Electrochemical Activation Of Sulfate With S/N-co-doped TiO₂ Nanotube Arrays Anode For Berberine Degradation

Berberine is a typical kind of antibiotic,which has not only significant antibacterial and anti-inflammatory effects,but also important application prospects in the cardiovascular system and nervous system.However,in the process of production and use of berberine,a large amount of wastewater containing berberine residues will be produced.If the wastewater is directly discharged into the environment,there will be severe damage to the balance of the environment and ecology and human health.Therefore,it is urge to reduce the risk of the berberine wastewater.However,the traditional water treatment technologies barely have the satisfactory treatment performance due to their limitation.In recent years,electrochemical advanced oxidation process based on sulfate radicals(SO₄^·-)has been received enormous attention due to its high efficiency and eco-friendly.Among various ways,electro-activated sulfate(SO₄^2-)was considered as an alternative method to to generate SO₄^·-due to the low-cost and environmental friendliness.The choice of electrodes was vital for electrochemical advanced oxidation process.TiO₂nanotube arrays were proven to be a promising electrode material,and their electrical conductivity can be improved by non-metallic doping.In addition,previous studies have clarified FeOOH is able to effectively avoid the accumulation of peroxodisulfate(S₂O₈^2-)during the electroactivation of SO₄^2-.Consequently,in this study,sulfur/nitrogen-co-doped TiO₂nanotube arrays（S/N-TNA）were set up as an anode activating SO₄^2-to generate SO₄^·-for berberine removal.In addition,the practical application performance of FeOOH catalyst was also investigated.Firstly,S/N-TNA anodes were prepared by anodization and electrodeposition,its structure,morphology,element valence were characterized and the electrochemical properties were analyzed by field emission scanning electron microscopy（FE-SEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）.As the results shown,S/N-TNA has a highly ordered nanotube arrays structure with evenly distributed S and N.It is also confirmed that the synthesized TiO₂is anatase phase,and the existence of Ti-O-N bond proves that S/N doping causes oxygen vacancies.Besides,the S/N-TNA anode is of a high O₂overpotential（2.51 V vs RHE）,and its resistance reduced from 44.25Ωto 3.54Ωafter S/N doping.Secondly,an S/N-TNA anode system was established to oxidatively degrade berberine wastewater.Under the condition that the current density is 8 m A/cm²,the concentration of Na₂SO₄solution is 0.15 M,and the initial p H is 7,5 mg/L berberine can be completely removed in 50 min.In addition,the stability of S/N-TNA is satisfactory because the removal efficiency was still over 83%after 5 cycles repeated degradation of berberine.The active oxygen species in the system were proved to be·OH and SO₄^·-by electrolyte comparison,EPR test and free radical inhibition experiment,also,we calculated the relative contribution rates of·OH and SO₄^·-.In addition,three possible berberine degradation pathways were speculated by identifying and analysing the intermediate products through LC-MS.Finally,δ-FeOOH was prepared by rapid oxidation co-precipitation method,and its morphology,crystal structure and element bonding state were characterized by FE-SEM,XRD and XPS.Then,the S/N-TNA-FeOOH system was set up to degrade berberine.When the FeOOH loading is 150 mg,the current density is 6 m A/cm²,the concentration of Na₂SO₄solution is 0.15 M,and the initial p H is 9,94.38%of berberine solution with a concentration of 10 mg/L can be removed within 60 min.It is proved that FeOOH can effectively promote the oxidative degradation of berberine by S/N-TNA anode,and it is a catalyst with practical application significance.In conclusion,this study provides an effective,promising and economical method for antibiotic wastewater treatment.