First-Principles Study on Optoelectronic Properties of Fe-Doped Montmorillonite Clay

Abstract

A theoretical investigation is conducted to describe optoelectronic properties of Fe-doped montmorillonite nanoclay under spin states of low spin (LS), intermediate spin (IS), and high spin (HS). Ground state electronic properties are studied using spin-polarized density functional theory calculations. The nonradiative and radiative relaxation channels of charge carriers are studied by computing nonadiabatic couplings (NACs) using an "on-the-fly" approach from adiabatic molecular dynamics trajectories. The NACs are further processed using a reduced density matrix approach with the Redfield formalism. The computational results are presented for electronic density of states, absorption spectra, charge carrier dynamics, and photoluminescence (PL) by comparing various spin multiplicities. Results on spin α and spin β components are independent and quite different because of the partial occupation of Fe 3d states. Overall, HS is the most stable with the largest Fe−O distances. One finds different nonradiative relaxation pathways in space and on the time scale for electrons and holes. The Redfield PL reveals obvious Fe 3d−3d transitions for LS and IS.

Exploring the biointerfaces: ab initio investigation of nano-montmorillonite clay, and its interaction with unnatural amino acids

“…[18][19][20] Therefore, the use of polymer-based nanocomposites, including PCNs, represents a promising avenue for developing new materials with improved properties for tissue engineering applications. [21][22][23][24][25][26][27][28][29][30][31][32] In our study, we utilized a nanocomposite system to mimic the bone tissue environment, which consists of nano MMT clay co-doped with Fe and Mg. This clay, with the chemical formula NaSi 16 (Al 6 FeMg)O 20 (OH) 4 , exhibits negative charge states resulting from the isomorphic substitution of Al by Mg and Fe in MMT.…”

“…33 It consists of H, O, Si, Al, Mg, and Fe atoms arranged in two tetrahedral sheets and one octahedral sheet, with space between the triple-sheet layers. 21,34 A model for the mechanical behavior of Na-Montmorillonite clay 22 along with some first-principle studies conducted previously, provide valuable insight when examining the optical, structural, and electronic properties of transition metal-doped MMT 23,24 and Kaolinite 25 clay surfaces. Understanding the atomic-scale behavior of the montmorillonite clay surface is crucial due to its chemical properties, which enable the intercalation of organic molecules such as amino acids.…”

“…24 DFT+U approach was widely applied for the description of the layer structure and the electronic properties of iron-containing clay minerals. 23,49,50 The energy convergence criterion was set to 10 À6 eV, while the force convergence criterion of the ionic steps was 10 À2 eV Å À1 . A vacuum spacing of 15 Å was set to avoid interaction with the periodic image in the z-direction.…”

“…18–20 Therefore, the use of polymer-based nanocomposites, including PCNs, represents a promising avenue for developing new materials with improved properties for tissue engineering applications. 21–32…”

Molecular insights into the temperature and pressure dependence of mechanical behavior and dynamics of Na-montmorillonite clay

“…Among different clay minerals, montmorillonite (MMT) is a type of smectite (2 : 1) clay mineral with the chemical formula Al 2 Si 4 O 10 (OH) 2 . 5,6 These MMT clay minerals have a signicant impact on nuclear waste disposal, 7,8 shale gas formation or extraction, 9,10 and carbon dioxide geologic sequestration. 11 For example, bentonite, consisting mostly of MMT minerals, is a feasible buffer material for deep geological disposal of nuclear wastes because of its low permeability, excellent self-healing capability, and adsorption potential of radionuclides.…”