Dr. Esperanza Pavón González

Swelling layered clay minerals form an important sub-group of the phyllosilicate family. They are characterized by their ability to expand or contract in the presence or absence of water. This property makes them useful for a variety of applications, ranging from environmental technologies to heterogeneous catalysis, and including pharmaceutical and industrial applications. Solid State Nuclear Magnetic Resonance (SS-NMR) has been extensively applied in the characterization of these materials, providing useful information on their dynamics and structure that is inaccessible using other characterization methods such as X-ray diffraction. In this review, we present the key contributions of SS-NMR to the understanding of the mechanisms that govern some of the main applications associated to swelling clay minerals. The article is divided in two parts. The first part presents SS-NMR conventional applications to layered clay minerals, while the second part comprises an in-depth review of the information that SS-NMR can provide about the different properties of swelling layered clay minerals. © 2021 The Authors

Heavy metal contamination is a critical environmental issue, often involving complex multicomponent systems. Swelling brittle micas, a family of designer sorbents, have demonstrated exceptional heavy metal removal capabilities, yet their behabior in competitive adsorption systems remains largely unexplored. This study systematically investigates the simultaneous uptake of Pb²⁺, Cd²⁺, and Hg²⁺ on both as-synthesized brittle mica and its thiol-functionalized counterpart. Using X-ray diffraction (XRD) and nuclear magnetic resonance (NMR), we reveal critical structural transformations occurring at both short- and long-range scales during adsorption. Our findings demonstrate that competitive adsorption governs metal uptake, leading to a reduction in total adsorption capacity compared to single-metal systems. However, selectivity toward specific metal cations remains unchanged, irrespective of competing species or surface functionalization. Overall, this study not only improves our understanding of heavy metal adsorption but also paves the way for more effective and sustainable sorbent design in environmental remediation.

The development of effective and environmentally friendly methods for separating hazardous radionuclides from waste poses a significant technological challenge. 137Cs and 131I are among the most important radionuclides discharged into the environment by nuclear power plants. One of the best ways to eliminate them involves adsorption on clay minerals. In this regard, studies have demonstrated that organofunctionalized clay minerals are effective adsorbents. Thus, this study investigates the capability of organofunctionalized synthetic design clay minerals to jointly eliminate cesium and iodine. The adsorbents studied are a range of organofunctionalized clay minerals with alkylammonium cations of different alkyl chain lengths (2, 3 and 18) and some physical mixtures of raw clay minerals and octadecylammonium compounds. Organofunctionalized synthetic swelling highly charged micas are effective adsorbents for the simultaneous adsorption of cesium and iodine. In addition, the optimal system is a mixture of Na-M4 with octadecylammonium (50% w/w).

Bionanocomposites based on layered inorganic components, as clays, and polymers of biological origin, as chitosan, have a major impact in medical and environmental fields, being economical and environmentally friendly materials. Na-Mn micas (n = 2 and 4) with controlled surface charge, high cation exchange capacity and swelling behaviour, are attractive inorganic composite components that exhibit improved adsorption properties compared to other inorganic solids which makes them potentially useful for bionanocomposites. The goal of this research was to explore the potential use of those synthetic brittle micas to form eco-friendly bionanocomposites with chitosan biopolymer. Hence, chitosan-mica bionanocomposites were prepared by ion-exchange reaction between chitosan solution and synthetic high charge mica. X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis, MAS-NMR spectroscopy and zeta-potential have been employed for bionanocomposites characterization. The results showed that the adsorption of chitosan is effective, although a chitosan portion remains in the outer surface being hydrogen-bonded to the tetrahedral sheet of the silicate. © 2019, The Author(s).

The stability under different atmospheres (dry or wet nitrogen or air, HF, reaction medium) and the catalytic performances of BaF2-LaF3 based catalysts for the fluorination of 2-choropyridine by Cl/F exchange with HF as fluorinating agent were investigated. Thermal decomposition of metal trifluoroacetate and precipitation from nitrate precursor methods were used as synthesis methods. Depending on the synthesis method and the La/La + Ba molar ratio (x), an intimate mixture of BaF2 and LaF3 metal fluorides or a Ba1−xLaxF2+x mixed metal fluoride with high specific surface area were formed. In comparison with BaF2, the mixed metal fluorides led to higher specific surface areas and prevented the sintering phenomenon observed under wet atmosphere which led to a significant decrease of the specific surface area. Moreover, Ba1−xLaxF2+x catalysts had not evolved under the fluorination reaction contrary to BaF2 for which a stable BaF2−xClx material (with x close to 0.8) was formed by reaction with the by-product HCl. The turn over frequency (TOF) was similar for all barium based catalysts for the fluorination of 2-chloropyridine. Nevertheless, among the studied materials, Ba0.5La0.5F2.5 was the most promising catalyst for the transformation of 2-chloropyridine due to high activity (related to its high specific surface area and its moderate strength of Lewis acidity) and high stability. © 2016 Elsevier B.V.