Steric effects in the sorption of n-butanol and tert-butanol by tailored phenyl-modified porous silicas

Sorption of n-butanol and tert-butanol on tailored phenyl-modified microporous and mesoporous silicas has been investigated. For the microporous sorbent, the form of the sorption isotherm depends on the stereochemistry of the alcohol. Sorption of straight chain n-butanol molecules gives a Type IV isotherm with partial blocking of pores by sorbed molecules. Sorption of the near-spherical tert-butanol molecules gives a Type I isotherm, without pore blocking. Sorption isotherms for the isomeric alcohols on the mesoporous sorbent are very similar, reflecting condensation in the same pore structure. In comparison to the weak adsorptive-adsorbent interactions found in earlier studies of water sorption (in which a hydrophobic surface was characterised), the alcohols show strengthened adsorptive-adsorbent interactions, the initial binding to the surface being via H-bonds with additional attractive interactions between the alkyl groups and the surface-attached phenyl moieties.