Direct synthesis and solid-state NMR characterization of cubic mesoporous silica SBA-1 functionalized with phenyl groups

Hsien Ming Kao, Chia Hsiu Liao, Tzu Ti Hung, Yu Chi Pan, Anthony S.T. Chiang

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Well-ordered mesoporous silicas SBA-1 (cubic Pm3n symmetry) functionalized with phenyl groups have been synthesized via co-condensation of tetraethoxysilane (TEOS) and phenyltriethoxysilane (PhTES) under acidic conditions. The synthesis parameters such as temperature, type of surfactant, and synthesis composition have been systematically investigated as a function of PhTES contents. The phenyl-containing units are incorporated quantitatively and reach a maximum PhTES loading up to 33 mol % (based on silicon) without a significant degradation of the structural ordering of the Pm3n mesophase. A combination of multinuclear (1H, 13C, 29Si) solid-state NMR and two-dimensional (2D) solid-state NMR correlation techniques such as 13C{1H} and 29Si{1H} HETCOR (heteronuclear correlation) and 1H-1H exchange NMR has been used to establish framework locations of phenyl functional groups that are incorporated in the mesoporous structure and their interactions with the surfactant molecules. 2D 13C{1H} HETCOR NMR experiments reveal that the phenyl moieties are in close spatial proximity to the trimethylammonium headgroups of the cationic surfactant species in the as-synthesized materials, suggesting that there are some specific interactions between them to maintain the surfactant packing parameter (g) smaller than 1/3 necessary for the formation of the cubic mesophase. The detection of couplings between the protons associated with various 29Si species via 29Si{1H} HETCOR NMR established that the T silicon species due to the phenyl groups incorporated are in closer proximity to the Q 4 silicon species than to the Q3 silicon species. This observation also provides direct molecuiar-level evidence for the co-condensation of PhTES and TEOS in the synthesis of mesoporous organosilicas.

Original languageEnglish
Pages (from-to)2412-2422
Number of pages11
JournalChemistry of Materials
Issue number6
StatePublished - 25 Mar 2008


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