Electrochemical degradation of tris(2-chloroethyl) phosphate by metal-oxide-coated Ti anodes: Kinetics, toxicity and mechanism

Abstract The current study presents a comprehensive and novel attempt to degrade aqueous tri(2-chloroethyl) phosphate (TCEP) by metal-oxide-coated Ti anodes for the first time. Six metal-oxide-coated Ti electrodes (Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2, Ti/SnO2-Sb/La-PbO2, Ti/SnO2-Sb/Ce-PbO2, Ti/SnO2-Sb/Ga-PbO2 and Ti/SnO2-Sb/Zr-PbO2) were prepared. Ti/SnO2-Sb/La-PbO2 showed the highest pseudo-first-order reaction rate constant (2.1 × 10−2 min−1) and lowest energy consumption (21.35 Wh L-1) in the degradation of 1 mg L-1 TCEP at 10 mA cm-2, mainly because of its highest oxygen evolution potential and •OH production. Higher current density and neutral condition favored TCEP degradation, while the presence of Cl- or NO3- could suppress the degradation. In the electrochemical degradation of 10 mg L-1 TCEP, mineralization percentage of 48.0% (mineralization current efficiency of 0.30%) and PO43- release percentage of 72.7% were achieved at 150 min. By the attack of •OH on the C─O and C─Cl bonds in TCEP molecular structure, products of chloroethanol, Cl- and PO43- were released, with the major electrocatalytic degradation pathways of dechlorination and hydroxylation. Based on the results of flow cytometry, the relative toxicity to Escherichia coli effectively decreased to 4.93% in TCEP degradation. Compared with the UV-AOPs, electrochemical oxidation process is proved to be feasible and effective for mineralization and detoxification of TCEP in water.