Degradation Of Antibiotics By Advanced Oxidation Technology Based On Chlorite Activation

Antibiotics have received widespread attention due to their persistence and ecological risks in the aquatic environment.Even trace levels of antibiotics can remain and accumulate in soil and water environments.Residual antibiotics can induce the accumulation of bacterial resistance and the generation of antibioticresistance genes in microorganisms,and damage ecosystems.Therefore,it is urgent to deal with the contamination of antibiotics.Chlorine dioxide(ClO2)has selective oxidation characteristics and exhibits highly selective oxidation for pollutants containing electron-giving groups.In addition,CIO2 carries out oxidative degradation of pollutants by electron transfer without chlorination and does not produce organic disinfection by-products(DBPs).Therefore,ClO2 is commonly used in the fields of water micro-pollutants,odor elimination and disinfection.However,ClO2 solutions are difficult to store and transfer for long periods of time and can only occur on-site and be stored away from light.In addition,the inorganic DBPs chlorite(ClO2-)and chlorate(CIO3-)are produced during ClO2 application.Among the ClO2 preparation methods,the chlorite method is widely used due to its simple operation,mild reaction conditions and high purity.However,the conversion ratio of chlorite to ClO2 is low;in addition,the introduction of impurities in the preparation process leads to the generation of inorganic DBPs,which limits the application of chlorite method.Therefore,it is necessary to develop a new efficient and environmentally friendly method to generate ClO2 using chlorite as a precursor to solve the disadvantages and occurrence problems of ClO2 itself.In this dissertationbased on a large amount of related literature at home and abroad,the visible-light activated chlorite(vis-BiOX/chlorite)system and the oxygen vacancy(OVs)mediated BiOX activated chlorite(OV-BiOX/chlorite)system were constructed with bismuth halide oxide(BiOX,X=Cl,Br and I)as catalysts.The mechanism of ClO2 generation by activation of chlorite in both systems were investigated in depth,and the performance and mechanism of degradation of antibiotic pollutants by both systems were explored separately with sulfamethoxazole(SMX)as the target pollutant.The main studies and results are as follows.1.Three kinds of bismuth halides(BiOX,X=Cl,Br and I)were synthesized by chemical precipitation.and their components,morphology and photocatalytic performance were compared by XRD,Raman,FT-IR,SEM.TEM.XPS.electrochemistry and other characterization methods;three kinds of BiOX were used as photocatalysts to compare their performance of activating chlorite to degrade sulfonamide under visible light.On the basis of this,the best BiOI was selected as the catalyst to construct a visible-light activated chlorite(vis-BiOI/chlorite)system,and the dominant active species and activation mechanism of chlorite in the visBiOI/chlorite system was further investigated.In addition,the effect of this system on the degradation efficiency of SMX under different reaction conditions was investigated,which clarified the superiority of the vis-BiOI/chlorite system compared with the photocatalytic or chlorine dioxide oxidation process.The results showed that BiOI showed the best ability of activation of chlorite compared with BiOCI and BiOBr,and the complete degradation of SMX could be achieved within 30 min.In the vis-BiOI/chlorite system,photogenerated electrons(e-)and holes(h+)are generated by visible light excitation of BiOI,followed by photogenerated radicals(-OH,·O2-)to achieve the activation of chlorite to produce ClO2.In addition,the combined system not only has a wide pH range,but also achieves efficient degradation of SMX under the interference of coexisting ions and organic matter,and has good cycling stability and photo-corrosion resistance.In addition,the combined system not only has better degradation effect than the pure photocatalytic system,but also has much higher resistance to water matrix interference,and its degradation effect is more sustainable than the single chlorine dioxide oxidation system.The toxicity of SMX degradation products was evaluated by the quantitative structure-activity relationship(QSAR)model,and the toxicity of SMX degradation products was basically reduced;the yield of organic DBPs was low,and all ClO2-was converted to non-toxic Cl-,indicating that the potential environmental hazards of SMX were significantly degraded by the vis-BiOI/chlorite system.2.Oxygen vacancy-mediated BiOX-activated chlorite degradation system was developed to achieve efficient activation of chlorite and degradation of SMX under light-free conditions.The morphology of the three materials and the concentration of oxygen vacancies were analyzed by XPS and EPR characterization.The performance of BiOX-activated chlorite degradation of SMX was compared,and based on this,the oxygen vacancy-mediated chlorite activation(OV-BiOI/chlorite)system was constructed by selecting the best performing BiOI as the catalyst.Through characterization and DFT calculations,the mechanism of oxygen vacancy involvement in the activation of chlorite by catalysts,and the influence and mechanism of action of high-valent metals and protons on the activation of chlorite by catalysts were clarified,and the mechanism of activation of chlorite by OVBiOI/chlorite system was investigated in depth.The effects of pH,coexisting anions,organic matter and different water conditions on the performance of the system in degrading SMX were investigated.The potential degradation pathways and degradation products of SMX were analyzed by LC-MS and DFT calculations.The results show that BiOI has the highest content of surface oxygen vacancies,which can provide more central reaction sites for efficient activation of chlorite and generate more high-valent metals(Bi4+)during the reaction,thus facilitating the metal ion redox cycle.Meanwhile,acidic conditions favored the activation of chlorite,suggesting that protons were also involved in the reaction.EPR and radical quenching experiments confirmed that the OV-BiOI/chlorite system was dominated by CIO2,with ·OH and ·O2-acting synergistically to degrade SMX.The OV-BiOI/chlorite system showed good SMX degradation performance and stability under different reaction conditions,which proved the practicality of the system.The toxicity of SMX degradation products and environmental hazards were reduced by using toxicity prediction tools,and all ClO2-was converted to non-toxic Cl-,which demonstrated the environmental friendliness of the system.