Enhanced Resolution Analysis for Water Molecules in MCM-41 and SBA-15 in Low-Field T2 Relaxometric Spectra.

Grzegorz Stoch,Artur T Krzyżak

doi:10.3390/molecules26082133

Abstract

Mesoporous silica materials are the subjects for relaxometric NMR studies in which we obtain information on the properties of molecules in confined geometries. The signal analysis in such investigations is generally carried out with the help of the Inverse Laplace Transform (ILT), which is accompanied by a regularization procedure. The appropriate selection of the regularization method may positively affect the resolution of the spectrum and the essence of the final conclusions. In this work, we examined the MCM-41 and SBA-15 model systems in various saturation states, using L-Curve regularization for relaxation spectra based on our own version of the fast fast ILT implementation. In a single relaxometric spectrum, the water contributions from the internal volume in the pores and between the silica particles were identified, which allowed us to trace the dynamics of the corresponding drying trends during the removal of water from the sample as a function of total water saturation.

Highlights

Spectra T2 obtained with L-Curve regularization are shown in Figure 3 for MCM-41
Intensities for different locations found from spectra along a series of water concentrations are presented in Tables 1 and 2, and visualized in and in Figure 4 for SBA-15
We understand here series of water concentrations are presented in Tables 1 and 2, and visualized in Figas the sum of values in the range containing the maximum of the line

Summary

Introduction

Water molecules trapped in silica mesoporous materials behave differently than free water. As shown by Grünberg et al [1] with the help of 1 H MAS NMR spectra, we are able to identify different water contributions in such materials due to different chemical environments for the surface water and the water from the pore’s interior space. What makes this identification feasible is standard Fourier transform (FT) methodology that splits the overall signal into groups of spins rotating with different Larmor frequencies, embodied in the frequency-domain spectrum

Results

Discussion

Conclusion