Αs-plot Method Research Articles

Influence of carbon structure/porosity on the electrochemical performance in Li–sulfur batteries

The porous structure of three different, commercially available porous carbonaceous materials is investigated by the αS-plot method and by the t-plot method. Subsequently, the electrochemical properties of sulfur-free porous carbon electrodes from inspected materials are studied by cyclic voltammetry. The comparison of double-layer capacitances with the corresponding adsorption isotherms of N2 reveals the role of micropores during the capacitive charging of carbons by Li+. The studied carbons are added to the sulfur cathodes and evaluated. The cyclic voltammograms show no contribution of micropores in the carbon structure to the electrochemical processes taking place in the lithium–sulfur coin cell. The highest specific capacity of 816 mAh/g is observed for material with the lowest content of micropores in the structure (14%). The partially mesoporous and partially microporous (65%) sample and the predominantly microporous one (87%), show specific capacities of 664 mAh/g and 560 mAh/g, respectively. The galvanostatic cycling of lithium–sulfur coin cells with carbonaceous additives reveals that the mesopores and macropores in the carbon structure increase the specific charge capacity of the lithium–sulfur batteries and that the micropores improve the cycling stability of these batteries.Graphical abstract

Multilevel Morphology of Complex Nanoporous Materials.

This work exploits gas adsorption and small-angle X-ray scattering (SAXS) to determine the morphology of complex nanoporous materials. We resolve multiple classes of porosity including previously undetected large-scale texture that significantly compromises the canonical interpretation of gas adsorption. Specifically, a UVM-7 class mesoporous silica was synthesized that has morphological features on three length scales: macropores due to packing of 150 nm globules, 1.9 nm radius spherical mesopores inside the globules, and >7 nm pockets on and between the globules. The total and external surface areas, as well as the mesopore volume, were determined using gas adsorption (αs-plot) and SAXS. A new approach was applied to the SAXS data using multilevel fitting to determine the surface areas on multiple length scales. The SAXS analysis code is applicable to any two-phase system and is freely available to the public. The total surface area determined by SAXS was 12% greater than that obtained by gas adsorption. The macropore interfacial area, however, is only 30% of the external surface area determined by the αs-plot. The overestimation of the external surface area by the αs-plot method is attributed to capillary condensation in nanoscale surface irregularities. The discrepancy is resolved assuming that the macropore-globule interfaces harbor fractally distributed nooks and crannies, which lead to gas adsorption at pressures above the mesopore filling pressure.

Validation of BET specific surface area for heterogeneous Ziegler-Natta catalysts based on αS-plot

Specific surface area based on the BET method in N2 adsorption has historically posed poor correlation with olefin polymerization activity of heterogeneous Ziegler-Natta (ZN) catalysts. We have investigated the validity of the BET surface area for ZN catalysts based on the αS-plot method, where non-porous core–shell MgO/MgCl2/TiCl4 catalysts were used as a reference material. The αS-plots for typical industrial ZN catalysts clarified the presence of two classes of micropores and resultant difficulty to isolate a multilayer adsorption region for the BET method. The results cast doubt on the application of the BET method to evaluate the surface area of heterogeneous ZN catalysts.

Synthesis of highly ordered supermicroporous silica using short-chain cationic trimeric surfactant as structure-directing agent

Highly ordered supermicroporous silica was synthesized by short chains cationic trimeric surfactant [C10H21N+(CH3)2(CH2)2N+(CH3)(C10H21) (CH2)2N+(CH3)2C10H21] · 3Br− (denoted C10-2-10-2-10) with a short spacer group (s = 2) as the structure-directing agent and tetraethyl orthosilicate as the precursor. The obtained samples were characterized by small-angle X-ray diffraction, high resolution transmission electron microscopy, and N2 adsorption–desorption. The results showed that the pore structure of the resulting samples belonged to the two-dimensional hexagonal structure (space group 2D-p6mm) with a pore size from 1.92 to 2.16 nm, which was within the supermicroporous range. The high-quality supermicroporous silica was formed at a low molar ratio of C10-2-10-2-10 to tetraethyl orthosilicate (0.08:1), which indicated that the self-assembly ability of C10-2-10-2-10 was stronger than that of corresponding monovalent surfactants. We strictly compared the methods of calculating surface area and pore size of supermicroporous materials, and the surface area was found to be in the range of 910–1,135 m2 g−1 by the αs plot method. With the increase of hydrothermal temperature, the ordering of the supermicroporous structure increased first then decreased, at the same time the pore size was enlarged.

Argon adsorption studies of porous structure of nongraphitized carbon blacks

Structural properties of a series of commercial nongraphitized carbon blacks were studied by means of argon adsorption at 87 K and 77 K. The specific surface area of the samples was calculated using the standard BET method. The micropore volume and external surface area were both calculated by the αs-plot method. Pore volume and adsorption energy distributions were calculated numerically by using the regularization method. The above mentioned quantities obtained from argon adsorption isotherms were compared with those evaluated from nitrogen adsorption at 77 K.

Mesostructured Silica SBA-16 with Tailored Intrawall Porosity Part 1: Synthesis and Characterization

Mesostructured silica materials of SBA-16 type were synthesized under varying conditions affecting the pore size distribution. The αs-plot method allows us to identify two populations of intrawall pores and measure their respective specific volumes. A semiquantitative treatment of these data yields an estimate for the intrawall pore radius. These results are discussed and related to the behavior of the long polar chains of the F127 surfactant in the synthesis gel.

Empirical Procedures for the Analysis of Physisorption Isotherms

Empirical methods, which can be used for the analysis of physisorption isotherms, involve the input of adsorption data on reference adsorbents. In particular, the αS-plot method can be used for the characterisation of a porous material when the corresponding standard isotherm has been determined on a well-defined non-porous solid of similar surface structure. The interpretation of αS-plots is based on established principles underlying the mechanisms of physisorption: monolayer–multilayer adsorption, preferential filling of narrow micropores (ultramicropores), monolayer adsorption followed by the filling of wider micropores (supermicropores) and capillary condensation in mesopores. Various distinctive features of αS-plots allow these different processes to be identified and the internal and external areas and effective pore volumes to be quantified. The validity of BET-nitrogen areas can be checked and also, by using probe molecules of different sizes, one can obtain a semi-quantitative evaluation of the m...

Comparative Analysis of Structural and Morphological Properties of Large-Pore Periodic Mesoporous Organosilicas and Pure Silicas

A systematic study on the structural properties and external morphologies of large-pore mesoporous organosilicas synthesized using triblock copolymer EO20PO70EO20 as a template under low-acid conditions was carried out. By employing the characterization techniques of SAXS, FE-SEM, and physical adsorption of N2 in combination with αs-plot method, the structural properties and external morphologies of large-pore mesoporous organosilicas were critically examined and compared with that of their pure-silica counterparts synthesized under similar conditions. It has been observed that unlike mesoporous pure silicas, the structural and morphological properties of mesoporous organosilicas are highly acid-sensitive. High-quality mesoporous organosilicas can only be obtained from synthesis gels with the molar ratios of HCl/H2O between 7.08 × 10-4 and 6.33 × 10-3, whereas mesoporous pure silicas with well-ordered structure can be obtained in a wider range of acid concentration. Simply by adjusting the HCl/H2O molar r...

ＣＯ２賦活スギ樹皮活性炭の特性評価

Pyrolyzed Japanese cedar (Cryptomeria japonica D. Don) bark was activated in a stream of CO2 at 1123-1173K for 1h. Adsorption of N2 at 77K and DRIFTS spectra were measured to investigate the porosity and surface properties of the activated materials. The resultant fibrous activated carbons showed the development of micro porosity which was characterized by large specific surface area greater than 1000m2g-1, small external surface area of ca. 10m2g-1, and total pore volume of 0.45-0.65mlg-1. Pore size of the activated carbon distributed sharply around 0.3-0.4nm radius, indicating that micropores were selectively formed during activation reactions, while the amounts of meso- and macro-pores were negligibly small. Analysis of adsorption isotherms by αs-plot method suggests that surface properties of the activated carbons from the cedar bark are different from those of ordinary carbon black. Peaks appeared in 900-1350cm-1 region in the DRIFTS difference spectra between the activated carbon and the carbon black showed that principal functional groups on the surface of the cedar bark activated carbon were ether groups such as ether bridges between aromatic rings and cyclic ethers containing COCOC groups. It is indicated that the oxygenated functional groups produced on the surface of the activated carbons from the cedar bark may affect the surface characteristics of the activated ones.

A New Composite Adsorbent Produced by Chemical Activation of Elutrilithe with Zinc Chloride

We tried to utilize elutrilithe, coal waste, as a starting material to produce a low-cost adsorbent as a substitute for activated carbons. The elutrilithe was chemically activated with zinc chloride. The activated products were characterized by nitrogen adsorption isotherms, thermogravimetric analysis (TGA), and atomic absorption spectrometry (AAS). The BET and αs-plot method were used to evaluate surface area and micropore volume of the samples. A systematic investigation of the effect of ZnCl2/elutrilithe ratios, activation temperatures, and activation time on the properties of the adsorbents was carried out. Since the carbon in the matrix was activated, the elutrilithe became a highly microporous material so that the adsorption behavior of the substrate was significantly improved. As a result, the new composite adsorbent exhibited high affinities toward organic compounds and an adsorption capacity comparable to a commercial activated carbon.