New Insights into the Mechanism of TiO2 Photocatalysis: Thermal Processes beyond the Electron-Hole Creation

MENDIVE C.; BAHNEMANN D.

Beijing

Conferencia; The 6th International Conference on Interfaces Against Pollution (IAP-2010); 2010

ATR Infrared spectroscopic studies of UVA irradiated layers of TiO2 nanoparticles in contact with aqueous solutions free of any photocatalytic degradable compound showed that water is incorporated in the layer. Such a phenomenon reveals important aspects of the mechanism operating in the system of semiconductor nanoparticles with profound consequences on photocatalytic reactions. Upon UVA illumination, deaggregation of particle agglomerates proceeds and particles separate resulting in an expansion of the layer followed by incorporation of additional      water from the solution. According to thermodynamic measurements [1], the energy requirements for deaggregation arise from the capacity of the system to use the energy released non-adiabatically by recombination of photogenerated electrons and holes. In this mechanism, bonds responsible for maintaining nanoparticles agglomerated are broken allowing the particles to separate, and water molecules from the solution can then fill the space in between the particles. The potential impact of these processes for photocatalysis is great since upon UVA illumination the exposed TiO2 area increases, hence promoting an enhancement of the adsorption capacity of the photocatalyst. The increased adsorption of aqueous oxalate [2] and aqueous dichloroacetate on TiO2 under UVA illumination observed by means of ATR Infrared spectroscopy is therefore a first step to be considered in the overall mineralization process via the photocatalytic action of TiO2. Since the use of TiO2 is bluntly central in fundamental and applied photocatalysis, we will discuss the deaggregation mechanism in the frame of the needs for a true comprehension of the yet not fully understood reactions occurring upon irradiation of these systems.