Substitutional Iron (Fe) in 2:1 clays

A. V. GIL REBAZA.; R.E. ALONSO; M. L. MONTES; V. L. DIAZ DE ROSA; M. A. TAYLOR.

Workshop; IX Workshop on novel methods for electronic structure calculations; 2021

Environmental pollution is a present-day concern. In particular. water pollution has become one of the most important issues due to its direct impact on life. Some widely used remediation technologies are based on the process of sorption of pollutants. Among the sorbent materials, clay minerals such as montmorillonite (MMT) are well qualified (1). Recently, efforts are being made to design remediation materials that possess permanent magnetism. This allows to manipulate them by external magnetic fields, thus reducing the potential health risks associated with direct manipulation methods (2) The present work summarizes the preliminary results of a theoretical-experimental study of the influence of substitutional Fe on Na-MMT, Na0.41 [(MgAl3O8, n(H2O). The present results will allow further studies on magnetically modified clays. The modelling of Fe-containing clays was performed within the Density Functional Theory framework. Pseudopotential and plane-wave method (Quantum Espresso Code (3)) was used for the ab-initio calculations, with the GGA-PBE approximation for the exchange correlation term (4). The starting structure was the pristine phase Na-MMT (5). First, the magnesium (Mg) atom was replaced by Fe in the unit cell, and then the dilution was decreased by means of 2x1x1 and 2x2x1 supercells, by replacing one Mg atom by one Fe. The electric field gradient in the different atoms and the hyperfine parameters for Fe were determined using the GIPAW code (6), and then compared with the experimental results obtained by Mössbauer spectroscopy. Also, the d001 of the different proposed structures was calculated to compare with those obtained by XRD for Na-MMT. It was observed that the replacement of Mg by Fe in all the unit’s cells considered decreases d001 Reference1. Uddin MK. A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade. Chemical Engineering Journal. 2017;308:438-62. 2. Montes ML, Barraqué F, Bursztyn Fuentes AL, Taylor MA, Mercader RC, Miehé-Brendlé J, et al. Effect of synthetic beidellite structural characteristics on the properties of beidellite/Fe oxides magnetic composites as Sr and Cs adsorbent materials. Materials Chemistry and Physics. 2020;245:122760. 3. Giannozzi P, Andreussi O, Brumme T, Bunau O, Buongiorno Nardelli M, Calandra M, et al. Advanced capabilities for materials modelling with Quantum ESPRESSO. J Phys: Condens Matter. 2017;29(46):465901. 4. Perdew JP, Burke K, Ernzerhof M. Generalized Gradient Approximation Made Simple. Phys Rev Lett. 1996;77(18):3865-8. 5. Scholtzová E, Jankovič L, Tunega D. Stability of Tetrabutylphosphonium Beidellite Organoclay. J Phys Chem C. 2018;122(15):8380-9. 1,2,4(OH)4(Si8O12)]26. Yates JR, Pickard CJ, Mauri F. Calculation of NMR chemical shifts for extended systems using ultrasoft pseudopotentials. Phys Rev B. 2007;76(2):024401.