Ab Initio Study of the Interaction of Dimethyl Methylphosphonate with Rutile (110) and Anatase (101) TiO2 Surfaces

Density functional theory has been applied to an ab initio study of the molecular and the dissociative adsorption of dimethyl methylphosphonate (DMMP) on TiO2. Rutile (110)-(1 × 1) and anatase (101)-(1 × 1) surfaces, free of defects and of OH, have been modeled using two-dimensionally periodic slabs (2-DPS) and also clusters with unsaturated edge atoms terminated with pseudohydrogen. Molecular adsorption occurs via the formation of a Ti5c···O═P dative bond at unsaturated, 5-fold-coordinated Ti surface sites. C−H···O bonds between CH3 groups and surface O atoms also contribute, but dative bonding between methoxy O atoms and Ti5c sites has no significant effect. In 2-DPS calculations, all TiO2 surfaces considered give about the same adsorption energy (ΔEads) for molecular adsorption. There does, however, appear to be a small variation among the different substrates whereby ΔEads increases with surface energy. Two spectroscopic signatures of molecular adsorption have been computed. One is a shift of −70 cm−1...