–65°C). The textural properties of these new wormhole mesostructures are comparable to those of hexagonal SBA-15 derivatives and large pore MCM-48. However, unlike the SBA-15 structure type, wherein the 3D pore network is formed by connecting 1D cylindrical mesopores through micropores, MSU-J mesophases have wormhole framework structures containing fully interconnected 3D mesopores that can minimize the diffusion limitations often encountered in adsorption and chemical catalysis. Also, unlike large pore MCM-48, which requires cost-intensive tetraethylorthosilicate as a silica source and the use of a co-surfactant as a pore expander under strong acid conditions, MSU-J mesostructures are assembled from low-cost sodium silicate in the presence of a single Jeffamine or Surfonamine porogen at near-neutral pH. [Copyright &y& Elsevier]

Abstract: We report the properties of a porous synthetic clay (saponite, denoted SAP) for the reinforcement of rubbery and glassy epoxy polymers. Remarkably, reinforcement properties superior to those of organo-montmorillonite can be achieved without the need for a surface organic modifier, as evidenced by the improvements in tensile strength, modulus and toughness at temperature above and below the glass transition temperature of the polymer. The disordered stacking of clay platelets ∼50nm in lateral dimension gives rise to aggregated tactoids with a BET surface area of 920m2/g, an average BJH pore size of 5.0nm, and a pore volume of 1.98cm3/g. These unique textural properties facilitate the dispersion of the tactoids into the polymer matrix and allow reinforcement of the polymer matrix in the absence of an organic modifier. [Copyright &y& Elsevier]

Abstract: PMMA–mesoporous silica nanocomposites were prepared for the first time through in situ batch emulsion polymerization of methyl methacrylate in the presence of large pore MSU-F silica with a mesocellular foam structure (24.8nm average cavity size) and subsequent compression molding of the polymer–silica nanoparticle mixtures. For composites containing 5.0wt % silica, the onset decomposition temperature and the temperature at 10% weight loss for the nanocomposite increased 41°C and 50°C, respectively, in comparison to pure PMMA. The glass transition temperature of the nanocomposite increased 9.3°C, as determined by differential scanning calorimetry. In addition, the storage modulus determined by dynamic mechanical analysis increased 17% and 80% at 50°C and 100°C, respectively. Substantial improvements in tensile strength (+50%) and modulus (+72%), were achieve at 10wt % nanoparticle loading. Composites made by compression molding of physical mixtures of PMMA and MSU-F silica powders provide less improvement in thermal stability, glass transition temperature and mechanical properties in comparison to the composites made through in situ batch emulsion polymerization. Unlike previously reported composites made from nanoclays, the silica composites reported here show improvements in both thermal stability and mechanical reinforcement. [Copyright &y& Elsevier]

Abstract: Mesoporous forms of silica with wormhole framework structures prepared from tetraethylorthosilicate (denoted MSU-J-TEOS) or from sodium silicate (denoted MSU-J-SS) and an amine surfactant as the structure-directing porogen are highly effective reinforcing and toughening agents for rubbery and glassy epoxy polymers. The improvements in tensile strength and modulus provided by MSU-J silicas with a large average framework pore size (e.g., 5.9 and 21.3nm) are superior to those provided by the corresponding silicas made from the same TEOS or SS precursors but with smaller framework pore sizes (e.g., 4.2 and 5.2nm). The improved performance of the larger pore structures is realized even though the surface areas (∼670m2/g) are substantially lower than the surface areas of the smaller pore analogs (812–1025m2/g), most likely, because of more efficient polymer impregnation of the particle mesopores. In comparison to the MSU-J-TEOS silica assembled from TEOS, MSU-J-SS silica made from SS exhibits a more uniform pore distribution and smaller particles. These latter textural features lead to improved tensile strength and modulus without compromising the strain-at-break for both rubbery and glassy epoxy polymers. The exceptional strength and toughness provided by MSU-J-SS silica in comparison to MSU-J-TEOS silica are correlated with the high degree of dispersion of the mesophase particles in the epoxy matrix for the more effective distribution of stress and the deflection of microcracks. [Copyright &y& Elsevier]

Abstract: Palygorskite, a silicate clay with a pleated 2:1 layered structure, has a lath-like particle morphology that makes it an attractive candidate for the formation of polymer nanocomposites. Here, we report the properties of palygorskite in pristine and silylated forms for the reinforcement of rubbery and glassy epoxy matrices. Three silylation reagents were used for surface modification of the mineral, namely, γ-aminopropyltrimethoxysilane (APTMS), N-dodecyltriethoxysilane (DTES), and 1,1,1,3,3,3-hexamethyldisilazane (HMSZ). The silylated palygorskite derivatives provided better dispersions in rubbery epoxy matrices than the pristine mineral, affording improvements in mechanical properties at low loadings levels of 2 and 5% (w/w). But at higher loadings where increases in the viscosity of the pre-polymer helps to stabilizes the mineral dispersion, little or no differences were observed for the reinforcement benefits provided by the pristine and silylated forms of palygorskite. Glassy epoxy nanocomposites formed from both pristine and silylated palygorskite exhibited marginal improvements in tensile properties regardless of the mineral loading level, suggesting that the tensile strength of the pleated sheet silicate may be approaching that of the polymer matrix. [Copyright &y& Elsevier]

Abstract: Polymeric mesocomposite membranes were prepared via wet phase inversion processes by incorporating surfactant-templated mesoporous silica particles, denoted MSP-1, into polysulfone matrices formed with and without PEG as a molecular porogen. Transmission electron microscopy and N2 adsorption–desorption measurements showed higher surface area (354m2/g), smaller average pore size (53nm), and larger pore volume (2.92cm3/g) with a narrower pore size distribution (26nm width at half-maximum) for surfactant-templated mesoporous silica particles compared to those of precipitated commercially available mesoporous silica, HiSil. The distinct morphological changes induced by PEG and by MSP-1 were redundant from the membrane performance point of view as they translated into similar performance gains that were not additive, pointing to the potential use of mesoporous additive as an alternative porogen. The higher hydrophilicity and unique structural features of MSP-1 resulted in enhanced performance of the prepared membranes compared to MSP-free controls and HiSil-based mesocomposites. Mechanical properties of mesocomposites and neat polysulfone membranes were comparable. Electron microscopy coupled with flux and rejection measurements were used to investigate the influence of polymer content, MSP loading, and the presence of porogen on the structure and separation properties of mesocomposite membranes. Mesocomposite membranes showed increased water flux and dextran rejection. For ultrafiltration membranes the figure of merit, operationally-defined as the product of water flux and rejection of 12kDa dextran, increased by the factor of 2.8 (for membranes cast with a porogen) and 6.3 (in the absence of porogen) upon incorporation of the mesoporous additive at the loading of 10wt%. Enhancement factors were 3.7 and 11.2 for less permeable membranes cast from mixtures with higher (20wt%) polymer content. Fouling tests with humic acid solutions demonstrated that mesocomposite membranes experienced lower flux decline and showed higher rejections. [Copyright &y& Elsevier]

Abstract: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the prototypical aryl hydrocarbon receptor (AhR) ligand, exhibits immune suppression in vivo and in vitro. Suppression of primary humoral immune responses in particular has been well characterized as one of the most sensitive functional immune endpoints in animals treated with TCDD. Previous studies have used purified TCDD to elucidate the mechanisms by which TCDD and dioxin-like compounds (DLC) impair IgM production by B cells, but did not represent the route by which animals and humans are likely to be exposed environmentally. In the studies reported here, mice were treated with TCDD adsorbed onto a well-defined synthetic silica phase of known purity and physical properties, followed by sensitization with sheep erythrocytes to initiate a humoral immune response. We found that surfactant-templated mesoporous forms of amorphous silica provided an ideal combination of purity, dispersibility and textural properties for immobilizing TCDD. TCDD-adsorbed silica distributed to the spleen and liver after oral administration as assessed by induction of cyp1a1 gene expression. Most notably, TCDD delivered in the adsorbed state on amorphous silica and as a solute in corn oil (CO) produced similar suppression of the anti-sheep red blood cell immunoglobulin M antibody forming cell (sRBC IgM AFC) response at equivalent doses of TCDD. These results suggest that TCDD immobilized on silicate particles found in soils distributes to the spleen and suppresses humoral immunity. [Copyright &y& Elsevier]

Abstract: The complete understanding of the properties of a material goes in close relationship with a correct description of their structure. This is particularly true for mesoporous silica that exhibits different shapes and sizes of the porous framework as well as different degrees of crosslinking of the silica network itself. These variations can affect drastically the specific properties of these materials as well as their hydrothermal resistance. Hydrothermal resistance and adsorption properties are governed by the surface structure, but the later parameter is not frequently studied because it can be difficult to characterize. Therefore a simple parameter such as surface roughness could be helpful in relating the properties of materials with their surface structure. The direct determination of surface roughness is impossible, but it has been demonstrated that a single mathematical parameter, the surface fractal dimension Ds, can be related within a certain limit with surface roughness. Here we demonstrate using nitrogen adsorption data that a correlation can be drawn between the values of the surface fractal dimension Ds used as a gauge of the surface roughness and the structural evolution of a series of mesoporous silicas. Among the different adsorption models for obtaining Ds that are available nowadays, we selected the one proposed by Avnir and Jaroniec. We demonstrate in this report that there exists a real correlation between the evolution of Ds, when applied to a series of samples prepared under different synthesis conditions, with the evolution of their structure and properties. By example, this study allowed us to link the range of hydrothermal resistance of different mesoporous silicas (e.g. the HMS, MSU, MCM, SBA families of silicas) with their surface roughness. Moreover, we found that HMS silica, a very resistant material toward hydrothermal treatment, exhibits actually the lowest surface roughness. We could demonstrate too how different synthesis parameters such as temperature, can modify this surface roughness, hence the final properties of the mesoporous silica. Finally, we show that this method can even be applied to water ellipsoporometry and help to follow the crystallization of thin layers of metal oxide. Bearing in mind that Ds is a parameter that can readily be determined using the existing software – based on different models – associated with most commercial adsorption equipment, we urge the broader use of the Ds parameter for the structural characterization of surface roughness in mesoporous materials and metal oxide thin layers. [Copyright &y& Elsevier]

Abstract: In the present study two synthetic mesoporous carbons, a highly ordered CMK-3 sample with hexagonal structure and a disordered mesoporous carbon (denoted DMC) were investigated for the sorption of Remazol Red 3BS (C.I. 239) dye in comparison to three commercial activated carbons and a HMS mesoporous silica with a wormhole pore structure. The structural, porosity and surface characteristics of the materials were evaluated using XRD, TEM, N2 porosimetry, FT-IR spectroscopy and zeta-potential measurements. Optimal dye sorption occurred at pH ∼2. Equilibrium sorption data followed the Langmuir model and showed that the two synthetic mesoporous carbons exhibit higher sorption capacities (q max ∼500–580mg/g at 25°C) in comparison to the commercial activated carbons which possessed either microporous (Takeda 5A and Calgon carbon) or combined micro-/mesoporous (Norit SAE-2) structures and to the HMS mesoporous silica. Thermodynamic parameters as the change in free energy, enthalpy, and entropy of sorption were also estimated. Kinetic studies were carried out and showed a rapid sorption of dye in the first ca. 30min while equilibrium was reached after ca. 3h. The sorption kinetics of dye was best described by a second-order kinetic model. A surfactant enhanced carbon regeneration (SECR) technique was used to regenerate the dye-loaded carbon sorbents. [Copyright &y& Elsevier]

Abstract: Ti(IV)-functionalized derivatives of mesostructured HMS and MCM-41 silica with 3D wormhole and 1D hexagonal framework structures, respectively, were examined as catalysts for the oxidation of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde using tert-butylhydroperoxide (TBHP) and aqueous hydrogen peroxide as oxidizing agents in acetonitrile solution. In an effort to achieve optimal site-isolation of reactive Ti(IV) centers, functionalization was carried out through the grafting of titanocene dichloride to the framework walls of the pre-assembled mesostructures, followed by calcination. Clear evidence for the undesirable clustering of Ti(IV) centers with increasing Ti(IV) loading was obtained by UV–Vis spectroscopy. Thus, the Ti(IV)-loading in the silica framework was limited to values below 8mol%. Maximal 23.6% and 21.8% conversions of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde with >99% selectivity were observed for 4.8% Ti-HMS and 4.8% Ti-MCM-41 catalysts using TBHP as the oxidant. Substantially lower conversions were obtained with H2O2 as the oxidant due to clustering of Ti(IV) centers under reaction conditions and the catalyzed disproportionation of H2O2 by those clusters. A 2.0% Ti-HMS derivative prepared by direct assembly from tetraethylorthosilicate and tetraisopropylorthotitanate, denoted Ti-HMS(DS), was less active than Ti(IV)-functionalized mesostructures prepared by post-assembly grafting reaction with titanocene dichloride. Direct assembly places too much Ti(IV) at inaccessible positions within the framework walls, whereas grafting ensures optimal access to site-isolated Ti(IV) sites at the pore surfaces. [Copyright &y& Elsevier]

Abstract: The in situ upgrading of biomass pyrolysis vapors with two mesoporous aluminosilicate materials (MSU-SBEA) assembled from zeolite Beta (BEA) seeds was tested in the present study, in comparison to conventional Al-MCM-41 and to non-catalytic biomass pyrolysis. The first sample (MSU-S/HBEA) exhibited an hexagonal mesopore structure while the second one (MSU-S/WBEA) possessed a wormhole-like mesopore structure with high textural porosity. The catalytic tests were performed on a fixed-bed reactor, the reaction temperature was 500°C and the feed was a lignocellulosic biomass based on beech wood. The use of the MSU-S catalytic materials led to significantly lower organic phase in the produced bio-oil and also to higher coke and char yields, compared to non-catalytic pyrolysis and to the use of Al-MCM-41 which induced a small increase in the yields of liquid oil and coke. Pyrolysis gases were also affected by all mesoporous catalysts. The MSU-S catalytic materials were very selective towards polycyclic aromatic hydrocarbons (PAHs) and heavy fractions, while they produced negligible amounts of acids, alcohols and carbonyls, and very few phenols. The MSU-S materials appeared to possess stronger acid sites than Al-MCM-41, resulting in enhanced yields of aromatics, PAHs and coke, as well as propylene in the pyrolysis gases. [Copyright &y& Elsevier]