The characterization of microporosity in carbons with molecular sieve effects

Abstract

The apparent and the real micropore size distributions (PSDs) of molecular sieve carbons can be assessed by combining the adsorption of CO 2 at 273 K with immersion calorimetry into liquids of increasing molecular dimensions. On the basis of model isotherms resulting from computer simulations, the adsorption of carbon dioxide, a relatively small probe, leads to the overall PSD of the carbon (essentially the internal micropore system). Immersion calorimetry, on the other hand, reveals the distribution of the pores accessible directly from the liquid phase, that is without constrictions. Liquid CS 2 probes the same volume as CO 2 and can be used as a reference. The paper describes the case of an industrial molecular sieve carbon obtained by blocking partly the entrance to a relatively broad micropore system, thus limiting its accessibility to molecules with diameters below 0.5-0.6 nm. It is shown how activation by steam at 900°C removes the constrictions and leads to a gradual overlap of the two PSDs. The distribution of the pore widths on the surface, observed directly by scanning tunnelling microscopy, is also given.

Correlation between capacitances of porous carbons in acidic and aprotic EDLC electrolytes

“…(differences between the two graphs are due to the fact that the surfaces areas S tot vary from carbon to carbon). The obvious deviation observed for carbon T-0 may be attributed to the fact that this material displays a gate effect around 0.6 nm [9]. Accordingly, this reduces the accessibility of the micropore system to the large (C 2 H 5 ) 4 N + ions.…”

“…Carbon T-0 [9], a molecular sieve with a marked 'gate' effect around 0.60 nm was also investigated. This 'gate' effect limits the internal surface area accessible to larger ions such as (C 2 H 5 ) 4 N + (0.69 nm), as opposed to the solvated SO 2À 4 ion (0.53 nm).…”

Synthesis of Bamboo-Based Activated Carbons with Super-High Specific Surface Area for Hydrogen Storage

“…Prior to the adsorption experiments, the samples were degassed for 24 h under a vacuum at 563 K. The N2 adsorption data were processed to generate the following: (i) the surface area, SBET, by the BET calculation method (Brunauer et al 1938); (ii) the micropore volume, VDR, according to the Dubinin-Radushkevich (DR) method (Dubinin and Polstyanov 1989); and (iii) the total pore volume, V0.99, defined as the volume of liquid nitrogen corresponding to the amount adsorbed at the relative pressure P/P0 = 0.99 (Gregg and Sing 1982). The average micropore diameter, L0 (Stoeckli et al 2002), and the pore size distributions, PSD, were also calculated by the application of density functional theory (DFT) (Tarazona 1995). EA represented the characteristic adsorption energy of nitrogen and was derived from the corresponding adsorption isotherms at 77 K by applying the DR method (Dubinin and Polstyanov 1989).…”

Hydrothermal Doping of Nitrogen in Bamboo-Based Super Activated Carbon for Hydrogen Storage

“…The average micropore diameter, L0, (Stoeckli et al 2002) and the pore size distributions (PSD) by application of the Density Functional Theory (DFT) (Tarazona 1995) were also calculated. EA is the characteristic adsorption energy of nitrogen and was derived from the corresponding adsorption isotherms at 77 K, applying the DR method (Dubinin and Polstyanov 1989).…”