Open Pore System Research Articles

Influence of textural parameters on the catalytic behavior for CO oxidation over ordered mesoporous Co3O4

Ordered mesoporous Co3O4 has been synthesized by nanocasting from three-dimensional cubic KIT-6 template. The cobalt precursor is introduced into the silica pores by the “bi-solvent” method. The structure and textural characteristics are investigated by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, nitrogen sorption at 77K. By changing the hydrothermal temperature of the KIT-6 template, two kinds of Co3O4 replicas with different mesostructured symmetries are obtained. Mesoporous Co3O4 oxides prepared from KIT-6 aged at low temperature have uncoupled sub-frameworks while mesoporous Co3O4 oxides prepared from KIT-6 aged at high temperature possess coupled sub-frameworks. CO oxidation is carried out as a model reaction to evaluate the catalytic activity. Co3O4 replicas with uncoupled sub-frameworks which possess higher surface area and more open pore system exhibit better performance than Co3O4 replicas with coupled sub-frameworks. The light-off temperature of CO oxidation reaches as low as 68°C with a space velocity of 120,000 mL h−1 gcat−1 over the uncoupled Co3O4 replica. Calcination temperature of the cobalt precursor only has negligible or slight impact on the catalytic activity.

Preparation of Magnetically Separable Mesoporous Silica Microspheres with Open Pore Systems in Supercritical Carbon Dioxide

Magnetically separable mesoporous silica microspheres with open pore systems have been synthesized in supercritical carbon dioxide (SC-CO2). In the experiments, using the excellent transport properties of supercritical carbon dioxide, an acetone solution containing iron(III) acetylacetonate [Fe(acac)3] was easily infiltrated into the mesopores of the microspheres. After thermal decomposition, the Fe(acac)3 was easily transformed into Fe3O4 nanoparticles. A comparison experiment verified that the carrying effect of Fe(acac)3 using SC-CO2 was better than that observed for the common method. The magnetic microspheres were characterized by transmission electron microscopy, energy-dispersive X-ray analysis (EDAX), powder X-ray diffraction, and nitrogen adsorption−desorption. The magnetically separable property of the microspheres was also tested.

Synthesis of mesostructured conducting polymer-carbon nanocomposites and their electrochemical performance

A conducting polymer layer was introduced into the pore surface of mesoporous carbon via vapor infiltration of a monomer and subsequent chemical oxidative polymerization. The polypyrrole, conducting polymer has attracted considerable attention due to the high electrical conductivity and stability under ambient conditions. The mesoporous carbon-polypyrrole nanocomposite exhibited the retained porous structure, such as mesoporous carbon with a three-dimensionally connected pore system after intercalation of the polypyrrole layer. In addition, the controllable addition of pyrrole monomer can provide the mesoporous carbon-polypyrrole nanocomposites with a tunable amount of polypyrrole and texture property. The polypyrrole layer improved the electrode performance in the electrochemical double layer capacitor. This improved electrochemical performance was attributed to the high surface area, open pore system with three-dimensionally interconnected mesopores, and reversible redox behavior of the conducting polypyrrole. Furthermore, the correlation between the amount of polypyrrole and capacitance was investigated to check the effect of the polypyrrole layer on the electrochemical performance.

Ordered mesoporous silica materials (SBA-15) with good heat-resistant magnetism

A series of highly ordered mesoporous materials (CF-SBA-15) with heat-resistant magnetism have been successfully prepared from impregnation of cobalt salt, iron salt, and citric acid with as-synthesized SBA-15. XRD and N 2 isotherms indicate that these materials have highly ordered hexagonal mesoporous symmetry and open pore systems. The measurement of magnetic property shows that these materials are ferromagnetic even if calcined at 550 °C for 10 h in air, indicating their good heat-resistant magnetism. These results would be very important for recycle and regeneration of adsorbents and catalysts in practical applications. Moreover, this method may be useful for other mesoporous materials with thermally stable magnetism from a combination of other mesoporous materials such as MCM-41 with magnetic nanoparticles of MnFe 2O 4 and NiFe 2O 4.

Novel Calcium Phosphate Glass for Hard-Tissue Regeneration

Purpose: The aim of this review is to introduce a novel bone-graft material for hard-tissue regeneration based on the calcium phosphate glass(CPG). Materials and Methods: CPG was synthesized by melting and subsequent quenching process in the system of CaO-CaF2-P2O5-MgO-ZnO having a much lower Ca/P ratio than that of conventional calcium phosphates such as HA or TCP. The biodegradability and bioactivity were performed. Effects on the proliferation, calcification and mineralization of osteoblast-like cells were examined in vitro. Influence in new bone and cementum formations was investigated in vivo using calvarial defects of Sprague-Dawley rats as well as 1-wall intrabony defect of beagle dogs. The application to the tissue-engineered macroporous scaffold and in vitro and in vivo tests was explored. Results: The extent of dissolution decreased with increasing Ca/P ratio. Exposure to either simulated body fluid or fetal bovine serum caused precipitation on the surface. The calcification and mineralization of osteoblast-like cells were enhanced by CPG. CPG promoted new bone and cementum formation in the calvarial defect of Sprague-Dawley rats after 8 weeks. The macroporous scaffolds can be fabricated with 500~800μ m of pore size and a three-dimensionally interconnected open pore system. The stem cells were seeded continuously proliferated in CPG scaffold. Extracellular matrix and the osteocalcin were observed at the 2 nd days and 4 th week. A significant difference in new bone and cementum formations was observed in vivo (p＜0.05). Conclusion: The novel calcium phosphate glass may play an integral role as potential biomaterial for regeneration of new bone and cementum. (J Korean Acad Periodontol 2008;38:273-298)

Structural control of mesoporous ethane-silicas with trans-(1 R,2 R)-diaminocyclohexane in the pore and asymmetric catalysis

Design and synthesis of periodic mesoporous materials containing chiral functionalities remain to be a challenging and interesting research topic. In this study, the mesostructures of the ethane-silicas with trans-(1 R,2 R)-diaminocyclohexane in the pore were controlled in acidic medium using KCl and 1,3,5-trimethylbenzene (TMB) as additives in the presence of triblock copolymer P123. It was observed that an increase in Si/P123 molar ratio leads to a gradual increase in the pore diameter. Simultaneously, the 2-D hexagonal mesostructure gradually transforms from open pore system into plugged pore system. The addition of TMB not only expands the pore diameter but also induces the mesophase transformation from 2-D hexagonal mesostructure into mesostructured cellular foam (MCF). Inorganic salt KCl plays a key role in the formation of ordered pore structure. Through adjusting the amount of KCl and TMB, the mesoporous materials with bimodal pore structure can be obtained. Increasing the amount of KCl can increase the pore diameter of the material in the presence of TMB. After complexed with [Rh(cod)Cl] 2, the catalytic properties of the trans-(1 R,2 R)-diaminocyclohexane functionalized mesoporous ethane-silicas with various pore structures were tested in the asymmetric transfer hydrogenation of acetophenone. The catalysts show medium enantioselectivity and high activity. The catalyst with plugged pore structure exhibits the highest catalytic activity among all the catalysts investigated.

Feasibility of three-dimensional macroporous scaffold using calcium phosphate glass and polyurethane sponge

Tissue engineering presents an alternative approach to the repair of a damaged tissue by avoiding the need for a permanent implant made of an engineered artificial material. A suitable temporary scaffold material that exhibits adequate mechanical and biological properties is required to enable tissue regeneration by exploiting the body’s inherent repair mechanism, i.e. a regenerative allograft. Synthetic bioresorbable polymers have been attracting attention as tissue engineering scaffolds. However, a number of problems have been encountered such as inflammatory responses and lack of bioactivity. Another good candidate for a tissue engineering scaffold is the calcium phosphates because of their good biocompatibility and osteointegrative properties. Their slow biodegradation is still remains problem, especially for the filling of large bony defects. In this study, we investigated the fabrication method of a three-dimensional reticulated scaffold with interconnected pores of several hundred micrometers using calcium phosphate glass in the system of CaO-CaF2-P2O5-MgO-ZnO and a polyurethane sponge as a template. Calcium phosphate glass slurry was homogenously thick coated when the weight percentage of the calcium phosphate glass powder was 40% with 8 wt% of polyvinyl alcohol as a binder. Addition of 10 wt% dimethyl formamide as a drying control chemical additive into a slurry almost prevented the crack formation during drying. Sintering of the dried porous block at 850°C exhibited the densest microstructure as well as the entire elimination of the organic additives. Repeating the process significantly increased compressive strength of sintered porous body due to the thickening of the struts. To summarize, macroporous calcium phosphate glass can be fabricated with 500∼800 μm of pore size and a three-dimensionally interconnected open pore system. It is thought that this kind of biodegradable glass scaffold combined with osteogenic cells has potential to be studied further as a tissue-engineered bone substitute.

Modelling of radiation transfer in metallic powders at laser treatment

Absorptances and deposited energy profiles are calculated for thin layers of metallic powder placed on a reflective substrate at normal incidence of collimated radiation. Radiation transfer equation is analytically solved by the two-flux method. The effective optical parameters of the powder are estimated in geometrical optics approximation taking into account dependent scattering. The cases of specularly and diffusely reflecting particles are studied. Due to multiple reflections in an open pore system, laser radiation can penetrate in powder to considerable depths, much greater than the characteristic particle diameter. Total laser energy absorbed in a thin powder layer on a reflective substrate increases with its thickness but the deposited energy density decreases. Generally, the absorptance and the energy density for specular reflection are slightly greater than these values for diffuse reflection. The results obtained in the limit of deep powder bed essentially agree with known ray tracing simulations. The present model is in good agreement with experimentally observed correlation between effective absorptance of metallic powders and absorptance of corresponding dense metals.

Transparent cubic Fd3m mesoporous silica monoliths with highly controllable pore architectures

Ordered cubic Fd3m mesoporous silica monoliths (HOM-11) were fabricated by using lyotropic and microemulsion phases of block copolymers (EOm–POn–EOm) as templates. Aromatic and aliphatic hydrocarbon molecules were used in the formation of true microemulsion liquid crystal phases, in the expansion of pore sizes, and in the changes in the phase geometrical shape. Large cylinder-like pores in the range of 6–11 nm with uniform constrictions and bimodal mesopore sizes can be easily produced (within minutes) by adopting this simple and reproducible strategy. The degree of solubilization of the hydrocarbons crucially influenced the generation of the more open-pore systems with cylindrical cubic Fd3m channels. Our results also show that enlargement of pore sizes of cubic Fd3m monoliths was achieved with the use of a high concentration of copolymers in the composition phase domains, a high degree of swelling and a large size of PO–EO blocks (core–corona) of the copolymer templates. In addition, this synthetic approach is also efficient in designing cubic Fd3m silica monoliths with large-sized glass, thick-walled frameworks up to 30 nm thick and high mesopore/micropore volumes. Although XRD patterns show well-defined Bragg diffraction peaks indicative of highly ordered cubic Fd3m structures, TEM micrographs reveal that worm-like mesopore channels in large domains were observed with samples synthesized from copolymers with small EO–PO block ratios. This finding indicates that the molecular nature (i.e. the flexibility of the corona- and core-blocks) of the copolymer templates not only led to disordered pore channels but also reduced the ability to design more mesostructured phases.

Fabrication of Magnetically Separable Mesostructured Silica with an Open Pore System.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Studies on natural CXN zeolite: Modification, framework De‐alumination and ion‐exchange

AbstractA natural CXN zeolite (stilbite, type code‐STI) discovered in China was modified with NH: exchange by using ammonium salt and calcinations (procedure I), or with NH: exchange followed by treatment with acid (procedure rr). The coordination state of Si and Al atoms in the framework. the property of ion exchange, and the adsorption of the H‐STI zeolite samples prepared by different modification procedure were investigated with XRD, EDX, 29Si and 27Al MAS NMR, Ag+ ion exchange and N2 adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and A1 atoms, the content of non‐framework aluminum. and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H‐STI zeolite prepared by the procedure II possesses high ion exchange capacity, open and perfect pore system, and hgh thermal stability.

Fabrication of magnetically separable mesostructured silica with an open pore system.

Magnetically separable mesostructured silica with an unobstructed pore system was fabricated through the deposition of cobalt nanoparticles on the outer surface of the submicron-sized silica particles. These cobalt nanoparticles were further protected by a nanometer-thick carbon shell against acid erosion. Due to the fact that the magnetic particles are grafted on the outer surface of the porous silica, the pores are still accessible for further modification, which could widen the application range of porous silica.

Comments on the threshold porosity for fission gas release in high burn-up fuels

This letter challenges two recent papers in this journal, suggesting that the high burn-up structure of LWR-fuels would evolve towards an open pore system, facilitating gas release. In contrast, recent experimental results and supporting calculations reviewed here as well as new evidence from a 3D pore-reconstruction strongly suggest that the materials in question would show closed porosity conditions and hence reduced probability of gas release, at least up to porosity fractions of about 25%. This value is most likely conservative.

Single-Crystal Particles of Mesoporous Niobium−Tantalum Mixed Oxide

Single-crystal particles of mesoporous niobium−tantalum mixed oxide with a wormhole-like structure were successfully prepared and characterized. The mixed oxide was prepared by a neutral templating method, and the samples provided have thick walls and an unordered pore structure. Neutral block copolymer, HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H, and metal chlorides were used as the template and inorganic source in propanol. The crystallized mesoporous single-crystal structures were obtained by a two-step calcination process; the first calcination process removes the template, forming a mesoporous structure with amorphous wall material, and the second calcination process crystallizes the pore walls while maintaining the mesoporosity. The submicrometer mesoporous particles forming the walls were confirmed by transmission electron microscopy to be single crystals. The pore diameter was found to increase upon crystallization, while retaining the open-pore system. N2-gas adsorption−desorption analysis indicate...

Studies on natural STI zeolite: modification, structure, adsorption and catalysis

A natural STI zeolite discovered in China was identified as a calcium-rich and stellerite-isotype zeolite of stilbite with high crystallinity and an open pore system. Both ion exchange and dealumination can stabilize the framework of the zeolite. The structural properties of the parent and the modified STI zeolites were investigated by X-ray diffraction (XRD), thermogravimetric/differential thermogravimetric/differental thermal analysis (TG/DTG/DTA), Fourier transform infrared spectroscopy (FTIR), and 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance spectroscopy (NMR). The Langmuir surface area and pore volume of H-STI and Na-STI were ∼550 m 2 g −1 and ∼0.20 ml g −1, respectively, as measured by N 2 adsorption. The adsorption heats of NH 3 and CO 2 on H-STI were determined from the adsorption isotherms at different temperatures. Investigation of the adsorption isotherms of ethylene, propylene, water, methanol, ethanol and 1-propanol on Na-STI reveal an unusual selectivity to the length of the carbon chain in the organic molecules. The zeolite shows good catalytic selectivity in the isomerization of n-butene to iso-butene.

Novel fabrication of open-pore chitin matrixes.

A novel method has been developed to produce open-pore chitin matrixes. Chitin solutions were loaded with calcium carbonate (CaCO3) crystals and the mixture cast to form gels. The CaCO3-chitin gels were submerged in 1 N HCl solution to produce highly porous matrixes with good water vapor permeability, water uptake profile, and enhanced mechanical properties. The open-pore system is obtainable because CaCO3 loaded into the chitin gel reacts with 1 N HCl solution to produce gaseous carbon dioxide. Evolution of carbon dioxide during the reaction results in continuous pore structures from the matrix' bulk to surface. When the concentration of CaCO3 loaded into the chitin gel is controlled, defined homogeneous pores measuring 100-500 and 500-1000 microns, with porosities of approximately 76% and 81%, respectively, can be produced.

Pt hybrid catalysts containing HY zeolite and sulfate-promoted zirconia or acidic/mesoporous silicaalumina for the conversion of n-octane

Pt hybrid catalysts containing Y zeolite as main component and sulfate-promoted zirconia or acidic/mesoporous silicaalumina as co-catalyst show enhanced activity in the hydroisomerization/ydrocracking of n-octane. This synergistic effect is due to the surface acidic and textural properties of the co-catalyst. The best co-catalyst must have a high surface acidity, a large surface area and an open pore system. The best Pt hybrid catalyst had the Pt species homogeneously spread over the three components of the catalyst.

Investigation on structure and morphology of the thermally treated glassy alloy (Fe,Cr)80(P,C,Si)20 by means of ESCA and SEM/EDXA

Metallic glass ribbons of the chemical composition (Fe,Cr)80(P,C,Si)20 have been thermally treated in the region between 530 and 980°C for 72 h. The SEM/EDXA investigations indicate that a phase transformation takes place between 575 and 980°C in a surface layer of 5 μm thickness. Thus, a Cr-rich phase occurs between 760 and 800°C which is converted into an open-pore system between 850 and 900°C. The oxidation process reaches its maximum at 760°C. The ESCA spectra of the material in the “as received” state and of the thermally treated samples indicate that different oxygen species are formed within the analysed surface layer of 10 nm. The oxygen of the original material is incorporated as hydroxyl groups in species such as FeO(OH) and CrO(OH). After thermal treating the hydroxyl content decreases and the oxide content increases. Species of Si exist in the surface layer as SiOx-like compounds (peak at BE=102.0 eV). A majority phase of transition metal phosphide species is coexisting with oxidised phosphate species.

Inclusion Polymerization and Doping in Zeolite Channels: Polyaniline

Abstract Aniline has been polymerized in the three-dimensional channel system of zeolite Y. The monomer was diffused into zeolites with different levels of acidity from hexane solution. Subsequent admission of peroxydisulfate or iodate from aqueous solution yielded the intrazeolite polymers, as demonstrated by FT-IR, electronic absorption data and recovery of the included polymer. With S2O8 2-, the intrazeolite products are a function of the proton content of the zeolite. Polymer is only formed when a sufficient supply of protons is present in the zeolite host. When neutral iodate solution is used, no polymer is formed in NaY and acid zeolites, but at low pH aniline polymerizes in all zeolites. The open pore system of the zeolite host can be accessed by base such that the intrazeolite protonated polymer is transformed into the corresponding neutral polymer. The polymer chains encapsulated in zeolite hosts represent a new class of low- dimensional electronic materials.

Study of ultramicroporous carbons by high-pressure sorption. Part 2.—Nitrogen diffusion kinetics

Sorption–desorption kinetics for nitrogen in the as-received TCM 128 ultramicroporous carbon fibre are reported at 35 °C over a wide range of pressures. The nitrogen sorption kinetics at low pressures follow the Fickian model. As the pressure increases, the deviations from the model become more pronounced, and at sufficiently high pressure a sigmoid kinetic response shape is observed which is indicative of a non-Fickian diffusion process. An additional timescale must be active to account for the non-Fickian transport behaviour. This second timescale process may correspond to adsorbate surface rearrangements leading to locally time-dependent clearing of constrictions at a rate with a characteristic kinetic constant. The nitrogen desorption kinetics are found to be less affected by the non-Fickian transport, thus leading to higher apparent diffusion coefficients for the same average pressures. At high pressures and very long sorption times, slow protracted uptake becomes apparent into restricted regions. The kinetics for this process can be described by a barrier model and are sufficiently slow to allow treatment independent of the processes occurring in the more open pore system.