Structural and Electronic Properties of Iron-Doped Sodium Montmorillonite Clays: A First-Principles DFT Study

[Image: see text] First-principles calculations done via density functional theory were used to study the structural and electronic properties of sodium montmorillonite clay (Mt-Na(+)) of general formula M(x)Al(3)Si(8)O(24)H(4)Na·nH(2)O (M(x): Mg or Fe). The final position of the interlamellar sodium atom is found to be close to the oxygen atoms located on the upper surface of silica. Following Fe-Mt-Na(+) system relaxation, with subsequent analysis of magnetic moment and magnetic states, the electroneutrality of the system established that both Fe(2+) and Fe(3+) oxidation states are possible to occur. The Mg(2+)-Mt-Na(+) material shows a band gap energy greater than that of Fe(2+)-Mt-Na(+) when iron is in the octahedral site. It is found that the valence-band maximum and the conduction-band minimum of iron-doped montmorillonite are both at the Γ-point, while it is at V → Γ for magnesium-doped montmorillonite. The calculated band gap from hybrid functional (HSE06) of Fe(2+)-Mt-Na(+) is equal to 4.3 eV, exhibiting good agreement with experimental results obtained from ultraviolet–visible spectroscopy of the natural Mt-Na(+) (Cloisite-Na(+)).