Tailoring the Hydrophobic Character of Mesoporous Silica by Silylation for VOC Removal

MCM-41 and non-ordered mesoporous silica were modified using hexamethyl-disilazane (HMDS). The hydrophobic and hydrophilic properties of grafted materials were studied and compared to a purely all silica BEA zeolite by using competitive and noncompetitive water toluene adsorption. A linear correlation between the silylation degree and the hydrophobicity measurements has been found for MCM-41 materials. Even if highly silylated MCM-41 material have more hydrophilic sites (silanol groups) than all silica zeolite, water molecule condensation is not observed because these sites are isolated. Thus, the highly silylated MCM-41 sample exhibits not only hydrophobicity 2.3 times higher than all silica BEA zeolite but also possesses a storage capacity for toluene and chlorobenzene 3 times higher than this zeolite. In competition with water, the organic molecule (toluene or chlorobenzene) adsorption is always favored even if water adsorption is enhanced by chlorobenzene polarity.