Structural and thermodynamic investigation of the hydration-dehydration process of Na+-Montmorillonite using DFT calculations

DFT Simulation of the Water Molecule Interaction with the (00l) Surface of Montmorillonite

“…The (001) surface simplified models of Na-and Ca-MMT were both realized starting from a stoichiometric pyrophyllite bulk structure [Al 2 Si 4 O 10 (OH) 2 , space group C1] that was theoretically investigated in previous work [38]. In detail, the required steps can be summarized as follows: a single Mg 2+ /Al 3+ substitution in the octahedral sheet was inserted in the PYP model, and the resulting negative charge of the 2:1 layer was balanced by a sodium ion, which was initially placed over the hexagonal siloxane ring and above the ditrigonal holes, according to previous findings [26,27,29]. This model (Na-MMT, Figure 1a) has a chemical formula Na( glected in past theoretical studies [14,26,37], and here this important physical aspect was considered when dealing with charged layered silicates.…”

“…a (001) slab model of pyrophyllite with a doubled a lattice parameter was "cut" from the bulk of the mineral. This model has lateral dimensions a = 10.335 Å and b = 8.983 Å, with surface area 92.841 Å 2 and formula Al8Si16O40(OH)8 (Z = 4); 2. a single Mg 2+ /Al 3+ substitution in the octahedral sheet was inserted in the PYP model, and the resulting negative charge of the 2:1 layer was balanced by a sodium ion, which was initially placed over the hexagonal siloxane ring and above the ditrigonal holes, according to previous findings [26,27,29]. This model (Na-MMT, Figure 1a) has a chemical formula Na(Al7Mg)Si16O40(OH)8, which is similar to that of a Wyoming-type montmorillonite [Na0.66(Al, Mg)4Si8O20(OH)4] [39]; 3. finally, two Al 3+ ions in the O sheet were substituted by Mg 2+ and, to counter-balance the resulting double negative charge, a calcium ion was placed over the layer as in the previous point.…”

“…There are several studies on the investigation of the dehydration, rehydration, and swelling behaviour of montmorillonites, at both the experimental and theoretical levels [7,[26][27][28][29][30]. The latter ones are mainly focused on the swelling of expandable clay minerals at the atomic level, providing a correlation between the observable properties and the crystal structure.…”

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

“…Computational simulations provide a powerful tool to determine the most probable positions of the cations in the lamellae, as well as the number of cations in the interlamellar domain. Tavares et al and Costa et al, using ab initio density functional theory (DFT) calculations with periodic boundary conditions, were able to accurately predict crystallographic and electronic properties of clays such as double lamellar hydroxides. , There are several theoretical studies that analyze the hydration of ions confined in the interlayer space of montmorillonites, − investigations that involve the interaction of organic components which exploit the adsorptive properties of Mt − for application as adsorbent of pollutants, and other medical applications.…”

Hidrólise básica de garrafas de pet pós-consumo: reciclagem química

“…O pico da fase em 2θ do Quartzo no intervalo 26,597° não se deslocou para ângulos menores este resultado confirma que as antocianinas se intercalaram apenas nas lamelas da Mnt. O deslocamento em relação ao padrão teórico pode estar relacionado ao aumento do volume do parâmetro de rede, durante a incorporação de antocianinas as partículas são sucessivamente plasticidade e ampliadas, a diminuição do fator de multiplicidade e com fator de orientação preferencial indo para um estado amorfo (BOURG et al, 2007;FONSECA et al, 2017). Confirmando a intercalação das antocianinas entre as camadas de Mnt.…”