Theoretical Study of H<sub>2</sub>O Adsorption on
Zn<sub>2</sub>GeO<sub>4</sub> Surfaces: Effects of Surface State and
Structure–Activity Relationships
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Abstract
We employed the density functional
theory to investigate the interaction of H<sub>2</sub>O with Zn<sub>2</sub>GeO<sub>4</sub> surfaces, considering both perfect and defective
surfaces. The results revealed that the interaction of H<sub>2</sub>O with Zn<sub>2</sub>GeO<sub>4</sub> surfaces was dependent on the
structure of the latter. For perfect surfaces, H<sub>2</sub>O adsorbed
at the Ge<sub>3c</sub>···O<sub>2c</sub> site of a (010)
surface could spontaneously dissociate into an H atom and an OH group,
whereas H<sub>2</sub>O tended to adsorb at the O<sub>2c</sub>-M<sub>3c</sub>-O<sub>3c</sub> site of a (001) surface by molecular adsorption.
The presence of oxygen defects was found to strongly promote H<sub>2</sub>O dissociation on the (010) surface. Analysis of the surface
electronic structure showed a large density of Ge states at the top
of the valence band for both perfect and defective (010) surfaces,
which is an important factor affecting H<sub>2</sub>O dissociation.
In contrast, perfect and defective (001) surfaces with surface Ge
states buried inside the valence band were significantly less reactive,
and H<sub>2</sub>O was adsorbed on these surfaces in the molecular
form. This information about the adsorbate geometries, catalytic activity
of various surface sites, specific electronic structure of surface
Ge atoms, and their relevance to surface structure will be useful
for the future design of the Zn<sub>2</sub>GeO<sub>4</sub> photocatalyst,
as well as for the atomistic-level understanding of other structure-sensitive
reactions