RESUMO
Lollingite (FeAs2) is considered an arsenic-bearing mineral that is oxidized faster than arsenopyrite. The geometric configuration, chemical valence bond, and microscopic reaction of the oxidation on the surface of lollingite were systematically studied, which are of great significance for understanding the mechanism of oxidative dissolution. X-ray photoelectron spectroscopy (XPS) measurements and density functional theory (DFT) calculations were carried out to characterize the (101) surface oxidation process of lollingite under the O2/O2 + H2O conditions. XPS results confirmed that the participation of water molecules can promote the formation of abundant OH structures on the surface of lollingite, while the relative concentration of O, As(III), and Fe(III) increased. Moreover, the DFT results demonstrated that the (101) As-terminal plane of FeAs2 was the most stable surface with the lowest surface energy. H2O molecules were physically adsorbed onto the Fe atoms of the lollingite surface, while oxygen molecules can readily be adsorbed on the Fe-As2 site by chemical adsorption processes. The oxidation process of the lollingite surface with water includes the following mechanisms: adsorption, dissociation, formation of the hydrogen bond, and desorption. The dissociation of the H2O molecule into OH and H led to the hydroxylation of both Fe and As atoms and the formation of hydrogen bonding. The participation of H2O molecules can also reduce the reaction energy barrier and accelerate the oxidation reaction of the lollingite surface, especially as far as the water dissociation and formation of hydrogen bonds are concerned. According to PDOS data, there is considerable hybridization between the d orbitals of bonded Fe atoms and the p orbitals of O atoms, as well as between the p orbitals of bonded As atoms and the p orbitals of O atoms. Due to a strong propensity for orbital hybridization and bonding between the s orbitals of the H atoms in H2O molecules and the p orbitals of the O atoms on the (101) surface, water molecules have the ability to speed up the oxidation on the surface.
RESUMO
BACKGROUND: The increasing number of organic and inorganic structures promotes the development of the "Big Data" in chemistry and material science, and raises the need for cross-platform and web-based methods to search, view and edit structures. Many web-based three-dimensional (3D) structure tools have been developed for displaying existing models, building new models, and preparing initial input files for external calculations. But few of these tools can deal with crystal structures. RESULTS: We developed a user-friendly and versatile program based on standard web techniques, such as Hyper Text Markup Language 5 (HTML5), Cascade Style Sheet (CSS) and JavaScript. Both non-periodic organic molecule and crystal structure can be visualized, built and edited interactively. The atom, bond, angle and dihedral in a molecule can be viewed and modified using sample mouse operations. A wide range of cheminformatics algorithms for crystal structure are provided, including cleaving surfaces, establishing vacuum layers, and building supercells. Four displayed styles, namely "Primitive cell", "Original", "In-cell" and "Packing" can be used to visualize a unit cell. Additionally, the initial input files for Vienna Ab-initio Simulation Package (VASP) and Gaussian can be obtained by interacting with dialog boxes in 3DStructGen. CONCLUSIONS: 3DStructGen is a highly platform-independent program. It can provide web service independently or can be integrated into other web platforms. Other than local desktop software, it does not require any additional effort to install the system but a web browser supporting HTML5. 3DStructGen may play a valuable role in online chemistry education and pre-processing of quantum calculations. The program has been released under MIT open-source license and is available on: https://matgen.nscc-gz.cn/Tools.html.