Distribution of amino groups on a mesoporous silica surface after submonolayer deposition of aminopropylsilanes from an anhydrous liquid phase

The reaction of mesoporous silica MCM-41 with various aminopropylsilanes was investigated. The distribution of grafted amino groups after submonolayer deposition from anhydrous toluene was probed by fluorescein labeling in conjunction with photoluminescence spectroscopy and pore size analysis. Monoalkoxysilanes generally distributed more uniformly than monopodal and dipodal trialkoxysilanes. The outcome of the grafting reaction additionally depended on the nature of the amino group. Secondary amines grafted more efficiently than their primary analogues. Moreover, it was found that the polarity of the solvent strongly affects the distribution of the amino groups in the case of strongly interacting aminopropylsilanes.