Adsorption of oxalate on anatase (100) and rutile (110) surfaces in aqueous systems: experimental results vs. Theoretical predictions

MENDIVE C.; BREDOW T.; FELDHOFF A.; BLESA M. A.; BAHNEMANN D.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2009 vol. 11 p. 1794 - 1808

1463-9076

A combined experimental and theoretical study of the adsorption of oxalic acid from the aqueousphase at the surface of anatase nanoparticles has been performed. The interfaces were investigatedby ATR-FTIR measurements and quantum-chemical calculations using the semiempirical methodMSINDO. The vibration spectra of the most stable surface complexes have been calculated andused for the interpretation of experimental results. The theoretical studies have been done usingthe anatase (100) surface to model the adsorption of oxalic acid and water. The effect ofinteraction of water and oxalic acid on the adsorption mechanism and the vibration spectra wastaken into account in the theoretical models. Inclusion of solvation effects was found crucial todetermine the type of denticity and structure of adsorbed complexes. By comparison ofexperimental data and theoretical calculations the most likely surface species and the effects ofhydration in their relative stabilities were determined. The present results are compared toprevious studies preformed also by combination of experimental and theoretical calculations ofanalogous systems using nanoparticulate rutile [C. B. Mendive et al., Phys. Chem. Chem. Phys.,2008, 10, 1960, ref. 1]. Differences between surface complexes on anatase and rutile lie mainly onthe denticity type. Whilst in the case of rutile the most stable species consist of two bidentatesurface complexes followed in third place by a monodentated form, anatase allows the formationof four species in which the stability order is reversed with respect to the denticity type. In thecase of anatase, the main contributors to the surface speciation are two monodentate speciesdiffering in the position of the H atom within the molecule (being more stable when it is placed inthe O–C–O moiety not bound to the surface); and two bidentate species, one deprotonated andone monoprotonated, in which the C–C bond was parallel or perpendicular to the TiO2 surface,respectively.