Pore Diameters In Range Research Articles

Controlling Pore Geometries and Interpore Distances of Anodic Aluminum Oxide Templates via Three-Step Anodization.

Porous alumina membranes have attracted much attention because they are very useful templates for the fabrication of various nanostructures important to nanotechnology. However, there are challenges in controlling pore geometries and interpore distances in alumina templates while maintaining highly ordered hexagonal pore structures. Herein, a three-step anodization method is utilized to prepare anodic alumina templates with various pore morphologies (e.g., arched-shape, tree-like, branched-shape) and tunable interpore distances. Such structures are not found within the more traditional alumina templates fabricated by a two-step anodization of aluminum films. The range of interpore distances and pore diameters within the modified templates increases with increasing voltages. In contrast, under decreasing voltages, hexagonally ordered pores can also branch into several pores with smaller sizes and reduced interpore distances. Electrochemical growth of metal nanowires in the modified templates helps to highlight details of the pore structures and which pore channels are active.

Solar water splitting for hydrogen production with Fe2O3 nanotubes prepared by anodizing method: effect of anodizing time on performance of Fe2O3 nanotube arrays

Self-organized iron oxide nanotubes were successfully prepared on the iron foils by a simple electrochemical anodization method in NH4F organic electrolyte. The Fe2O3 nanotubes were characterized by field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, UV–vis absorbance spectra, and X-ray diffraction spectroscopy. Scanning electron microscopy images show that dependent upon the anodizing time, the pore diameters range from 30 to 45 nm. Crystallization and structural retention of the synthesized structure are achieved upon annealing the initial amorphous sample in oxygen atmosphere at 450 °C for 1 h. The crystallized nanoporous film, having a 2.04 eV bandgap, exhibited a maximum photocurrent density of 0.68 mA cm−2 in 1 M NaOH at 0.5 V versus Ag/AgCl. The current potential characteristics showed that the water-splitting photocurrent strongly depends on the anodizing time and its increases with anodization time.

Polarizability anisotropy relaxation in nanoconfinement: molecular simulation study of water in cylindrical silica pores.

We report the results of a molecular simulation study of polarizability anisotropy relaxation for water confined in approximately cylindrical silica pores, with diameters in the range from 20 to 40 Å. In our calculations, we use a polarizability model that includes molecular and interaction-induced components. In agreement with optical Kerr effect experimental data, we find strong confinement effects on the relaxation rate of water polarizability anisotropy. Given that water molecular polarizability anisotropy is small, much of the intensity of the polarizability anisotropy response comes from the interaction-induced component. However, we find that, at longer times, the relaxation properties of this component strongly resemble those of collective reorientation, the mechanism by which the molecular polarizability anisotropy relaxes. We also find that the relevant collective orientational relaxation differs considerably from single molecule reorientation and that this difference varies with the extent of confinement. Our investigation of the effects of axial-radial pore anisotropy indicates that these effects play a minor role in water polarizability anisotropy relaxation in this pore diameter range.

Optimizing the synthesis and properties of Al-modified anatase catalyst supports by statistical experimental design

The important variables in the synthesis of stable, high surface area, aluminum-modified anatase TiO2 catalyst supports were identified and optimized using statistically designed experiments (DOEs). The first DOE examined ten variables at two levels and a second DOE studied eight variables at three levels. Equations were developed to predict the conditions to obtain the highest surface area and pore volume at the desired pore diameter and predict the pore diameter range that may be obtained. Confirmation trials closely matched predicted surface areas, pore volumes, and pore diameters in all but one trial. Rinsing order (before or after calcination) was the most significant factor. Other important factors were calcination temperature, mol% aluminum, and water addition speed. The results of this study demonstrate (a) the power of DOEs in identifying and controlling synthesis variables in relatively few experiments and (b) how analysis of factor effects can provide insight into the formation mechanism.

Porosity and pore size distribution of Ultisols and correlations to soil iron oxides

The pore structure of soils greatly influences soil functions and processes. The Ultisols developed on Quaternary red clay in the subtropical China were collected to characterize the porosity and pore size distribution (PSD). Mercury intrusion porosimetry (MIP) and nitrogen adsorption/desorption (NAD) methods were used to quantitatively describe the PSD of soil in the range of equivalent pore diameter of 100–0.003 and 0.1–0.001μm, respectively. The total MIP porosity of Ultisols ranged from 33.0% to 44.9% with a mean value of 36.5%. The soils exhibited three-modal PSDs with peaks at the pore diameter of about 0.01–0.05μm, 0.1–2μm, and >70μm, indicating the heterogeneous nature of the pore system. The ultramicropores (0.1–5μm) and cryptopores (<0.1μm) were dominant pore classes representing an average of 35% and 30% of total pore fraction, respectively. Among the different land use types, bare land (BL) had significantly higher cryptopore (0.01–0.1μm) volume compared with forest land (FL) and orchard land (OL). Higher volume of cryptopores under BL could be attributed to the higher iron oxide and low organic matter contents. The free iron oxide (Fed) and clay contents were positively and significantly correlated with crytoporosity (<0.1μm) while negatively correlated with ultramicroposity. The pores with 0.001–0.1μm diameter were mainly attributed to the pores associated with the structure of clay and iron oxides. The ultramicroporosity (0.1–5μm) increased with increasing soil aggregation index: mean weight diameter (MWD) and geometric mean diameter (GMD). No significant correlation was observed between soil porosity and soil organic matter and macro-, meso-, and microporosity were independent of soil components. Our data suggest that high Fed and clay contents lead to increase <0.1μm pore volume. The Fed and clay contents played an important role in determining the pore structure of Ultisols.

Pore Size Distribution Patterns in Tropical Soils Obtained by Mercury Intrusion Porosimetry: The Multifractal Approach

Mercury intrusion porosimetry (MIP) is commonly used to determine soil pore size distributions (PSDs) in a wide, but incomplete, range of equivalent pore diameters. Mono‐ and multifractal analyses of soil PSDs are useful for analyzing the soil porous system. The main objective of this work was to characterize PSDs from tropical soils using the multifractal approach. Duplicate PSDs were measured by MIP for 54 horizons collected from 19 soil profiles in Minas Gerais, Brazil. Although 10 of the studied soils were Ferralsols (Oxisols or Latosols), other soil groups such as Nitisols, Acrisols, Alisols, Luvisols, Planosols, Cambisols, Andisols, and Leptosols also were sampled. Different patterns of PSDs were observed, depending on soil type, texture, and weathering intensity. Textural porosity (0.005–0.2 μm) was positively and significantly correlated to clay and Al2O3 contents and soil specific surface area. Comparison of multifractal analysis from Hg intrusion curves and N2 adsorption isotherms (NAIs) showed entropy dimension values and width of the singularity spectra smaller for the former than for the latter. Multifractal analysis of MIPs and NAIs allowed a thorough characterization of the complexity and heterogeneity of the soil pore space at different scales and was useful to provide new insights for portraying the soil pore system.

Growth control of carbon nanotubes using by anodic aluminum oxide nano templates.

Anodic Aluminum Oxide (AAO) template prepared in acid electrolyte possess regular and highly anisotropic porous structure with pore diameter range from five to several hundred nanometers, and with a density of pores ranging from 10(9) to 10(11) cm(-2). AAO can be used as microfilters and templates for the growth of CNTs and metal or semiconductor nanowires. Varying anodizing conditions such as temperature, electrolyte, applied voltage, anodizing and widening time, one can control the diameter, the length, and the density of pores. In this work, we deposited Al thin film by radio frequency magnetron sputtering method to fabricate AAO nano template and synthesized multi-well carbon nanotubes on a glass substrate by microwave plasma-enhanced chemical vapor deposition (MPECVD). AAO nano-porous templates with various pore sizes and depths were introduced to control the dimension and density of CNT arrays. The AAO nano template was synthesize on glass by two-step anodization technique. The average diameter and interpore distance of AAO nano template are about 65 nm and 82 nm. The pore density and AAO nano template thickness are about 2.1 x 10(10) pores/cm2 and 1 microm, respectively. Aligned CNTs on the AAO nano template were synthesized by MPECVD at 650 degrees C with the Ni catalyst layer. The length and diameter of CNTs were grown 2 microm and 50 nm, respectively.

Direct Coal Liquefaction: Low Temperature Dissolution Process

The front-end design of a direct coal liquefaction process for the conversion of lignite into coal liquids by solvent extraction was investigated. The experimental work focused on physical coal dissolution in the temperature range 25–150 °C. It was found that the kinetics of physical coal dissolution was rapid and essentially complete within 2 min at 25 °C. There was a limiting extract yield, which increased with increasing temperature. Within the pore diameter range 0.1–10.7 μm, the volume of only pores with diameters <5 μm increased measurably on solvent extraction, while the shape of the pore size distribution remained the same. Additional pore volume created during extraction exceeded that of the liquid extract. Extraction took place from the bulk of the coal. Packed bed extraction was more efficient than batch extraction at otherwise similar conditions; an explanation was proposed. Even at the least severe conditions, 25 °C for 2 min, mass transport was not limiting and the solvent-to-coal ratio did ...

Variation of the crystal growth of mesoporous silica nanoparticles and the evaluation to ibuprofen loading and release

Mesoporous silica nanoparticles (MSNs) were synthesized with variable microwave power in the range of 100–450W, and the resulting enhancement of MSN crystal growth was evaluated for the adsorption and release of ibuprofen. X-ray diffraction (XRD) revealed that the MSN prepared under the highest microwave power (MSN450) produced the most crystallized and prominent mesoporous structure. Enhancement of the crystal growth improved the hexagonal order and range of silica, which led to greater surface area, pore width and pore volume. MSN450exhibited higher ibuprofen adsorption (98.3mg/g), followed by MSN300(81.3mg/g) and MSN100(74.1mg/g), confirming that more crystallized MSN demonstrated higher adsorptivity toward ibuprofen. Significantly, MSN450 also contained more hydroxyl groups that provided more adsorption sites. In addition, MSN450 exhibited comparable ibuprofen adsorption with conventionally synthesized MSN, indicating the potential of microwave treatment in the synthesis of related porous materials. In vitrodrug release was also investigated with simulated biological fluids and the kinetics was studied under different pH conditions. MSN450showed the slowest release rate of ibuprofen, followed by MSN300 and MSN100. This was due to the wide pore diameter and longer range of silica order of the MSN450. Ibuprofen release from MSN450 at pH 5 and 7 was found to obey a zero-order kinetic model, while release at pH 2 followed the Kosmeyer–Peppas model.

High-performance anode based on porous Co3O4 nanodiscs

In this article, two-dimensional, Co3O4 hexagonal nanodiscs are prepared using a hydrothermal method without surfactants. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been employed to characterize the structural properties. As revealed by the SEM and TEM experiments, the thickness of our as-fabricated Co3O4 hexagonal nanodiscs is about 20 nm, and the pore diameters range from several nanometers to 30 nm. As an anode for lithium-ion batteries, porous Co3O4 nanodiscs exhibit an average discharge voltage of ∼1 V (vs. Li/Li+) and a high specific charge capacity of 1161 mAh g−1 after 100 cycles. They also demonstrate excellent rate performance and high Columbic efficiency at various rates. These results indicate that porous Co3O4 nanodiscs are good candidates as anode materials for lithium-ion batteries.

Short synthesis of ordered silicas with very large mesopores

SBA-15 silicas with cylindrical mesopores of diameter from 10 to ∼30 nm were synthesized within hours (2.5–7.5 hours) instead of one or more days required in hitherto reported syntheses of large-pore SBA-15 with (100) interplanar spacing above 13 nm. The synthesis was carried out using Pluronic P123 surfactant, 1,3,5-triisopropylbenzene swelling agent and silica hydrolysis/condensation catalyst, NH4F, under low-temperature initial synthesis conditions (12–17 °C) similar to those used in our earlier report on the synthesis of SBA-15 with a wide range of pore diameters (10–26 nm). Herein, it is shown that the low temperature step at which the ordered material forms can be shortened to one hour and the mesoporous material can be recovered at this stage. However, the attainment of a larger pore size and/or better structural ordering requires a hydrothermal treatment, which can be as short as 1–6 hours, if appropriately high temperature (150–170 °C) is selected. Additionally, improved synthesis conditions are reported for ultra-large-pore SBA-15 with (100) interplanar spacing of 25–30 nm. Standard SBA-15 synthesis without a swelling agent was also streamlined. Moreover, the synthesis of large-pore FDU-12 silica with face-centered cubic structure of spherical mesopores using Pluronic F127 surfactant and 1,3,5-trimethylbenzene swelling agent can be shortened to ∼9 hours. The streamlined synthesis procedures can be followed by surfactant removal via calcination with high ramping rate and short dwell time. The synthesis approach based on a short self-assembly step and short high-temperature hydrothermal treatment provides a convenient way to produce large-pore ordered mesoporous silicas suitable for numerous applications.

Pore Geometry Optimization of Titanium (Ti6Al4V) Alloy, for Its Application in the Fabrication of Customized Hip Implants.

The present study investigates the mechanical response of representative volume elements of porous Ti-6Al-4V alloy, to arrive at a desired range of pore geometries that would optimize the reduction in stiffness necessary for biocompatibility with the stress concentration arising around the pore periphery, under physiological loading conditions with respect to orthopedic hip implants. A comparative study of the two is performed with the aid of a newly defined optimizing parameter called pore efficiency that takes into consideration both the stiffness quantity and the stress localization around pores. To perform a detailed analysis of the response of the porous structure over the entire spectrum of loading conditions that a hip implant is subjected to in vivo, the mechanical responses of 3D finite element models of cubic and rectangular parallelepiped geometries, with porosities varying over a range of 10% to 60%, are simulated under representative compressive, flexural as well as combined loading conditions. The results that are obtained are used to suggest a range of pore diameters that lower the effective stiffness and modulus of the implant to around 60% of the stiffness and modulus of dense solid implants while keeping the stress levels within permissible limits.

On the electrochemical activation of alkali-treated soft carbon for advanced electrochemical capacitors

The electrochemical activation process of the so-called “alkali-treated soft carbon” (ASC) has been examined in organic electrolyte solutions. SEM observation demonstrated that the edge plane of graphene structure of the ASC particle becomes rough after the activation, and XRD measurements indicated that the average lattice constant of graphene stacking in ASC increases after the activation process. Ex-situ 7Li NMR measurements proved that the insertion of cation (Li+) into the pore structure of ASC is associated with the activation process in the electrolyte dissolving Li salt. The pore-size distribution determined from N2-gas adsorption for ASC electrodes before and after the electrochemical activation indicates that the pore structure becomes developed after the electrochemical polarization, especially in the pore-diameter range of 2–10 nm. A schematic model of the activation process has been presented, which includes electrochemical insertion of ions into the inside of the ASC.

Nanopore formation on the surface oxide of commercially pure titanium grade 4 using a pulsed anodization method in sulfuric acid

Titanium and its alloys form a thin amorphous protective surface oxide when exposed to an oxygen environment. The properties of this oxide layer are thought to be responsible for titanium and its alloys biocompatibility, chemical inertness, and corrosion resistance. Surface oxide crystallinity and pore size are regarded to be two of the more important properties in establishing successful osseointegration. Anodization is an electrochemical method of surface modification used for colorization marking and improved bioactivity on orthopedic and dental titanium implants. Research on titanium anodization using sulphuric acid has been reported in the literature as being primarily conducted in molarity levels 3 M and less using either galvanostatic or potentiostatic methods. A wide range of pore diameters ranging from a few nanometers up to 10 μm have been shown to form in sulfuric acid electrolytes using the potentiostatic and galvanostatic methods. Nano sized pores have been shown to be beneficial for bone cell attachment and proliferation. The purpose of the present research was to investigate oxide crystallinity and pore formation during titanium anodization using a pulsed DC waveform in a series of sulfuric acid electrolytes ranging from 0.5 to 12 M. Anodizing titanium in increasing sulfuric acid molarities showed a trend of increasing transformations of the amorphous natural forming oxide to the crystalline phases of anatase and rutile. The pulsed DC waveform was shown to produce pores with a size range from ≤0.01 to 1 μm(2). The pore size distributions produced may be beneficial for bone cell attachment and proliferation.

Effect of pore size on the performance of immobilised enzymes

Porous materials are widely employed as supports in the immobilisation of enzymes. Traditionally macroporous materials with pore diameters >50 nm were believed to be the most suitable support material, ensuring no spatial restrictions upon enzyme molecules entering such large pores. In recent years however, there has been growing emphasis in the use of mesoporous supports with pore diameters ranging between 2 and 50 nm. It is thought this smaller pore range may offer enhanced conformational stability to immobilised enzymes while not being so small as to restrict enzyme access. Despite their increasing popularity, many argue that mesoporous materials have not yet proven superior to traditional macroporous supports for enzyme immobilisation. Through the design and application of a unique confidence rating system we were able to accurately compare data and establish trends between pore characteristics and protein loading. By analysing published data (182 experiments in total) and extracting pore characteristics and protein loading values, we have described three categories of pore diameters in which correlations between pore characteristics and protein loading are noted. With pore diameters less than 10 nm we see a general decrease in protein loading as the enzymes find physical restrictions in accessing the high surface offered in this pore diameter range. At pore sizes greater than 100 nm, protein loading generally decreases due to a concomitant reduction in available surface area. In the pore range of 10-100 nm there it is expected to see a decrease in protein loading level with increasing pore diameter. In fact protein loading in this range remains largely constant, suggesting some degree of protein-protein interaction blocking pores and restricting access to the increasing surface area available at decreasing pore diameters. No trends were established between pore characteristics and retention of activity.

Wetting behaviour of hydrophilic and hydrophobic nanostructured porous anodic alumina

This paper investigates the effect of surface structure and chemistry on the wetting properties of nanostructured porous anodic alumina (PAA). Measurements of the equilibrium apparent contact angle (APCA) were first taken on as produced hydrophilic nanoporous alumina with a range of pore diameters from 10 to 170nm, yielding a range of contact angles from 10 to 100°. The PAAs were then coated with a fluorosilane to change the surface chemistry of the nanostructures. The same trend was observed as in the hydrophilic case, but the contact angles increased from 106 to 150° for pores sizes ranging from 10 to 100nm for the hydrophobic PAA. These results probe the limits of the current wetting models such as the Cassie-Baxter and Wenzel equations for nanostructured materials. A geometric model has been developed using the equation proposed by Marmur to explain the wetting properties of the bare- and silanized-PAA.

Facile solvent-deficient synthesis of mesoporous γ-alumina with controlled pore structures

We report a simple, one-pot, solvent-deficient process using different aluminum salts to synthesize mesoporous γ-alumina without external templates or surfactants. Samples prepared from aluminum inorganic salts have a close-packed morphology, where randomly stacked fibrous crystallites of γ-alumina are obtained when utilizing aluminum alkoxides. After calcination at 700°C for 2h, surface areas of these nanostructured γ-aluminas range from 210 to 320m2/g. The average pore diameters range from 6 to 18nm, the crystallite diameters range from 3 to 4nm, and pore volumes range from 0.4 to 1.7cm3/g. This synthetic method provides a facile route to synthesize stable, high surface-area mesoporous aluminas having a wide range of pore sizes and volumes.

Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

We present molecular dynamics (MD) simulations of water-filled silica nanopores such as those that occur in ordered oxide ceramics (MCM-41, SBA-15), controlled pore glasses (such as Vycor glass), mesoporous silica, bioglasses, and hydrous silica gel coatings of weathered minerals and glasses. Our simulations overlap the range of pore diameters (1–4 nm) where confinement causes the disappearance of bulk-liquid-like water. In ≥2 nm diameter pores, the silica surface carries three statistical monolayers of density-layered water, interfacial water structure is independent of confinement or surface curvature, and bulk-liquid-like water exists at the center of the pore (this last finding contradicts assumptions used in most previous neutron diffraction studies and in several MD simulation studies of silica nanopores). In 1 nm diameter pores, bulk-liquid-like water does not exist and the structural properties of interfacial water are influenced by confinement. Predicted water diffusion coefficients in 1–4 nm diameter pores agree with quasi-elastic neutron scattering (QENS) data and are roughly consistent with a very simple “core–shell” conceptual model whereupon the first statistical water monolayer is immobile and the rest of the pore water diffuses as rapidly as bulk liquid water.

Silica microparticles as a solid support for gadolinium phosphonate magnetic resonance imaging contrast agents.

Particle-based magnetic resonance imaging (MRI) contrast agents have been the focus of recent studies, primarily due to the possibility of preparing multimodal particles capable of simultaneously targeting, imaging, and treating specific biological tissues in vivo. In addition, particle-based MRI contrast agents often have greater sensitivity than commercially available, soluble agents due to decreased molecular tumbling rates following surface immobilization, leading to increased relaxivities. Mesoporous silica particles are particularly attractive substrates due to their large internal surface areas. In this study, we immobilized a unique phosphonate-containing ligand onto mesoporous silica particles with a range of pore diameters, pore volumes, and surface areas, and Gd(III) ions were then chelated to the particles. Per-Gd(III) ionic relaxivities ranged from ∼2 to 10 mM(-1) s(-1) (37 °C, 60 MHz), compared to 3.0-3.5 mM(-1) s(-1) for commercial agents. The large surface areas allowed many Gd(III) ions to be chelated, leading to per-particle relaxivities of 3.3 × 10(7) mM(-1) s(-1), which is the largest value measured for a biologically suitable particle.

ACOUSTICALLY ASSESSED INFLUENCE OF AIR PORE STRUCTURE ON FAILURE OF SELF-COMPACTING CONCRETES UNDER COMPRESSION / AKUSTIŠKAI ĮVERTINTA ORO PORŲ STRUKTŪROS ĮTAKA SUSITANKINANČIO BETONO SUSILPNĖJIMUI VEIKIANT GNIUŽDYMUI

The paper presents the results of investigations into the influence of pore structure on the failure of self-compacting concretes modified with superplasticizers commonly used in construction. Pore structure examinations were carried out in practically the whole range of pore diameters by means of an image analyzer and a mercury porosimeter. The failure of the self-compacting concretes under compression, was investigated by the acoustic emission technique and other methods. The levels of cracking initiating stress σiand critical stress σcr, demarcating the different stages in the failure process, were determined. It has been shown that there is a relationship between the pore structure parameters and the levels. The fatigue strength of the self-compacting concretes was calculated from the experimental results and on this basis the suitability of the concretes for structures subject to cyclic loads was determined. Santrauka Straipsnyje pateikiami porų struktūros įtakos susitankinančio betono su superplastikliais susilpnėjimui tyrimų rezultatai. Buvo atlikti praktiškai visų skersmenų porų struktūros tyrimai naudojant vaizdo analizatorių ir gyvsidabrio porosimetrą. Susitankinančio betono susilpnėjimas esant gniuždymui buvo tiriamas akustinės emisijos ir kitais metodais. Nustatyti pleišėjimo lygiai ir įtampos, žymintys skirtingus susilpnėjimo lygius. Parodyta, kad yra ryšys tarp porų struktūros parametrų ir susilpnėjimo lygių. Pagal eksperimentinius rezultatus suskaičiuotas betono atsparumas ir nustatytas betono tinkamumas konstrukcijoms, atsižvelgiant į ciklines apkrovas.