Characterizing the Behavior of Water Interacting with a Nano‐Pore Material: A Structural Investigation in Native Environment Using Magnetic Resonance Approaches

• Published in: Chemphyschem 2024-08, Vol.25 (15), p.e202400053-n/a
• Main Authors: Ye, Kai, Chin, Sze Yuet, Xi, Nicole Lin, Sharma, Bhargy, Lu, Yunpeng, Xue, Kai
• Format: Article
• Language: English
• Subjects: confined fluid; Density functional theory; Liquid phases; Magnetic resonance imaging; MAS-NMR; MRI; nano pore; NMR spectroscopy; Pore size; Quantitative analysis; Silica glass; Size determination; Structural analysis
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.202400053

The study of fluid absorption, particularly that of water, into nanoporous materials has garnered increasing attention in the last decades across a broad range of disciplines. However, most investigation approaches to probe such behaviors are limited by characterization conditions and may lead to misinterpretations. In this study, a combined MRI and MAS NMR method was used to study a nanoporous silica glass to acquire information about its structural framework and interactions with confined water in a native humid environment. Specifically, MRI was used for a quantitative analysis of water extent. While MAS NMR techniques provided structural information of silicate materials, including interactive surface area and framework packing. Analysis of water spin‐spin relaxation times (T2) suggested differences in water confinement within the characterized framework. Subsequent unsuccessful delivery of paramagnetic molecule into the pores enabled a quantitative assessment of the dimensions that “bottleneck” the pores. Finally, pore sizes were derived from the paramagnetic molecular size, density function theory (DFT) simulation and characterizations on standard samples. Our result matches with Brunauer‐Emmett‐Teller (BET) analysis that the pore size is less than 1.3 nm. The use of a paramagnetic probe for pore size determination introduces a new approach of characterization in the liquid phase, offering an alternative to the conventional BET analysis that uses gas molecule as probes. In this work, we proposed a new characterization protocol to acquire structural information on frameworks and their interactions with confined water. By combining MRI, MAS NMR and the addition of a paramagnetic center, a more holistic elucidation of liquid‐structure interactions, framework structures, and pore accessibility was achieved. It provides the possibility to perform such structural characterization of porous materials in a hydrated environment.