(196c) Internal Surface Functionalization of Pure-Silica Zeolite MFI Crystals and Film with Amines, Aromatics, and Amino-Alcohols

The organic functionalization of zeolites has been attracting much attention because it can significantly widen the range of their applications. Internal surface functionalization of zeolite could be accomplished by covalently binding organic groups within the micropore structure. The functionalized zeolite would then become an organic-inorganic hybrid with a potential for a diverse range of new applications, made possible by variations in structure and functionality of the incorporated organic moiety. One of the potential applications of zeolite functionalized crystals is to be used as selective separation agents. The functionalization of zeolite films could also lead to enhanced selectivity by fine tuning the zeolite pore sizes and enhancing the adsorption selectivity.

In this study, we have functionalized pure silica MFI zeolite crystals and films with three functional groups: aliphatic alcohols, amines, and aromatics. Aliphatic alcohols have shown increased hydrophobicity in mesoporous materials after treatment. Amines are known to have large affinity for CO₂ molecules. Successful aromatic functionalization is also important, because it enables using aromatic group for further functionalizations.

Towards this end, we report the preparation and characterization of pure-silica MFI zeolite crystals whose internal pore structures are functionalized with aliphatic alcohols (1-butanol, 1-hexanol), aromatic alcohols (benzenemethanol), amino-alcohols (3-amino-1-propanol), and amines (1-propanamine, and 1,3-propanediamine). The contents of these functional groups in the functionalized materials are between 0.72 to 0.93 mmol/SiO₂ which corresponds to roughly one functional group located at every channel intersection in the zeolite pore network. Our ¹³C cross-polarization magic angle spinning (CP-MAS) NMR and TGA/DSC investigation suggests that these functional groups are chemically bound to the internal pore sites. ²⁹Si CP-MAS NMR studies suggest that the functional group loading is strongly dependent on the concentration of internal silanol defects. We also demonstrate the use of the functionalization method for MFI zeolite films, and characterize the presence of functional groups by photoacoustic FTIR spectroscopy.