1 research outputs found
Adsorption of Nitrate and Bicarbonate on Fe-(Hydr)oxide
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)Āoxide surfaces
using acidic, neutral, and basic simulated pH conditions. High-spin
states that follow the 5<i>N</i> + 1 (<i>N</i> is the number of Fe atoms, each having five unpaired electrons)
rule are preferred. Monodentate mononuclear (MM<sub>1</sub>) surface
complexes are shown to lead to the most favorable thermodynamic adsorption
for both bicarbonate and nitrate with ā63.91 and ā28.25
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