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

Abstract

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 ia H-bonds with additional attractive interactions between the alkyl groups and the surface-attached phenyl moieties.