Combined XAFS Spectroscopy and Ab Initio Study on the Characterization of Iron Incorporation by Montmorillonite

Abstract

Iron occurs in clay minerals in both ferric and ferrous forms. Depending on its oxidation state and the environmental conditions, it can participate in redox reactions and influence the sorption processes at surfaces of clay minerals. Knowing the oxidation state and the preferential structural position of Fe and Fe is essential for the detailed understanding of the mechanism and kinetics of such processes. In this study, molecular dynamics (MD) calculations based on density functional theory (DFT+U) were applied to simulate the incorporated Fe in bulk montmorillonite and to explain the measured Fe K-edge X-ray absorption fine structure (XAFS) spectra. The analysis of the experimental data and simulation results suggested that iron in montmorillonite is preferentially incorporated as Fe into the octahedral layer. The simulations showed that there is no preferential occupation of cis- or trans-sites by Fe and Fe in bulk montmorillonite. A very good agreement between the ab initio simulated and the measured XAFS spectra demonstrate the robustness of the employed simulation approach.

Framework Modifications and Dehydration Path of a Ag+-Modified Zeolite with STI Framework Type

“…The amplitude reduction factor ( 2 0 S ) was set to 1. A similar protocol was recently used for EXAFS spectra of structural Fe in clay minerals 51,52 .…”

Biochemical, Histological Changes, Protein Electrophoretic Pattern, and Field Application of CuPb–Ferrite/TiO2 Nanocomposites for Controlling Terrestrial Gastropod Eobania vermiculata (Müller)

“…The spectra of the obtained NPs show distinctive bands at 451 cm –1 (metal ion–oxygen at the octahedral site) and 679 cm –1 (metal ion–oxygen at the tetrahedral site), which are the major bands of −Fe 2 O 4 groups in CuPb–Ferrite/TiO 2 NPs. , A critical examination of the FTIR spectra reveals the absorbance peak at 451 cm –1 can be assigned to the inherent stretching vibrations of the metal at the tetrahedral site, whereas the v2-lowest band, seen in the range 400 cm –1 and below, is caused by the octahedral metal stretching. In general, Fe 3+ ions prefer to occupy octahedral and tetrahedral positions . Additional observations reveal high absorption peaks at 3408, 1477, and 1374 cm –1 .…”

Atomic scale mechanism of clay minerals dissolution revealed by ab initio simulations

“…al, 2007). This setup model parameters have been proven to reproduce structural data for clay minerals in our previous simulations (Keri et al, 2017;Keri et al, 2019). Before the start of the ab initio MetaDynamics run the system was equilibrated for 2 ps.…”