2 research outputs found
Adsorption and Desulfurization Mechanism of Thiophene on Layered FeS(001), (011), and (111) Surfaces: A Dispersion-Corrected Density Functional Theory Study
Layered transition-metal
chalcogenides have emerged as a fascinating new class of materials
for catalysis. Here, we present periodic density functional theory
(DFT) calculations of the adsorption of thiophene and the direct desulfurization
reaction pathways on the (001), (011), and (111) surfaces of layered
FeS. The fundamental aspects of the thiophene adsorption, including
the initial adsorption geometries, adsorption energies, structural
parameters, and electronic properties, are presented. From the calculated
adsorption energies, we show that the flat adsorption geometries,
wherein the thiophene molecule forms multiple π-bonds with the
FeS surfaces, are energetically more favorable than the upright adsorption
geometries, with the strength of adsorption decreasing in the order
FeS(111) > FeS(011) > FeS(001). The adsorption of the thiophene
onto the reactive (011) and (111) surfaces is shown to be characterized
by charge transfer from the interacting Fe d-band to the π-system
of the thiophene molecule, which causes changes of the intramolecular
structure including loss of aromaticity and elongation of the C–S
bonds. The thermodynamic and kinetic analysis of the elementary steps
involved in the direct desulfurization of thiophene on the reactive
FeS surfaces is also presented. Direct desulfurization of thiophene
occurs preferentially on the (111) surface, as reflected by the overall
exothermic reaction energy calculated for the process (<i>E</i><sub>R</sub> = −0.15 eV), with an activation energy of 1.58
eV
Structures and Properties of As(OH)<sub>3</sub> Adsorption Complexes on Hydrated Mackinawite (FeS) Surfaces: A DFT-D2 Study
Reactive
mineral–water interfaces exert control on the bioavailability
of contaminant arsenic species in natural aqueous systems. However,
the ability to accurately predict As surface complexation is limited
by the lack of molecular-level understanding of As–water–mineral
interactions. In the present study, we report the structures and properties
of the adsorption complexes of arsenous acid (AsÂ(OH)<sub>3</sub>)
on hydrated mackinawite (FeS) surfaces, obtained from density functional
theory (DFT) calculations. The fundamental aspects of the adsorption,
including the registries of the adsorption complexes, adsorption energies,
and structural parameters are presented. The FeS surfaces are shown
to be stabilized by hydration, as is perhaps to be expected because
the adsorbed water molecules stabilize the low-coordinated surface
atoms. AsÂ(OH)<sub>3</sub> adsorbs weakly at the water–FeS(001)
interface through a network of hydrogen-bonded interactions with water
molecules on the surface, with the lowest-energy structure calculated
to be an As–up outer-sphere complex. Compared to the water–FeS(001)
interface, stronger adsorption was calculated for AsÂ(OH)<sub>3</sub> on the water–FeS(011) and water–FeS(111) interfaces,
characterized by strong hybridization between the S-<i>p</i> and O-<i>p</i> states of AsÂ(OH)<sub>3</sub> and the surface
Fe-<i>d</i> states. The AsÂ(OH)<sub>3</sub> molecule displayed
a variety of chemisorption geometries on the water–FeS(011)
and water–FeS(111) interfaces, where the most stable configuration
at the water–FeS(011) interface is a bidentate Fe–AsO–Fe
complex, but on the water–FeS(111) interface, a monodentate
Fe–O–Fe complex was found. Detailed information regarding
the adsorption mechanisms has been obtained via projected density
of states (PDOS) and electron density difference iso-surface analyses
and vibrational frequency assignments of the adsorbed AsÂ(OH)<sub>3</sub> molecule