Electrophotocatalytic decolorization of an azo dye on TiO2 self-organized nanotubes in a laboratory scale reactor

It was investigated the feasibility of decolorization of an azo dye (DG 26) using a large scale nanotubular TiO2 structured electrode in a laboratory photoelectrochemical reactor (0.8 L). Catalyst was grown by anodic oxidation directly on Ti surface and its microstructure and crystalline structure were characterized with SEM and XRD. TiO2/Ti photoactivity under different anodic polarization values was evaluated via photoelectrochemical tests. The nanostructured TiO2 was used in a reactor as photo-anode under UV monochromatic irradiation (254 nm) and it was subjected to bias (+ 1.5 V vs. SCE). A comparison with photolysis and photocatalysis processes was carried out under the same operating conditions to evaluate the synergistic action of photocatalysis and TiO2/Ti electrochemical polarization.Electrophotocatalysis was proven to be more effective than photocatalysis in DG 26 decolorization. Catalyst polarization resulted in synergistic effect on process yields. The complete decolorization of a 40 mg/L solution of DG 26 was achieved in 24 h, without adding chemical reagents, and catalyst durability was demonstrated over 360 h tests. Therefore, the work done is challenging to prove that the process (irradiation + catalyst + polarization) is feasible and effectively up-grading to pilot and demonstrative scale applications after a fluid dynamics optimization of the photoreactor.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Nanotubular TiO2 grown by anodic oxidation directly on Ti conductive support. ► TiO2 used in a reactor as photo-anode under UV monochromatic irradiation (254 nm). ► TiO2 biased to reduce electron-hole recombination, main drawback of photocatalysis. ► Relevant synergistic enhancement of photocatalysis yields in decolorization tests. ► Good TiO2 durability over usage time: constant performances and no surface damages.