Investigation about iron(III) incorporation into layered double hydroxides: Compositional and structural properties of Mg2FeyAl(1−y)(OH)6-Cl and Zn2FeyAl(1−y)(OH)6-Cl

Effect of Iron Isomorphic Substitution in Mg:Al and Zn:Al-Layered Double-Hydroxide Structures by Means of First Principle Calculations

“…This behavior of the LDH structures has also been observed in Mg- and Zn-LDH crystals synthesized experimentally in the laboratory. 16 , 17 By comparing both theoretical and experimental results ( Figure 5 ), we find that the computational method used here not only provides crystal structures with cell parameters in good agreement with those previously reported but also reproduces a slight change in the a / b cell axes measured in synthesis experiments with different iron contents. This behavior was also observed experimentally in LDH hydrotalcite–pyroaurite systems Mg(AlFe), showing the same slope (0.05) of these linear relationships.…”

“…However, after several trials, no convergence was obtained. Therefore, the best approach for calculating the LDH with Fe 3+ is to use Hubbard correction with the optimized spin state (SP+U) and with the minimal net spin state equal to zero (SP0+U), whose optimized cell parameters are in good agreement with the previously reported experimental results 17 ( Table 1 ). The SP+U method yields the closest cell parameters to the experimental values.…”

“…In the ZnFeLDH structures, the same differences have been observed, changing the positions of the peaks from 59.2 to 58.3° for (110) and from 61.3 to 59.7° for (113) by increasing the Fe content. Figueiredo et al 17 described the same behavior of the (110) and (113) peaks with the increasing amount of iron in the structure, i.e., their position moved to lower 2θ angles. This result also confirms the goodness of our calculations, since in addition to reproducing the structure, the same behavior has been observed with the increase of the iron content in the LDH structure, as described in previous works, i.e., the increasing the parameter a and b axes and the displacement toward lower angles of the peaks (110) and (113) in the diffractograms.…”

“…The diffractograms are similar to those experimentally obtained in the previous works on the LDH structures. 16 , 17 , 32 Taking into account that no symmetry was imposed in these calculations, some small peaks appear in the calculated diffractograms, in addition to the main LDH peaks that cannot be assigned to any LDH plane, which are spurious planes produced for considering a small number of unit cells. In our theoretical diffractograms ( Figure 7 ), the positions of the (003) and (006) peaks are quite close for the different amounts of Fe cations considered; for example, in the case of the (003) peak, the positions are around 11.9° for both MgFe-LDH and ZnFeLDH structures.…”

“… 12 − 14 In all cases, it was found that M 3+ cations avoid close contact. 13 , 15 Rozov et al 16 found crystallographic changes with the presence and content of Fe in MgFe-LDH without considering the Fe distribution along the crystal lattice, which has been subsequently demonstrated by Figueiredo et al 17 The Fe 3+ cation distribution in the octahedral sheet of minerals can affect some properties, such as the nuclear magnetic resonance (NMR) and infrared spectroscopy properties in clay minerals. 18 − 20 …”