Probing Functionalities and Acidity of Calcined Phenylene-Bridged Periodic Mesoporous Organosilicates Using Dynamic Nuclear Polarization NMR, Diffuse Reflectance Infrared Fourier Transform Spectroscopy, and X-ray Photoelectron Spectroscopy

Owing to their high surface area, their high stability, and their hydrophobicity, periodic mesoporous organosilica (PMO) materials represent promising catalytic support for environmentally 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 X-ray photoelectron spectroscopy prove that calcination at 450 {\deg}C results in the oxidation of phenylene bridges into (poly)phenols but also into 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 {\deg}C still exhibit ordered mesopores. We show that the phenol and carboxylic acid functionalities of PMOB calcined at 450 {\deg}C protonate the NH2 group of 1-(3-aminopropyl)imidazole (API) in water at room temperature, but no formation of a covalent bond between API and the calcined PMOB functionalities has been detected.