Experiments and Computer Simulations as a Green Chemistry Approach: New Mechanisms for TiO2 Photocatalysis

MENDIVE C.; BREDOW T.; BAHNEMANN D.

Gent

Conferencia; Sustainable Approaches to Remediation of Contaminated Land in Europe (SARCLE-2010); 2010

The comparison of experimental results and theoretical calculations allowed the suggestion of several surface photoreactions of adsorbed oxalic acid on rutile and anatase nanoparticles, respectively, under UVA illumination. Besides the traditional photocatalytic reactions initiated by bandgap illumination the TiO2 surfaces, their adsorption complexes are centres for direct UVA light absorption resulting in different photoreactivities and consequently different reaction routes and mechanisms: monodentate complexes interconvert into bidentate species which are subsequently oxidized to CO2 or produce ·OH radicals; reduction of oxalate forms the corresponding aldehyde which in close vicinity to an oxidized surface OH group can lead to the formation of an adsorbed OOH radical. Our results strongly suggest that the initial reactions of the electron/hole pairs created at the surface complexes upon UVA illumination are extremely fast thus constituting the primary step of the photocatalytic reactions. Consequently, the radical attacks are only a secondary process, in which ·OH radicals can even be generated from the adsorbed organic compounds and not only from chemisorbed water molecules.