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

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/SnO 2 -Sb, Ti/SnO 2 -Sb/PbO 2 , Ti/SnO 2 -Sb/La-PbO 2 , Ti/SnO 2 -Sb/Ce-PbO 2 , Ti/SnO 2 -Sb/Ga-PbO 2 and Ti/SnO 2 -Sb/Zr-PbO 2 ) were prepared and characterized. Ti/SnO 2 -Sb/La-PbO 2 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 NO 3 − 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 PO 4 3− 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 PO 4 3− 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.