Electrochemical Oxidation Of Carbamazepine In Water Using Ti-porous/blue TiO₂ Nanotube Arrays Anode

As a psychostatic drug,carbamazepine（CBZ）has been widely used in the treatment of epilepsy,neuropathic pain,schizophrenia,depression and post-traumatic stress disorder,and the low removal efficiency of CBZ in wastewater treatment plants has led to its frequent detection in aquatic environment.CBZ has a half-life of tens to hundreds of days in natural water bodies,which allows it to be accumulated in organisms with toxicity and cause long-term effects on the entire ecosystem through the food chain,and poses a potential risk to human health.Adsorption,membrane separation and biodegradation were used for the removal of CBZ in water,but are accompanied with low degradation efficiency,long processing time and complicated operation.Therefore,it is an imperative task to develop cost-effective,eco-friendly and efficient methods to eliminate CBZ from wastewater.Advanced oxidation processes（AOPs）have been proven to be effective methods for removing organic pollutants.Among AOPs,the electrochemical oxidation which degrades organic pollutants by the generated free radicals,has many advantages such as high removal efficiency,low cost,gentle reaction conditions and environmental friendliness.In electrochemical oxidation process,the removal efficiency of organic pollutant is mainly dependent on the anode type.As a novel material,the blue TiO₂nanotube arrays（blue TiO₂NTA）anode with various advantages of low cost,easy preparation,non-toxicity,high oxygen evolution potential,excellent·OH generation ability and good chemical stability,has exhibited excellent performance in the degradation of organic pollutants.During the electrochemical oxidation process,the degradation of containments is strongly dependent on the production of·OH from Ti³⁺self-doped TiO₂nanotubes on Ti-plate substrate.If enlarging the electroactive surface area of blue TiO₂NTA anode,its electrochemical performance and·OH generation ability may be further enhanced,and thus improved the removal efficiency of organic pollutant.Inspired by Ti-porous with various features,we fabricated blue TiO₂NTA on Ti-porous substrate（Ti-porous/blue TiO₂NTA）by simple and mild anodic oxidation-in-situ cathodic reduction.The physical and chemical characteristics and electrochemical properties of the prepared anode were comprehensive characterized by various means,and the removal efficiency,kinetic characteristic and energy consumption during the degradation of CBZ using Ti-porous/blue TiO₂NTA anode were discussed.The degradation mechanism and transformation pathway of CBZ were preliminatively analyzed,and the following research results were obtained:1.The removal efficiencies of CBZ in four repeated electrochemical oxidation were used as the index to obtain the optimal conditions for the preparation of Ti-porous/blue TiO₂NTA electrode.The anodic oxidation conditions were:ethylene glycol containing 0.3%NH₄F as the electrolyte,a voltage of 40 V and an oxidation time of 4 h.The cathodic reduction conditions were:10%formic acid as the electrolyte,a current density of 5 m A·cm^-2and a reduction time of 5 min.SEM images showed the anode has a developed porous structure,and a great number of well-aligned uniform nanotubes can be observed on the anode surface.EDS analysis suggested the formed titanium oxide may not be highly crystallographic TiO₂.XRD patterns and Raman spectra revealed that the anode has a typical crystal structure of anatase TiO₂,and the slight red-shift in the Raman spectra indicated the appearance of Ti³⁺in the TiO₂lattice.In XPS spectra,the peak intensity of Ti and the abundance of Ti³⁺in TiO₂NTA was increased after the reduction reaction.The electrochemical properties of Ti-plate/blue TiO₂NTA and Ti-porous/blue TiO₂NTA were compared:the CV analysis showed that the blue TiO₂NTA on Ti-porous substrate has high electrochemical activity with electroactive area of 10.94 cm²·cm^-2,which is 4.1 times as much as that of Ti-plate substrate;LSV curves,Tafel curves and EIS Nyquist plots indicated that the Ti-porous/blue TiO₂NTA has higher oxygen evolution potential（2.68 V vs.SCE）and better electron transport capacity compared to the Ti-plate/blue TiO₂NTA.2.The effect factors of the electrochemical oxidation of CBZ were investigated.The removal efficiency of CBZ was increased with the increase of the supporting electrolyte（Na₂SO₄）concentration from 0.01 to 0.05 mol·L^-1,but no significant improvement in CBZ removal was found in 0.06 mol·L^-1Na₂SO₄.Efficient removal of CBZ can be achieved in p H 3-11,but the alkaline environment suppressed the activity of·OH,leading to a decay in CBZ degradation.The removal efficiency of CBZ was increased from 63.34%to 99.50%when the current density increased from2 to 8 m A·cm^-2,but no significant changes occurred after further increase the current density.The CBZ degradation was inhibited when adding NO₃^-,H₂PO₄^-and HCO₃^-,and promoted when adding Cl^-,but the toxic chlorinated products may be generated.3.Under the optimal experimental conditions,the degradation of 1,5,10,20,and 40 mg·L^-1of CBZ were investigated,and the degradation process accords with the first-order reaction kinetic equation,with the rate constants of 0.146,0.120,0.106,0.101 and 0.059 min^-1,and the energy consumption for 90%removal were2.19,2.45,2.89,4.23 and 7.42 k W h·m^-3,respectively.The Ti-porous/blue TiO₂NTA anode can achieve efficient removal of CBZ in tap water and lake water,indicating its environmental adaptability.The removal efficiency of CBZ still maintained above90%after 10th repeat cycles,and rebounded to 98.40%using newly regenerated anode,which indicates the better stability and reusability of Ti-porous/blue TiO₂NTA anode than that of the Ti-plate/blue TiO₂NTA anode.4.After 60 min electrochemical oxidation of CBZ,the solution TOC decreased from 14.95 to 6.63 mg·L^-1.The concentration of NO₃^-reached 1.36 mg·L^-1,which indicates the cleavage of amido bond during the CBZ degradation.The results of the EPR tests and free radical quenching experiments demonstrated that·OH,SO₄·^-and O₂·^-were present in the electrochemical oxidation reaction system with Ti-porous/blue TiO₂NTA as the anode,and the·OH played a key role in CBZ degradation.The generation rate of·OH at 8 m A·cm^-2on Ti-porous/blue TiO₂NTA anode surface was 216.0 mmol·L^-1·min^-1·m^-2,which is 1.3 times as much as that of Ti-plate/blue TiO₂NTA anode.The degradation products of CBZ were identified by LC-MS/MS,and three possible oxidation pathways which involving deamidation,hydroxylation and ring opening reactions were proposed.