Solar photoelectrocatalytic degradation of Acid Orange 7 azo dye using a highly stable TiO2 photoanode synthesized by atmospheric plasma spray

Authors: Sergi Garcia-Segura, Sergi Dosta, Josep M. Guilemany, Enric Brillas

Abstract:
A TiO₂ coating composed of 29% rutile, 9% anatase and 62% of Ti₇O₁₃ on stainless steel support has been prepared by atmospheric plasma spray technology. This novel photoanode was coupled to an air-diffusion cathode that generates H₂O₂ in a photoelectrochemical cell submitted to direct sunlight irradiation to degrade 100 mL of Acid Orange 7 (AO7) azo dye solutions in 0.05 M Na₂SO₄ by solar photoelectrocatalysis (SPEC). The photoanode presented excellent mechanical properties as well as large stability and long durability up to 2.0 mAcm⁻². The decolorization process in SPEC was synergistic of the individual processes in solar photocatalysis and anodic oxidation with generated H2O2 under comparable conditions owing to the larger production of •OH from the higher amounts of photogenerated holes that can be separated of photogenerated electrons. The best operating variables for SPEC were 15 mg L⁻¹ AO7, pH 7.0 and anodic current density (janod) of 1.0 mAcm⁻². Under these conditions, the azo dye disappeared in 100 min and the solution was totally decolorized in 120 min, but only 40% mineralization was attained after 240 min of electrolysis. The AO7 decay followed a pseudo-first-order reaction as found by reversedphase HPLC and it was accelerated with increasing janod due to the higher amounts of •OH generated from the production of more photogenerated holes and the enhancement of anodic oxidation of water. Ion-exclusion HPLC allowed the identification of generated carboxylic acids like phthalic, tartaric, succinic, acetic and oxamic, which were the main components of long-time electrolysis. Their persistence explains the low mineralization of AO7 in SPEC. The initial N of the azo dye was mineralized as NH₄ ⁺ ion, in larger proportion than NO₃ ⁻ ion, although it was mainly loss as volatile species. 

Keywords:
Acid Orange 7
Photocatalysis
Photoelectrocatalysis
Sunlight
Water treatment

Published in: Applied Catalysis B: Environmental (Volumes 132–133, Pages 1-552, 27 March 2013)

Publisher: Elsevier  

ISSN Information: 0926-3373

Solar photoelectrocatalytic degradation of Acid Orange 7 azo dye using a highly stable TiO2 photoanode synthesized by atmospheric plasma spray

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