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Tuning of the Surface-Exposing and Photocatalytic Activity for AgX (X = Cl and Br): A Theoretical Study
journal contribution
posted on 2012-09-13, 00:00 authored by Xiangchao Ma, Ying Dai, Jibao Lu, Meng Guo, Baibiao HuangThe underlying physical mechanism and dynamics of crystal
growth
in tuning the crystal morphology and surface exposing by adjusting
the concentration of the precursor NaCl are elucidated by examining
the surface energies, adsorption energy, and total energy for several
surfaces upon adsorption of Cl in AgCl based on first-principles calculations.
Our results indicate that the specific surface structures of different
surfaces and the nature of ionic interactions between Ag and adsorbed
Cl atoms in AgCl facilitate the reversal of relative surface energy
upon adsorption of Cl, enabling the possibility of tuning the crystal
morphology and surface exposing by adjusting the concentration of
precursor NaCl. Two critical concentrations of NaCl at which the morphology
of crystal changes are predicted, in satisfactory accordance with
the experimental observations. Moreover, for the first time, we propose
that the morphology and surface exposing of AgBr can be controlled
by subtly tuning the concentration of precursor NaBr; however, the
adjustment is quite demanding due to the weaker interaction between
Br and Ag on the surfaces in AgBr. In addition, the analysis of electronic
structures indicates that the (111) surface with Ag exposure exhibits
higher photocatalytic activities due to the reduction of band gap
resulting from the dangling bonds of surface Ag atoms without altering
the oxidation potential. On the other hand, because adsorption of
Cl on all surfaces decreases the oxidation potential, one should eliminate
the surface adsorbates as much as possible to obtain higher photocatalytic
activities.