Effect of alumina content on surface area and micropore distribution of porous glass prepared from borosilicate glass

The surface area and micropore distribution of porous glass prepared from borosilicate glass were controlled by the addition of alumina up to 8 wt%. The surface area increased with increased alumina content in the range from 0 to 3 wt%, but it suddenly decreased when the percent alumina exceeded 4 wt%. The mean pore diameter and micropore volume also decreased with increased alumina content. When nickel ion was supported into the porous glass, the surface area decreased to about one-half that of the original glass. Since the amount of nickel supported on the porous glass increased directly with surface area, the silanol group was considered to be uniformly distributed on the glass.     

Effects of micropore development on the physicochemical properties of KOH-activated carbons

Effects of micropore development through varying the KOH/char ratio on the porous, electrochemical, electronic, and adsorptive properties for corncob-derived activated carbons (ACs) prepared by means of the KOH activation method were systematically compared. The pore properties of ACs, including BET surface area, total pore volume, micropore volume ratio, bulk density, and product yield based on the raw material were investigated to gain an understanding for the influence of KOH dosage on the pore development. Element analysis and temperature-programming desorption (TPD) were used to obtain the information of chemical composition and surface oxygen functional groups on ACs in order to propose the reaction mechanism of KOH activation. Based on the pore development, KOH-activated carbons can be classified into two groups: a combination of physical activation and chemical KOH etching at low KOH/char ratios (0.5-2) as well as chemically uniform etching at high KOH/char ratios (≥3.0). From the adsorption study for five organics with molecular weights varying from 129 to 466 g/mol, the specific adsorption capacity of ACs for organics is independent of their specific surface area. The specific capacitance of ACs reached a maximum as the KOH/char ratio was equal to 3, attributed to a compromise between the specific surface area and electronic resistance of ACs.     

Some physical properties of Canadian coals and their effects on coal reactivity

The pore volume, surface area and compressibility of eleven Canadian coals, varying in rank from lignite to semianthracite, have been determined by mercury porosimetry, gas adsorption method and relations derived from helium and mercury densities. The total pore volume was measured in the diameter range of 0.2 nm–2.98 μm, which was subdivided into two groups, namely the micropore region (< 0.0036 μm) and the combined meso- and macropore region (0.0036–2.98 μm). It has been determined that the porosity of the eleven coals studied varies from 2 to 39%. It has been found that the total pore volume, micropore volume, surface area and the apparent compressibility of these coals decrease with increase in the carbon content, or the rank of the coals. The effect of the total pore volume, micropore volume and surface area on chemical reactivity of the coal is discussed separately. A good correlation was obtained between the carbon content and helium density of the coal after correction is made for the mineral content.     

The complete pore structure analysis of fine porous solids

A new method is presented for the determination of the distribution of pore volume and surface in micropores. The analysis facilitates obtaining typical parameters of micropore structure from the adsorption isotherm. The calculated characteristic micropore radii and the micropore surface area for a model of cylindrical pores agree with the data from small-angle X-ray scattering. Micropore cumulative distribution curves for two typical active carbons were joined together with a high pressure mercury porosimetry data. The overall porosity cumulative distribution curve agrees with the Dubinin model of the porous structure of active carbons.     

氮吸附法和压汞法测量生物质焦孔隙结构的比较

采用氮吸附法和压汞法对四种生物质焦（稻壳、树叶、玉米杆、棉花杆）的孔隙结构进行了测量,得到了两种测量方法下焦样的比表面积和孔径分布。结果表明不同测量方法得到的焦样比表面积和孔径分布有明显差别。氮吸附法主要测量焦样中微孔的孔隙结构,压汞法主要测量焦样大孔（和部分中孔）的孔隙结构。微孔对焦样的比表面积贡献最大,大孔对焦样的孔容积贡献最大。当热解温度升高时,焦样的微孔结构迅速增多,氮吸附法测得的比表面积变化大;而热解温度对大孔的影响较小,所以压汞法测得的比表面积变化不大。     

Densification of ordered microporous carbons and controlling their micropore size by hot-pressing

Ordered microporous carbons synthesized by the template method using zeolite Y were hot-pressed at 573 K up to 147 MPa, aiming at densification of the templated carbons for the future use as energy storage media. Upon the hot-pressing, the powdery templated carbons were easily pelletized without any binder and the bulk density was significantly increased from 0.2 g/cm³ to 0.7-0.9 g/cm³. As a result, both the surface area and micropore volume per unit volume were increased. Surprisingly, it was found that the hot-pressing treatment reduced the average micropore size and it was tunable by simply adjusting a pressure in the treatment. In contrast, such changes in the density and the pore structure were not observed for commercial KOH-activated carbons when they were hot-pressed under the same conditions. The observed peculiar behavior of the templated carbons upon the hot-pressing can be explained by their unique molecular structure as compared to the conventional activated carbons.     

Effect of micropore structure on cellular concrete shrinkage

This paper presents the results of studies on the effect of micropore structure on the shrinkage of autoclaved cellular concrete with sand aggregate. It has been found that the shrinkage of cellular concrete is the function of volume and specific surface of micropores of radii $\text{75 <}\text{r}\text{< 625}\text{A}\text{?}$. On the base of mathematical analysis the requirements concerning the micropore structure of cellular concrete have been proposed to ensure the proper shrinkage characteristic of this material.     

微孔分散法制备超细CaCO3

引言 超细CaCO3的粒径范围通常为0.02～0.1μm[1],具有纳米尺度效应和特殊的性能,作为一种优质填料和白色颜料,广泛应用在橡胶、塑料、造纸、涂料、油墨、医药等众多行业.超细Ca-CO3的商业产品主要由湿化学沉淀法合成的,即用CO2气体和Ca(OH)2/H2O体系进行化学反应来制备.     

Characterization and modeling of micromixing performance in micropore dispersion reactors

Micropore dispersion reactors have been considered as one of the most promising micro-structured devices. For reliable design of this kind of microreactors, the micromixing performance in those microreactors with different detailed geometric structures have been investigated in this work. The pore size, pore shape, pore number and pore distance were varied and the micromixing performance was characterized by the Villermaux/Dushman parallel competing reaction. The results showed that the mixing performance was greatly influenced by the geometric structures. The segregation indexes, X_S, were found in the range of 10⁻² to 10⁻³, indicating that the micropore dispersion reactors have high micromixing efficiency. To deeply understand the micromixing process, CFD simulation was carried out to describe the flow fields in the reactors. Based on the simulation results a mathematical model was developed and a new area parameter, S, was defined by considering both mixing region surface and mass transfer distance. A linear relationship between S and lg(X_S) was obtained at last, which is very helpful for optimizing the structure design of micropore dispersion reactors.     

Determination of surface area/monolayer capacity or limiting micropore volume of carbons from binary and ternary mixtures

It is shown that one can predict the adsorption of binary and ternary mixtures in any percentage ratio from the adsorption of individual component gases by means of John's isotherm equation. The surface area of mesoporous materials or the limiting micropore volume of microporous materials from binary and ternary mixture adsorption isotherms is given. The relation given by Lewis et al. may be used to prove the validity of the above method and determine the contribution of each component of the mixture.     

Preparation of ultrafine calcium carbonate particles with micropore dispersion method

Ultrafine particles of CaCO₃ were synthesized by dispersing the mixture of CO₂ and N₂ into the Ca(OH)₂/H₂O slurry with a micropore-plate. Because the micropore is micrometers scale, process of momentum transfer, mass transfer and reaction was significantly enhanced. The carbonation process of Ca(OH)₂/H₂O system was monitored with pH and conductivity. Operation conditions were investigated on the specific surface area of particles, such as initial slurry concentration and volume, gas flowrate and concentration, and temperature. The crystal structure of particles was characterized with BET, IR, TEM, SEM, etc. Results showed ultrafine particles were calcite with general shape of cube, whose size was about 40 nm and specific surface area was more than 25 m²/g. This preparation method is easy to operate.     

Novel ideas in the theory of the physical adsorption of vapors on micropore adsorbents

A general equation has been derived for the physical adsorption of vapors on adsorbents with nonhomogeneous microporous structure, in which the energy of adsorption is increased as a result of the effect of superposition of dispersion force fields of the opposite micropore walls. The equation is based on experimentally determined reciprocal dependence of the generalized dimensions of the micropores expressed as their radii of inertia and the characteristic adsorption energy. The expression of the inertia radii of micropores takes into account their geometrical sizes. The nonhomogeneity of the microporous structure is described in terms of normal distribution of the micropore volumes with respect to reciprocal values of the characteristic adsorption energies. For a homogeneous elementary micropore volume, the adsorption equation derived from the theory of volume filling of the micropores is used. The adsorption equation obtained contains three parameters: the total micropore volume, the characteristic adsorption energy at the maximum of the distribution curve and the dispersion. The equation can be used for micropores with various geometric shapes. It leads to the following consequences: If the dispersion equals zero, then the Dubinin-Radushkewich equation is obtained for homogeneous microporous structures; the Dubinin-Stoeckli equation is obtained for the model of slitlike micropores in carbonaceous adsorbents. The parameters of the equation were found to be effective quantities for increased mesopore surface areas in microporous adsorbents. We considered methods for determining the specific surface areas of mesopores; these methods are necessary for obtaining realistic parameters for the microporous structure of adsorbent.     

硝基苯催化加氢Pt-MoS2/C催化剂的制备及使用寿命的研究

采用浸渍法制备Pt/C和Pt-MoS2/C催化剂,用于催化硝基苯加氢反应。采用BET、压汞仪等测试方法测定新鲜催化剂和重复使用后的催化剂的比表面积和孔容。结果表明,比表面积下降27.3%,微孔孔容下降13.2%,总孔容下降5.8%。催化剂失活的主要原因为有机物覆盖在催化剂表面,造成表面积下降和孔堵塞。负载MoS2可使Pt/C催化剂延缓比表面积下降和孔堵塞,寿命显著提高,可循环使用14次左右。     

Response of human chondrocytes on polymer surfaces with different micropore sizes for tissue‐engineered cartilage

Response of chondrocytes on polymer surfaces is important for applications of tissue‐engineered cartilage, and tissue engineering contains the interaction of cells on material surfaces. We examined the behavior of human chondrocytes cultured on polycarbonate (PC) membranes with different micropore sizes (0.2–8.0 μm in diameter). The adhesion and proliferation of chondrocytes were evaluated by measuring the number of attached cells after 1, 2, and 4 days of culture and morphological observations. It seems that the cell adhesion and proliferation were progressively inhibited, as the PC membranes had micropores with increasing size, probably due to surface discontinuities produced by track‐etched pores. On the PC membrane with smaller micropore sizes, the cells seemed to override these surface discontinuities. Phenotype of chondrocyte was assessed by Safranin‐O staining for anionic sulfated proteoglycans. Chondrocytes on the 8.0 μm‐diameter membrane surface proliferated, on 8 days, formed morphology of round shape, and expressed proteoglycans, because of limitation of spreading by the track‐etched micropores. They maintained their phenotype under conditions that support a round cell shape on the large pore diameter substrate, whereas chondrocyte phenotypes lost on the small pore diameter membranes. In conclusion, this study demonstrated that micropore sizes as well as pore‐to‐pore distance play an important role for adhesion, proliferation, and phenotype of human articular chondrocytes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2784–2790, 2004     

Storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere by the sealing of the micropore outlet

The storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere was examined by hydrogen filling into the micropore and the following sealing of the micropore outlet to prevent the release of hydrogen to the outside. The surface grafting of 1,4-bis(hydroxydimethylsilyl)benzene onto ZSM-5 zeolite was applied to the sealing of the micropore outlet. Pressurized hydrogen (10 MPa) was filled into the micropore of ZSM-5 at liquid nitrogen temperature (−196 °C), and then the sample was heated at 150 °C for forming strong binding between the zeolite surface and the disilane compound under the hydrogen pressure. The hydrogen sorption isotherm at −196 °C showed that the adsorption of hydrogen onto the disilane-grafted ZSM-5 thus obtained was reduced to less than 20% from the original ZSM-5. The remarkable hysteresis between the adsorption and desorption branches of the isotherm indicated that the kinetic trap of hydrogen occurred by the narrowed outlets of the micropores of ZSM-5 with the disilane compound. Even after exposing the disilane-grafted ZSM-5 to the atmosphere over a few months, hydrogen could be discharged by heating over 150 °C. This result demonstrated that molecular hydrogen was successfully stored into ZSM-5 zeolite in the ambient atmosphere for a long time.     

酸处理后坡缕石的孔结构变化

在90℃,坡缕石分别用不同浓度的盐酸处理1.5h,对制得样品的物相、比表面积和微孔结构以及微观形貌进行了研究.结果表明:酸处理可以提高坡缕石的比表面积,改变坡缕石晶体的孔结构,随着酸浓度的改变,坡缕石的总比表面积、微孔比表面积和外比表面积都随之发生改变.当酸浓度小于等于3 mol/L时,坡缕石颗粒聚集体逐步被解离,溶蚀作用主要发生在孔道内,晶体结构能保持相对完整;当酸浓度大于3 mol/L时,部分颗粒被溶蚀掉.结果说明H 能进入到坡缕石的晶体孔道中产生作用,使晶体的孔道不断扩大,孔径最大可以达到0.62～0.75nm,但孔径超过0.62～0.75nm后晶粒会被破坏.     

Impact of surface loading on catalytic activity of regular and low micropore SBA-15 in the Knoevenagel condensation

The mesopores of SBA-15 are well-suited for immobilizing catalytic aminosilanes for converting substrates for fine chemicals, but these materials have micropores that could impact the observed reaction rate of immobilized catalysts. Materials are synthesized with conventional methods that produce micropores (Regular Micropore SBA-15; REG) and compared to materials with limited to no micropore volume (NMP SBA-15). These materials are functionalized with aminosilanes for testing in the Knoevenagel condensation. For low amine loadings, NMP materials have a higher observed reaction rate compared to REG materials, achieving twice the conversion in the same time. As the surface density increases, the reaction rate for NMP materials decreases since organosilane functionalization consumes surface silanols that interact cooperatively with the amine. Regardless of surface density, the NMP materials have higher observed reaction rate than the REG materials. These results demonstrate the importance of reducing micropore volume to create highly active catalytic materials.     

Structure and electrochemical capacitance of carbon cryogels derived from phenol-formaldehyde resins

Highly porous carbon cryogels derived from phenol-formaldehyde (PF) resin formulated in ethanol have been prepared and investigated. Different P/F molar ratios have been used for obtaining a series of alcogels that have been freeze-dried and next pyrolysed at 900 °C. Carbonaceous materials having different bulk densities and textural properties have thus been obtained. These materials were fully characterised by helium and mercury pycnometry, mercury porosimetry, nitrogen adsorption, and tested as porous electrodes of electrochemical double-layer capacitors working in 4 M H₂SO₄ aqueous electrolyte. For that purpose, cyclic voltammetry and galvanostatic charge/discharge experiments have been carried out. The derived specific capacitances, around 100 F/g, were shown to depend strongly both on pore availability to the electrolyte and on average micropore width. The cryogel having the highest surface area and micropore volume is thus the one presenting the lowest capacitance because of its poorly accessible and too narrow microporosity.     

Non-destructive investigations of pore morphology of micropore carbon materials

Pore morphology of experimental micropore carbon materials was explored using non-destructive methods. The influence of the heat treatment on porosity of two micropore carbon materials was investigated using helium porosimetry (HP) and X-ray micro-computed tomography (µCT). Methodology of µCT image processing and separation of the total and the open porosity is presented. In both materials open pores were found over the whole height of the sample. The local pore thickness and tortuosity of the materials were calculated. The increase of the porosity after heat treatment is observed for both materials.     

Inhomogeneous microporous structures of carbonaceous adsorbents

Ways for theoretical calcultion of the geometric surface area of the micropore walls of carbonaceous adsorbents with inhomogeneous microporous structures are considered for the slitlike micropore model. Two calculations methods have been worked out based on the theory of volume filling of micropores (TVFM) from the parameters of the adsorption equation proposed by Stoeckli and from the parameters of the binomial TVFM equation. An independent method for determining the geometric surface area of the micropore walls from water vapor adsorption isotherms served as a reference. When we used an active carbon with a wide micropore distribution all the three methods led to practically identical results, which indicated that the concept of the geometric surface area of carbonaceous adsorbents is physically feasible. The physical unfeasibility of a specific surface determined by the BET method for a microporous adsorbent is shown.