Computational study of the adsorption of dimethyl methylphosphonate (DMMP) on the (0 1 0) surface of anatase TiO 2 with and without faceting

Abstract

The adsorption of dimethyl methylphosphonate (DMMP) on the (0 1 0) surface of anatase TiO 2, which is isostructural with the (1 0 0), has been studied using density functional theory and two-dimensionally-periodic slab models. The experimentally-observed faceting of this surface has, for the first time, been included in the modeling. The relaxations of bare surfaces both with and without faceting are similar, leading to an atomic-scale roughening due to inward (outward) displacement of fivefold-coordinated Ti 5c (sixfold-coordinated T 6c) atoms together with outward displacement of threefold-coordinated O 3c atoms. Molecular adsorption occurs by formation of a Ti 5c⋯O P dative bond with one or more C H⋯O 2c bonds between CH 3 groups and unsaturated, twofold-coordinated (O 2c) sites. The energies for molecular adsorption, obtained using the B3LYP functional, are virtually identical (about −21.0 kcal/mol) for the two surfaces and are also close to those found elsewhere for the rutile (1 1 0) and anatase (1 0 1) surfaces. A possible first step in the dissociative adsorption of DMMP has also been modeled and is found to be thermodynamically favored over molecular adsorption to a degree which depends on faceting.