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
L. Cossarutto et al., 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, APPL SURF S, 177(3), 2001, pp. 207-211
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.