The distribution of lithium ions in heated synthetic montmorillonites was studied by using 19F, 7Li MAS and 7Li{19F} TEDOR nuclear magnetic resonance technics. To get the best of NMR spectroscopy, ...Na-montmorillonites, free of paramagnetic centres (Fe2+, Fe3+), were synthesized in fluoride medium, in order to have substitution of some hydroxyl groups by fluorine in the octahedral layer (Na0.35(Al1.69Mg0.36)VI(Si3.86Al0.14)IVO10(OH0.95F0.05)2). After Li+ exchange, mild heat treatments (from 110 to 250 °C during 24 h) were applied to follow the lithium migration. Both 19F and 7Li MAS spectra indicate that the lithium migration operates in two steps: at 110 °C, 86% of the lithium ions have moved to the hexagonal site. The remaining interlayer ions move progressively to this site when the heating temperature is in the range 170–250 °C. For the first time a direct fluorine–lithium distance of 2.23 Å was measured by 7Li{19F} TEDOR, which uses fluorine as a highly selective and NMR-sensitive witness of atomic-scale motions inside porous media, and which agrees with the preferred hexagonal site for Li+ migration.
•Synthetic fluorine-substituted montmorillonite specially tailored and treated to monitor the lithium migration upon heating•Fluorine and lithium MAS NMR spectra revealed highly resolved features, with unprecedentedly narrow linewidths•7Li{19F} TEDOR NMR experiments gave a direct Li-F internuclear measurement of 2.23 Å•This study is in favour of a lithium migration toward the montmorillonite hexagonal site upon heat treatment.
Richard Klemen was the first teacher of enzymology at the University of Ljubljana. His early career in Ljubljana ended in January 1942 when he moved to Vienna, Austria. During the war he conducted ...experiments that led him to describe the so-called Hofmann-Klemen effect in clay. Later he was a research assistant and titular associate professor in the field of biochemical technology at the Vienna Technical University and finally a lecturer at the University of Natural Resources in Vienna. His life is an interesting example of a scientist and educator whose Gottscheer German origin would probably prevent him from continuing his career in post-war Yugoslavia. At the same time, he did not achieve in Austria the positions and status that his former colleagues and students had achieved in Slovenia. Although he was almost forgotten, he remains important as the first trained enzymologist and teacher of enzymology in Slovenia. This article also presents his full bibliography.
Neutron powder diffraction measurements on lithium and cesium saturated montmorillonite samples before and after heat treatment at 300°C are studied, in order to undertake a complete refinement of ...crystal structure and unravel the migration mechanism for the interlayer cations of Li or Cs. Rietveld analysis of the corresponding diffraction patterns finds that montmorillonite crystallizes in the
C
2/
m
space group with unit cell dimensions consistent with the size of the specific interlayer cation. We show that thermal treatment affects the two types of samples in a different way. This is with respect to their unit cell dimensions and the migration of Li from the 2b to the 2c clay lattice site, in constrast to the Cs positioning which remains effectively unchanged.
The layer charge reduction of two Li-saturated montmorillonites is referred to application of microwave radiation at 2.45 GHz for dispersions and 30.0 GHz for the solid powders. Efficiency of these ...treatments was compared to the same conditions applying conventional heating. The samples were heated in the temperature and time windows corresponding to 190–270 °C and 30–120 min, respectively. Changes in the mean layer charge were monitored by the determination of cation exchange capacity values using exchange of triethylene tetraamino copper ions. The charge reduction of the montmorillonites in aqueous dispersions was rather low (<30%) despite the fact, that high Li+ concentration dissolved in solution was selected (1 mol L−1). This behaviour was attributed to the very high water content in used dispersions and high hydration enthalpy of Li+ cations. Nevertheless, the microwave heated dispersions (2.45 GHz) showed detectable layer charge reduction as compared to conventionally heated dispersions, where no significant changes were found.
Solid powders with different content of exchangeable lithium ions were prepared with solutions having different molar fraction of Li+ and Na+ cations (0%, 20%, 40%, 60%, 80%, 100% of Li+). Final composition of interlayer cations was analysed with ICP-OES. In contrary to dispersions, the microwave treatment of the prepared powders revealed high layer charge reduction, which was much higher than for conventionally heated powders. The efficiency was enhanced with increasing interlayer lithium content but reached a limiting value depending on the montmorillonite used. Migration of the lithium into the structure of the montmorillonite supported with microwaves was extremely fast, finished probably within the few minutes of the treatments. The exchangeable Li+ cations are accelerated through alternating electric field of microwaves and highly efficient layer charge neutralisation occurs. Infrared spectroscopy showed that the products obtained with microwave treatments correspond to the materials heated conventionally for much longer periods of time. Hence, applying microwaves the time and energy requirement can be significantly reduced. The X-ray diffraction showed that montmorillonite layers were able to swell in ethyleneglycol upon charge reduction, if the cation exchange capacity was not reduced more than 20–40%.
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