Adsorption of HPOx and CaHPOx (x=1,…,4) molecules on anatase TiO2 (001) surfaces

Abstract We perform DFT calculations within the COSMO framework to study the adsorption properties of the CaHPO x ( x = 1 , … , 4 ) phosphate family, and of the related HPO x acids, on a paradigmatic anatase (001) surface. Of particular interest is CaHPO 4 , a precursor of hydroxyapatite, which forms during osseointegration of titanium implants. Our results, obtained within the COSMO framework, are based on total energy calculations, and are interpreted in terms of electronegativity differences between the relevant system components. They show that adsorption of HPO x , and in particular of HPO 4 , is highly enhanced by the presence of Ca adatoms on the TiO 2 substrate, a result which is in agreement with our previous work on the wettability of anatase surfaces. We also study the adsorption of CaHPO x molecules on TiO 2 surfaces, and show that molecular adsorption is strongly favoured for x = 4 , while for x = 1 , 2 dissociative adsorption of HPO x molecules and Ca adatoms prevails.