Alkaline electrochemical advanced oxidation process for chromium oxidation at graphitized multi-walled carbon nanotubes

•Cr(III) was efficiently oxidized by the in-situ electro-generated ROS.•Graphitized MWCNTs exhibit excellent ORR catalytic behavior.•Graphitization process significantly improves 2e ORR for the carbon nanotubes.•Novel Cr(III)-induced electro-Fenton-like systems were successfully developed.

Alkaline electrochemical advanced oxidation processes for chromium oxidation and Cr-contaminated waste disposal were reported in this study. The highly graphitized multi-walled carbon nanotubes g-MWCNTs modified electrode was prepared for the in-situ electrochemical generation of HO2−. RRDE test results illustrated that g-MWCNTs exhibited much higher two-electron oxygen reduction activity than other nanocarbon materials with peak current density of 1.24 mA cm−2, %HO2− of 77.0% and onset potential of −0.15 V (vs. Hg/HgO). It was originated from the highly graphitized structure and good electrical conductivity as illustrated from the Raman, XRD and EIS characterizations, respectively. Large amount of reactive oxygen species (HO2− and ·OH) were in-situ electro-generated from the two-electron oxygen reduction and chromium-induced alkaline electro-Fenton-like reaction. The oxidation of Cr(III) was efficiently achieved within 90 min and the conversion ratio maintained more than 95% of the original value after stability test, offering an efficient and green approach for the utilization of Cr-containing wastes.

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