ATR-FTIR for the aqueous TiO2 interface

TAUCHERT E.; MENDIVE C.; BAHNEMANN D.

Conferencia; 6th European Meeting on Solar Chemistry and Photocatalysis: Environmental Applications (SPEA6); 2010

Research Centre for Nanosurface Engineering

Solar chemistry and photocatalysis are undoubtedly linked to TiO2, especially when targeting the goal of environmental applications. The use of TiO2 is bluntly central in fundamental and applied photocatalysis; and hence the need for a true comprehension of all types of mechanisms occuring upon irradiation of the systems. For instance, a complex scenario for a thorough physicochemical study is given by a photocatalytic system in aqueous phase. Beyond the limitations arising from the theoretical point of view, i.e., the number of parameters is huge, a challenging experimental set-up is usually required to properly asses events occurring at the solid-liquid interface. Since adsorption, as a first step, and subsequent reactions depending on the adsorbed pollutant are therefore unequivocally a crucial factor, we focus here our attention on the Attenuated Total Reflection technique by Fourier Transformed Infra-red spectroscopy which demonstrates the ability to investigate surface concentrations of chemisorbed organic compounds in a direct manner. We present an ATR-FTIR study using a commercial TiO2 material (anatase, PC500 from Millennium Inorganic Chemicals) in contact with low concentration aqueous solutions of our model compound, dichloroacetic acid (DCA). We were able to successfully detect adsorbed DCA in systems whose original solutions produce very small absorbance bands before any contact to the TiO2 nanoparticles. Furthermore, for the same given initial DCA concentration, the bands corresponding to the adsorbed species appear to be considerably higher than those of the dissolved one. The sensitivity of the ATR-FTIR technique also allowed the identification of an additional band corresponding to adsorbed DCA providing key structural information for the elucidation of the adsorption mode. The detection of an inverse absorbance band led us to the suggestion of surface replacement by DCA molecules of previously adsorbed impurities at the TiO2 nanoparticles.