Adsorption of Nitrate and Bicarbonate on Fe-(Hydr)oxide

Nancy Y. Acelas, Cacier Hadad, Albeiro Restrepo, César Ibarguen, Elizabeth Flórez

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Abstract

© 2017 American Chemical Society. In this work, we used density functional theory calculations to study the resulting complexes of adsorption and of inner- and outer-sphere adsorption-like of bicarbonate and nitrate over Fe-(hydr)oxide surfaces using acidic, neutral, and basic simulated pH conditions. High-spin states that follow the 5N + 1 (N is the number of Fe atoms, each having five unpaired electrons) rule are preferred. Monodentate mononuclear (MM1) surface complexes are shown to lead to the most favorable thermodynamic adsorption for both bicarbonate and nitrate with −63.91 and −28.25 kJ/mol, respectively, under neutral conditions. Our results suggest that four types of regular and charged-assisted hydrogen bonds are involved in the adsorption process; all of them can be classified as closed-shell (long-range or ionic). The formal charges induce unusually short and strong hydrogen bonds. The ability of high multiplicity states of Fe clusters to adsorb oxyanions in solvated environments arises from orbital interactions: the 4s virtual orbitals in Fe have a large affinity for the 2p-type electron pairs of oxygens.
Original languageAmerican English
Pages (from-to)5455-5464
Number of pages10
JournalInorganic Chemistry
Volume56
Issue number9
DOIs
StatePublished - 1 May 2017

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