Surface Decoration of MgO Nanocubes with Sulfur Oxides: Experiment and Theory

We investigated the effect of surface sulfate formation on the structure and spectroscopic properties of MgO nanocubes using X-ray diffraction, electron microscopy, several spectroscopic techniques, and ab initio calculations. After CS2 adsorption and oxidative treatment at elevated temperatures the MgO particles remain cubic and retain their average size of ~6 nm. Their low coordinated surface elements (corners and edges) were found to bind sulfite and sulfate groups even after annealing up to 1173 K. The absence of MgO corner specific photoluminescence emission bands at 3.4 and 3.2 eV substantiates that sulfur modifies the electronic properties of characteristic surface structures, which we attribute to the formation of (SO3)2- and (SO4)2- groups at corners and edges. Ab initio calculations support these conclusions and provide insight into the local atomic structures and spectroscopic properties of these groups.