Fabrication and characterization of Ti/polyaniline-Co/PbO2–Co for efficient electrochemical degradation of cephalexin in secondary effluents

The traditional interlayer of PbO2 electrode possessed many problems, such as short service lifetime and limited specific surface area. Herein, a novel and efficient Ti/polyaniline-Co/PbO2-Co electrode was conctructed employing cyclic voltammetry to introduce a Co-doped polyaniline interlayer and anodic electrodeposition to synthetize a β-PbO2-Co active layer. Compared with pristine PbO2 electrode, Ti/polyaniline-Co/PbO2-Co exhibited more compact crystalline shape and higher active sites amounts. Pratically, the electrochemical degradation of 5 mg L-1 cephalexin in real secondary effluents was effectively achieved by the novel anode with 87.42% cephalexin removal and 71.8% COD mineralization after 120 min of 15 mA cm-2 electrolysis. The hydroxyl radical production and electrochemical stability were increased by 3.16 and 3.27 times respectively. The cephalexin degradation pathway was investigated by combining a density functional theory-based theoretical approach and LC-QTrap-MS/MS. The most likely cleavage point of the β-lactam ring was the O=C-N bond, whose attack would produce small molecular compounds containing the thiazole and 4, 6-thiazine rings. Further oxidation produced inorganic ions; quantitative investigations indicated the amino groups to undergo decomposition to form aqueous NH4+, which was further oxidized to NO3-. The accumulation of NO3- and SO42-, combined with a decrease in toxicity toward Escherichia coli, demonstrated the efficient mineralization of cephalexin on the Ti/polyaniline-Co/PbO2-Co electrode.