Oxidative degradation of azo dye by hydrogen peroxide electrogenerated in situ on anthraquinonemonosulphonate/polypyrrole composite cathode with heterogeneous CuO/γ-Al₂O₃ catalyst

Heterogeneous electrocatalytic wet H₂O₂ oxidation technique for the removal of azo dye amaranth from aqueous solution was studied in the presence of solid CuO/γ-Al₂O₃ catalyst and anthraquinonemonosulphonate/polypyrrole (AQS/PPy) composite cathode able to electrogenerate H₂O₂ in situ. The spherical CuO/γ-Al₂O₃ catalysts with various CuO loadings and calcined at different temperatures were characterized by BET, ESEM-EDS, XRD and XPS. Several parameters affecting H₂O₂ electrogeneration and dye degradation such as solution pH, cathode potential (E_ca), oxygen flow rate (VO2), CuO loading, reaction temperature as well as catalyst calcination temperature were investigated. Experimental results revealed that the optimal condition for H₂O₂ electrogeneration on the AQS/PPy composite modified cathode is VO2=0.4 ml min-1, E_ca=-0.4V and pH 4.3. On this occasion, ca. 90% chroma decay and 60% TOC removal of dye were achieved with 450°C-calcined 5.78wt%-CuO/γ-Al₂O₃ catalyst and 70°C reaction temperature. Dye degradation follows the second-order kinetics. Leaching tests showed that the leaching copper amount during the oxidation is only 4.0-7.0% per run and the role of heterogeneous activity is dominant. The catalytic activity of CuO/γ-Al₂O₃ catalyst could be recovered after multiple runs by a re-calcination step. Furthermore, the stability of the AQS/PPy composite after consecutive operation was also investigated by chronoamperometric and EIS techniques. © 2011 Elsevier B.V.