Adsorption of [60]fullerene from toluene solutions on MCM-41 silica: A flow microcalorimetric study

Flow microcalorimetry has been used to study the adsorption of [60]fulleren e from toluene solutions on mesoporous MCM-41-type silica at room temperatu re. A silicate mesophase was prepared making use of tetradecyltrimethylammo nium (C14TMA) hydroxide as surfactant template. Two samples of the same bat ch were calcined at different time periods. A fine-pore silica was prepared in the presence of octyltrimethylammonium bromide. The three samples were characterized by nitrogen gas adsorption-desorption at 77 K and 1-butanol a dsorption from n-heptane at 298 K. Flow microcalorimetry was subsequently u sed to quantify the adsorption of [60]fullerene in terms of the amount adso rbed and the heat evolved at different solution concentrations and flow rat es. The two MCM-41 samples prepared using C14TMAOH, the first of which was calcined 10 months before the other, displayed almost identical textural an d surface properties, including the quantity and the enthalpy of fullerene adsorption. Fullerene adsorption is completely reversible and the amount ad sorbed is very small even at equilibrium concentrations close to the solubi lity limit. The thermal effects accompanying adsorption and desorption cycl es are unexpectedly high, and evidence is presented to substantiate the con cept of hydrodynamic effects, which give an exothermic and flow rate-depend ent contribution to the total enthalpy change.