Bifunctional ordered mesoporous materials: direct synthesis and study of the distribution of two distinct functional groups in the pore channels

Abstract

In this paper, we report the study of the distribution (regular or irregular distribution or segregation) of two distinct functional groups located within the pore channels of ordered mesoporous organosilicas. For that purpose, we have chosen two probes, both of them depending on the proximity of two organic groups. One was based on the chelating property towards EuCl₃ of acetyl acetonate (acac) and carboxylate groups. The other concerns the ion-exchange capability of the sulfonic acid moieties, which depends on the proximity of the acid groups. In the first part, various ordered monofunctional mesoporous organosilicas were prepared by co-condensation of tetraethylorthosilicate (TEOS) and an organotriethoxysilane Σ–(CH₂)₃–Si(OEt)₃ (with Σ = acetylacetonate (acac), CN, SH, Cl, NH₂ and H) in the presence of the triblock copolymer P123 as a structure-directing agent at pH = 1.5. Thanks to the probes, we have first showed that all the organic groups (SH, CN, acac) are accessible and regularly distributed within the channel pores of monofunctional mesoporous materials. In the second part, several ordered mesoporous materials containing two distinct functional groups including at least one probe were prepared in one step by co-condensation of TEOS and two organotriethoxysilanes Σ–(CH₂)₃–Si(OEt)₃ and Σ′–(CH₂)₃–Si(OEt)₃, under the same experimental conditions as previously. Taking into account the results obtained with the monofunctional materials as references, the distribution of two distinct functional groups located on the pores surfaces of mesoporous materials was determined and discussed.