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Carbons



Carbons

CarbonCarbons are widely used in industrial applications, for instance carbon blacks are used as pigments in printing ink and printer toner, filler in rubber products such as tires, and in plastic compounds. Nanoporous carbons such as activated carbons are porous solids which primarily contain micropores, although meso- and macropores can also be present depending on the carbon precursor and the synthesis procedure applied. Due to their low cost and the possibility to tailor their porous structure and surface chemistry using pre- and post-synthesis treatment, activated carbons have found important industrial applications such as adsorption and separation of gas mixtures, water treatment, catalysis, and others. Recent developments have led to the synthesis of carbons with well-defined and tailored micro- and mesopore structures such as ordered mesoporous carbons (e.g. CMK carbons), carbon nanotubes, nanohorns, as well as novel carbon aerogels of high porosity which contain pores in the micro- to macropore size range. These advanced carbon materials show great potential for applications in the areas of gas and energy storage, batteries (e.g. supercapacitors), among others.



Characterization

In order to optimize applications of carbon materials, a comprehensive characterization with regard to their surface area, pore volume/size distribution, etc. is required. For this task, gas adsorption can be considered a standard technique, because it allows for assessing a wide range of pore sizes. High resolution adsorption experiments with (preferably) argon at 87 K or nitrogen at 77 K coupled with CO2 adsorption at 273 K has become a standard tool for the assessment of microporous carbons. Pore filling of narrow micropores (< 0.7 nm) with nitrogen or argon at cryogenic temperatures occurs at very low pressures (< 100 mTorr) and coupled with these low pressures and temperatures is the well-known problem of restricted diffusion, which prevents nitrogen and argon molecules from entering the narrowest micropores, i.e. pores of width < 0.45 nm. In order to address this, the use of CO2 as adsorptive at temperatures close to room temperature (i.e. 273 K) has been suggested which allows one to overcome such diffusion limitation and to obtain reliable pore size and volume information of the most narrow pores. With regard to the analysis of the adsorption data, it has been shown that methods for pore size analysis based on non-local density functional theory (NLDFT) and molecular simulation lead to reliable pore size and volume information over the complete range of micro- and mesopores. These methods are available for many different adsorptive/adsorbent pairs and are also featured in international standards such as ISO standard ISO 15901-3. More recent advances include the development of quenched solid density functional theory (QSDFT), which quantitatively takes into account the surface geometrical inhomogeneity characterized by a roughness parameter. It has been demonstrated that QSDFT significantly improves the accuracy of the pore size distribution for many micro- and mesoporous carbons.

Instruments; all manometric (volumetric) Quantachrome sorption analyzers:
Autosorb iQ, Autosorb 6iSA, Quadrasorb evo, Nova e, iSorbHP, VSTAR, DynaSorb.

Selected Literature
Thommes, M., Cychosz, K.A., Neimark, A.V.: Advanced physical adsorption characterization of nanoporous carbons. In: Tascon, J.M.D. (eds.) Novel Carbon Adsorbents, pp. 107-145. Elsevier (2012)

Quantachrome Technote 35, Micropore Size Analysis of Porous Carbons Using CO2 Adsorption at 273 K (0°C)

Neimark, A.V., Lin, Y., Ravikovitch, P.I., Thommes, M.: Quenched solid density functional theory and pore size analysis of micro-mesoporous carbons. Carbon 47, 1617-1628 (2009)

Gor, G.Y., Thommes, M., Cychosz, K.A., Neimark, A.V.: Quenched solid density functional theory method for characterization of mesoporous carbons by nitrogen adsorption. Carbon 50, 1583-1590 (2012)

Zhu, Y., Murali, S., Stoller, M.D., Ganesh, K.J., Cai, W., Ferreira, P.J., Pirkle, A., Wallace, R.M., Cychosz, K.A., Thommes, M., Su, D., Stach, E.A., Ruoff, R.S.: Carbon-based supercapacitors produced by activation of graphene. Science 332, 1537-1541(2011)