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]fullerene from toluene solutions on mesoporous MCM-41-type silica at room temperature. A silicate mesophase was prepared making use of tetradecyltrimethylammonium (C14TMA) hydroxide as surfactant template. Two samples of the same batch 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 adsorption from n-heptane at 298 K. Flow microcalorimetry was subsequently used to quantify the adsorption of [60]fullerene in terms of the amount adsorbed and the heat evolved at different solution concentrations and flow rates. The two MCM-41 samples prepared using C14TMAOH, the first of which was calcined 10 months before the other, displayed almost identical textural and surface properties, including the quantity and the enthalpy of fullerene adsorption. Fullerene adsorption is completely reversible and the amount adsorbed is very small even at equilibrium concentrations close to the solubility limit. The thermal effects accompanying adsorption and desorption cycles are unexpectedly high, and evidence is presented to substantiate the concept of hydrodynamic effects, which give an exothermic and flow rate-dependent contribution to the total enthalpy change.