Mesopore Pore Volume Research Articles

Mesoporous titania with anatase framework synthesized using polyphenolic structure-directing agent: Synthesis domain and catalytic metal loading

Crystalline anatase TiO2 with nanosponge-like mesoporous morphologies was solvothermally synthesized following the recently reported route using random copolymer (4-vinylphenol and methyl methacrylate) as structure-directing agent. In particular, the synthesis conditions were varied over a wide range of synthesis gel compositions. Crystallinity of the titania products was checked with X-ray powder diffraction. Mesopore diameters, pore volume and specific surface area were analyzed using nitrogen adsorption. The result provided proper synthesis domains for highly mesoporous titania materials. The mesoporous materials were evaluated as supports for catalytic Pt nanoparticles to apply for alcohol-to-aldehyde partial oxidation reactions.

Adsorption of water vapor on mesoporosity-controlled singe wall carbon nanohorn

The adsorption mechanism of water vapor in hydrophobic carbon mesopores is not clearly understood. Single wall carbon nanohorns (SWCNH) having different tube diameters in the range of 2 to 6nm were oxidized at a lower temperature than the widely used temperature of 823K. Oxidation at 633K can selectively open thinner tubes of SWCNH and then the oxidation at different times can control the mesoporosity. The porosity of thus-oxidized SWCNH was evaluated from the nitrogen adsorption isotherms at 77K. The pore volume ratio of micropores to mesopores was in the range of 0.50 to 0.90. The linear relationship between water adsorption amount and the pore volume of micropores and small mesopores (<5nm) was observed, showing that water molecules are adsorbed even in small mesopores by the cluster-mediated filling mechanism as well as in micropores.

Mesoporous calcium-silicon xerogels with mesopore size and pore volume influence hMSC behaviors by load and sustained release of rhBMP-2.

Mesoporous calcium–silicon xerogels with a pore size of 15 nm (MCS-15) and pore volume of 1.43 cm3/g were synthesized by using 1,3,5-mesitylene (TMB) as the pore-expanding agent. The MCS-15 exhibited good degradability with the weight loss of 50 wt% after soaking in Tris-HCl solution for 56 days, which was higher than the 30 wt% loss shown by mesoporous calcium–silicon xerogels with a pore size of 4 nm (MCS-4). The pore size and pore volume of MCS-15 had significant influences on load and release of recombinant human bone morphogenetic protein-2 (rhBMP-2). The MCS-15 had a higher capacity to encapsulate a large amount of rhBMP-2; it could adsorb 45 mg/g of rhBMP-2 in phosphate-buffered saline after 24 hours, which was more than twice that with MCS-4 (20 mg/g). Moreover, the MCS-15 system exhibited sustained release of rhBMP-2 as compared with MCS-4 system (showing a burst release). The MCS-15/rhBMP-2 system could promote the proliferation and differentiation of human mesenchymal stem cells, showing good cytocompatibility and bioactivity. The results indicated that MCS-15, with larger mesopore size and higher pore volume, might be a promising carrier for loading and sustained release of rhBMP-2, which could be used as bone repair material with built-in osteoinduction function in bone reconstruction.

USY zeolites with tunable mesoporosity designed by controlling framework Fe content and their catalytic cracking properties

Tunable mesoporosity was successfully generated by introducing Fe cations into the framework of NaY as starting points, and then by sequential ammonium ion exchange and steaming deferrization–dealumination treatment. Accordingly, the pore diameter and volume of mesopores depended on the content of framework Fe. The zeolite products were characterized by a complementary combination of X-ray diffraction (XRD), N2 physisorption, TEM, DSC, Py-IR, and 27Al MAS NMR. The results show that the mesopore volumes of the Fe-induced mesoporous ultra-stable Y (USYFe) zeolites, which prepared via sequential deferrization-dealumination by steaming, are all higher than 0.21 cm3 g−1 with an additional thermal stability. The highest one reaches 0.23 cm3 g−1, over 53% of enhancement compared to USY (0.15 cm3 g−1) without deteriorating acidity. Furthermore, the most probable mesopore distributions can be finely tuned, typically in the range of 9–17 nm. In addition, it is found that large mesopores (8–50 nm) are surprisingly boosted with the increase in the Fe content used for the preparation of USYFe samples. In the catalytic cracking of adsorbate molecule of 1,3,5-triisopropylbenzene, the mesopores-enriched zeolites exhibit higher activity and lower deactivation tendency than USY with time on stream. The results demonstrated that the mesoporous material originating from the modification of zeolite with the pre-set Fe sites aided the diffusion into and out of the micropores via mesopores, and thus produced a positive influence on the catalytic performance.

Hierarchical zeolite Y supported cobalt bifunctional catalyst for facilely tuning the product distribution of Fischer–Tropsch synthesis

A two-step method consisting of acid leaching and base leaching was developed and applied to create hierarchical pores on a general microporous Y zeolite. Characterization with BET and TEM on the texture, morphology and structure of the prepared hierarchical Y zeolite confirmed the co-existence of mesopores with zeolitic walls. The analysis results showed that the mesopore surface area and pore volume of the hierarchical zeolite Y (Y-ABx, A: acid leaching, B: base leaching, “x” represents for base leaching time) increased with increasing the base leaching time. The hierarchical zeolite Y supported Co as catalysts were employed to catalyze the hydrogenation of carbon monoxide to form hydrocarbons through Fischer–Tropsch synthesis (FTS) reaction. The CO conversion and C5–11 selectivity on Co/Y-ABx catalysts increased significantly compared with those on the pristine Y supported Co catalyst. The isoparaffin selectivity of Co/Y-AB4 catalyst reached up to 52.3% and middle hydrocarbons became the main FTS products due to the optimized hydrocracking and isomerization function afforded by the hierarchical zeolite Y with the strong Brønsted acid/Lewis acid (B/L) ratio and textural property.

Effect of seawater salinity on pore-size distribution on a poly(styrene)-based HP20 resin and its adsorption of diarrhetic shellfish toxins

In the present study, okadaic acid (OA) and dinophysistoxin-1 (DTX1) were spiked into artificial seawater at low, medium and high estuarine salinities (9‰, 13.5‰ and 27‰). Passive samplers (HP20 resin) used for solid phase adsorption toxin tracking (SPATT) technology were exposed in these seawaters for 12-h periods. Adsorption curves well fitted a pseudo-secondary kinetics model. The highest initial sorption rates of both toxins occurred in the seawater of medium salinity, followed by seawater of low and high estuarine salinity. Pore volumes of micropores (<2nm) and small mesopores (2nm<diameter<10nm) of HP20 resin decreased after adsorption of toxins in seawater at high and low salinity but not in seawater at medium salinity, which demonstrated that the toxin molecules entered into micropores and mesopores (below 10nm in size) in seawaters of high and low salinity. More toxin or other matrix agglomerates were displayed on the surface of resin deployed in the seawater of medium salinity. Taking into consideration the pore-size distribution and surface images, it appears that intra-particle diffusion governs toxin adsorption in seawater at high salinity while film diffusion mainly controls the adsorption process in seawater at medium salinity. This is the first study to confirm that molecules of OA and DTX1 are able to enter into micropores (<2nm) and small mesopores (2–10nm) of HP20 resin in estuarine seawater with high salinity (∼27‰).

Synthesis of novel porous graphene nanocomposite and its use as electrode and absorbent

A novel three-dimensional nanostructured porous graphene nanocomposite was synthesized by sol–gel polymerization of hydroquinol (H) and formaldehyde (F) with sodium carbonate as a catalyst in graphene oxide (GO) suspension, followed by carbonization of HF and thermal reduction of GO to graphene at high temperature. The resulting material shows a BET surface area of 427 m2 g−1 and a total volume of 1.2764 cm3 g−1 with abundant mesopores. The porous graphene nanocomposite (HFG) can be used as anode for lithium ion batteries due to the porosity and thermal stability. Also, with the strong surface hydrophobicity, high mesopore ratio and pore volume, the HFG shows good absorption capacity for various organics, which makes the HFG a candidate for removal of organic contaminants from water.

Effects of Air-Phosphoric Acid Activation on Pore Structure and Adsorption Property of Mesoporous Carbon from Hemp Stem

Mesopore activated carbons were prepared using hemp stem as feedstock by air-phosphoric acid activation method. The crystallite size of hemp stem-based mesoporous carbon is small, and its pores is larger. The phosphoric acid solution concentration has a signification effect on pore structure and adsorption property of mesopore activated carbons from hemp stem. The mesopore activated carbon attained at phosphoric acid solution concentration of 50% exhibits a maximum BET(Brunauer Emmett and Teller) specific surface area of 1351m2/g, total pore volume of 1.21 cm3/ g, mesopore pore volume of 0.90 cm3/ g and a mesopore fraction of 74.4%. And the resulting carbon has smaller crystal size, developed pore structure, wider pore size distribution.

Micron-Sized Single-Crystal-like CoAPO-5/Carbon Composites Leading to Hierarchical CoAPO-5 with Both Inter- and Intracrystalline Mesoporosity

Commercial mesopores-containing carbon (carbon black BP2000) has been used as crystallization host as well as hard template of intracrystalline mesopores in CoAPO-5 materials prepared with N-methyldicyclohexylamine as specific structure-directing agent. As a result, micrometer-sized AFI-structured terminated-tip (pencil-like) hexagonal prims have been obtained. Despite the appearance of single crystals, the crystals are actually composites formed by a large number of elongated-shape CoAPO-5 and carbon nanodomains. Indeed, the removal of carbon by calcination leaves an inorganic Co-doped AlPO4-based material having a complex hierarchical pore system, formed by the expected microporosity for an AFI-structured material and both intra- and intercrystalline mesoporosity. In good agreement with the nanocomposite nature of these micrometer-sized crystals, the size of their fibers generated by burning the carbon matrix can be relatively controlled by the conditions of the calcination processes. Under optimized synthesis and calcination conditions, AFI-structured materials with high mesoporous surface area and pore volume can be afforded.

Effect of Solvents on the Structure and Properties of Mesoporous SiO2 Supported Phosphotungstic Acid

HPW/BMMs catalyst was prepared by supported phosphotungstic acid on mesoporous SiO2 with two different mesoporous structures via impregnation method, and characterized by means of XRD, FTIR, nitrogen adsorption- desorption, TG and SEM. The effects of solvents, such as water, ethanol, acetone and acetonitrile, on the structure and properties of supported phosphotungstic acid were systematically investigated. The results showed that the mesoporous structures of BMMs were maintained in the catalysts synthesis process, however, the mesopores order degree, surface area and pore volume of the catalysts (HPW/BMMs) decreased as the increase of HPW loading. A new HPW species in HPW/BMMs appeared at lower loadings and disappeared as the increasing of HPW amount. In addition, the influence of aqueous solution on the Keggin structure of HPW in HPW/BMMs was remarkable, al- though the HPW crystal remained intact with the uniform dispersion. The acid density of the catalyst synthesis in water with 40% HPW loading (40HPW/BMMs-WA) was up to 1.381 μmol/m 2 . In contrast, when acetonitrile was used as solvent, the Keggin structure of HPW was more likely to be maintained, but the HPW crystal phase was se- verely destroyed with a low dispersing inside the mesoporous channels. In comparison, the effects of ethanol and

TiO2 nanocrystal embedded ordered mesoporous carbons as anode materials for lithium-ion batteries with highly reversible capacity and rate performance

The ordered mesoporous carbon/TiO2 (OMCT) nanocomposites with TiO2 nanocrystals embedded within ordered mesoporous carbon (OMC) were prepared by a simple solvothermal method. The effect of TiO2 nanoparticle incorporation in OMC matrix on the mesoporous structure, pore size, pore volume, surface area and microstructure of OMCT composites was investigated using X-ray diffraction, N2 adsorption–desorption and Brunauer–Emmett–Teller method, scanning electron microscopy and transmission electron microscopy. The electrochemical lithium storage capacities of OMCT composites with different incorporated TiO2 nanoparticles are comparatively investigated using cyclic voltammetry and galvanostatic charge–discharge techniques. It is suggested that the OMCT composites as anode materials for lithium ion batteries display a greatly improved electrochemical performance with high reversible capacity, coulombic efficiency, rate capability and cycling performance. As an anode electrode for Li-ion battery, OMCT15 composite with an incorporated TiO2 nanocrystal content possesses a high reversible capacity of 540.9 mA h g−1 even up to 60 cycles at a high current density of 100 mA g−1, with a stable coulombic efficiency of 98% and good rate capability. Especially at the current density of 1600 mA g−1 after 50 cycles, the reversible capacity of the OMCT15 remains at a value of 260 mA h g−1, 5 times that of the OMC (48.9 mA h g−1) and 21 times that of the pure TiO2 (12.4 mA h g−1) electrodes, respectively. The improved electrochemical lithium storage performance of high reversible capacity, coulombic efficiency, rate performance and cycling ability can be mainly attributed to the synergic effects between the TiO2 nanoparticles and the three dimensional OMC matrices.

A simple approach to prepare monodisperse mesoporous silica nanospheres with adjustable sizes

A new and facile approach has been developed to prepare monodisperse mesoporous silica nanospheres (MMSNs) with controlled particle sizes and pore structures. In our approach, MMSNs were synthesized simply in a sodium acetate solution without adding any other alkali or alcohol additives. MMSNs have a spherical shape and uniform particle sizes, which can be adjusted from 50 to 110nm by increasing the reaction temperature from 40 to 80°C. By performing a subsequent hydrothermal treatment (HT) under basic condition (pH=∼11.5) at 130°C, the mesoporous pore volume and surface area can be enhanced, while keeping the mono-dispersion characteristics and the mesopore size almost unchanged. The pore sizes of MMSNs can be adjusted from 2.8 to 4.0nm under acidic solutions by changing the HT temperature from 100 to 130°C. The formation process of MMSNs has been investigated by transmission electron microscopy (TEM) and attenuated total reflection Fourier transform infrared (ATR-FTIR) techniques. A spherical micelle templating mechanism is proposed to explain the formation of MMSNs in our system, which is different from that of traditional highly ordered mesoporous silica nanoparticles (MCM-41).

Characterization and behavior of anesthetic bioactive textile complex in vitro condition

In this study, a bioactive complex containing nonwoven textile material (polypropilene (PP)/viscose), chitosan hydrogel, and lidocaine hydrochloride, was designed. The purpose of such biomedical textile was in the treatment of painful sites. Mercury intrusion porosimetry was used in order to estimate the influence of medical impregnation on porous structure of nonwoven material. It was estimated that more than 97% of pores in untreated nonwoven sample were larger than 15 μm. Anesthetic treatment of nonwoven reduced total pore volume of ultramacropores and macropores, while total pore volume of mesopores slightly increased. Lidocaine hydrochloride release from the anesthetic/chitosan hydrogel/nonwoven complex was measured in vitro by Franz diffusion cell technique. Mathematical model was developed to estimate the release of the lidocaine from obtained bioactive textile material. The diffusive transport of lidocaine hydrochloride through three connected layers, i.e., polymer hydrogel, membrane, and solution is modeled based on Fick's second law. Taking all the relevant conditions, regarding this experiment, into consideration, the coefficient of lidocaine diffusion through the polymer hydrogel, as well as the concentration ratio parameter were determined by the mathematical model.

Inorganic-organic hybrid materials through post-synthesis modification: Impact of the treatment with azides on the mesopore structure.

Hybrid, hierarchically organized, monolithic silica gels, comprising periodically arranged mesopores and a cellular macroscopic network, have been prepared through a co-condensation reaction of tetrakis(2-hydroxyethyl)orthosilicate with chloromethyl-trimethoxysilane or 3-(chloropropyl)-triethoxysilane. Subsequent conversion of the chloro groups into azido groups, by nucleophilic substitution with NaN3 in N,N-dimethylformamide, was conducted upon preservation of the monolithic structure. However, treatment with NaN3 had a strong influence on the structure in the mesoporous regime, with changes such as an increase of mesopore diameter, pore volume and lattice constants, as well as a concomitant decrease of the pore wall thickness, as confirmed by small angle X-ray scattering, transmission electron microscopy, and nitrogen sorption analysis. Similar effects were observed for unmodified silica gels by simple ageing in azide-containing media, whether a relatively small or a sterically demanding counter ion (Na+ or (H3C)4N+) was used. The structural modification did not seem to depend greatly on whether an organic aprotic solvent (N,N-dimethylformamide, 1,1,3,3-tetramethylurea, 1,3-dimethyl-2-imidazolidinone) or a protic solvent that can form hydrogen bonds, such as water, was used.

Effect of Microwave on Iron Potassium Catalyst Fischer-Tropsch Synthesis

Fe-K/SiO2 catalysts were prepared by microwave irradiation or by the steep and calcine conventional method. They were then tested by analyzing the products on-line with a gas chromatograph (GC 508) equipped with thermal conductivity detector (TCD) and in-series of packed columns Porapak-Q. The structure and morphology of the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) as well as N2 physisorption with the BET method. The result show that microwave radiation of the catalyst led to an increase in the surface area, mesopores pore volume, the catalyst proved to have more reaction activity than that prepared by conventional method.

Bioactive SrO–SiO2 glass with well-ordered mesopores: Characterization, physiochemistry and biological properties

For a biomaterial to be considered suitable for bone repair it should ideally be both bioactive and have a capacity for controllable drug delivery; as such, mesoporous SiO2 glass has been proposed as a new class of bone regeneration material by virtue of its high drug-loading ability and generally good biocompatibility. It does, however, have less than optimum bioactivity and controllable drug delivery properties. In this study, we incorporated strontium (Sr) into mesoporous SiO2 in an effort to develop a bioactive mesoporous SrO–SiO2 (Sr–Si) glass with the capacity to deliver Sr2+ ions, as well as a drug, at a controlled rate, thereby producing a material better suited for bone repair. The effects of Sr2+ on the structure, physiochemistry, drug delivery and biological properties of mesoporous Sr–Si glass were investigated. The prepared mesoporous Sr–Si glass was found to have an excellent release profile of bioactive Sr2+ ions and dexamethasone, and the incorporation of Sr2+ improved structural properties, such as mesopore size, pore volume and specific surface area, as well as rate of dissolution and protein adsorption. The mesoporous Sr–Si glass had no cytotoxic effects and its release of Sr2+ and SiO44− ions enhanced alkaline phosphatase activity – a marker of osteogenic cell differentiation – in human bone mesenchymal stem cells. Mesoporous Sr–Si glasses can be prepared to porous scaffolds which show a more sustained drug release. This study suggests that incorporating Sr2+ into mesoporous SiO2 glass produces a material with a more optimal drug delivery profile coupled with improved bioactivity, making it an excellent material for bone repair applications.

Synthesis of hierarchical nanocrystalline ZSM-5 with controlled particle size and mesoporosity

Development of new zeolite based materials is essential for a variety of applications in catalysis, separations, and medicine. Increasing the specific surface area and decreasing the micropore diffusion pathlength in zeolites are important factors for improving the performance of zeolites in catalytic applications and these factors can be optimized by decreasing the zeolite particle size. Creation of a hierarchical zeolite material that possesses both micro- and mesopores with very large surface areas and improved mass transport properties is an effective solution. In this study, a facile approach to a one step synthesis of nanocrystalline ZSM-5 zeolite from a single template system in 12–24 h at 140 °C and with high yield is presented. ZSM-5 zeolite crystals as small as 6 nm which form mesoporous aggregates of approximately 200 nm in diameter were synthesized using this method. The mesopore volume and size distribution showed a dependence on particle size such that smaller particles lead to higher mesopore volumes and narrower pore size distributions. The size of individual crystals, as well as mesopore surface area and pore volume can be controlled by adjusting the pH of the reaction mixture, as well as the hydrothermal treatment temperature and duration.

A non-destructive technique to analyze Si content in evaluation of pore blockage of ferrihydrite-modified diatomite using XANES and BET

A non-destructive technique was developed in this study to analyze Si content. Pore blockage of ferrihydrite-modified diatomite (FHMD) by Si-containing ferric oxides was investigated using X-ray absorption near-edge structure (XANES) spectroscopy and Brunauer–Emmett–Teller (BET) analysis. The Si content of Si-containing ferric oxides of FHMD was represented by relative heights of pre-edge peak in Si L 3,2-edge TEY XANES spectra. The relative heights of the pre-edge peak in the spectra of reference Si-containing ferric oxides were best fit by a sigmoidal function. The Si content of ferric oxides of FHMDs made with FeCl 2 concentrations of 0.5, 1, 1.5, 2, and 2.5 M determined using this function were 0.23, 0.19, 0.12, 0.03, and 0.01, respectively. These results indicate the Si-containing ferric oxides present on the surface of 0.5- and 1-FHMD are ferrihydrite; on the surface of 1.5-FHMD are ferrihydrite and lepidocrocite; and on the surface of 2- and 2.5-FHMD are hematite. BET analyses indicated a sharp shift toward lower pore diameters in the pore size distributions of 0.5- to 1.5-FHMD and the presence of a type H2 hysteresis loop in the nitrogen adsorption–desorption isotherms; these were attributed to the deposition of ferrihydrite. In 2- and 2.5-FHMD, the significant increase in the pore volume of larger mesopores (between 10 and 50 nm) and the presence of a type H3 hysteresis loop were attributed to the deposition of hematite.

Aniline as a Dispersant and Stabilizer for the Preparation of Pt Nanoparticles Deposited on Carbon Nanotubes

A novel method has been developed to debundle carbon nanotubes (CNTs) and load Pt nanoparticles on them without damaging their graphene structures. In this article, the aniline acts as a very efficient dispersing agent to debundle CNTs from 200 to 50 nm at a very low concentration of 0.5% in an IPA/water solution. The aniline-stabilized CNTs have a larger pore volume and larger amount of mesopores than pristine CNTs, and the debundling of CNTs by aniline appears to be a physical rather than a chemical process. Meanwhile, under the presence of aniline, the Pt nanoparticles are anchored on CNTs with a uniform dispersion and small particle size distribution (1.9 ± 0.4, 2.1 ± 0.3, and 2.4 ± 0.4 nm for 14.9%, 29.1%, and 49.0% Pt/CNT, respectively). It is clear that aniline functions as a dispersant and a stabilizer in this paper. These nanocomposites are applied as electrocatalysts for the cathode of a direct methanol fuel cell. The electrochemical active surface areas of Pt/CNT catalysts are higher than that ...

Acid and aluminium modification of sepiolite and its application in FCC catalysis

AbstractThe effects of acid and Al concentration, type of Al salt, treatment temperature and time of removal of Mg from sepiolite have been investigated, as has the use of modified sepiolite as an active fluid catalytic cracking (FCC) matrix. The samples were characterized by N2 adsorption and X-ray diffraction. Mg removal from sepiolite increased with increasing acid and Al ion concentration, treatment time and temperature. The temperature had the greatest impact on Mg removal. After acid and Al modification, 29% of the Mg was removed. When using the modified sepiolites as active matrices in FCC catalysts, the specific surface area, pore volume and mesoporous pore volume of the catalysts increased and they exhibited excellent performance in resisting the effects of heavy-metals as a result of the introduction of Mg oxide from the modified sepiolite.