RESUMEN
Chalcopyrite, the world's primary copper ore mineral, is abundant in Latin America. Copper extraction offers significant economic and social benefits due to its strategic importance across various industries. However, the hydrometallurgical route, considered more environmentally friendly for processing low-grade chalcopyrite ores, remains challenging, as does its concentration by froth flotation. This limited understanding stems from the poorly understood structure and reactivity of chalcopyrite surfaces. This study reviews recent contributions using density functional theory (DFT) calculations with periodic boundary conditions and slab models to elucidate chalcopyrite surface properties. Our analysis reveals that reconstructed surfaces preferentially expose S atoms at the topmost layer. Furthermore, some studies report the formation of disulfide groups (S22-) on pristine sulfur-terminated surfaces, accompanied by the reduction of Fe3+ to Fe2+, likely due to surface oxidation. Additionally, Fe sites are consistently identified as favourable adsorption locations for both oxygen (O2) and water (H2O) molecules. Finally, the potential of computer modelling for investigating collector-chalcopyrite surface interactions in the context of selective froth flotation is discussed, highlighting the need for further research in this area.
RESUMEN
The increasing demand for natural gas as a clean energy source has emphasized the need for efficient gas separation technologies. Metal-organic frameworks (MOFs) have emerged as a promising class of materials for gas separation, with anion-pillared MOFs (APMOFs) gaining attention for their fine-tuned pore design and shape/size selectivity. In this study, we investigate the dynamical and electronic properties of three APMOFs, SIFSIX-3-Cu, SIFSIX-2-Cu-i, and SIFSIX-2-Cu, for the separation of methane from ethane, ethene, propane, propene, and N using computational simulations. Our simulations employ Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) techniques combined with Density Functional Theory (DFT) calculations. We find that that all three APMOFs exhibit promising separation capabilities for methane from propane and propene based on both thermodynamics and kinetics parameters. In addition, we use Noncovalent Interaction (NCI) analysis to investigate intermolecular interactions and find that the fluorine atoms in the MOF can polarize gas molecules and establish electrostatic interactions with hydrogen atoms in the molecule. Finally, we show that SIFSIX-2-Cu-i is a potential candidate for separating N2/CH4 due to its interpenetration.
RESUMEN
The oxidation of chalcopyrite, CuFeS2, is still not well understood and relevant in the context of the hydrometallurgical extraction of copper. Herein, we used DFT calculations within the periodic boundary conditions formalism to study the adsorption of O2 and [Fe(H2O)2(OH)3] molecules on the (001) and (112) surfaces of CuFeS2. The O2 molecule adsorbs strongly by a dissociative pathway at sulfur atoms on the (001) surface with an adsorption energy of - 76.5 kcal mol-1. The surface is chemically modified forming SO2 groups, in which the S-O bond length is calculated to be 1.47 and 1.54 Å. PDOS and Löwdin charges analyses indicate the oxidation of the sulfur atoms on the surface. We tested different adsorption modes of [Fe(H2O)2(OH)3], and a bidantade coordination with the Oads-Fesur and Feads-Ssur bond lengths of 2.02 and 2.47 Å is the most favorable with an adsorption energy of - 18.8 kcal mol-1 on the (001) surface. Adsorptions of each species are also observed on the (112) surface, but they are weaker than those observed on the (001) surface.
RESUMEN
The selective adsorption of CO2 in mixture with other greenhouse gases by porous materials is challenging and it has several consequences from the environmental and economic point of view. We carried out DFT calculations with periodic boundary conditions and plane waves basis set to better understand the adsorption of CO2, CO, CH4, N2, O2, and H2 within the pore of the metal-organic frameworks (MOFs) SIFSIX-2-Cu, SIFSIX-2-Cu-i, and SIFSIX-3-Cu. These porous materials have a copper ion coordinated to an organic linker and the inorganic SiF62- pillar, and they show a remarkable CO2 uptake. Our results show that the adsorption occurs preferentially close to the inorganic pillar SiF6, which polarizes the gas molecule, increasing the electrostatic contribution to the interaction. The adsorption strength correlates with the size of the pore, and it is stronger in the smaller porous of SIFSIX-3-Cu for all gases. The successive loading of CO2 in a T-shape form inside the porous indicates a synergic polarization effect, increasing the adsorption energy in SIFSIX-2-Cu and SIFSIX-2-Cu-i, but not in SIFSIX-3-Cu. For all materials, we observe the following order in the adsorption energy: CO2 > CH4 > CO > N2 > O2 > H2, suggesting that a thermodynamic separation could be possible; however, kinetic effects are also important in SIFSIX-3-Cu. Graphical abstract.
RESUMEN
A new dynamical discrete/continuum solvation model was tested for NH(4)(+) and OH(-) ions in water solvent. The method is similar to continuum solvation models in a sense that the linear response approximation is used. However, different from pure continuum models, explicit solvent molecules are included in the inner shell, which allows adequate treatment of specific solute-solvent interactions present in the first solvation shell, the main drawback of continuum models. Molecular dynamics calculations coupled with SCC-DFTB method are used to generate the configurations of the solute in a box with 64 water molecules, while the interaction energies are calculated at the DFT level. We have tested the convergence of the method using a variable number of explicit water molecules and it was found that even a small number of waters (as low as 14) are able to produce converged values. Our results also point out that the Born model, often used for long-range correction, is not reliable and our method should be applied for more accurate calculations.