Eur. Phys. J. Plus (2011) 126: 98
https://doi.org/10.1140/epjp/i2011-11098-4

Regular Article

Anchoring functional molecules on TiO₂ surfaces: A comparison between the carboxylic and the phosphonic acid group

¹ Physical Chemistry, Technische Universität Dresden, Bergstrasse 66b, D-01062, Dresden, Germany
² Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf e.V., P.O. Box 51 01 19, D-01314, Dresden, Germany

^* e-mail: regina.luschtinetz@chemie.tu-dresden.de

Received: 2 May 2011
Revised: 13 May 2011
Accepted: 22 September 2011
Published online: 21 October 2011

Abstract

The adsorption of formic acid on clean TiO₂ anatase (101) and rutile (110) surfaces is studied by density-functional-based methods and compared with the results for coupling related phosphonic acids to titania surfaces. The preferred adsorption mode of the formic acid on both surfaces is a dissociative bridging bidentate complex, which is similar to the adsorption geometry of phosphonic acid. Higher adsorption energies and shorter Ti-O bond lengths indicate that phosphonic acid binds more strongly to TiO₂ than formic acid. The preference for the bidentate adsorption mode is supported by a detailed analysis of the charge distribution in the adsorption complexes. The strong interfacial electronic coupling between the adsorbate orbitals and the electronic states of the anatase (101) surface slab leads to additional states in the band gap of the clean surface. For rutile (110) no or only weak coupling of the adsorbate orbitals and the surface states occurs at the band edges, which leads to an increase of the band gap.