Chemical reactivity of amino-functionalized mesoporous silica thin films obtained by co-condensation and post-grafting routes

Amino-functionalized mesoporous hybrid thin films were synthesized by co-condensation and post-grafting routes. These materials were characterized by X-ray photoelectron spectroscopy (XPS), small angle X-ray scattering (SAXS-2D), X-ray reflectometry (XRR) and transmission electron microscopy (TEM). The chemical reactivity of the amine functional groups was determined via amidation with trifluoroacetic acid anhydride and characterized with XPS and contact angle measurements. We found that the amidation reaction proceeds successfully in both cases showing that the amine functionalities are available for reaction in the films obtained by both synthesis routes. However we also found that the fraction of amine functionalities available for reaction depends strongly on the functionalization route: ∼37% of amine functional groups are available for reaction in post-grafted films whereas ∼16% of them are available in co-condensed films. This difference can be rationalized in terms of the different nature of the synthesis routes employed as in co-condensed films a fraction of amine functions are contained within the oxide backbone and thus unavailable for reaction. Our findings are important in the designed of functional materials where chemical functionalization might be a crucial step.