Comparison of water and benzene as probe liquids in thermoporometry of mesoporous carbons

Abstract

Water and benzene were compared as probe liquids for thermoporometric characterization of mesoporous carbons. For testing, four different carbonaceous materials were prepared by soft- or hard-templating procedures with mesopore diameters in the range 3–12 nm. In addition, all materials were tested in hydrophobic (pristine, carbonized at 900 °C) and hydrophilic (moderate oxidation by persulphate) form. The results show that both tested liquids express a good linear correlation between heat of melting in pores (measured as DSC peak area) and volume of mesopores. Melting point depression of probe liquid confined in pores related to mesopore size was found out to be steeper for benzene confirming a higher value of Gibbs-Thomson constant of benzene compared to water. Neither heat of melting in pores nor melting point depression were affected by carbon surface oxidation. Contrary, the non-freezing layer (δ layer) of a liquid in pores was considerably wider for most of hydrophilic samples than hydrophobic ones when water was employed, while it stayed nearly constant when benzene was applied. Nevertheless, both tested probe liquids generally enable to obtain similar pore size distributions if appropriate values of δ layers are used. Benzene as a probe liquid in thermoporometry of carbons have some advantages compared to water but only in limited cases. Benzene can be recommended for characterisation of large mesopores and its usage can be beneficial for comparison of analogous samples with different surface chemistry.