Evidence of Specific Interactions between Laser-Polarized Xenon and Arenesulfonic Acid Groups in Functionalized SBA-15 Materials

Abstract

SBA-15 samples functionalized with different arenesulfonic organic contents and prepared at 373 K were characterized by hyperpolarized 129Xe NMR spectroscopy. Variable-temperature measurements provide information on the organic groups distribution in the materials and on Xe diffusion in the mesopores. The heat of adsorption of xenon on the surface as well as its chemical shift value in interaction with the surface are deduced from the temperature dependence of the 129Xe chemical shift. The arenesulfonic group surface coverage was determined, and consequently, the “organic phase” contribution to the shielding constant was estimated. The evolution of the chemical shift with pressure allowed us to evaluate the “xenon−organic phase” interactions and hence distinguish the different organic contents. The slope of the pressure chemical shift dependence reveals the way in which the functionalization process took place. For low organic content (0.05 and 0.10), the slope is negative, indicating the presence of shallow micropores, while for high organic content (0.15 and 0.20), the chemical shift remains unchanged with the pressure showing that the modified mesoporous surface is homogeneous and micropores exempt. Information about the vicinity of Xe−organic phase are obtained from 129Xe−H CP and SPINOE experiments.

Probing the mobility of ibuprofen confined in MCM-41 materials using MAS-PFG NMR and hyperpolarised-129Xe NMR spectroscopy

“…This great enhancement of the signal intensity opens the possibility of exploring the accessibility of the nanochannels and the distribution of organic molecules in functionalized ordered mesoporous silica materials. 10 Magic-Angle Spinning (MAS) and Pulsed-Field Gradient (PFG) NMR techniques are also widely applied for probing porous media. 11 MAS NMR allows the obtention of high resolution spectra of adsorbed phases in nanoporous systems whereas PFG-NMR is used for understanding host-guest interactions by quantitatively determining the diffusion coefficients of adsorbed phases.…”

Infrared investigations of arenesulfonic modified mesoporous materials by the use of complementary probes

“…In most of the cases [20,22], TEOS is added to the acidic solution of the templating agent (Pluronic P123) and the precursor of the sulfonic group introduced later. We showed earlier [51][52][53] that mesoporous materials with rather good textural parameters are also obtained when TEOS is pre-hydrolysed in the absence of Pluronic P123. The specific surfaces and pore volumes of the resulting solids, SBA(R), decrease from 850 m 2 g -1 and 1.05 cm 3 g -1 (R = 0.05) to 470 m 2 g -1 and 0.4 cm 3 g -1 (R = 0.20) with increasing amounts of CSPTMS in the synthesis gel [53].…”

“…[42][43][44][45][46][47][48][49]). As part of our continuous effort to explore the porosity and the chemical properties of arenesulfonic modified mesoporous materials by spectroscopic methods [50,51], we proposed here, for the first time, an infrared study of their acidity using two basic probes of CO and NH 3 . The possibility mechanism also was discussed.…”

129Xenon NMR: Review of recent insights into porous materials

“…It has been also confirmed to be a powerful tool to obtain fast and reliable information concerning the distribution of metal particles inside the porosity [135] or the internal structure of organically-modified mesoporous materials [136]. and interconnections between main channels.…”