Effect of Mg(II) and Na(I) Doping on the Electronic Structure and Mechanical Properties of Kaolinite

Abstract

Because kaolinite has multiple defects, it is very important to study the effect of different doped cations on the electronic structure and mechanical properties of kaolinite (Al4Si4O18H8) from the microscopic point of view with the first-principle calculation method. The results exhibited that the doping of Mg(II) and Na(I) makes the ion bond and layer spacing of kaolinite crystal change, and the bond length of the chemical bond between the doped and O atom is positively related to the atomic radius of the doped cations. Compared with undoped kaolinite crystal, the band gap width of the Mg-doped and Na-doped kaolinite crystal was larger, but the typical insulator characteristics were still maintained. Compared with undoped kaolinite crystal, Mg-doped and Na-doped kaolinite crystal had more electron transfer to O, while the Mg–O bond and Na–O bond had more ionic bond properties and less covalent bond composition than the Al–O bond. Finally, the elastic properties of undoped, Mg-doped, and Na-doped kaolinite crystal were further analyzed by calculating the elastic constant matrix. The influence of doping Mg(II) and Na(I) on C11 and C22 was greater than that on C33, indicating that doping had a greater influence on the stiffness in the direction of the parallel crystal plane. The doping of Mg(II) and Na(I) weakened the rigidity of kaolinite crystal materials and improved the plasticity and ductility of the materials. The atom-scale information provided a basis for explaining the mechanical behavior of kaolinite and is expected to provide guidance for solving the deformation problems in soft rock roadways.

Local Environments in Iron-Bearing Clay Minerals by DFT Approaches: The Case of Structural Fe in Kaolinite

“…This structure was used as the clay mineral host lattice, in which an Fe atom is introduced as a bulk impurity, replacing one Al atom in the 34-atom unit cell. The resulting doping amount is similar to that considered in recent studies for other heavy doped-kaolinites (Fu and Yang, 2017;Zhao et al, 2020).…”

“…Iron octahedral environment parameters obtained using DFT and DFT-D2+U approaches for the charge states 0 and − 1 (indicated in parenthesis): octahedron volume V, average distance <Fe-O>, distortion parameters ζ, ∆, Σ, and Θ, distance H between the octahedron faces at the inner and outer surfaces, distance h from Fe atom to the face at the outer surface, and h/H ratio. kaolinite (Nisar et al, 2011;Chao et al, 2012;Richard and Rendtorff, 2019;Zhao et al, 2020). In a similar way, in Fig.…”

“…In regard to theoretical studies, first-principles calculations based on the Density Functional Theory (DFT) have become very useful tools to model kaolinites and other related clay minerals. In the last decade, DFT-based methods were successfully used to investigate different properties of defect-free kaolinites (Mercier and Le Page, 2008;Zhou et al, 2009;Smrcok et al, 2010;Paris, 2014) and also kaolinite with defects (vacancies and impurities) (He et al, 2009;Nisar et al, 2011;Johnson and Otero-de-la-Roza, 2012;Pietzsch et al, 2015;Fu and Yang, 2017;Zhao et al, 2020). In particular, DFT modeling aided to reconcile discrepancies regarding the exact geometry of the kaolinite layer structure (White et al, 2009;Richard and Rendtorff, 2019).…”

Heterogeneous Photocatalysis of Amoxicillin under Natural Conditions and High-Intensity Light: Fate, Transformation, and Mineralogical Impacts

“…Conversely, the amoxicillin degradation was lower in kaolinite (band gap = 4.99 eV) [ 43 ] presence under irradiated conditions than the Light Control. The observed rate constant was 0.00105 h −1 (R 2 = 0.997) with a half-life of 660 h. The photocatalytic effect of the kaolinite for amoxicillin degradation is insignificant due to limited light penetration in the presence of clay particles.…”

Atomic Structure, Electronic and Mechanical Properties of Pyrophyllite under Pressure: A First-Principles Study

“…C 55 , C 56 , and C 66 are calculated by a Taylor expansion of the total energy of the system with respect to a small strain of the lattice primitive cell volume [41]. The strain amplitude δ is varied in steps of 0.01 from δ = −0.06 to 0.06.…”