Photodesorption of organic matter from titanium dioxide particles in aqueous media

Photo-induced desorption of organic compounds from TiO2 particles in aqueous media during photocatalysis has promising applications in water treatment. Photodesorption is a relatively fast phenomenon that facilitates the regeneration of photocatalysts with low energy consumption while concentrating the waste products in an energy and water efficient process. We propose that this transport phenomenon involves a significantly reduced affinity between the photocatalyst and pollutants upon UV illumination, and leads to the rapid detachment/decomposition of adsorbed pollutants. In this study, we report the effect of experimental conditions (pH, photocatalyst loading, organic loading, UV light irradiation and flow rate) on this phenomenon in a recirculating photocatalysis continuous reactor. Initially, organic compounds were allowed to adsorb on the surface of the photocatalyst (Degussa P25) until adsorption equilibrium was achieved. The photodesorption phenomenon was observed shortly after UV-light illumination of TiO2 but before the bulk photocatalytic oxidation takes place. The pH of the solution was found to affect both the adsorption and the desorption percentages revealing the role of particle charge on this phenomenon. Additionally, a 1 g/L loading of photocatalyst showed an optimum photodesorption rate using a single strength synthetic wastewater at pH 7.