Heterogeneous electrophotocatalysis on self-organized TiO2 nanotubes for organic removal

The electrophotocatalytic decolorization of a textile azo dye (Reactive Red 243, RR243), by large scale nanotubular structured TiO2 electrodes, was optimized assessing the influence of some operating parameters (bias voltage, lamp emission wavelength, catalyst surface and catalyst positioning with respect to the lamp, initial dye concentration, radical scavengers as alkalinity), by photoelectrochemical characterization and decolorization trials. Nanostructured TiO2 was grown by anodic oxidation directly on Ti substrate and the TiO2/Ti catalyst was used as photo-anode under UV irradiation, subjected to anodic polarization (bias). Reactor configuration and operating conditions were optimized in order to maximize catalyst photoactivation and decolorization yields, so that an improved reactor configuration (1.8 L) was developed. TiO2/Ti electrophotocatalysis was compared with a benchmark consisting of P-25 Degussa TiO2 in slurry phase at the same catalytic surface. Reactor optimized configuration permitted to achieve the complete decolorization of a 25 mg/L Reactive Red 243 solution in 60 minutes and its mineralization at 80% in 100 minutes. Electrophotocatalysis was proven to be more competitive than P-25 benchmark, since the latter reached complete decolorization in 360 minutes. Neither chemical reagents nor catalyst separation phases were required.