Letter Surface free energy g d s ) of active carbons determined by inverse gas chromatography: in¯uences of the origin of precursors, the burn off level and the chemical modi®cation L. Cossarutto, C. Vagner, G. Finqueneisel, J.V. Weber * , T. Zimny LCASPP, Universite  de Metz, IUT, Dept Chimie, Rue Victor Demange, 57500 Saint Avold, France Received 17 January 2001; accepted 10 March 2001 Abstract The dispersive component of the surface free energies g d s ) of commercial active carbons AC) from various origins were determined by inverse gas chromatography at in®nite dilution IGC-ID). This method discriminates clearly the AC produced from wood and activated/carbonised with phosphoric acid) and those from coconut-shell carbonised and steam activated at 8508C).ThevaluesforthelastACfromcoconut)aretwicehigherthanthevaluesforACofwoodorigin.Thestructureand shapeoftheporeshavetobeconsideredtoexplainthesevalues.ItseemsthatforAC,IGC-IDgloballycharacterisesthemost energetic micropores. This can be observed, in this work, by two ways: i) washing of commercial AC chemically activated) allows to liberate a part of the micropores blocked by soluble phosphate and consequently increases the g d s value; ii) modifying coconuts AC by chemical treatment formamide) results in a strong decrease of both microporosity and g d s value. On the contrary, thermal activation of the modi®ed AC increases at the same time the microporosity and the surface free energy. Finally, we demonstrate that the IGC method is also an useful tool to monitor in situ the evolutions of the surface properties of carbonaceous materials. # 2001 Elsevier Science B.V. All rights reserved. PACS: 68.35.Md; 82.65.D Keywords: Surface free energy; Inverse gas chromatography; Active carbon 1. Introduction ActivecarbonsAC)arewidelyusedasadsorbents in industrial processes like gas cleaning or water treatment. Different AC, adapted to their ®nal utilisa- tions,areproposedaccordingtotheprecursorsandthe methodsofproduction.Theclassicalcharacteristicsof AC are derived from adsorption/desorption isotherms i.e. surface area and pores distribution) [1]. If these parameters are of great practical importance, never- theless interesting information like the energy of adsorption is usually not taken into account. Some methodsweredeveloped,andrecentlyimprovedwith thisaim,likehighresolutionargonadsorption[2,3]or inverse gas chromatography IGC) [4±10]. This last technique allows the determination of surface free energy of adsorption g d s ). Brie¯y, gaseous molecular probesareelutedthroughthestudiedsolidstationary phase) in gas chromatographic conditions. The g d s value is obtained by combination of Gray's method Applied Surface Science 177 2001) 207±211 * Corresponding author. Tel.: 33-3-87-93-91-00; fax: 33-3-87-93-91-01. E-mail address: jvweber@iut.univ-metz.fr J.V. Weber). 0169-4332/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0169-433201)00228-8