Sequential Flow-through Adsorption And Electrochemical Degradation Mechanism Of Triclosan In Low Conductivity Water

Pharmaceuticals and personal care products（PPCPs）have given rise to worldwide attentions due to their high detection frequencies and potential threats to aquatic environments and human health.Electrochemical oxidation process has been widely used in the treatment of refractory organic pollutants in aqueous due to its advantages of strong oxidation ability and easy handling.However,electrochemical oxidation process has the problems of limited degradation performance and secondary pollution caused by electrolyte addition in low conductivity water environment.To solve the above problems,in this paper,the prepared porous Ti O₂nanotube array reactive electrochemical membrane（Ti O₂NTA REM）was used as the cores to develop sequential flow-through adsorption and electrochemical degradation（SAED）process.The pollutants were pre-adsorbed on the electrode surface and the adsorbed pollutants were degraded in-situ,which realized the efficient and rapid removal of triclosan from low conductivity water.The main research contents and results were summarized as follows:（1）Ti O₂NTA REM electrode was prepared by anodizing on porous Ti substrate.The effects of technological parameters on physical properties,adsorption properties and degradation properties of Ti O₂NTA REM electrode were investigated.The optimal preparation conditions of Ti O₂NTA REM electrode were determined as follow:NH₄F content and H₂O content in ethylene glycol electrolyte were 0.3 wt%and 5 wt%,respectively,which oxidation time was 4 h,and oxidation voltage was 40 V.The prepared electrode had well-developed porous structure,and self-doped Ti³⁺was formed in the Ti O₂lattice,and the median pore diameter（volume）was 13.96μm.The specific surface area of Ti O₂NTA was1.57 m²g^-1,which was 10.5-fold larger than that of porous Ti substrate(0.15 m²g^-1).（2）The effects of initial solution p H,applied voltage and the circulation flow rate on the adsorption of TCS on Ti O₂NTA REM were studied.The adsorption of TCS followed pseudo-second-order kinetics model and Langmuir thermodynamic model.The adsorption mechanism of TCS might be a complex combination of hydrophobic interaction and electrostatic attraction.Compared with adsorption at 0 m L min^-1（static adsorption）,the initial adsorption rate and the maximum adsorption capacity of TCS increased 18.8-fold and73.8-fold at 300 m L min^-1,respectively.（3）The electrochemical oxidation degradation of TCS on Ti O₂NTA REM electrode was studied.Ti O₂NTA REM electrode exhibited strong oxidation performance for TCS in Flow-through mode,which degradation kinetic constant(0.17 min^-1)in Flow-through mode was 5.7-fold larger than that in Flow-by mode(0.03 min^-1).The electrochemical degradation pathways of TCS were hydroxylation,disproportionation,dichlorination and cleavage of ether bond.（4）In the four SAED cycles,Ti O₂NTA REM electrode had stable adsorption properties and degradation properties for TCS.The in-situ electrochemical degradation ratio of the adsorbed TCS reached 99.8%within 25 min.The SAED process based on Ti O₂NTA was an efficient and feasible technology of the removal of TCS in waters with low conductivity.