Characterising porous carbons

Materials World magazine
2 Aug 2007
Porous carbons

Quantachrome Instruments, based in Boynton Beach, Florida, USA, has launched a novel pore size calculation tool for porous carbons and activated carbon fibres.

The quenched solid density functional theory (QSDFT), unlike previous non-local density functional theory (NLDFT) models, is designed to take into account surface roughness and chemical heterogeneity.

The NLDFT tools are based on analysis of slit-shaped pores with smooth graphitic walls. They simulate gas adsorption behaviour at a molecular level on the surfaces and in the confines of the carbon pores using complex computer models. This enables scientists to characterise the properties of the gas molecules on the surface alongside the size and shape of the pores.

Quantachrome collaborated with Professor Alex Neimark of Rutgers University, New Jersey, USA, and Dr Peter Ravikovitch (formerly of TRI Princeton, USA) to extend functionality.

Dr Matthias Thomas, Quantachrome’s Director of Applied Science, explains, ‘Most real porous solids are not perfectly smooth, parallel, or chemically homogeneous. Without accounting for these variations, simple DFT models can yield misleading pore size results.’

Neimark and Ravikovitch have proposed QSDFT,which models gas adsorption in pores with heterogeneous walls and has been commercialised with Quantachrome’s data reduction software. The technique is a multicomponent NLDFT, where the carbon solid is treated as a quenched component with fixed spatially distributed density, eliminating the artificial gaps in pore size distributions that are typical of NLDFT calculations. Pore size, porosity and surface area characteristics can now be calculated in the pore width range of 0.35-40nm.

Thomas envisages the more reliable QSDFT kernel being applied where carbons are used for energy storage, supercapacitators, carbon dioxide capture and sequestration, and gas separation.