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 (Eca), oxygen flow rate (VO2)(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−1VO2=0.4 ml min−1, Eca = −0.4 V and pH 4.3. On this occasion, ca. 90% chroma decay and 60% TOC removal of dye were achieved with 450 °C-calcined 5.78 wt%-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.

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► AQS/PPy composite can cause efficient electrocatalytic reduction of O2 to produce H2O2.
► Heterogeneous CuO/γ-Al2O3 catalyst can efficiently activate H2O2 to produce OH.
► Heterogeneous electrocatalytic oxidation of dye follows the second-order kinetics.
► Heterogeneous CuO/γ-Al2O3 catalyst can be recovered and reused.