Nitrogen Adsorption Porosimetry Research Articles

Synthesis and Characterization of UV-Induced Interpenetrating Polymer Network (IPN) Structure of Poly(urethane acrylate) (UA Polymer)/Silica Hybrids

High transparent and homogeneous poly(urethane acrylate) (UA Polymer)/silica hybrids were obtained by using strong ionic interaction between carboxylic acid groups of the UA Polymer and amino moieties of silica resulting from 3-aminopropyltriethoxysilane (APTEOS). The ionic interaction was directly confirmed by FT-IR measurement. The homogeneity of the obtained UA Polymer/silica hybrids was examined by SEM, TM-AFM and nitrogen adsorption porosimetry studies. Thermal property of the polymer hybrids was also checked by TGA study. Furthermore, the semi-interpenetrating polymer network (semi-IPN) structured UA Polymer/silica hybrids, where UA Polymer was dispersed in silica gel matrix, were changed to the IPN structured polymer hybrids by photo-induced cross-linking between UA Polymers. The change of the surface hardness, solvent-resistant property, and surface roughness on nanometer scale depending on the formation of IPN structure was investigated.

Multiporous Polymeric Materials from Thermoreversible Poly(vinylidene fluoride) Gels

Thermoreversible gels of poly(vinylidene fluoride) (PVF2) in organic diesters [(CH2)n−(COOEt)2] were dried by replacing the high boiling diesters with a guest solvent cyclohexane and followed by leaching with methanol. The porosity of the samples was measured using mercury intrusion porosimetry (MIP) for pore size > 6 nm and by nitrogen adsorption porosimetry using the Barett−Joyner−Halenda (BJH) technique for pore size 3−6 nm. Samples dried from gels in diethyl adipate (n = 4), diethyl suberate (n = 6), and diethyl azelate (n = 7) were studied. Porosity in different dimensions, e.g., micro, meso, and macro sizes, was observed in the same sample making them as multiporous materials. Both nano- and macroporosity increase with increasing “n” of diesters, and pore volumes and surface areas were also found to increase in a similar fashion. Field emission scanning electron micrographs also support the above points. The differential scanning calorimeteric thermograms at higher heating rate (40 °C/min) show two peaks; the higher melting peak increases with decreasing “n”. The porous PVF2 materials have α-polymorphic structure as evidenced from X-ray diffraction. Both nano- and macroporosity decrease with increasing polymer concentration in the gel. The materials show hysteresis loop in the intrusion and extrusion histograms of MIP and nitrogen adsorption porosimetry, indicating ink bottle or interconnected channel structure in the material. Samples dried from increased polymer concentration in the gel have lower nanopore concentration, lower surface area, and lower pore volume.

Multiresponsive Photopatterning Organic−Inorganic Polymer Hybrids Using a Caged Photoluminescence Compound

The caged photoluminescence compound 2-(2‘-benzoylphenyl)benzoxazole (BzPO) modified with poly(N,N-dimethylacrylamide) was synthesized. Transparent polymer hybrids with the obtained polymer were prepared by using hydrogen bond interactions between amide groups of the organic polymer and silanol groups resulting from hydrolysis of tetramethoxysilane. By UV irradiation upon the obtained polymer hybrids, the cage-released reaction of BzPO quickly took place even in a silica gel matrix, and the resulting polymer hybrids showed strong green photoluminescence deriving from a phototautomer of 2-(2‘-hydroxyphenyl)benzoxazole (HPBO) dye. The preparation of “photoresist-like” photopatterning polymer hybrids could be also accomplished by using a photomask during UV irradiation. Furthermore, the photoluminescence of the polymer hybrids was reversibly quenched and emitted by the recaging of the hydroxyl group of HPBO with adsorption and desorption of water molecules. The miscibility of polymer hybrids depending on UV irradiation was evaluated by SEM and nitrogen adsorption porosimetry studies.

Adsorption Enhancement Mechanisms of Silica−Titania Nanocomposites for Elemental Mercury Vapor Removal

A novel nanocomposite that combines high-surface area silica with the photocatalytic properties of titania has been developed that allows for effective capture of elemental mercury vapor. The adsorption capability of the developed material has been found to improve after periods of photocatalytic oxidation. In this study, the mechanisms for adsorption enhancement were identified. BET nitrogen adsorption and mercury porosimetry were used to evaluate pore structure, and the results suggest that a decrease in contact angle was likely to be responsible for improved mercury capture over time. Contact angle measurements showed a significant change of more than 10 degrees, indicating greater attraction to mercury for the used pellets due to deposited mercuric oxide. ICP and TGA analyses showed that mercury was captured as both elemental mercury (Hg0) and mercuric oxide (HgO). In addition, it was shown that pellets used for nearly 500 h still showed greater than 90% removal efficiency and had an average capacity of 10 mg of Hg/g based on mass balance calculations, while some pellets had a capacity over 30 mg of Hg/g according to ICP and TGA analyses. Mercuric oxide doped pellets removed 100% of elemental mercury without pretreatment. The superior mercury removal efficiency combined with various advantages of the novel composite demonstrates its use as an effective alternative to conventional activated carbon injection technology.

Synthesis of anionic polymer–silica hybrids by controlling pH in an aqueous solution

Optically transparent organic–inorganic polymer hybrids with anionic polymers such as poly(acrylic acid) (PAA) and poly(styrene sulfonic acid) (PSSA) could be easily synthesized by controlling pH in an aqueous solution. It is well known that the conformation of the anionic polymer depends on pH in an aqueous solution. Therefore, it is thought that the electrostatic repulsion between organic polymer chains should deter the aggregation of the organic polymer during the preparation of the polymer hybrid. The miscibility of anionic polymer–silica hybrids was examined by SEM, tapping-mode AFM and nitrogen adsorption porosimetry studies. The thermal properties of anionic polymer–silica hybrids were checked by TGA and DSC. The hygroscopicity of polymer hybrids with anionic polymers was also investigated.

Structural and surface chemical properties of sol–gel derived TiO 2–ZrO 2 oxides

Pure titania, zirconia, and binary TiO 2–ZrO 2 oxides with Ti/Zr molar ratios of 1:3, 1:1 and 3:1 were prepared by a modified sol–gel method. The samples were calcined at different temperatures and characterized by nitrogen adsorption porosimetry, XRD, DSC–TGA and FT-IR. After calcination at 450 °C the pure titania and zirconia are in the crystalline phase (anatase and tetragonal, respectively) while the binary oxides remain in the amorphous phase. The binary oxides are crystallized after calcination at temperatures above 800 °C, but only the TiO 2–ZrO 2 (1:1) sample is in the single phase of crystalline TiZrO 4 while the other two binary oxides contain TiZrO 4 and tetragonal (or monoclinc) zirconia and rutile phases, respectively. The crystallization temperature for the formation of ZrTiO 4 phase in the three binary oxides increases with titania content (respectively at 606, 716 and 754 °C). Different from the pure oxides, which exhibit two types of surface OH group, the binary oxides after calcination at 450 °C only have surface terminal OH group. The OH surface density decreases and, after passing through a minimum at about equimolar composition of Ti/Zr, increases with increasing titania content. The mixed oxides exhibit a large amount of surface acid sites.

Effects of matrix variations on pH and Cu2+sensing properties of sol–gel entrapped Eriochrome Cyanine R

Eriochrome Cyanine R has been entrapped in a range of acid- and base-catalysed silica sol–gel matrices using various values of the water ∶ alkoxide ratio (R) and total precursor volume and incorporating varying amounts of the organic modifier methyltriethoxysilane (MTES). Diffuse reflectance spectra of thin films of polyisobutylene-bound finely-ground samples of these carefully aged materials have been measured as a function of time in solutions of various pH and Cu2+ concentration. Effects of pore size distribution and organic modification on these sensing properties have been interpreted in terms of data from nitrogen adsorption porosimetry and EXAFS. Optimum sensitivity to low Cu2+concentrations is achieved for gels incorporating 10% MTES, and the use of the polymer-bound ground samples increases response speed by a factor of 300 relative to bulk monolith sol–gel samples with elimination of cracking effects.

Porous glasses as a matrix for incorporation of photonic materials. Pore determination by positron annihilation lifetime spectroscopy

Abstract Porous glasses prepared by the sol–gel technique have a variety of applications when incorporated by photonic materials: tunable lasers, sensors, luminescence solar concentrators, semiconductor quantum dots, biological markers. The known methods of pore size determinations, the nitrogen adsorption and mercury porosimetry allow to determine the sizes of open pores. Positron annihilation lifetime spectroscopy (PALS) allows to determine pore sizes also of closed pores. As an example we have performed measurements of non-doped zirconia–silica–polyurethane (ZSUR) ormocer glasses and the same glasses doped with lead sulfide quantum dots. The pore radii range between 0.25–0.38 nm, total surface area 15.5–23.8 m 2 /g.

Pore size modification of macroporous crosslinked poly(dicyclopentadiene)

AbstractThis article describes the pore size modification and in situ surface functionalization of macroporous crosslinked poly(dicyclopentadiene), produced by chemically induced phase separation, with norbornene‐functionalized poly(ethylene glycol) telechelic oligomers. The microstructure of the open porosity materials produced with this technique consisted of agglomerated particles. The incorporation of these telechelic oligomers allowed a substantial decrease in the pore size and a related increase in the internal surface area. These functionalized oligomers acted as stabilizers around the primary particles produced by phase separation and blocked their growth so that the materials resulting from the agglomeration of these smaller particles showed finer microstructures. The resulting porous materials were characterized by scanning electron microscopy, density measurements, nitrogen adsorption, and mercury porosimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2036–2046, 2003

Porous cobalt spheres for high temperature gradient magnetically assisted fluidized beds

Porous metallic cobalt spheres have been prepared as high temperature capable media for employment in gradient magnetically assisted fluidization and filtration technologies. Cobalt impregnated alginate beads are first formed by extrusion of an aqueous suspension of Co 3O 4 into a Co(II) chloride solution. The organic polymer is thermally decomposed yielding cobalt oxide spheres, followed by reduction to the metallic state, and densification. Cobalt beads have been produced with porosities ranging between 10 and 50%, depending upon sintering conditions. The product media have been characterized by scanning electron microscopy (SEM), nitrogen adsorption porosimetry, and vibrating sample magnetometry.

Mercury intrusion porosimetry, nitrogen adsorption, and scanning electron microscopy analysis of pores in skin.

Stability of collagenous matrixes such as skin and leather with respect to changes in their dimensions on heating has long been correlated with degree and type of cross links formed and short-range ordering in angstrom unit scales. Macroscopic dimensional changes may be expected to involve alterations in the long-range order as well as supramolecular assemblies in skin and leather. This study relates thermal shrinkage of skin matrixes with alterations observed in micro-, meso-, and macroporic structures. Changes in the pore structure of skin associated with thermal shrinkage have been studied using nitrogen adsorption and mercury intrusion porosimetry measurements. A comparison of results obtained using both techniques has been made. These results indicate that although the percentage porosity of the matrix decreases, the BET specific surface area increases on shrinkage. An insight into the changes in the pore systems of skin induced by thermal shrinkage has been gained.

Influence of fractal pore structure in Claus catalyst performance

The Claus process is an efficient way of removing H 2S from acid gas streams and it has been widely practised in industries such as natural gas processing, oil refining and metal smelting. Catalytic stage plays a paramount role in Claus units performance. Different samples of Claus reaction alumina catalyst were characterised by the fractal dimension parameter employing nitrogen adsorption porosimetry. The influence of such a dimension over Claus reactor performance was studied employing a reactor model. Significant differences between fractal and smooth catalysts performance were found as well as implications in reactor design. Deactivated catalyst samples were also characterised and its behaviour as Claus catalyst shows influence of the fractal dimension value. Fractal dimension appears as a useful parameter to the Claus catalyst selection procedure.

The sol–gel preparation and characterization of nanoporous silica membrane with controlled pore size

A thin nanoporous silica membrane was prepared by the two-step sol–gel method. First, silica membrane was formed onto the α-alumina support as an intermediate layer with fibrous silica colloid. Then, silica nanoparticles were deposited on the first layer of silica membrane surface again by the sol–gel method. It is generally found that gelation process, as liquid evaporates during drying, begins with the formation of fractal aggregates. Since an aggregate having the higher fractal dimension has the more complex void space than the aggregate having the lower fractal dimension, the silica nanoparticle concentration in the coating solution for the second step modification was selected low enough to avoid the aggregates with the higher fractal dimension. Thus, the prepared membrane had a dense skin layer with a nanospace as interparticle void space, which was proved by the AFM surface image analysis and the result from nitrogen adsorption porosimetry.

Structural changes in phenol-intercalulated hydrotalcite caused by heating

AbstractThermal analysis (DTA-TG-DTG), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption and mercury intrusion porosimetry techniques were used to assess the structural changes induced upon heating of two hydrotalcite-phenol (trichloro- and trinitrophenol, HT-TCP and HT-TNP) complexes, and the results were compared with those obtained for the original hydrotalcite (HT) sample. The DTA revealed thermal effects that depended on the nature of the interlayer ion in the complexes. The total weight loss (TG-DTA) increased from 37% for the original HT to 40% for HT-TCP and 77% HT-TNP, as the amount of phenol increased. The XRD and FTIR spectroscopy showed that the calcination product (550°C) of the HT-phenol complexes was indistinguishable from that formed from the original HT. Since HT-phenol complexes were prepared by phenol adsorption on calcined HT, our results confirm the recyclability of HT-like compounds as sorbents for phenols.

Characterization of asymmetric ceramic membranes by modified permporometry

A simple permporometry method based on varying membrane temperature is demonstrated for measuring the pore size distribution of active layer in asymmetric ceramic membranes. This modified permporometry technique can be used to characterize asymmetric ceramic membranes with pores of 2 to 100 nm in diameter. The pore size distribution data of the γ-Al 2O 3 membranes measured by the modified permporometry using cyclohexane and carbon tetrachloride as condensable vapor agree favorably with those measured by the nitrogen adsorption porosimetry and permporometry data reported in the literature.

Preparation of SiO 2 and NiO/Al 2O 3 aerogels by supercritical CO 2 drying and their catalytic activity

Aerogels of SiO 2 and NiO/Al 2O 3 were prepared by means of sol-gel method followed by supercritical CO 2 drying. Aerogels were characterized in terms of BET surface area, pore size distribution by both nitrogen adsorption and mercury porosimetry, and TEM microscope observation in comparison with xerogels that were prepared by ambient drying of alcogel. Aerogels had higher surface area and pores in meso- and macropore size region. TEM microscopy revealed that aerogels had large pores and a highly divided state of NiO on Al 2O 3 matrix. Catalytic activity of NiO/Al 2O 3 aerogels was measured for partial oxidation of iso-butylene. Aerogel catalyst was selective to methylacrolein over acetone, whereas xerogel catalyst was not selective.

Redox Activity of Nonstoichiometric Cerium Oxide-Based Nanocrystalline Catalysts

Nonstoichiometric cerium oxide-based catalysts were investigated for SO 2 reduction by CO to elemental sulfur, CO oxidation, and complete methane oxidation. Nanocrystalline processing by inert gas condensation was exploited for its unique potential to generate nonstoichiometric ultrahighly dispersed oxides. Nanocrystalline CeO 2− x materials, pure or doped with 10 at.% La or 15 at.% Cu, were generated by magnetron sputtering from pure or mixed metal targets, followed by controlled oxidation. These materials allowed us to investigate the effects of oxide nonstoichiometry and dopants on catalytic activity in oxidation reactions. The nonstoichiometric materials were characterized by X-ray diffraction, nitrogen adsorption porosimetry, and X-ray photoelectron spectroscopy. Catalytic properties were studied in a packed-bed reactor and compared to materials of similar composition prepared by coprecipitation. In general, the nonstoichiometric CeO 2-based materials exhibited greater catalytic activity than precipitated ultrafine materials. The light-off temperatures for SO 2 reduction by CO, CO oxidation, and CH 4 oxidation were 100-180°C lower for the nanocrystalline pure and La-doped CeO 2− x catalysts than for the respective precipitated materials. The Cu-doped form of both types of catalysts possessed comparable activity. The nonstoichiometric materials did not show a hysteresis behavior in the activity profile for SO 2 reduction by CO, unlike the precipitated catalysts. They further demonstrated a remarkable stability against CO 2 poisoning in this reaction. The differences between the nanocrystalline and the precipitated materials are discussed in terms of the stoichiometry of these oxide catalysts.

Unusual Sintering Behavior of Porous Chromatographic Zirconia Produced by Polymerization-Induced Colloid Aggregation

The effects of sintering temperature and duration on the pore structure of chromatographic zirconia particles produced by the controlled polymerization-induced aggregation of 1,000 {angstrom} colloids are studied with an eye toward optimally strengthening the aggregates and eliminating small pores while preserving large pores. Nitrogen adsorption and mercury porosimetry are used to estimate the surface area, pore volume, and pore size distribution. Pulsed field gradient NMR measurements of solvent diffusion are used to estimate the diffusion tortuosity of the pore space. Initially of course, the pore volume and surface area decrease significantly, the decrease being more pronounced at higher temperatures. With prolonged sintering, the pore size, pore volume, and surface area change much more slowly, but the diffusion tortuosity seems to be minimized at a sintering temperature and time at which pores are allowed to redistribute so as to optimize large pores. The aggregates synthesized by this aggregation method apparently produce metastable large pores which are not easily collapsed.

Chemically controlled porosity in silica aeroglass

The relationship between the initial compositional make up and the ultimate pore structure has been probed by varying the initial amounts of methanol and water relative to the silica precursor. The gels were dried under conditions that were supercritical to the inter-pore liquid to yield aeroglasses. The structure of these materials has been investigated using nitrogen adsorption and mercury intrusion porosimetry. The primary compositional factor in determining the structure of sol-gel materials is the relative amount of water. A secondary but very important consideration is the relative dilution of the silane in the alcoholic solvent. Increasing this dilution has been shown to affect the shape of the isotherm, and the pore size distributions calculated from the adsorption and desorption branches. As the dilution increases the pore diameters show a general increase. This is related to the level of molecular separation between the condensing species. The relationship between the surface area and dilution is not as clear cut; the estimated BET area generally decreases with increasing dilution, with a possible maximum at a dilution of RA=2 (where RA is the molar ratio of the alcohol with respect of the silane).

Novel polystyryl resins for size exclusion chromatography

AbstractNew size exclusion chromatography (SEC) resins based on a crosslinker having independent vinyl groups have been produced and compared with SEC resins based on divinylbenzene‐55 (DVB). 1,2‐Bis(p‐vinylphenyl)ethane (p,p‐BVPE) and its meta‐isomers were suspension‐copolymerized with p‐methylstyrene in the presence of different porogens to give particles of about 5 μm average diameter. The porous particles were slurry‐packed into stainless steel columns for SEC evaluation. Calibration curves were obtained using narrow disperse polystyrene standards with molecular weights ranging from 580 to 3,040,000. The calibration curves for the new BVPE resins covered wider useful molecular weight ranges than those for comparable divinylbenzene resins. Particle size, surface morphology and the properties of pores were studied using a Coulter Multisizer II, scanning electron microscopy, nitrogen adsorption, and mercury porosimetry. © 1994 John Wiley & Sons, Inc.