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The textural properties of synthetic and natural clays in the sodium form and exchanged with tetramethylammonium cations (TMA+) were characterized using N2 and Ar physisorption isotherms at cryogenic temperatures. Specific surface areas and micro/mesoporous volumes were determined using the BET and the t-plot models. The t-plot analysis requires the use of reference isotherms measured at the same temperature on the surface of non-porous materials with an identical chemical composition. In order to better assess the effects of chemical heterogeneities in the clay particles, reference isotherms representative of silica surfaces were taken into account in the analysis of the t-curve and corrected to account for variations in curvature at the interface of the film adsorbed in the micropores. In addition, high-resolution Ar adsorption isotherms at 87 K were analyzed using the Derivative Isotherm Summation (DIS) method to quantify the energy contributions of adsorption sites and determine the fractions of basal and lateral surfaces of clay particles. The high-energy adsorption sites, identified in the low-pressure range, were attributed to intra-particle microporosity due to stacking defects and/or open inter-layer spaces. These sites were differentiated from those on the lateral and basal surfaces of the particles. A modification of the DIS method was proposed to measure these contributions and improve the fit with the experimental data. The results show that TMA+ cation exchange significantly increases the microporosity of clays compared to their sodic form, which can be attributed to the increased contribution of intra-particle adsorption sites due to interlayer expansion. [ABSTRACT FROM AUTHOR]

A composite of γ-alumina and activated carbon made of cassava peels was studied in terms of its pore structures and its properties. The objective of this study was to determine the interaction and structure, as well as the character and pore size of γ-alumina – activated carbon composite. Carbon made of cassava peels was activated by H2SO4 and its activities were tested according to the Indonesian Industrial Standards (SII). The addition of activated carbon into γ-alumina made in variations of 10, 20, 30, 40 and 50 % w/w, of the total weight of 10 grams. The composite of γ-alumina - activated carbon was characterized by FTIR, SAA (Surface Area Analyzer), XRD, and determination of Hysteresis Loop composites. The greater addition of activated carbon to γ-alumina causes intermolecular interactions between –O-H groups form rehydrated hydrogen bonds in the composite is greater. The structure of γ-alumina in the composites remain intact although the percentage of activated carbon in composite is large. The total pore volume and surface area using the BET method of the composite decreases with increasing activated carbon percentage. The greater addition of activated carbon to γ-alumina causes size of mesoporous composites decreased with the characteristic of a composite formed is closer to the activated carbon.

Nitrogen adsorption at 77 K on metal-organic framework (MOF) is investigated by means of molecular simulations. We consider both regular Cu-BTC crystal and a MOF-based hierarchical porous solid consisting of a mesopore carved out of a Cu-BTC crystal. The t-plot method is applied to these solids by using a non-porous Cu-BTC surface as the reference sample. The values of the mesoporous and external surface areas are determined from the t-plot, and the validity of the method for this type of hierarchical solid is discussed. [ABSTRACT FROM AUTHOR]

The perfluorosulfonic acid (PFSA)/SiO composite catalysts were prepared by sol-gel method. Differences concerning pore structure analysis of PFSA/SiO catalysts were discussed on the basis of nitrogen adsorption. Their surface area and pore size distributions were evaluated by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. The nitrogen adsorption-desorption isotherms associated with adsorption hysteresis of PFSA/SiO catalysts were analyzed in detail. The adsorption isotherms of PFSA/SiO catalysts belonged to Type IV isotherms accompanied by hysteresis loops of Type H1 for PFSA/SiO catalysts with content of 5%, 13% and 20% PFSA (PFSA-5, PFSA-13 and PFSA-20), and the hysteresis loop of Type H2 for PFSA/SiO catalyst with 40% PFSA content (PFSA-40). It indicated that PFSA-5, PFSA-13 and PFSA-20 catalysts had narrow pore size distributions and the well-defined cylindrical pores, while PFSA-40 catalyst had wide pore size distribution and inkbottle-like pores. The pore structure of PFSA-40 catalyst from the analysis of the hysteresis loop was not in agreement with that from BJH method. As an emendation for evaluation of pore size distributions of PFSA/SiO catalysts, the comparison plots method was introduced, which was helpful to evaluate the pore structure of PFSA/SiO catalysts more factually. [ABSTRACT FROM AUTHOR]

Abstract: Three of the most common methods to analyze sorption isotherms with respect to micropore volume and specific surface, respectively, are the Brunauer–Emmett–Teller (BET) theory, established for the specific surface area of meso- and macroporous materials, the t-plot-method, which separates micropore from multilayer adsorption and the micropore analysis based on the work of Dubinin and Radushkevich (DR). While BET-analysis is assumed to be sensitive to multilayer adsorption on the external surface area, the DR-method is expected to be in particular sensitive to the micropores. However, the data for a series of synthetic carbons investigated reveal that the values derived by both methods are equivalent, despite the different underlying assumptions. [Copyright &y& Elsevier]

Abstract: The central theme of this investigation is to evaluate the feasibility of using bituminous coal as a precursor material for the production of chars and activated carbons using physical and chemical activation processes. The chemical activation process was accomplished by impregnating the raw materials with different dehydrating agents in different ratios and concentrations, prior to heat treatment (ZnCl2, KCl, KOH, NaOH and Fe2(SO4)3·xH2O). Steam activation of the precursor material was adopted for the preparation of activated carbon using physical activation technology. Different types of bituminous coal; namely, contaminated Columbian (contaminated with pet. coke), pure Columbian, Venezuelan and New Zealand bituminous coal were used in the production processes. BET surface area, micropore area, pore size distribution and total pore volume of the chars and activated carbons were determined from N2 adsorption/desorption isotherm, measured at 77K. Charring conditions, charring temperature of 800°C and charring time of 4h, proved to be the optimum conditions for preparing chars. Contaminated Columbian were found to be the best precursor material for the production of char with reasonable physical characteristics (surface area=138.1m2 g−1 and total pore volume of 8.656×10−0.2 cm3 g−1). An improvement in the physical characteristics of the activated carbons was obtained upon the treatment of coal with dehydrating agents. Contaminated Columbian treated with 10wt% ZnCl2 displayed the highest surface area and total pore volume (surface area=231.5m2 g−1 and total pore volume=0.1227cm3 g−1) with well-developed microporisity (micropore area=92.3m2 g−1). Venezuelan bituminous coal using the steam activation process was successful in producing activated carbon with superior physical characteristics (surface area=863.50m2 g−1, total pore volume=0.469cm3 g−1 and micropore surface area=783.58m2 g−1). [Copyright &y& Elsevier]

Abstract: Effect of preparation variables on the aromatization activity of Pt/KL catalysts was studied. The aromatic content as well as C5 + liquid yields were greatly influenced by the nature of binder material used in catalyst preparation. Detailed characterization of the catalysts indicated that two factors, namely (1) nature of binder and (2) size and volume of pores, influenced the catalytic activity. Among the catalysts studied the one prepared by MgO doped basic binder exhibited better performance. Pt loading was also observed to influence the pore volume and aromatization activity of the catalysts, where the catalyst exhibited decrease in pore volume above 0.4wt.% Pt loading. [Copyright &y& Elsevier]

Abstract: Standard (master) nitrogen and argon (at 77K) and argon (at 87K) isotherms on non-porous alumina, titania, magnesia and controlled-pore glass (CPG) were obtained. The absence of pores in these materials was controlled and confirmed. Reproducibility and accuracy of adsorption measurements were affirmed by replicated adsorption runs. α(x) and t(x) dependences were constructed for nitrogen and argon at 77K and argon at 87K. [Copyright &y& Elsevier]

Problems concerning analysis of the pore structure of the MCM-41 mesoporous materials were discussed on the basis of nitrogen adsorption. Calculation results from both adsorption isotherms and MD simulations were taken into account in this analysis. It was found that the thickness of an adsorption layer in cylindrical mesopores was higher than that in macropores and it increased with the decrease in the mesopore diameter. This increase was relatively slow for the diameters falling down to ca. 4 nm. For this region, the values of the statistical film thickness can be obtained from the equations (e.g., Harkins–Jura) that are independent of the pore size. For pore diameters lower than 4 nm, the above growth is more pronounced and taking into account the dependence of the adsorption layer thickness on the pore diameter appears necessary. [Copyright &y& Elsevier]

Polycrystalline ZSM-5 zeolites were studied in the cracking of n-pentane and the isomerization of m-xylene. It was found that slow deactivation rates and low p-selectivity are related to large external surface areas determined by the t-plot method. [ABSTRACT FROM AUTHOR]

Evaluation of microporosity by t-plot method of a series of NHY samples stabilized by different hydrothermal treatments with subsequent HCl extraction shows the strong influence of stabilizing conditions on the solubility of extraframework aluminium species created. [ABSTRACT FROM AUTHOR]

Silica/biopolymer hydrogel-based materials constitute very attractive platforms for various emerging biomedical applications, particularly for bone repair. The incorporation of calcium phosphates in the hybrid network allows for designing implants with interesting biological properties. Here, we introduce a synthesis procedure for obtaining silica–chitosan (CS)–tricalcium phosphate (TCP) xerogels, with CS nominal content varying from 4 to 40 wt.% and 10 to 20 wt.% TCP. Samples were obtained using the sol-gel process assisted with ultrasound probe, and the influence of ethanol or water as washing solvents on surface area, micro- and mesopore volume, and average pore size were examined in order to optimize their textural properties. Three washing solutions with different soaking conditions were tested: 1 or 7 days in absolute ethanol and 30 days in distilled water, resulting in E1, E7, and W30 washing series, respectively. Soaked samples were eventually dried by evaporative drying at air ambient pressure, and the formation of interpenetrated hybrid structures was suggested by Fourier transformed infrared (FTIR) spectroscopy. In addition the impact that both washing solvent and TCP content have on the biodegradation, in vitro bioactivity and osteoconduction of xerogels were explored. It was found that calcium and phosphate-containing ethanol-washed xerogels presented in vitro release of calcium (2–12 mg/L) and silicon ions (~60–75 mg/L) after one week of soaking in phosphate-buffered saline (PBS), as revealed by inductive coupled plasma (ICP) spectroscopy analysis. However, only the release of silicon was detected for water-washed samples. Besides, all the samples exhibited in vitro bioactivity in simulated body fluid (SBF), as well as enhanced in vitro cell growth and also significant focal adhesion development and maturation. [ABSTRACT FROM AUTHOR]

Plant microRNA (miRNA) is a crucial regulator of gene expression. It has been reported that more than one miRNA/miRNA duplex could be produced from a microRNA precursor (pre-miRNA). In this study, we performed a comprehensive search for the novel miRNA candidates on the pre-miRNAs of Arabidopsis. AGO1 enrichment, co-existence of the miRNA-like coordinates, and unique genome-wide match sites were taken into consideration for candidate screening. As a result, 43 miRNA-like candidates derived from 25 pre-miRNAs were identified. Among these candidates, 31 strong candidates from 22 pre-miRNAs passed all the filtering steps. Interestingly, some of these miRNA-like candidates showed organ-specific expression patterns. After target prediction and degradome sequencing data-based validation, five miRNA candidate-target pairs (ath-miR863-5p.2-AT1G76550.1, ath-miR822.2-AT5G03552.1, ath-miR822.3-AT5G02350.1, sRNA4-AT1G66290.1 and sRNA6-AT1G66310.1) were identified, providing a basis for in-depth functional analysis of these miRNA candidates. These results could update the current understanding of the biogenesis and the action of the plant miRNAs., (© 2013.)