New insights into the surface properties of hard-templated ordered mesoporous carbons

Abstract

Although hard-templated ordered mesoporous carbons (OMCs) have been widely studied in the past decades, their surface properties, especially surface wettability, have not been investigated in detail. This study shows that as-synthesized hard-templated OMCs (sucrose- and anthracene-derived OMCs, i.e., OMC-S and OMC-A, respectively, formed using the identical hexagonal mesoporous silica template) have very different surface characteristics, with OMC-S being significantly more hydrophobic than OMC-A. This is attributed to the presence of a thin, hydrophobic, microporous carbon shell layer surrounding the mesoporous core of the OMC-S particles, seen here for the first time by transmission electron microscope tomography and confirmed by the slower water uptake and slower electrochemical kinetics of OMC-S vs. OMC-A. At the same time, the mesopores within both OMC-S and OMC-A remain hydrophilic, as shown primarily by water vapor sorption measurements, due to the high density of surface oxygen groups inside the pores, as also confirmed by cyclic voltammetry. These oxygen groups are proposed to have been derived from COSi bonds that formed at the carbon/silica interface during the carbonization process, leaving COH groups behind after removal of the silica template. These findings are relevant to a broad range of nanoporous carbon surfaces prepared with hard templates.