# A Wide-Ranging NMR Probe for Multiscale Structures
## 5 Applications
### Other Materials  
Due to the high level of detail provided by xenon NMR spectroscopy, this technique has been used to study the porous structure and connectivity of crystalline mesoporous TiO\({}_{2}\) prepared via a single-step synthesis [137]. Variable temperature hyperpolarized spectra showed two distinct downfield peaks which coalesced at 233 K, indicating the existence of at least two different environments accessible by xenon. With the aid of XRD and TEM, these two environments were determined to be mesopores formed from aggregation of anatase nanoparticles and mesoporous channels constituted by rutile nanorods. Furthermore, their interconnectivity was observed with 2D EXSY experiments acquired at different exchange times. As an example of the application of \({}^{129}\)Xe NMR for the study of naturally occurring porous systems, in 2012, this technique was employed to characterize a series of Italian building stone materials [138]. The porous structures of several different materials were characterized, and the differences were correlated to the mineral composition and to the microscale characteristics of the samples, as determined by other experimental techniques. Moreover, the spectra of some of the samples showed negative chemical shift signals up to \(-30\) ppm, as can be seen in Figure 14, which were attributed to the presence of transition metal cations, in agreement with the elemental compositions. Lastly, the effects of weathering were studied by freshly cutting one of the samples starting from the bulk material and acquiring spectra at different exposure times to the atmosphere. Significant changes in the porous structure were observed with varying the exposure time, proving that the material adsorbed relevant amounts of atmospheric chemicals, such as water and oxygen. In a similar example, [PERSON] et al. have characterized the porous structures of hydrated cements and Chinese shales [139]. While the cements gave \({}^{129}\)Xe signals compatible with the presence of mesopores, the spectra of the shales showed extremely large signals, from about \(-300\) ppm to \(300\) ppm, with two maxima at \(-140\) ppm and at \(50\) ppm. This peculiar feature was attributed to the presence of paramagnetic Fe and Mn species. Minerals containing these metals were also detected in the XRD analyses of shale samples. In a subsequent work, shales from USA were analyzed and compared to the Chinese ones [140]. These samples did not show the presence of paramagnetic impurities, contrary to the Chinese shales. Furthermore, from \({}^{129}\)Xe NMR spectra, the authors were able to estimate the pore sizes to be between \(1\) and \(10\) nm. Another study on naturally occurring materials was published in 2011 [141]. Porous soil materials and model systems representative of soil components were analyzed using conventional and hyperpolarized \({}^{129}\)Xe NMR. These techniques allowed defined and interconnected meso and micropores, structural constrictions (bottle-necks), and multi-domain particle structures to be distinguished. Mesoporous silicon sponges (MSS) have been recently proposed as anode materials for Li-Ion batteries. Their intrinsic meso/macroporous structure allows to overcome the problem of Si volume expansion during the lithiation process, which leads to the pulverization of silica particles and to a rapid loss of performances of conventional silicon anodes [142]. In 2017, [PERSON] and co-workers employed hyperpolarized \({}^{129}\)Xe NMR to characterize a series of MSS with different pore and particle sizes [143]. Spectra acquired at \(300\) K showed broad peaks for all the materials, indicating the presence of heterogeneous pore size distributions (Figure 15). Moreover, the chemical shift was observed to increase with increasing particle sizes. This result was interpreted in terms of the exchange between the inside and the outside of the particles.