Probable Pore Size Research Articles

Removing Nano Particles by Filtration Using Materials with Ordered Mesoporous Structure

The usage of porous materials to remove Nano Particles (Nanoparticles, NPs) is one of the critical ways to purify the air. The present study employed three typical mesoporous structures, CMK-3, SBA-15 and MCM-41 to conduct removal experiments, in which NPs were generated, ranging from 2 nm to 20 nm, aiming at exploring the practical feasibility and relative theory foundation about the filtration of mesoporous structures towards NPs. Based on the physical and chemical characterization of the three mesoporous structures above, coupled with the adsorption experiments, the results acquired indicated that the most probable pore size of mesoporous structures coupled with certain mesoporous capacity of a mesoporous structure are the key to remove NPs. However, the distribution of micropore contributed hardly to the removal of NPs. Based on this, exploration was made to observe the effect that different flow rates and thicknesses had on the efficiency of NPs removal. The consequences showed that most penetrating particle size (MPPS) of NPs decreased with the increase of flow rates. Meanwhile, the corresponding removal efficiency of MPPS decreased. Furthermore, MPPS did not change with the change of thicknesses. This study provided technical evidence for the removal of NPs on mesoporous structures.

Chloride Distribution Feature in Surface Layer of Cement Paste under Cyclic Drying-Wetting Condition

This research focuses on chloride distribution in the surface layer of cement paste and the relation between chloride distribution and pore structure under two different drying-wetting regimes. The results of chloride profiles obtained by three different methods reveal that it dose exist a feature that chloride content first gose up then down with a maximum value Cmaxappearing in the homogeneous surface layer of cement paste subjected to indoor cyclic dry-wet condition. Besides, the Cmaxincreases with the ratio of water to cement (W/C) increasing. And the regime with higher drying temperature and longer wetting time leads to higher Cmax. Moreover, Cmaxappears at the same location for both total and free chloride. In addition, Cmaxincreases with total porosity, the most probable pore size, and average radius increasing, while it decreases with tortuosity decreasing.

Characteristics of a sintered porous Ni–Cu alloy cathode for hydrogen production in a potassium hydroxide solution

A porous Ni–Cu alloy with a most probable pore size of 2.4 μm and an open porosity over 31.5% was synthesized by step sintering pressed compacts consisted of mixed Ni and Cu powders in a vacuum furnace. The electrocatalytic activity and stability of the fabricated porous Ni–Cu alloy as cathode for the HER (hydrogen evolution reaction) in 6.0 mol/L potassium hydroxide solution were investigated by cathodic current–potential curves, CV (cyclic voltammetry) and EIS (electrochemical impedance spectroscopy) techniques. Results show that the onset potential of the porous Ni–Cu for HER greatly shifts to the positive direction compared with the dense Ni and dense Ni–Cu alloy. The electrochemical activation energy is determined to be 26.7 kJ mol−1 for the porous Ni–Cu alloy, against 44.1 kJ mol−1 and 32.6 kJ mol−1 for the dense Ni and dense Ni–Cu alloy, respectively. The increased activity of the porous Ni–Cu alloy for HER is related to the micro-porous structure as well as synergistic interaction of Ni and Cu. Besides, the fabricated porous Ni–Cu alloy displays good corrosion resistance in potassium hydroxide solution during the immersion test, which makes it possible for long-time running as cathode in the process of hydrogen evolution reaction.

A new evolution model of concrete porosity under continuous hydration

Pore structure is an important micro-structure of concrete. The mechanical properties, such as strength, stiffness, as well as durability, significantly depend on the pore structure. In this study, evolution of pore structure of concrete after curing for 28 days was analysed by the mercury PoreMaster experimental method. The test was performed for 209 days. Variation in mass of concrete was detected by weight method. The results revealed that the average pore diameter, most probable pore size, the total pore volume, and porosity decrease while mass increases in the continuous hydration process. According to chemical reaction of cement hydration, as well as related reaction rate, the differential equations on the evolution of mass and porosity were derived, and a new evolution model of porosity was then suggested.

Template-Engaged In Situ Synthesis of Carbon-Doped Monoclinic Mesoporous BiVO4: Photocatalytic Treatment of Rhodamine B

In this paper, carbon-doped monoclinic scheelite mesoporous bismuth vanadate was synthesized through template-engaged in situ method. The bismuth nitrate pentahydrate and ammonia metavanadate were used as bismuth and vanadium precursors, respectively, glucose as carbon source, and mesoporous SiO2 aerogel as a hard template. Carbon-doped monoclinic mesoporous BiVO4 were obtained by heat treatment of BiVO4/glucose/template to carbonize glucose and form monoclinic crystal, followed by etching with NaOH solution to remove the SiO2 template. The samples were characterized by x-ray diffraction, N2 adsorption and desorption, UV-visible spectroscopy, Energy dispersive spectrometry, Raman spectroscopy, and Transmission electron microscopy. It was found that the sample with a carbon content of 0.5 wt.% possesses a specific surface area of 10.2 m2/g and has mesoporous structure with the most probable pore size of 13.9 nm. The band gap of carbon-doped monoclinic mesoporous BiVO4 was estimated to be 2.33 eV, indicating the superior photocatalytic activity under visible light. The photocatalytic efficiency of carbon-doped monoclinic mesoporous BiVO4 for the degradation of Rhodamine B under visible light (λ > 400 nm) in 120 min reaches 98.7%, Besides, the carbon-doped monoclinic mesoporous BiVO4 photocatalyst still showed high stability: 85% for Rhodamine B degradation after ten recycles.

Influences of nano-TiO2 on the properties of cement-based materials: Hydration and drying shrinkage

To better understand the influences of nano-TiO2 on the properties of cement-based materials, the hydration process, the compressive strength development, and the drying shrinkage of cement-based materials with the addition of nano-TiO2 of 25nm were investigated. Results showed that nano-TiO2 increased the compressive strength of cement mortar through its acceleration on cement hydration and the pore-refining effect: 5wt.% nano-TiO2 accelerated cement hydration process for 2h and reduced the most probable pore size by 19.4%, 48.5%, and 54.4%, respectively. In addition, the influences of the hydrophilicity of nano-TiO2 on the water loss and volume stability of hardened cement pastes were primarily investigated and discussed in this work. For a comparison study, nano-SiO2 of 30nm size was also used. Results showed that the decline of the contact angle and the refining of pore structure with the addition of nano-TiO2 slowed down the water loss of hardened cement paste, which resulted in a comparable drying shrinkage to that of the control sample at 1month age.

Effects of organic templates on the structural properties of porous clay heterostructures: a non-micellar template model for porous structure

In this study, a series of surfactants with different chain lengths were used to investigate the effect of organic templates on the structural properties of porous clay heterostructures (PCH). The variation tendencies of structural properties and chemical component were characterized by X-ray diffraction, CHN elemental analysis, major element analysis, and nitrogen adsorption/desorption at −196 °C. Non-local density functional theory was employed to characterize pore size distributions in both micropore and mesopore regions owing to the bi-model pore structures of PCH. The major textural parameters of PCH samples increased with increasing the chain length and the intercalated amount of template agent, while the most probable pore size remained unchanged around 1.3–1.4 nm. Based on the structural and chemical component results of PCH, a non-micellar template model was presented to explain the formation mechanism of porous structure. By the extrusion and occupation of polymerizate of TEOS within interlayer, a fixed number of hydrocarbon chains congregate together to form surfactant aggregates (template). The aggregates with different chain lengths cause the increase of pore volume in depth dimension rather than in diameter. The obtained results also shed some light on the different roles of inorganic base clay and organic template agents in the formation of porous structure. Montmorillonite as the inorganic host supplies the space for pillaring reaction and controls the arrangement of template agent within interlayer. As the template agent and modifying agent, the cationic surfactant is the dominant factor in forming pores relative to amine. The neutral amine mainly serves as catalyst for the polymerization of TEOS besides its co-template effect.

Modified precipitation processes and optimized copper content of CuO–CeO2 catalysts for water–gas shift reaction

The precipitation processes of CuO–CeO2 catalysts preparation were modified, and their optimized copper content were also studied in detail. As indicated by the experimental results, the WGS catalytic activities of the CuO–CeO2 catalysts can be ranked as: stepwise precipitation (SP) > deposition–precipitation (DP) > co-precipitation (CP), suggesting that stepwise precipitation (i.e., a modified DP) is a convenient and effective method to prepare CuO–CeO2 WGS catalysts. The optimized copper contents of CuO–CeO2–SP and CuO–CeO2–CP catalysts are 20 wt.% and 25 wt.%, respectively. Their catalytic activities can be strongly correlated with the results from XRD, XPS, Raman, N2-physisorption, N2O chemisorption and H2-TPR. For DP and SP, a certain amount of copper has substitutively incorporated into ceria lattice with multiple Ce3+ and oxygen vacancies, which is considered as one relatively strong interaction between copper and ceria support. The substitutional incorporation of copper creates larger lattice distortion, lattice defect (embodying as larger lattice cell contraction of CeO2, microstrain and Raman shift) and stronger reducibility (i.e., lower reduction temperature of H2-TPR), as a consequence, higher surface energy and catalytic activity for WGS reaction. While for CP, copper nitrate and cerium nitrate were simultaneously precipitated, resulting in the burial of many copper species in ceria supports, i.e., occupancy incorporation of isolated copper into ceria lattice vacant site, which is considered as another weak interaction between copper and ceria support. Accordingly, combined with N2O chemisorption results, it is demonstrated that surface copper species of CuO–CeO2–CP are fewer and less active than those of CuO–CeO2–DP and CuO–CeO2–SP. Lastly, there is a direct relationship between the pore volume along with most probable pore size of the as-synthesized catalysts and their corresponding catalytic activities for WGS reaction.

Characterization of Pore Structure of Hardened Cement-Asphalt Paste by Mercury Intrusion Porosimetry

To know the pore structure of cement-asphalt pastes, mercury intrusion porosimetry was applied to measure the total porosity, pore distribution and accumulative volume distribution of pore size and the pore structures were analyzed. The results show that the total porosities decline with increase in ages and reduction in A/C ratio. The total porosities declines from 28% at 1d, to 15.8%~17.2% at 28d; the most probable pore size declines from 20nm at 1d to 5nm at 28d.At 28d, there is an increase in the magnitude of pore size between100nm and 5μm; the volume faction of smaller than 5μm is 40~50%; and the amount of pore size smaller than 5nm account for 6%.There are two peaks (5μm & 50μm) in the curves of pore distribution.

Investigation of Pore Structure for Manufactured Sand Mortar

This paper focuses on the pore structure parameters of mortars produced with manufactured sand and natural sand via water saturation and MIP methods. Test results show that, total porosity, as well as compressive strength, of manufactured sand mortar, is higher than that of natural sand mortar at fixed w/c and s/c ratio. Furthermore, considerable volume of large pores present in specimens of manufactured sand at higher w/c ratio rather not at the lower w/c ratio, which caused by the larger binder-aggregate interface. Manufactured fine aggregate in mortar probably accelerate hydrated reaction of cement, which result in the most probable pore size is finer than that of natural sand mortar. It can be concluded that the threshold region becomes flatten and threshold radius increases due to the aggregate volume concentration rises. Finally, a new theoretical model with a double-lognormal distribution function is demonstrated to be reasonable to fit pore size distribution in mortars.

Influence of pore structure on compressive strength of cement mortar.

This paper describes an experimental investigation into the pore structure of cement mortar using mercury porosimeter. Ordinary Portland cement, manufactured sand, and natural sand were used. The porosity of the manufactured sand mortar is higher than that of natural sand at the same mix proportion; on the contrary, the probable pore size and threshold radius of manufactured sand mortar are finer. Besides, the probable pore size and threshold radius increased with increasing water to cement ratio and sand to cement ratio. In addition, the existing models of pore size distribution of cement-based materials have been reviewed and compared with test results in this paper. Finally, the extended Bhattacharjee model was built to examine the relationship between compressive strength and pore structure.

An investigation on micro pore structures and the vapor pressure mechanism of explosive spalling of RPC exposed to high temperature

Reactive powder concrete (RPC) is vulnerable to explosive spalling when exposed to high temperature. The characteristics of micro pore structure and vapor pressure of RPC are closely related to the thermal spalling. Applying mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) techniques, the authors probed the characteristics of micro pore structures of plain RPC200 when heated from 20–350°C. The pore characteristics such as specific pore volume, threshold pore size and most probable pore size varying with temperatures were investigated. A vapor pressure kit was developed to measure the vapor pressure and its variation inside RPC200 at various temperatures. A thin-wall spherical pore model was proposed to analyze the thermo-mechanical mechanism of spalling, by which the stresses varying with the vapor pressure q(T) and the characteristic size of wall (K) at any point of interest were determined. It is shown that the pore characteristics including specific pore volume, average pore size, threshold pore size and most probable pore size rise significantly with the increasing temperature. 200°C appears to be the threshold temperature above which the threshold pore size and the most probable pore size climb up dramatically. The increase in the specific pore volume results from the growth both in quantity and in volume of the transition pores and the capillary pores. The appearance of the explosive spalling in RPC200 is mainly attributed to being unable to form pathways in favor of releasing water steam in RPC and to the rapid accumulation of high vapor pressures as well. The thin-wall sphere domain where the vapor pressure governs the spalling is bounded through the pore model.

Research on chloride ion diffusivity of concrete subjected to CO2environment

Carbonation is a widespread degradation of concrete and may be coupled with more severe degradations. An experimental investigation was carried out to study the effect of carbonation on chloride ion diffusion of concrete. The characteristic of concrete after carbonation was measured, such as carbonation depth, strength and pore structure. Results indicated that carbonation depth has a good linear relation with square root of carbonate time, and carbonation can improve compressive strength, but lower flexural strength. Results about pore structure of concrete before and after carbonation have shown that carbonation could cause a redistribution of the pore sizes and increase the proportion of small pores. It also can decrease porosities, most probable pore size and average pore diameters. Chloride ion diffusion of concrete after carbonation was studied through natural diffusion method and steady state migration testing method respectively. It is supposed that the chloride ion concentration of carbonation region is higher than that of the sound region because of the separation of fixed salts, and chloride ion diffusion coefficient was increased due to carbonation action evidently.

Synthesis and Electrochemical Performance of Mesoporous Carbon Foams by Microemulsion Method

In this paper, we demonstrated the preparation and electrochemical performance of mesoporous carbon foams as electrode materials for ultracapacitors. By using n-octane as oil phase, cetyltrimethylammonium bromide (CTAB) and butanol as emulsifiers, resorcinol and formaldehyde dissolved in water as the aqueous phase, an O/W microemulsion system was obtained. Mesoporous carbon foams (MCFs) were prepared by the polymerization of the O/W microemulsion, followed by drying and carbonization and subsequently activation at 1273 K by KOH under nitrogen atmosphere. The mesoporous carbon foams were characterized by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analyzer. The results show that MCFs have specific surface area of 666.7 m2/g, total pore volume of 0.36 cm3/g and the most probable pore size of 4 nm. The electrochemical properties of the resultant mesoporous carbon foams have been investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge with a three-electrode system in electrolyte of 6 mol/L KOH solution. The CV curves show quite rectangular shape under the scan rate of 5-20 mV/s, suggesting a typical nonfaradic adsorption/desorption reaction. The mesoporous carbon foams possess linear galvanostatic discharge curves under the current densities of 10-50 mA/cm2 and corresponding specific capacitance values are 132.6-172.1 F/g. Thus the MCFs have good electrochemical performance and they provide an important candidate for electrode materials used in ultracapacitors.

Double Templating Synthesis and Electrochemical Properties of Carbon Foams

In this paper, we demonstrated the synthesis and electrochemical properties of carbon foams for use as supercapacitor electrode materials. Carbon foams were prepared by double templating method in which emulsion and nanosilica were used as soft template and hard template, respectively. By using Span 80 and Tween 80 as emulsifiers, resorcinol/formaldehyde aqueous solution which contained nanosilica as aqueous phase and 1iquid paraffin as oil phase, an O/W emulsion was obtained. Carbon foams were obtained by emulsion polymerization, carbonization and the subsequent removal of the hard template. The as-prepared carbon foams were characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analyzer, and electrochemical workstation. The results indicate that the resultant carbon foams have specific surface area of 160 m2/g, total pore volume of 0.15 cm3/g and possess dual pore size distributions with macropore sizes of 0.5-2.0 μm and the most probable pore size of 4.1 nm. The electrochemical properties of the carbon foams have been investigated by cyclic voltammetry (CV) and galvanostatic charge- discharge with a three-electrode system in electrolyte of 6 mol/L KOH solution. The CV curves of the carbon foams show rectangular-like shape without obvious oxidation-reduction evolution peak, which suggests a typical nonfaradic adsorption/desorption reaction. The carbon foams present linear galvanostatic charge-discharge curve under the current densities of 1.0-5.0 A/g and their specific capacitance values are 60-90 F/g. The good electrochemical performances of carbon foams would provide candidate as electrode materials for supercapacitors.

Fe-doped TiO<sub>2</sub>/SiO<sub>2</sub> Aerogel Microspheres for Visible Light Photocatalysis Degradation of Methylene Blue

In this paper, we present a strategy for the preparation of Fe-doped TiO2/SiO2 aerogel microspheres (Fe-TSAMs) for visible light photocatalysis degradation of methylene blue. A water- in-oil (W/O) emulsion of Span 80–Tween 85/n-heptane–n-butanol/FeCl3-doped TiO2/SiO2 alcoholic sols–formamide was obtained. Wet TiO2/SiO2 gel microspheres were prepared by the sol-gel process in the W/O emulsion, then they were dried at ambient pressure condition to prepare Fe-TSAMs. The Fe-TSAMs were characterized by N2 adsorption and desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the resultant Fe-TSAMs possess nanoporous network structure comprising TiO2 and SiO2 nanoparticles with diameters of 10-20 nm. The Fe-TSAMs have a mean diameter of about 100 μm, an apparent density of 0.26 g/cm3, a specific surface area of 360 m2/g, a pore volume of 1.77 cm3/g and the most probable pore size of 18.7 nm with the porosity of 87.7%. By using methylene blue as a simulated aqueous pollutant, the visible light photocatalysis properties of the Fe-TSAMs were investigated. The results indicate that low concentration Fe ion doping (5 wt%) could avoid the formation of recombination centers for photo-generated electron/hole pairs. Compared with commercial P25 TiO2 powders, Fe-TSAMs exhibit excellent photocatalytic ability for degradation of methylene blue under visible light region. The Fe-TSAMs could be reclaimed conveniently and the reused Fe-TSAMs also have a good photocatalytic activity.

Study on Porous Structure and Surface Characteristics of Al-Pillared Montmorillonite

Al-pillared montmorillonite (Al-PILM) prepared with Keggin ions was studied by means of XRD, SEM-EDS and N2 adsorption-desorption isotherms.The rusults show that, compared to unpillared Na-montmorillonite (Na-M), the interlayer spacing d(001) value, BET specific surface area, surface fractal dimension and the proportion of microporous specific surface area of Al-PILM are larger and the surface is relatively rough. The BJH porous volume distribution of Al-PILM is the most probable distribution, and the most probable pore size is about 2 nm, belonging to mesopore. The porous structure of Al-PILM is characterized as parallel plate slit or “house-of-cards” wedge-shaped pore which is formed by novel meso-microporous delaminated structure and fragments. Besides, the results of elemental distribution show that the ions exchange action between Na+ and hydroxy-Al cations in pillaring solution occurs in the formation of Al-PILM.

Study on Microstructure Variation Laws of Al-Pillared Montmorillonite

Al3+/clay ratio is one of the important factors influencing microstructure of Al-pillared montmorillonite. Microstructure variation laws of Al-pillared montmorillonite prepared under the condition of different Al3+/clay ratio are systematically studied by XRD, FTIR, specific surface area and pore size analysis. The results show that the interlayer spacing and BET specific surface area of Al-pillared montmorillonite are remarkably affected by the Al3+/clay ratio. The interlayer spacing d(001) value and BET specific surface area of Al-pillared montmorillonite increase firstly and then decrease with the increases of the Al3+/clay ratio, and they reach to maximum when the Al3+/clay ratio is 10mmol/g. Besides, the BJH porous volume distribution of Al-pillared montmorillonite is the most probable distribution, and the most probable pore size is about 2 nm, which is attributed to mesopore. The porous structure of hydroxy-Al pillared montmorillonite is characterized as parallel plate slit or “house-of-cards” wedge-shaped pore which is formed by novel meso-microporous delaminated structure and fragments. With the increase of the Al3+/clay ratio, BJH total porous volume and mesoporous volume of hydroxy-Al pillared montmorillonite decreases, while the proportion of microporous volume in the total porous volume increases. The proportion of microporous specific surface area of all the hydroxy-Al pillared montmorillonite samples is about 62% and is much larger than that of Na-M and those of mesopore and macropore, indicating the main action of intercalation of hydroxy-Al pillaring solution into montmorillonite interlayer is to increase the micropore amount.

Direct Synthesis and Characteristics of NH<sub>4</sub>-βZeolite with Hierarchical Pore Structure

NH4-β zeolite with hierarchical porous structure was directly prepared in a nearly neutral synthetic system using nonionic compound(polyoxyethylene nonyl phenylether) as the mesoporogen and fluoride as a mineralizer.Samples were characterized by powder X-ray diffractometry(PXRD),scanning electron microscopy(SEM),NH3-temprature programmed desorption(NH3-TPD),N2 adsorption/desorption and differential thermogravimetry(DTG).N2 analysis results showed that the synthesized H-(NH4)-β zeolite contained stepwise distributed micro-mesoporous structure.The Barrett-Joyner-Halenda(BJH) method of analyzing the N2 adsorption isotherm showed that the mesopore volume was 0.67 cm3.g-1 and the most probable pore size was about 21.8 nm.This value was higher than that for the conventional H-β zeolite(0.37 cm.3g-1 and 3.8 nm).The large amount of Lewis acid and the moderate amount of Bronsted acid in the H-(NH4)-β zeolite was examined by means of Pyridine-IR spectroscopy.Compared to conventional H-β zeolite,the conversion in the catalytic cracking reaction of mixed C4 hydrocarbons using this H-(NH4)-β zeolite was improved by 15%.Yields for the olefins(ethene and propene) and aromatic hydrocarbons(benzene and toluene) increased by 10% and 3%,respectively.

Preparation and characterization of carbon pillared clay material

Carbon pillared clay material was prepared from montmorillonite modified by C19H42BrN and C10H16ClN. SEM, FT-IR, XRD, N2 adsorption-desorption, thermal-gravimetric analysis and differential scanning calorimetry were employed to characterize the pore structure and test the effect of surfactant. The results show that organic modifier combines with montmorillonite particles by covalent bond and ion embedded. The microstructure of carbon pillared material looks like needle slice. The most probable pore size distribution is about 1.7 nm. The clay material slice mainly consists of two-dimensional aperture supported by a carbonization pillar. The high-temperature stability of carbon pillared clay is improved.