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Title: Ar+ ion bombardment dictates glycine adsorption on pyrite (1 0 0) surface: X-ray photoemission spectroscopy and DFT approach
Authors: Gálvez Martínez, S.
Escamilla Roa, E.
Zorzano, María Paz
Mateo Martí, Eva
Keywords: Glycine;Pyrite surface;X-ray photoemission spectroscopy (XPS);Density Functional Theory (DFT);Sputtering process;Reactivity
Issue Date: 15-Nov-2020
Publisher: Elsevier BV
DOI: 10.1016/j.apsusc.2020.147182
Published version:
Citation: Applied Surface Science 530: 147182(2020)
Abstract: 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.
Description: Highlights Sulfur defects increase the selectivity of the adsorbed glycine species on pyrite. On a sputtered pyrite surface, the adsorption of the anionic form of glycine is favored. On a sputtered pyrite surface, glycine evolves from zwitterionic to anionic form. DFT calculations show that the atomic charge of Fe-vacancy atoms increases. DFT shows that the adsorption of zwitterionic glycine onto vacancies is exothermic.
ISSN: 0169-4332
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