Electrochemical degradation of neutral red on PbO2/α-Al2O3 composite electrodes: Electrode characterization, byproducts and degradation mechanism

Abstract PbO2/α-Al2O3 composite electrodes were successfully synthesized using composite electrodeposition technology and applied for the electrocatalytic degradation of neutral red (NR). The effect of α-Al2O3 particles on the surface morphology, structure, stability and electrochemical properties of PbO2/α-Al2O3 composite electrodes were characterized. The results showed that the incorporation of α-Al2O3 particles can fine the crystal size of lead dioxide and form compact film structure. PbO2/α-Al2O3 composite electrodes exhibited larger electrochemical active surface area, stronger hydroxyl radical generation ability and longer service lifetime than PbO2 electrodes. Electrochemical oxidization experiments showed that PbO2/α-Al2O3 composite electrodes had the higher neutral red and COD removal efficiency, lower energy consumption and minimum Pb dissolution than PbO2 electrodes. Finally, hypothetical electrocatalytic degradation pathway of neutral red on PbO2/α-Al2O3 composite electrode was proposed, which was dominated by hydroxyl radical mediated oxidization reaction. Under reaction with hydroxyl radicals, neutral red was gradually de-functionalized and hydroxylized to form π-delocalization shrink byproducts, which were transformed to multiple organic acids and then to inorganic substances H2O and CO2 ultimately.