Preparation Of Titanium-based PbO₂ Electrode And Its Effect On The Electrocatalytic Degradation Of Chloramphenicol

With the development of society,the problem of water environment pollution is gradually exposed.Emerging organic pollutants have become a hot issue for research in the environmental field.The entry of antibiotics such as chloramphenicol（CAP）into the environment has triggered a series of environmental pollution problems,such as the production of drug-resistant microorganisms and antibiotics resistence genes（ARGs）.The potential environmental risks that exist are much higher than those of parent antibiotics,causing harm to human health and ecological environment.Electrochemical advanced oxidation is considered to be the most promising,green and effective technology for the removal of antibiotics.The anode material is the key to the electrochemical oxidation technology and determines the pathway and extent of organic degradation.Ti/PbO₂ electrodes have been widely used because of their good mechanical properties,high electrical conductivity and high oxygen precipitation overpotential.In this thesis,Ti/PbO₂-La and Ti/PbO₂-Co-La electrodes were prepared by electrochemical deposition,and the effects of doping elements La and Co on the surface morphology,crystal composition and catalytic performance of Ti/PbO₂ electrodes were investigated.The mechanism of electrochemical degradation of CAP was explored,and the effect of CAP and its intermediate degradation products on bacterial communities and ARGs in natural water environment were investigated,which could provide new ideas for the preparation of Ti/PbO₂ electrodes with better performance and the safe and efficient degradation of antibiotics.The obtained results were as follows:Ti/PbO₂-Co-La electrode and Ti/PbO₂-La electrode were successfully prepared by electrodeposition method.The Ti substrate surface has been covered withβ-PbO₂ crystals in a cubic cone structure and Co and La have been successfully doped into the PbO₂ active layer.With increasing amounts of Co and La doping,the crystal structure of lamellar La₂O₃ and granular Co O gradually appeared on the electrode surface,and the average particle size of PbO₂ grains further decreased.When the Co and La doping amount reached 0.44 g/L,Co replaced Pb into the Pb-O lattice to control the growth direction of the crystal surface,a new Co-O nucleation centre was formed,and the dominant orientation was changed into（101）crystal surface.With the increase of Co and La doping,the conductivity,oxygen precipitation potential（OEP）,overpotential and corrosion potential of modified Ti/PbO₂ electrode increased,and then their service life increased.When Ti/PbO₂-La electrodes were used as the anode,the CAP degradation ratio gradually increased with increasing current density（2.5-30 m A/cm²）,and the TOC removal showed an increase followed by a decrease.The high current density of 30m A/cm² was not conducive to TOC removal instead.Electrolyte concentrations of Na₂SO₄ in the range of 0.050-0.150 mol/L had less effect on CAP degradation.The highest TOC removal was obtained when the concentration of Na₂SO₄ was 0.125 mol/L.As the initial concentration of CAP increased（5 mg/L-100 mg/L）,the degradation ratio of CAP gradually decreased and the degradation amount increased.The TOC removal ratio decreased with the increasing of the initial concentration of CAP（25 mg/L-200mg/L）.The degradation reaction started with better TOC removal at p H=5,and as the reaction progressed,p H=7 was more favorable for TOC removal.When Ti/PbO₂-Co-La electrodes were used as the anode,the degradation ratio of CAP tended to increase and then decrease with increasing current density（7.5-15.0m A/cm²）.The highest degradation ratio was obtained when the current density was 12.5m A/cm² under the experimental conditions.The most suitable electrolyte concentration for CAP degradation was 0.050 mol/L.Decreasing or increasing the concentration of electrolytes would decrease the ratio of CAP degradation.The highest rate of degradation was achieved at p H=6.7.The degradation ratio increased with increasing concentration of added chloride ions.The effect of current density（A）,electrolyte concentration（B）and solution p H（C）was explored by response surface curves.The regression equation was obtained as:CAP degradation（%）=98.38+1.30 x A+0.028 x B-1.63 x C+0.82x AB+1.35 x AC-0.69 x BC-1.56 x A²-2.04 x B²-2.08×C².The optimal degradation conditions were:current density 12.97 m A/cm²,electrolyte concentration 50 mmol/L and solution p H 6.38,and the highest degradation ratio of 98.84%could be achieved under the optimal conditions.The prepared Ti/PbO₂-Co-La electrodes had good mineralization ability and the addition of chloride ions inhibited the ability of the reactive groups to mineralize CAP to a certain extent in the reaction system.The electrochemical degradation of CAP on Ti/PbO₂ electrode was in accordance with the first order kinetics with a correlation coefficient of R²=0.93305.The result of molecular probe experiments persumably obtained that CAP degradation on Ti/PbO₂electrode was mainly due to the direct oxidation.The degradation products were analyzed by HPLC-MS,and the main degradation sites of CAP occurred on the acylamino group and the aromatic rings in the molecular structure.15 degradation products and 2 major degradation pathways were inferred.CAP and its electrocatalytic degradation products affected bacterial communities and resistance genes in the aqueous environment.At the bacterial phylum level,chloramphenicol-containing wastewater that was completely degraded electrochemically had the least effect on the bacterial community when discharged into the aqueous environment,and the bacterial composition was most similar between CK and EG720,while the untreat wastewater（EG0）had the greatest effect on the baterial community.At the genus level,the relative abundance of Thiobacillus,Methylotenera,Ellin6067,Hydrogenophaga,Anaeromyxobacter,Geothermobacter,Geothrix increased in the EG0,EG20,EG120 and EG720 treatment groups.The addition of CAP and intermediates to the river substrate increased the absolute abundance of int I1 gene,whie the complete degradation products of CAP had no effect.CAP and its intermediate products stimulated the expression of cml A,cmle3,tet X,sul1 and sul2,and inhibited the expression of tet G and tet B.CAP intermediate products had a slight suppressive effect on cata2,and complete products had the least effect on various genes.The results of redundancy analysis（RDA）showed that int I1 explained the highest variance in ARGs,followed by the microbial communities.