Molecular selective adsorption of alkylphenols and alkylanilines from water by alkyl-grafted mesoporous alumina: A comparative study to alkyl-grafted mesoporous silica

Molecular selective adsorption of alkylphenols and alkylanilines onto n-alkyl-grafted mesoporous alumina was investigated and compared to that onto n-alkyl-grafted mesoporous silica. Water adsorption isotherms revealed that the hydrophilic nanospaces of the mesoporous alumina became highly hydrophobic after dodecyl-grafting. Alkylanilines and alkylphenols with a large alkyl group, such as 4-heptylaniline (HA) and 4-heptylphenol (HP), were preferentially adsorbed by dodecyl-grafted mesoporous alumina (C12-MPA). A comparison of the adsorption isotherms of HA on C12-MPA with those on octyl-grafted mesoporous silica (C8-MPS) revealed that the surface density of the HA molecule adsorbed on C12-MPA was much lower than that adsorbed on C8-MPS. The different adsorption properties of the alkyl-grafted alumina and alkyl-grafted silica can be explained by a mechanism in which adsorbed molecules fit into the nanostructure by interacting with both the organic hydrophobic nanospaces and the inorganic pore walls, i.e. organic–inorganic cooperative molecular recognition within the nanostructure.