Abstract
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.
ACKNOWLEDGEMENTS
The authors would like to acknowledge E. Colnay for her helpful assistance for the TGA measurements.
Notes
a From TGA analysis.
a estimated from the t-plot plateau slope.
b estimated at the relative pressure value of P/P0 = 0.97.
c estimated from t-plot plateau y-intercept.
d estimated from t-plot by y-intercept of the linear regression calculated from t values between 0.44 and 0.74 nm.
e estimated from the BJH desorption plots.