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magnesium compounds; surface chemistry; adsorption; ab initio calculations; photodissociation; ultraviolet radiation effects; electron traps; ab-initio; magnesium-oxide; defect centers; color-centers; earth oxides; density; anions; nanoparticles; vacancies
Abstract:
We used UV light to generate site-selective O- hole centers at three-coordinated corner oxygen sites on MgO nanocubes. These highly reactive O- radicals split H-2 homolytically and, in the course of this reaction, become hydroxylated and produce hydrogen atoms. The hydrogen atoms adsorb predominantly at cube edges and dissociate into surface-trapped electrons and protons. We propose that the experimentally observed (H+)(e(-)) centers are formed adjacent to the hydroxyl groups generated in the homolytic splitting process and can be defined as (H+)(3C)center dot(e(-))(H+)(NC) centers where 3C and NC refer to the coordination numbers of the corresponding hydroxylated oxygen sites. Our ab initio embedded cluster calculations reveal that the electronic properties of (H+)(3C)center dot(e(-))(H+)(4C) centers situated along MgO nanocube edges are consistent with both the electron-paramagnetic-resonance signal parameters and the reported optical-absorption properties. The transformation of corner O- centers into the (H+)(3C)center dot(e(-))(H+)(NC)-type centers prevents their recombination with electronic surface centers and, hence, significantly alters the electronic structure of MgO nanocubes by introducing shallow electron traps.
