A density functional study of NO2 adsorption on perfect and defective MgO (1 0 0) and Li/MgO (1 0 0) surfaces
The density functional theory (DFT) in combination with embedded cluster model have been used to study the adsorption of nitrogen dioxide molecule (NO2) on Li atom deposited on the surfaces of metal oxide MgO (1 0 0) on both anionic (O2-) and defect (Fs and Fs+-centers) sites. The adsorption energy (Eads) of NO2 molecule (N-down as well as O-down) in different positions on O-2, Fs and Fs+-sites is considered. The geometrical optimizations have been done for the additive materials and MgO substrate surfaces. The formation energies have been evaluated for Fs and Fs+ of MgO substrate surfaces. The ionization potential (IP) and electron affinity (eA) for defect free and defect containing surfaces have been calculated. The adsorption properties of NO2 are analyzed in terms of the adsorption energy, the electron donation (basicity), the elongation of Nsbnd O bond length and the atomic charges on adsorbed materials. The densities of states (DOS) have been calculated and used for examining the adsorption properties. The NO2 molecule is dissociated due to the interaction with the defective substrate surface (Fs-site) producing an oxygen atom strongly chemisorbed to the vacancy of the substrate and gaseous NO far away from the surface. The presence of the Li atom increases the surface chemistry of the anionic O2--site of MgO substrate surfaces (converted from physisorption to chemisorption). On the other hand, the presence of the Li atom decreases the surface chemistry of the Fs and Fs+-sites of MgO substrate surfaces. Generally, the NO2 molecule is strongly adsorbed (chemisorption) on the MgO substrate surfaces containing Fs and Fs+-centers.