Proyecto de Investigación: SINTESIS DE MATERIALES EN CONDICIONES FUERA DE EQUILIBRIO
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ID
PCIN-2017-098
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Publicaciones
Ar+ ion bombardment dictates glycine adsorption on pyrite (1 0 0) surface: X-ray photoemission spectroscopy and DFT approach
(Elsevier BV, 2020-11-15) Gálvez Martínez, S.; Escamilla Roa, E.; Zorzano, María Paz; Mateo Martí, Eva; Agencia Estatal de Investigación (AEI); Zorzano, M. P. [0000-0002-4492-9650]; Unidad de Excelencia Científica María de Maeztu del Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Ar+ ion sputtering on pyrite surfaces leads to the generation of sulfur vacancies and metallic iron. Our research shows that sputtering and annealing processes drive electrostatic changes on the pyrite surface, which play an important role in the molecular adsorption of glycine. While both chemical species (anion and zwitterion) adsorb on a sputtered pyrite surface, the anionic form of glycine is favoured. Nevertheless, in both treatments (sputtered or annealed surfaces), molecules evolve from zwitterionic to anionic species over time. Quantum mechanical calculations based in Density Functional Theory (DFT) suggest the energy required to generate vacancies increases with the number of vacancies produced, and the atomic charge of the Fe atoms that is next to a vacancy increases linearly with the number of vacancies. This leads to enhanced redox processes on the sputtered pyrite surface that favour the adsorption of glycine, which is confirmed experimentally by X-ray Photoemission Spectroscopy (XPS). We have investigated theoretically the efficiency of the adsorption process of the zwitterionic glycine onto vacancies sites: this reaction is exothermic, i.e. is energetically favoured and its energy increases with the number of defects, confirming the increased reactivity observed experimentally. The experiments show a treatment-dependent molecular selectivity of the pyrite surface.
DFT study of the reduction reaction of calcium perchlorate on olivine surface: Implications to formation of Martian's regolith
(Elsevier BV, 2020-05-15) Escamilla Roa, E.; Zorzano, María Paz; Martín Torres, Javier; Hernández Laguna, A.; Sainz Díaz, C. I.; Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); 0000-0003-2286-8380; 0000-0002-4492-9650; 0000-0001-6479-2236; 0000-0003-0413-0761; 0000-0002-3872-0455; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Perchlorates have been found widespread on the surface of Mars, their origin and degradation pathways are not understood to date yet. We investigate here, from a theoretical point of view, the potential redox processes that take place in the interaction of Martian minerals such as olivine, with anhydrous and hydrated perchlorates. For this theoretical study, we take as mineral substrate the (1 0 0) surface of forsterite and calcium perchlorate salt as adsorbate. Our DFT calculations suggests a reduction pathway to chlorate and chlorite. When the perchlorate has more than 4 water molecules, this mechanism, which does not require high-temperature or high energy sources, results in parallel with the oxidation of the mineral surface, forming magnesium peroxide, MgO2, and in the formation of ClO3, which through photolysis is known to form ClO-O2. Because of the high UV irradiance that reaches the surface of Mars, this may be a source of O2 on Mars. Our results suggest that this process may be a natural removal pathway for perchlorates from the Martian regolith, which in the presence of atmospheric water for salt hydration, can furthermore lead to the production of oxygen. This mechanism may thus have implications on the present and future habitability of the Martian surface.
