Photoelectrochemical advanced oxidation processes on nanostructured TiO₂ catalysts: decolorization of a textile azo-dye

Abstract

This work describes a novel approach for water treatment by photoelectrocatalysis, based on nanostructured TiO₂. The decolorization of aqueous solutions containing the azo-dye RR243 is carried out in a tubular photocatalytic reactor working in semi-batch mode under electrical polarization of the catalyst. Two different nanostructured catalysts were tested: nanotubular TiO₂ obtained by conventional anodization (CA), and a novel photoactive nanoporous TiO₂, obtained by plasma electrolytic oxidation (PEO). Neither UV irradiation of the TiO₂ catalysts nor the electrical bias individually considered lead to a significant reduction of the dye concentration. By irradiating the catalysts with UVC light while applying an electrical bias to the same, the concentration of the dye decreased from 25 L to 2,5 mg/L using the nanotubular CA TiO₂ catalyst, and to less than 1,8 mg/L using the novel nanoporous PEO TiO₂ in 50 min. The main advantages of this method over current approaches for the degradation of pollutants are both the considerable processing time reduction and a suitable and easy-to-scale-up reactor design. A further advantage is the relatively easyness in the production of the TiO₂ catalysts by PEO.