Probing Functionalities and Acidity of Calcined Phenylene-Bridged Periodic Mesoporous Organosilicates Using (DNP)-NMR, DRIFTS and XPS #DNPNMR

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From The DNP-NMR Blog:

Probing Functionalities and Acidity of Calcined Phenylene-Bridged Periodic Mesoporous Organosilicates Using (DNP)-NMR, DRIFTS and XPS #DNPNMR

Pirez, Cyril, Hiroki Nagashima, Franck Dumeignil, and Olivier Lafon. “Probing Functionalities and Acidity of Calcined Phenylene-Bridged Periodic Mesoporous Organosilicates Using (DNP)-NMR, DRIFTS and XPS.” The Journal of Physical Chemistry C, February 19, 2020, acs.jpcc.9b11223.


https://doi.org/10.1021/acs.jpcc.9b11223.


Owing to their high surface area, their high stability and their hydrophobicity, periodic mesoporous organosilica (PMO) materials represent promising catalytic support for environmental-friendly chemical processes in water. We investigate here how the calcination of PMO material with benzene linkers (PMOB) allows its functionalization. Conventional and Dynamic Nuclear Polarization (DNP)-enhanced NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy and Xray photoelectron spectroscopy prove that calcination at 450°C results in the oxidation of phenylene bridges into (poly)phenols but also in carboxylic acids. Ketone, aldehyde as well as allyl and aliphatic alcohol functionalities are also observed but their amount is much lower than that of carboxylic acids. The calcination also cleaves the Si-C bonds. Nevertheless, N2 adsorption-desorption measurements, powder X-ray diffraction and transmission electron microscopy indicate that the PMOB materials calcined up to 600°C still exhibit ordered mesopores. We show that the phenol and carboxylic acid functionalities of PMOB calcined at 450°C protonate the NH2 group of 1-(3- aminopropyl)imidazole (API) in water at room temperature but no formation of covalent bond between API and the calcined PMOB functionalities has been detected.


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