Surface free energy (gamma(d)(s)) of active carbons determined by inverse gas chromatography: influences of the origin of precursors, the burn off level and the chemical modification

The dispersive component of the surface free energies (y(s)(d)) of commerci al active carbons (AC) from various origins were determined by inverse gas chromatography at infinite dilution (IGC-ID). This method discriminates cle arly the AC produced from wood (and activated/carbonised with phosphoric ac id) and those from coconut-shell (carbonised and steam activated at 850 deg reesC). The values for the last AC (from coconut) are twice higher than the values for AC of wood origin. The structure and shape of the pores have to be considered to explain these values. It seems that for AC, IGC-ID global ly characterises the most energetic micropores. This can be observed, in th is work, by two ways: (i) washing of commercial AC (chemically activated) a llows to liberate a part of the micropores blocked by soluble phosphate and consequently increases the y(s)(d) value; (ii) modifying coconuts AC by ch emical treatment (formamide) results in a strong decrease of both microporo sity and y(s)(d) value. On the contrary, thermal activation of the modified AC increases at the same time the microporosity and the surface free energ y. Finally, we demonstrate that the IGC method is also an useful tool to mo nitor in situ the evolutions of the surface properties of carbonaceous mate rials. (C) 2001 Elsevier Science B.V. All rights reserved.