Pore Size Region Research Articles

Revealing nanoscale sorption mechanisms of gases in a highly porous silica aerogel.

Geological formations provide a promising environment for the long-term and short-term storage of gases, including carbon dioxide, hydrogen and hydro-carbons, controlled by the rock-specific small-scale pore structure. This study investigates the nanoscale structure and gas uptake in a highly porous silica aerogel (a synthetic proxy for natural rocks) using transmission electron microscopy, X-ray diffraction, and small-angle and ultra-small-angle neutron scattering with a tracer of deuterated methane (CD4) at pressures up to 1000 bar. The results show that the adsorption of CD4 in the porous silica matrix is scale dependent. The pore space of the silica aerogel is fully accessible to the invading gas, which quickly equilibrates with the external pressure and shows no condensation on the sub-nanometre scale. In the 2.5-50 nm pore size region a classical two-phase adsorption behaviour is observed. The structure of the aerogel returns to its original state after the CD4 pressure has been released.

Experimental investigation on fractal characteristics of pores in air-entrained concrete at low atmospheric pressure

This study intends to investigate the characteristics of pore structure of air-entrained concrete at low atmospheric pressure (0.7P0 = 0.7 atm) and standard atmospheric pressure (P0 = 1 atm) through in situ experiments. By using the data obtained from mercury intrusion porosimetry (MIP) test, the surface fractal dimension in different pore size regions is computed and linear regressed based on thermodynamic model. The results show that low atmospheric pressure has great impact on the fractal properties of pores and pore volume. The surface fractal dimension of pores <10 nm prepared at 0.7P0 is 4.5%–27.6% smaller than that at P0; the surface fractal dimension of pores >1000 nm at 0.7P0 is 4.5%–13.6% bigger than that at P0. The volumes of pores <10 nm and >1000 nm at 0.7 P0 is respectively 9.4%–38.9% and 38.5%–66.7% lower than that at P0; and the volume of pores within 10–1000 nm at 0.7P0 is 19.8%–41.8% higher than that at P0. The mechanisms behind the abnormal structure of pores at 0.7P0 are discussed from perspectives of cement hydration and mechanical equilibrium of air bubble.

Electrosprayed polyamide nanofiltration membrane with uniform and tunable pores for sub-nm precision molecule separation

• Electrosprayed polyamide nanofiltration membrane. • Polyamide membrane with uniform and tunable pores. • Sub-nm precision molecule separation. Interfacial polymerized polyamide composite nanofiltration membrane has been widely used in wastewater treatment. Despite its high selectivity towards water and solutes, differentiation of solutes with similar size is still a great challenge. Herein, we propose that polyamide nanofiltration membrane with uniform and tunable pores and sub-nm precision selectivity can be achieved through electrospraying strategy via controlling relative humidity (ratio of practical vapor pressure P 1 and its saturated vapor pressure P s ). The enhanced relative humidity facilitated the dispersion of piperazine (PIP) monomers on substrate and the reaction with trimesoyl chloride (TMC). The membrane (M78) fabricated at high humidity (70%-80%) exhibited more uniform pore size and narrower size region (0.26 nm-0.49 nm) at a designed rejection difference (e.g., 50%) compared with the membrane (0.26 nm-1.0 nm) obtained at low humidity (30%-40%). Membrane selectivity (e.g., Na 2 SO 4 and NaCl) was an order of magnitude high when humidity increased from 30%-40% to 70%-80%. The current study offered a facile and effective strategy for fabricating polyamide nanofiltration membrane with uniform pores and sub-nm selectivity.

How clonal differences and within-tree heterogeneity affect pore properties of hybrid aspen wood and biochar?

Production of applicable and homogeneous biochar for soil amendment purposes would benefit from knowledge on how feedstock heterogeneity impacts key biochar pore properties and how the properties are transformed due to pyrolysis. This study aimed (1) to quantify how clonal differences and within-tree heterogeneity of a hybrid aspen feedstock (wood) impact biochar pore properties and (2) to estimate how pore properties of non-pyrolysed wood materials are transformed when pyrolysed into biochar. The study was conducted by collecting samples from a hybrid aspen (Populus tremula L. × Populus tremuloides Michx.) clonal field trial. Key pore properties of non-pyrolysed and pyrolysed wood samples were quantified with 3D X-ray imaging and quantitative image analyses. The results demonstrated how pyrolysis shifted distinctively bi-modal pore size distributions of the wood samples towards smaller pore size regions. The bi-modal wood tissue structure controlled the pore structure also in the biochars. Due to decreasing cell wall thicknesses, the pyrolysis increased the porosity of the materials. While the thermal process homogenized differences in the wall thicknesses, the thicknesses of the feedstock were also shown to control the resulting thicknesses in the biochars. Mechanisms of biochar pore property formation can be considered important when designing applicable biochars for a chosen purpose. Clonal differences and within-tree heterogeneity had a direct impact only on the wall thicknesses and the pore diameters of vessels. These impacts can be of interest when planning feedstock utilization in biochar production. However, the results suggest that relatively homogeneous biochar can be produced from hybrid aspen feedstocks.

Assessing carbonation in one-part fly ash/slag geopolymer mortar: Change in pore characteristics using the state-of-the-art technique neutron tomography

Carbonation has long been recognised as a durability issue attributed to corrosion of steel reinforcement in geopolymer materials. The currently available information, however, is not sufficient to gain a deep understanding of this issue, particularly the facet of the carbonation impact on the pore structure of such materials. This paper, thus, assessed the influence of carbonation on porosity and pore size characteristics of one-part fly ash/slag geopolymer mortar, by using neutron tomography. The cutting-edge thermal neutron tomography used in this study provided the prowess of non-destructive 3D analysis of exploring different regions within geopolymers. The results obtained showed that carbonation in the investigated geopolymer mortars drew their porosity down approximately 30% and shifted pore size regions to smaller pore areas. Other evaluations such as changing pH, carbonation front depth and elemental mapping by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS) were also performed in this study, in order to supplement the findings of neutron tomography.

Propagation and adsorption of nanoparticles in porous medium as traveling waves

This paper shows that a deposited distribution of nanoparticles transported by a liquid through a porous media is akin to a traveling wave propagating with a shape and velocity depending on the flow rate and the availability of particles with regard to the adsorption capacity. Confinements effects due to smaller pore size regions induce delayed deposition also described by traveling waves

In-situ pore size investigations of loaded porous concrete with non-destructive methods

Subject of this investigation is the in-situ evolution of pore volume and pore size distribution in Ytong (a porous concrete material) under increasing pressure with two different non-destructive analytical methods: Nuclear Magnetic Resonance (NMR) and X-ray Computed Tomography (CT). For both methods special strain devices to apply external pressure were constructed. The results from the two techniques yield complementary information on the pore size distribution and allows covering different pore size regions.

Removal of N-nitrosodimethylamine precursors with powdered activated carbon adsorption

The main objective of this study was to examine the roles of powdered activated carbon (PAC) characteristics (i.e., surface chemistry, pore size distribution, and surface area) in the removal of N-nitrosodimethylamine (NDMA) formation potential (FP) in surface and wastewater-impacted waters. Also, the effects of natural attenuation of NDMA precursors in surface waters, NDMA FP concentration, and carbon dose on the removal of NDMA FP by PAC were evaluated. Finally, the removal of NDMA FP by PAC at two full-scale DWTPs was monitored. Wastewater-impacted and surface water samples were collected to conduct adsorption experiments using different PACs and activated carbon fibers (ACFs) with a wide range of physicochemical characteristics. The removal efficiency of NDMA FP by PAC was significantly higher in wastewater-impacted than surface waters. Adsorbable NDMA precursors showed a size distribution in the waters tested; the adsorbable fraction included precursors accessing the pore size regions of 10–20 Å and <10 Å. Basic carbons showed higher removal of NDMA FP than acidic carbons on a surface area basis. The overall removal of NDMA FP by PAC on a mass basis depended on the surface area, pore size distribution and pHPZC. Thus, PACs with hybrid characteristics (micro and mesoporous), higher surface areas, and basic surface chemistry are more likely to be effective for NDMA precursor control by PAC adsorption. The application of PAC in DWTPs for taste and odor control resulted in an additional 20% removal of NDMA FP for the PAC doses of 7–10 mg/L. The natural attenuation of NDMA precursors through a combination of processes (biodegradation, photolysis and adsorption) decreased their adsorbability and removal by PAC adsorption.

Anodic oxidization of Ti–Ni–Si amorphous alloy ribbons and their capacitive and resistive properties

Amorphous titanium oxide film on Ti–Ni–Si amorphous alloy ribbons was prepared by anodic polarization process in ten kinds of electrolyte solutions. Addition of NH4F in (NH4)2SO4 solution accelerates an increase in current, i.e. formation of soluble Ti-fluoride complexes, resulting in the amorphous titanium oxide layers with nanometer-sized pores. Pore size decreases down to 12nm with decreasing of applied voltage from 30 to 5V. However, parallel capacitance Cp, series capacitance Cs, and RCs constant increase with decrease of pore size from 23 to 18nm and then decrease in pore size region from 18 to 12nm by formation of penetrating tunnels in the layer. It needs further enhancement of RCs for realization of superior electric storage capacitor.

Effect of bore fluid composition on microstructure and performance of a microporous hollow fibre membrane as a cation-exchange substrate

Micro-capillary film (MCF) membranes are effective platforms for bioseparations and viable alternatives to established packed bed and membrane substrates at the analytical and preparative chromatography scales. Single hollow fibre (HF) MCF membranes with varied microstructures were produced in order to evaluate the effect of the bore fluid composition used during hollow fibre extrusion on their structure and performance as cation-exchange adsorbers. Hollow fibres were fabricated from ethylene-vinyl alcohol (EVOH) copolymer through solution extrusion followed by nonsolvent induced phase separation (NIPS) using bore fluids of differing composition (100wt.% N-methyl-2-pyrrolidone (NMP), 100wt.% glycerol, 100wt.% water). All HFs displayed highly microporous and mesoporous microstructures, with distinct regions of pore size <1μm, 5–15μm and up to 50μm in diameter, depending upon proximity to the bore fluid. Scanning electron microscopy (SEM) revealed skins of pore size <1μm at the inner surface of HFs produced with water and glycerol, while NMP bore fluid resulted in a skinless inner HF surface. The HFs were modified for chromatography by functionalising the polymer surface hydroxyl groups with sulphonic acid (SP) groups to produce cation-exchange adsorbers. The maximum binding capacities of the HFs were determined by frontal analysis using lysozyme solutions (0.05–100mgml−1) for a flow rate of 1.0mlmin−1. The NMP–HF–SP module displayed the largest maximum lysozyme binding capacity of all the fibres produced (40.3mg lysozyme/ml adsorbent volume), a nearly 2-fold increase over the glycerol and 10-fold increase over the water variants at the same sample flow rate. The importance of NMP as a bore fluid to hollow fibre membrane performance as a result of inner surface porosity was established with a view to applying this parameter for the optimisation of multi-capillary MCF performance in future studies.

Use of preconditioning to control membrane fouling and enhance performance during ultrafiltration of plasmid DNA

Several recent studies have demonstrated that small pore size ultrafiltration membranes can be used for purification of supercoiled plasmid DNA for therapeutic applications, but the performance of these membrane systems is severely limited by membrane fouling. The objective of this work was to examine the potential of pre-conditioning, in this case accomplished by pre-elongating the DNA by passage through a region with large pore size, to minimize fouling and enhance DNA separations. Data were obtained using both asymmetric hollow fiber membranes, with flow in either the normal or reverse orientation, and with composite membrane structures made by placing a larger pore size flat sheet microfiltration membrane in series with an ultrafiltration membrane. In all cases, flow through the larger pore size region pre-stretched the plasmid, leading to an increase in plasmid transmission and a significant reduction in fouling. This pre-conditioning also provided a significant increase in selectivity for separation of the linear and supercoiled isoforms. These results clearly demonstrate the potential for dramatically increasing the performance of membrane systems for plasmid DNA separations by controlling the pore morphology to pre-stretch the DNA before passing through the narrow pores of an ultrafiltration membrane.

Influence of formulation method and related processes on structural, electrical and electrochemical properties of LMS/NCA-blend electrodes

Abstract The impact of different formulation methods, involving related process technologies, as well as the influence of dispersing intensity on the structural and electrical coating layer properties of LiMn2O4/LiNi0,80Co0,15Al0,05O2 (LMS/NCA) blends are studied. Findings are finally correlated with the electrochemical rate-capability in order to derive process-structure–property functions to facilitate systematical electrode development. LMS was found to be sensitive according mechanical stress but by processing LMS/NCA blend electrodes this problem can be avoided. In general carbon black (CB) agglomerate size and its distribution in the binder network were identified to be significant factors influencing rate-capability. Both were found to influence pore structure by utilizing representative low and high energy methods for the formulation of the suspensions. The specific pore volume in the pore size region of 10 μm ≥ dp ≥ 0.5 μm was discovered to strongly influence rate-capability. These highways for lithium-ion transport allow for higher mass of lithium-ions per unit time penetrating into the inner surface of the coating layer. Specific volume and thus rate-performance can either be increased by a binder solution based formulation method or by decreasing the specific energy input during dispersing process. Hence no superior formulation method exists. The adjustment of mixing intensity and therewith the achieved CB agglomerate size, referring to the formulation method used, is essential. Thus comparable electrochemical rate performance was found for the same specific volume of approximately 0.25 cc g−1 but for different dispersing intensities. Further, the pore size region of 1.5 μm > dp > 0.03 μm was identified to be characteristic for the CB agglomerate size and the corresponding CB treatment method used. Peakedness of the pore size distribution was found to follow electrode conductivity which was the largest for a distributive dry mixing method. For electrodes showing a good CB agglomerate distribution in the binder network rate-capability was found to be limited by the pore structure of the coating layer and, thus, preliminarily by the corresponding ion transport kinetic. Based on the findings a model concept on processes occurring during dispersing was proposed and discussed to describe viscosity evolution over dispersing time.

Surface fractal dimension: An indicator to characterize the microstructure of cement-based porous materials

This study investigates the surface fractal dimensions (SFDs) of pore structure of cement pastes and mortars with/without ground granulated blast-furnace slag (GGBS) incorporated into binder. The samples were subject to water curing and sealed curing. The fractal dimensions of samples are determined by Zhang’s model (Ind Eng Chem Res, 34 (1995):1383–1386) on the basis of mercury intrusion porosimetry (MIP) data. The results confirm the scale-dependent property of fractal dimension of pore structures and the micro-fractal, transition and macro-fractal regions are identified for all samples. The upper pore size range for micro-fractal regions is around 30nm, the transition regions cover 0.5–2 magnitude orders of pore size and macro fractal regions cover 1.5–3 magnitude orders. Both curing conditions and GGBS in binder have impact on the fractal properties of pore structure, and samples incorporating GGBS have substantially larger values for micro-fractal regions.

Visualization of vapor formation regimes during capillary-fed boiling in sintered-powder heat pipe wicks

The current study investigates capillary-fed boiling of water from porous sintered powder wicks used in emerging high-effective-conductivity vapor chamber heat spreaders intended for management of hot spots with heat fluxes exceeding 500Wcm−2. Characterization of 1mm thick wicks composed of 100μm sintered copper particles is performed in a test facility which replicates the capillary feeding conditions that occur in such devices. Boiling curves are obtained for a 5mm×5mm heated input area, along with high-speed in-situ visualization of the evaporation/boiling processes. Understanding the vapor formation regimes is essential to predictive modeling of the observed characteristics. Schematic representations of such regimes along the boiling curves are presented for homogeneous and modified wick structures. In general, incipience of boiling in sintered-powder wicks reduces the effective thermal resistance and, for small heat input areas, does not cause liquid starvation due to a capillary limitation. The thermal performance enhancement provided by two different augmentation methods is quantified and explained in terms of the observed vapor formation characteristics. Patterns fabricated within the sintered powder create multi-scale wicks with regions of different pore size. These patterns reduce thermal resistance throughout the boiling regime by increasing the permeability to vapor exiting the wick, as confirmed by visualization of the preferential vapor venting from the surface. At the highest heat fluxes investigated prior to dryout, a thin liquid film is observed to form in the recessed patterned areas at the base of the wick. Integration of copper-coated carbon nanotubes on to the sintered powder reduces the required superheat for boiling incipience, thus reducing the overall thermal resistance at low heat fluxes. Evaporation and boiling regime heat transfer predictions from several available correlations are compared to the current results, and are shown to corroborate the conclusions regarding vapor permeability.

Screening the attachment and spreading of bone marrow-derived and adipose-derived mesenchymal stem cells on porous silicon gradients

Nanoscale surface topography exerts profound effects on stem cell behaviour. Detailed knowledge of these effects is of key relevance to the development of advanced materials for tissue engineering. In order to gain such knowledge, high-throughput platforms for characterising cell-surface interactions are required. One suitable platform technology involves the use of lateral gradients where a continuous variation in a chemical or physical surface parameter of choice is investigated. Here, we fabricate porous silicon (pSi) gradients displaying pore sizes ranging from approximately 2 μm down to a few nm in diameter, and changing in solid surface fraction from 15% to 95% along the 12 mm length of the gradient. Cell attachment and spreading of primary rat bone marrow-derived mesenchymal stem cells (rBMSCs), human BMSCs (hBMSCs) and primary human adipose-derived mesenchymal stem cells (hASCs) were studied on these gradients. For all three MSC types, spreading was suppressed on the large pore size region of the gradient and spreading increased towards the other end of the gradient. MSC attachment density, on the other hand, was pore size- and cell type-dependent. In contrast to hASCs, the attachment density of rBMSCs and hBMSCs was low on the pSi gradient compared with flat Si. For hASCs, we observed a peak attachment density on the pore size region of 329 ±112 nm. F-actin staining showed clearly that cytoskeleton development was related to both cell spreading and cell type. The result hence showed that the pore size gradient format allows the screening of suitable surface topography parameters for the control of MSC behaviour. We also observed that MSCs derived from different sources respond differently to pore size at the nanoscale, suggesting that intrinsic differences between MSCs affect cell-surface interactions and justifying the need for high-throughput platforms, such as the one developed here.

제올라이트 13X와 실리카-알루미나의 흡착특성 비교

This work is to compare the experiment results by a continuous fixed-bed adsorption of water vapor, acetone vapor, and toluene vapor on zeolite 13X (SAU) and silica-alumina (SAK). SAU and SAK have very different pore structure but similar composition as inorganic adsorbent. The relationship between the equilibrium adsorption capacity and specific pore size range were studied. Adsorption of water vapor was more suitable on SAU than SAK because SAU has relatively more developed pores around 5 Å than SAK in the pore range of 10 ~ 100 Å. Adsorption of acetone vapor was more suitable on SAK than SAU because SAK has relatively more developed pores around 5~10 Å than SAK in the pore range of less than 10 Å. Adsorption of toluene vapor was more suitable on SAK than SAU because SAK has relatively more developed pores in the pore range of 10~100 Å than SAK. Adsorption capacity of the adsorbent was closely related to the surface area generated in the specific pore size region. But it was difficult to distinguish the relationships between adsorption capacity and micro area, and the external surface area of adsorbent.

On the interpretation of 1H 2-dimensional NMR relaxation exchange spectra in cements: Is there exchange between pores with two characteristic sizes or Fe 3+ concentrations?

We discuss the effect of paramagnetic impurity content (thought to be predominantly Fe 3+) in cement pastes on the interpretation of 1H NMR T 2– T 2 exchange spectra. Through measurements on synthesised C–S–H with greatly reduced paramagnetic impurity concentration, we show that the spectra cannot be explained by exchange between regions of different Fe 3+ concentration but rather are explained by exchange between regions of different pore size.

Microporosity of carbon deposits collected in the Tore Supra tokamak probed by nitrogen and carbon dioxide adsorption

Nitrogen and carbon dioxide adsorption experiments have been used to investigate the porosity of carbon deposits formed in the Tore Supra tokamak as a consequence of the erosion of the plasma-facing components. We compare BET, α s-, and Dubinin–Raduskevich methods to distinguish between micropore volume (∼0.04 cm 3 g −1) and external surface (∼90 m 2 g −1). Consistent results have been obtained for nitrogen and carbon dioxide, and the smallest pores are shown to be reversibly closed and opened under air exposure and outgassing at 600 °C, respectively, probably due to blocking of pore entrances by surface oxides. Pore size distribution is calculated using the non-local density functional theory: a novel and straightforward method is used to fit the experimental isotherms by Lorentzian distributions of pores centered in some relevant pore size regions. We thus show that the tokamak sample micropores are mainly ultra-micropores (∼75%) whose widths are centered at 0.6 nm. This latter result is in good qualitative agreement with the outgassing effect and in good quantitative agreement with what is deduced from α s-plot.

Adsorbate layering in narrow-pore materials

The conditions of layering of adsorbate molecules in porous systems with characteristic sizes of from 1 to 50–100 nm are discussed. The porous systems contain both very narrow pores, in which interaction potentials of pore walls overlap, and comparatively broad pores without overlapping of surface potentials. Three pore size intervals are distinguished. In the first interval, no adsorbate layering occurs, the second interval is characterized by capillary condensation with critical parameters different from their volume values, and, in the third interval, capillary condensation conditions are almost the same as in the volume adsorbtive phase. Criteria of the characteristic pore sizes of different geometries are formulated; the criteria correspond to small volumes in which first-order phase transitions are absent. The boundary between the first and second pore size regions is observed experimentally as the disappearance/appearance of hysteresis loops in adsorption-desorption isotherms measured under strictly equilibrium conditions as the size of pores decreases/increases. A nonuniform distribution of the surface potential is shown to be responsible for the multiplicity of local regions in porous media with their own vapor-liquid coexisting phases. The spinodal transitions in adsorption-desorption in pores can occur between various local regions. An analysis is performed in terms of the lattice gas model with short-range Lennard-Jones interaction of adsorbate molecules with each other and adsorbent walls.

Exploring Molecular Sieve Capabilities of Activated Carbon Fibers to Reduce the Impact of NOM Preloading on Trichloroethylene Adsorption

Adsorption of trichloroethylene (TCE) by two activated carbon fibers (ACFs) and two granular activated carbons (GACs) preloaded with hydrophobic and transphilic fractions of natural organic matter (NOM) was examined. ACF10, the most microporous activated carbon used in this study, had over 90% of its pore volume in pores smaller than 10 A. It also had the highest volume in pores 5-8 A, which is the optimum pore size region for TCE adsorption, among the four activated carbons. Adsorption of NOM fractions by ACF10 was, in general, negligible. Therefore, ACF10, functioning as a molecular sieve during preloading, exhibited the least NOM uptake for each fraction, and subsequently the highest TCE adsorption. The other three sorbents had wider pore size distributions, including high volumes in pores larger than 10 A, where NOM molecules can adsorb. As a result, they showed a higher degree of uptake for all NOM fractions, and subsequently lower adsorption capacities for TCE, as compared to ACF10. The results obtained in this study showed that understanding the interplay between the optimum pore size region for the adsorption of target synthetic organic contaminant (SOC) and the pore size region for the adsorption of NOM molecules is important for controlling NOM-SOC competitions. Experiments with different NOM fractions indicated that the degree of NOM loading is important in terms of preloading effects; however the waythatthe carbon pores are filled and loaded by different NOM fractions can be different and may create an additional negative impact on TCE adsorption.