Preparation Of Ti³⁺ Self-doped TiO₂ Nanotube Electrode And Its Degradation Of Chloramphenicol

In recent years,the problem of long-term retention of antibiotics in the environment has been widely discussed both at home and abroad,and the increased bacterial resistance caused by antibiotics has resulted in huge economic losses and personal hazards.Electrochemical advanced oxidation is thought to be the most promising technology for removing antibiotics from the aqueous environment,due to its benefits of being environmentally friendly and having a high efficiency without secondary pollution.The anode material,as the core component in the electrochemical advanced oxidation system,is directly related to the electrocatalytic ability,pollutant degradation,and mineralization capacity of the system.As a typical antibiotic,the study of electrochemical degradation process of chloramphenicol（CAP）can provide feasible ideas for safe and efficient degradation of antibiotics.In this study,a Ti³⁺self-doped titanium dioxide（Ti O₂）nanotube array（R-TNTs）electrode was successfully created,and tests were used to examine the effects of the self-doping on the electrode’s surface morphology,crystal structure,and catalytic performance.By using a single factor experiment and free radical verification technology,the mechanism of electrochemical degradation of CAP was examined.The change in overall biotoxicity following CAP degradation was reasonably predicted,which gave rise to a fresh idea for the creation of novel anode materials with improved comprehensive properties.The result was as follows:（1）Novel self-supported Ti³⁺-doped titanium dioxide nanotube arrays（R-TNTs）anodes were successfully prepared by two-step anodic oxidation and direct electrochemical reduction techniques.Scanning electron microscopy（SEM）,x-ray diffraction（XRD）,and x-ray photoelectron spectroscopy（XPS）analyses of the prepared R-TNTs anodes demonstrated the successful production of anatase type R-TNTs.The electrochemical activity of R-TNTs was studied by cyclic voltammetry（CV）,linear scan（LSV）,UV-vis absorption spectroscopy（UV-vis）,Raman spectroscopy（Raman）and Mott-Schottky.The electrochemical reduction treatment produced more Ti³⁺sites,stronger absorption in the UV-vis region,a 0.38 ev reduction in the forbidden band gap,a significant increase in the electron transfer rate,and an increase in the oxygen precipitation potential from 1.45（vs.Ag/Ag Cl）to 2.25（vs.Ag/Ag Cl）.（2）The electrochemical degradation of CAP simulated wastewater by R-TNTs electrode was investigated.The degradation process of CAP on R-TNTs electrode was in accordance with the primary reaction kinetics.The efficiency of CAP degradation and reaction rate constant increased with the increase of current density(2-10 m A cm^-2).The degradation rate of CAP under acidic conditions was higher than that under basic conditions.The most suitable electrolyte concentration was 0.1 M in the range of 0.02-0.13 M for Na₂SO₄ concentration.As the initial concentration of CAP(5-30 mg L^-1)was increased,the degradation rate at the same node gradually decreased,but the amount of degradation increased.At the optimal conditions of p H=5,current density of 8 m A cm^-2,electrolyte concentration of 0.1 M sodium sulfate,and initial CAP concentration of 10 mg L^-1,the CAP degradation rate exceeded 95%after 40 min.（3）The R-TNTs showed excellent stability.The degradation effect of chloramphenicol can be restored by electrochemical reduction after electrode failure.Under the optimal conditions,the CAP concentration was increased ten times for catalytic degradation experiments,and the two-stage mineralization current efficiencies were calculated to be 70.36%and 48.32%,respectively,with strong mineralization ability.（4）The electron paramagnetic resonance（EPR）experiments and molecular probe experiments identified the active species present in the system as·OH and SO₄^·-,where·OH dominated.13 intermediates were identified by high-performance liquid chromatography-mass spectrometry（HPLC-MS）,and,three possible degradation pathways of CAP were proposed.（5）The biotoxicity of intermediates produced was evaluated by the Toxicity Estimation Software Tool（T.E.S.T）software based on quantitative constitutive relationship（QSAR）prediction.The results showed that the acute toxicity of most of the intermediates was lower than that of chloramphenicol for blackhead minnow LC₅₀（96 h）and Daphnia magna LC₅₀（48 h）.The bioaccumulation factors of various intermediates were significantly reduced after electrochemical oxidation treatment with R-TNTs as the anode.The largest bioaccumulation factor of 90.8%was observed for intermediates（m/z=269）.The developmental toxicity of all intermediates except P5（m/z=334）was reduced,and several intermediates（m/z=194,m/z=166,m/z=137 and m/z=121）were even in the"developmentally non-toxic"zone.The results showed that the electrochemical oxidation with R-TNTs as the anode could completely remove chloramphenicol and effectively reduce its toxicity.