Grafting of paired 3-aminopropyltrialkoxy silanes onto mesoporous silica and adsorptions of isomers of benzenedialdehydes.

A pair of 3-aminopropyltriethoxysilane molecules coupled with m- and p-benzenedialdehydes are grafted onto SBA-15 mesoporous silica, followed by the removal of benzenedialdehyde by hydrolysis. These paired 3-aminopropyl-grafted SBA-15, denoted (m)N- and (p)N-SBA-15, respectively, adsorb their own template benzenedialdehydes with a larger Langmuir constant K(L) than in other combinations of adsorbates and adsorbents. In addition, K(L) for the m-isomer is larger in the adsorption on (m)N-SBA-15 than on (p)N-SBA-15 and vice versa for the p-isomer. In contrast to this quadruple preference in the adsorption, a larger K(L) in the adsorption of the m-isomer onto the (m)N-adsorbent than onto the (p)N-adsorbent is the only adsorption preference that is observed in the case of Cab-O-sil M7D-based adsorbents prepared by the same procedure. The difference between the two kinds of silicas can be attributed to the surface curvature, concave or convex on a nanometre scale, which is supported by the evidence from spectroscopic analyses.