ADSORPTION OF C-60 FULLERENE FROM ITS TOLUENE SOLUTIONS ON ACTIVE CARBONS - APPLICATION OF FLOW MICROCALORIMETRY

摘要

The adsorption of C-60 from its toluene solutions onto active carbons has been investigated. A flow adsorption microcalorimetry method was used to determine the amounts of adsorption and the corresponding enthalpies of displacement at 293 K for three active carbons: S-51 MB, S-51 WTX and Darco G-60. For S-51 MB the adsorption was measured at 5 different concentrations. For the remaining two carbons the measurements were made only at a C-60 concentration of 0.5 g L-1. The amounts of C-60 adsorbed and desorbed in two consecutive adsorption-desorption cycles, and the related integral molar enthalpies, were compared with those for a graphitised carbon black (Graphon). The BET specific surface areas, micropore volumes and mesopore surfaces, polar and apolar surface sites, and basal plane areas were estimated for all samples from the nitrogen adsorption isotherms (the BET plot and t-plot), enthalpies of adsorption of n-butanol from n-heptane and water, and enthalpies of adsorption of n-dotriacontane from n-heptane, respectively. Fullerene adsorption is a two-step process. At very low surface coverages strong irreversible adsorption of a small amount of C-60 produces a large molar integral enthalpy effect. At higher coverages, a weaker reversible component dominates the process and the enthalpy of displacement decreases with increasing density of adsorption, approaching a limited steady value. Darco G-60 has the highest adsorption capacity and irreversible component of adsorption at a given concentration of the equilibrium bulk phase (i.e. 0.5 g L-1). For Graphon, the adsorption of C-60 is completely reversible. (C) 1997 Elsevier Science Ltd. [References: 40]