Bimodal Pore Structure Research Articles

Template-dealloying synthesis of ultralow density Au foams with bimodal porous structure

Noble metallic foams with low density are desirable in high energy-density physical experiments. In this study, Au foams with ultralow density were successfully synthesized from a template-dealloying approach. Microspherical polystyrene (PS) was employed as the sacrificial template. Au and Ag nanoparticles were sequentially coated onto the PS surface from a three-step deposition process. Cylindrical PS/Au/Ag monoliths were formed by filter-casting of the nanoparticle coated PS suspension. The templates were removed and Au–Ag alloy foams were generated after calcination at 400 °C. Self-supported Au foams with bimodal porous structure were produced by dealloying of the less noble Ag component. Au foam with density as low as 0.36 g cm−3 can be achieved, which demonstrates high surface area of 23.6 m2 g−1 and pore volume of 0.15 m3 g−1.

Porous Polyimide-Silica Composite: A New Thermal Resistant Flexible Material

ABSTRACTWe developed a new highly porous polyimide (PI) -silica composite with high flexibility, mechanical strength, and heat resistance. The composite was prepared by a new process consisting of (1) phase separation of a mixture of PI precursor (polyamic acid), solvent, and silicon alkoxide, induced by high-pressure CO2 (40 °C, 20 MPa), (2) silicate formation by sol-gel reaction, and (3) supercritical CO2 extraction of the solvent. The composite had a bimodal porous structure with micropores of 10-30 μm and nanopores of ∼50 nm. In the PI matrix, silica nanoparticles (< 100 nm in diameter) were highly dispersed. Porosity of the composite was 78%, which is higher than that of conventional porous PI prepared by physical foaming technique. Relative dielectric constant of the material was lower than 1.4 at 1 MHz. The porous PI-silica composite sheet was flexible enough to be folded without cracking. Notably, the Young’s modulus (0.80 GPa) and the onset decomposition temperature (600 °C) of the PI-silica composite were higher than those of conventional porous PI with similar porosity, respectively. The porous PI-silica composite is promising as a flexible thermal insulator for high-temperature use and as a thermal resistant low-k material.

Synthesis, Characterization of Mesoporous Zeolite BEA and Its Application in Multicomponent Reactions

Strongly acidic mesoporous zeolite beta (MZB or Beta/MCM-41composite ) with bimodal pore structure and stepwise distributed acidity has been synthesized by novel route using zeolite BEA as silica-alumina source . The material was characterized by various techniques . Powder XRD showed the existence of well-structured microphase zeolite Beta and mesophase MCM-41 in the composite materials. The performance of the composite material as a catalyst was investigated for the synthesis of various biologically active compounds through MCRs. The composite Beta/MCM-41 displayed excellent activity towards the synthesis of diarylpyrimidinones and amidoalkyl naphthols through multicomponent reactions (MCRs) as compared to the microporous zeolite H-BEA. Keywords : mesoporous zeolite; composite Beta/MCM-41 ; heterogeneous catalyst; MCRs

Deformation of Ordered Mesoporous Silica Structures on Exposure to High Temperatures

Ordered mesoporous silica materials are of interest for a wide range of applications. In many of these, elevated temperatures are used either in the preparation of the material or during its use. Therefore, an understanding of the effect of high temperature treatments on these materials is desirable. In this work, a detailed structural study is performed on silicas with three representative pore structures: a 2‐D hexagonal pore arrangement (SBA‐15), a continuous 3D cubic bimodal pore structure (KIT‐6), and a 3D large cage pore structure (FDU‐12). Each silica is studied as prepared and after treatment at a series of temperatures between 300 and 900°C. Pore structures are imaged using Transmission Electron Microscopy. This technique is used in conjunction with Small‐Angle X‐ray Diffraction, gas physisorption, and 29Si solid state Nuclear Magnetic Resonance. Using these techniques, the pore size distributions, the unit cell dimensions of the mesoporous structures, and the relative occupancy of the distinct chemical environments of Si within them are cross correlated for the three silicas and their evolution with treatment temperature is elucidated. The physical and chemical properties before, during, and after collapse of these structures at high temperatures are described as are the differences in behavior between the three silica structures.

Improving the Electrochemical Performance of Li4Ti5O12 Anode through Confinement into Ordered Bimodal Porous Carbon Frameworks

Li4Ti5O12 (LTO) was confined into bimodal mesoporous carbon (BMC) framework, and the confinement effects of BMC on the crystal structure and electrochemical performances of LTO were comprehensively investigated by means of X-ray diffraction, small-angle X-ray spectroscopy, Brunaer–Emmett–Teller analysis, transmission electron microscopy, and electrochemical analysis for the first time. In comparison to bulk Li4Ti5O12 the rate capability and the cycling performance of Li4Ti5O12 confined in BMC (Li4Ti5O12@BMC) were largely improved. The rate capability of Li4Ti5O12@BMC was enhanced about 50 mA·h/g at each current rate. Li4Ti5O12@BMC showed a good cycling performance (about 245 mA·h/g at 0.5 C and 165 mA·h/g at 10 C) and high Coulombic efficiency. The enhanced properties can be attributed to the confinement effect of the hierarchical porous carbon which offered much more electrode/electrolyte interface owing to the large surface area, favored the Li+ and electron transportation due to the hierarchical bimodal pore structure, shortened the diffusion path of both Li ions and electrons, avoided the particle aggregation, and increased the conductivity of the matrix.

Fabrication and in vitro biocompatibility of biomorphic PLGA/nHA composite scaffolds for bone tissue engineering

In this study, biomorphic poly(dl-lactic-co-glycolic acid)/nano-hydroxyapatite (PLGA/nHA) composite scaffolds were successfully prepared using cane as a template. The porous morphology, phase, compression characteristics and in vitro biocompatibility of the PLGA/nHA composite scaffolds and biomorphic PLGA scaffolds as control were investigated. The results showed that the biomorphic scaffolds preserved the original honeycomb-like architecture of cane and exhibited a bimodal porous structure. The average channel diameter and micropore size of the PLGA/nHA composite scaffolds were 164±52μm and 13±8μm, respectively, with a porosity of 89.3±1.4%. The incorporation of nHA into PLGA decreased the degree of crystallinity of PLGA, and significantly improved the compressive modulus of biomorphic scaffolds. The in vitro biocompatibility evaluation with MC3T3-E1 cells demonstrated that the biomorphic PLGA/nHA composite scaffolds could better support cell attachment, proliferation and differentiation than the biomorphic PLGA scaffolds. The localization depth of MC3T3-E1 cells within the channels of the biomorphic PLGA/nHA composite scaffolds could reach approximately 400μm. The results suggested that the biomorphic PLGA/nHA composite scaffolds were promising candidates for bone tissue engineering.

Effect of unimodal and bimodal MCM-41 mesoporous silica supports on activity of Fe–Cu catalysts for CO2 hydrogenation

CO2 hydrogenation has been recognized as one of the most effective and economical ways to convert excess CO2 to valuable chemicals and/or fuels. In this research, CO2 hydrogenation to alcohols was carried out over Cu-based MCM-41 catalyst. The effects of pore characteristics of supports including unimodal and bimodal pore structures, loading amount of Fe, and reaction temperature on the catalytic performance were investigated. The bimodal MCM-41 (T) support revealed a short-range hexagonal pore structure with two different pore sizes, where the larger pore size was 30.5nm and the smaller pore (2.7nm) was equal to that of the unimodal MCM-41 (SS). Accordingly, Fe (0, 0.5, and 3wt.%) and Cu (10wt.%) loaded on bimodal MCM-41 (T) support was tested for CO2 hydrogenation and compared to that of MCM-41 (SS) support. The result showed that the activities of CO2 hydrogenation over xFe–10Cu/MCM-41 (T) catalysts were higher than xFe–10Cu/MCM-41 (SS) catalysts. Moreover, the addition of 3wt.% Fe on 10Cu/MCM-41 (T) catalyst exhibited the highest CO2 conversion of 20.8% at the reaction temperature of 350°C and the highest alcohol selectivity of 80–99% at low reaction temperature (160–200°C). Furthermore, the highest TOF of alcohols and CO (1.08×10−25 and 5.47×10−25molsurface metal atom−1min−1) were also obtained over 3Fe–10Cu/MCM-41 (T) catalyst due to the high active Cu and Fe atoms on bimodal MCM-41 (T). These outstanding catalytic activities could be attributed to the pore characteristics of the supports. The existence of larger mesopore could greatly improve the catalytic performance as it led to the formation of metals with larger sizes, resulting in less metal–support interaction of which more favorable in this reaction.

Effect of various structure directing agents on the physicochemical properties of the silica aerogels prepared at an ambient pressure

We studied the effects of various surfactants on the textural properties (BET surface area, pore size, and pore volume) of the silica aerogels prepared at an ambient pressure. A simple surface modification of silica gel prepared at an ambient pressure through hydrolysis and polycondensation of TEOS as a silica precursor was conducted using various structure directing agents. The treatment was found to induce a significant difference in the porosity of the silica aerogel. Highly porous silica aerogels with bimodal porous structures were prepared by modifying the surface of the silica wet-gel (alcogel) with trimethylchlorosilane (TMCS) in order to preserve its porosity. The samples were analyzed by small-angle X-ray scattering and nitrogen adsorption. In this work, a possible new type of highly porous hydrophobic silica aerogel with a bimodal porous structure is presented. A hydrophilic extremely porous (high surface area and large pore volume) silica aerogel was obtained by heating the as-synthesized hydrophobic silica aerogel at 400°C for 1h. There was a significant effect of structure directing agent on the textural properties, such as specific surface area, pore size distribution and cumulative pore volume of the silica aerogels.

Effect of solid-state synthesized alumina properties on the structure and catalytic performance of NiMo catalyst in hydrodesulfurization

In this paper, a precursor ammonium aluminum carbonate hydroxide (AACH) was synthesized by a low-temperature solid-state reaction, then alumina labeled as Al2O3-AC was obtained by the calcination of AACH, and finally, catalyst labeled as NiMo/Al2O3-AC supported on Al2O3-AC was prepared using the method of incipient wetness impregnation. The properties of both support and catalyst were investigated by a series of characterization methods. The results indicated that Al2O3-AC had unique bimodal porous structure, high acid content and five-fold coordinated aluminum (AlO5) on the surface. Moreover, NiMo/Al2O3-AC exhibited uniform dispersion of active components, higher Brőnsted acid sites concentration and weaker metal-support interaction. Encouraged by those excellent properties of Al2O3-AC and NiMo/Al2O3-AC, the catalyst NiMo/Al2O3-AC was evaluated in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), showing high conversion ratio of DBT.

Synthesis and Characterization of Magnesium Oxide Supported Catalysts with a Meso-Macropore Structure

Nanostructured magnesium oxide catalyst support materials with controlled morphology and size were synthesized from a supercritical carbon dioxide/ethanol solution via chemical reaction of soluble precursors and subsequent thermal decomposition. Leaf-like magnesium hydroxide precursors with high specific surface area were formed by a low-temperature chemical reaction at below 140 degrees C, while magnesium carbonate cubes with a very low surface area less than 3.3 m2/g were formed by temperature-induced phase transition from a loose to a dense structure during carbonation reaction at above 150 degrees C. The specific surface area has significantly increased higher than 90 m2/g due to the creation of highly porous MgO cubes with mesopore structure formed after thermal decomposition of the magnesium carbonate precursors. Ni-magnesium oxide catalysts with bimodal pore structure were finally formed by the consequence of packing heterogeneity of the porous magnesium oxides with different morphologies and sizes.

Microstructural Analysis and Energy‐Filtered TEM Imaging to Investigate the Structure–Activity Relationship in Fischer–Tropsch Catalysts

AbstractWe present herein the application of chemical imaging based on energy‐filtered TEM in 2 D and 3 D modes to determine the distribution of phases in Co/TiO2–SiC catalysts used in Fischer–Tropsch synthesis. In combination with more traditional techniques such as high‐resolution TEM imaging, it allowed us to precisely characterize the microstructure and the relative distribution of the three compounds, Co, Si, and Ti, before and after the catalytic reaction. We show that the TiO2 doping was almost homogenous within the bimodal porous structure of β‐SiC. The characteristics of the cobalt nanoparticles depended on the phase they are in contact with: small nanoparticles are found on TiO2 and larger nanoparticles close to SiC. Enhancement of the catalytic performance and higher stability were observed for the Co/TiO2–SiC catalyst relative to Co/SiC, which was attributed to the better dispersion of cobalt on TiO2‐doped SiC support and to the relatively strong Co–TiO2 interaction. From a general point of view, this work illustrates that the advanced TEM‐based techniques are unavoidable for the characterization and the optimization of heterogeneous catalysts.

DNA-templated Fabrication of Biphasic Calcium Phosphate Ceramics with a Bimodal Pore Structure for Tissue Engineering

Abstract Biphasic calcium phosphate (BCP) ceramics with well-controlled pores were fabricated by sintering mixtures of synthetic hydroxyapatite (HAp) and deoxyribonucleic acid (DNA). BCP ceramics with macro- and micropores revealed excellent cell proliferation as a result of suitable surface topography and phase composition.

A carbon foam with a bimodal micro–mesoporous structure prepared from larch sawdust for the gas-phase toluene adsorption

A carbon foam with a bimodal micro–mesopore distribution, was prepared by submitting larch sawdust to liquefaction, resinification, foaming, carbonization and KOH activation. The morphology, pore texture and crystal microstructure was characterized by scanning and transmission electron microscopy, nitrogen adsorption analysis and X-ray powder diffraction. A honeycomb structure with adjacent cells was observed for the precursor of carbon foam. After KOH activation, the cell wall of precursor shrunk and broke. This lead to the formation of a well-connected 3D network and developed ligament pore structure (surface area of 554–1918m2/g) containing bimodal pores, 2.1 and 3.9nm in diameter. The porous carbon foam prepared at 700°C exhibited a much higher gas-phase toluene removal than commercial activated carbon fiber owing to the 3D network and bimodal pore structure.

Poly(amidoamine) dendrimer-grafted porous hollow silica nanoparticles for enhanced intracellular photodynamic therapy

We report a novel photodynamic therapy (PDT) drug-carrier system, whereby third-generation (G3) polyamidoamine (PAMAM) was successfully grafted to the surface of porous hollow silica nanoparticles (PHSNPs), followed by the attachment of gluconic acid (GA) for surface charge tuning. The composite G3-PAMAM-grafted PHSNPs (denoted as G3-PHSNPs) with a diameter range of 100–200nm and about 30nm sized shell thickness retain bimodal pore structures (e.g. inner voids and porous structure of the shells) and PAMAM-functionalized outer layer with a large number of amino groups, allowing high loading efficacy of aluminum phthalocyanine tetrasulfonate (AlPcS4) and its effective release to target tissue. The GA-induced G3-PHSNPs were evidenced to be able to favorably cross tumor cell walls and enter into the cell interior. The generation of singlet oxygen (1O2) from AlPcS4-GA-G3-PHSNPs under visible light excitation was detected by the in situ electron spin resonance measurements and the oxidative reaction between the generated 1O2 and a chemical probe. In vitro cellular experiments showed that the photosensitive GA-G3-PHSNPs exhibited a good biocompatibility in the dark and a higher killing efficacy against MCF-7 tumor cells upon irradiation as compared with free AlPcS4, which implies that the preformed photosensitive drug-carrier system might be potentially applicable in PDT.

Preparation and Photocatalytic Activity of Robust Titania Monoliths for Water Remediation

TiO(2) monoliths were prepared, characterized, and evaluated for photocatalytic performance. The TiO(2) monoliths were found to have an interconnected void lattice and a bimodal porous structure with macropores and mesopores after calcination at 500-700 °C. Monoliths calcined at 500 °C had high specific surface area (93.1 m(2)/g) and porosity (68%), which were maintained after calcination at 700-1100 °C (51-46%). The calcined monoliths had relatively high Vickers hardness (∼104) despite their porous structure. Monoliths calcined at 500 and 700 °C exhibited high performance for methylene blue decolorization because of their high specific surface area.

A particle-stabilized diatomite foam with a bimodal pore structure

A particle-stabilized diatomite foam with a bimodal pore structure

Scaffolds with tubular/isotropic Bi-modal pore structures by gas foaming and fiber templating

The aim of this study was to engineer a scaffold for tissue engineering with double shape pore architecture, with tubular and isotropic pores. A novel method is herein proposed, based on the combination of gas foaming and fiber templating. In particular, the tubular pores have been obtained by leaching of melt–spun saccharide fibers (cotton candy) within CO2-foamed poly(ε-caprolactone). The optimization of the scaffold has been conducted via the selection of the proper saccharide, its thermal treatment to stabilize the spun fiber (crystallization), the formation of the polymer–fiber composite, the selection of the proper gas-foaming processing parameter and the final leaching in water.

High damping capacity in porous NiTi alloy with bimodal pore architecture

Porous NiTi exhibits pseudoelasticity, shape memory and low modulus, and thus shows application potential as high damping and bio-materials. Here Ni50.5Ti49.5 foam with bimodal pore structure was prepared by elemental powder sintering and high damping capacity demonstrated. NaCl particles of 500–600μm and 75–90μm diameters were adopted as space holder to create large and small pores with porosity of 40%. Incomplete densification of NiTi alloy created even smaller pores of 10–50μm and contributed another 21.47% porosity. This NiTi foam containing bimodal pores has a compressive modulus of 1.83GPa, smaller than that of foam with single pores or estimation by Gibson–Ashby model. This low modulus is attributed to the stress-induced martensite transformation under compressive load. The foam exhibits high damping capacities during phase transformation and at austenite region because of deformation, dislocation motion in thin nodes/walls and stress-induced martensite formation.

Preparation of copper-iron bimodal pore catalyst and its performance for higher alcohols synthesis

A multi-functional silica–silica bimodal pore catalyst support was prepared from silica sol and silica gel, which presented two kinds of main pores. Compared to the original silica gel, the obtained bimodal support had the enlarged surface area and decreased pore volume. This kind of bimodal pore support was applied firstly in higher alcohols synthesis, where both the copper and iron elements were supported as active sites. The bimodal pore catalyst exhibited favorite catalytic activity and high selectivity of C2+OH, due to the well dispersion of active metal sites and high diffusion efficiency of products inside the bimodal pore structures.

Fabrication and High Temperature Creep Behaviour of Interpenetrated Nickel–Chromium/Alumina Composites

AbstractA method to manufacture unique interpenetrating 50 vol% nickel–chromium/alumina composites, namely NiCr8020/Al2O3/50pp, is reported. Key process is a high temperature squeeze casting procedure at temperatures above 1500 °C used to infiltrate alloy NiCr8020 into porous alumina preforms exhibiting a bimodal pore structure. Microstructure and mechanical properties of this new composite material are presented. Bending creep tests at 1000 and 1150 °C are performed. The obtained results are discussed in comparison to a nickel based superalloy. It is shown, that particle preform reinforcement is a promising method to improve creep resistance of nickel based alloys significantly. Due to its outstanding creep resistance, the composite material has a high potential for structural and tribological applications at high temperatures in oxidizing atmospheres.