| Antibiotics is one of the most widely used drugs in the world.Due to abundant usages,and the characteristics of water-soluble,stability,difficult to volatilize,antibiotics is continuously entering the environment and presenting a lasting state.Antibiotics is becoming a new environmental pollutant and causing attentions in the world since the impacts on microbial communities in surface water bodies and sewage treatment plants,endangerments of aquatic ecological balance,and inducement of bacterial resistance.Sulfonamide antibiotics is the most commonly used in humans and animals.The production and usage of sulfanilamide antibiotics are very large and continuously increased.The situation of its environmental impacts is not optimistic.The presence,migration,transformation,removal and effects of sulfonamide antibiotics in the environment have become important topics in antibiotic research.Photochemical degradation is one of the main pathways for the degradation of sulfonamide antibiotics in the environment.The molecular structure and environmental conditions are the main factors affecting the photodegradation of sulfonamide antibiotics.Many components in natural water bodies may affect the photodegradation efficiency.At mean time,the secondary products formed in the process of photodegradation may also cause secondary toxicity to water bodies.Currently,municipal sewage is the main collection source of antibiotics.However,it is difficult to treat antibiotics by traditional waste water treatment methods.It is an important task for domestic and foreign academic circles to explore the technical methods of efficient treatment of antibiotics in water.There have been many studies on photodegradation of sulfonamide antibiotics,and a series of important progresses have been made.However,the research on the factors affecting the photodegradation of sulfonamide antibiotics,the relationship between the structure and stability of sulfonamide antibiotics,the toxicity changes during photodegradation and the photodegradation technology of sulfonamide antibiotics are still not clear and not systematic enough.Accordingly,the research work in this paper is divided into four parts.In the first part,typical sulfonamide antibiotics were selected to study their photodegradation behaviors under aerobic and anoxic conditions and their degradation in actual water bodies,to further explain the photodegradation rule of sulphonamides in the environment.The second part is to explore the feasibility of advanced oxidation technology for the degradation of sulfonamide antibiotics.The third part discusses the environmental toxicity of sulfonamide antibiotics during photodegradation.In the fourth part,the reactivity of sulfonamide antibiotics with different structures was evaluated by quantum chemical calculation,and the difficulty of photodegradation was predicted.The main research results are as follows:1.Photodegradation analysis of typical sulfonamide antibioticsTaking sulfamethoxazole?SMX?and sulfamethazine?SMT?as typical representatives of sulfonamide antibiotics containing five-membered ring substituents and six-membered ring substituents,the effects of dissolved oxygen and chloride ions on the photodegradation of different forms of SMX and SMT were discussed by experimental methods.On this basis,the photodegradation efficiencies of SMT in wastewater,seawater,river water,lake water and tap water were investigated,and the composite effects of each component on the photodegradation of SMT in water samples were analyzed.The experimental results show that SMX is much faster than SMT in photodegradation under the same conditions,which is related to the different substituent structures in SMX and SMT molecules.Under hypoxic conditions,the degradation rate of SMX in neutral molecule state was the highest,and the reaction rate was the lowest in anionic state.Dissolved oxygen has a great promoting effect on the photolysis of SMX with neutral molecular state.During the irradiation process,ROS such as 1O2,O2·?and·OH were formed,which further promoted the degradation of SMX.On the contrary,for SMX,dissolved oxygen inhibits the degradation of three forms of SMT.Under anoxic conditions,the degradation rate of SMT in ionic form is higher than that in neutral molecular state,which indicates that SMT degradation mainly comes from the direct degradation of excited state SMT molecules after photon absorption without dissolved oxygen participation.Under aerobic light,the self-sensitization of SMT is obvious,and the mechanism initiated by 1O2 is dominant.It quenches the triplet of SMT and inhibits the degradation of SMT.Cl?has no effect on the photodegradation of SMX in neutral molecular form,but inhibits the SMX in anionic state.High concentration of Cl?has a promoting effect on various forms of SMT.The degradation efficiency of SMT in different water media is higher than that in pure water.The order of degradation efficiency is sewage>sea water>Jianhu water>Yangtze River water>tap water>pure water.The results were the complex effect of various components in different media on SMT photodegradation.2.Advanced oxidation technology for SMT degradationThe degradations of SMT by solar photoelectro-Fenton system and UV-Vis/Fe?0?/H2O2 system were studied,and the degradation conditions were optimized.Solar photoelectro Fenton system makes use of solar light energy,and the effects of pH,applied voltage and system Fe?III?dosage on SMT processing were discussed.In UV-Vis/Fe?0?/H2O2 systems,the effects of light intensity,aeration,iron scrap type and concentration,hydrogen peroxide and initial SMT concentration on degradation were also discussed.Results show that under the same conditions,compared with solar photo-Fenton and electro-Fenton methods,the SMT degradation rate of solar photoelectron-Fenton technology can be raised from 19.1%to 74.5%.·OH generated by the solar photoelectron-Fenton system was positively correlated with the degradation rate of SMT,and the synergistic mechanism generated by the photo and electric interactions in the solar photoelctro-Fenton system promoted the generation of·OH.Under the experimental conditions,the best degradation conditions of 1 L 10mg·L-11 SMT by photoelectron-Fenton technology were as follows:Fe2+=25 mg·L-1,pH=3.0,and voltage E=3V.The effect of UV-Vis/Fe?0?/H2O2 system on the removal of sulfa was very significant,and complete removal could be achieved under the optimized conditions.The most effective conditions for the removal of 1.0 mg·L-11 SMT by UV-Vis/Fe?0?/H2O2 system were:pH=3.0,hydrogen peroxide?H2O2?concentration of5.0 mg·L-1and casting iron scrap concentration of 0.1 mg·L-1under aeration.3.Study on phototoxicity of sulfonamide antibioticsUsing acute toxicity test method for water quality,algal toxicity and luminescent bacterial toxicity were studied during SMX and SMT photodegradation under different conditions.Photoinduced algal toxicity was tested by spirulina platensis?S2?,spirulina maxima?S3?and chlorella generalis;and luminous bacteria toxicity was tested by the T3 variety of luminescent bacillus.The results of algal toxicity experiment show that the presence or absence of dissolved oxygen has a great influence on the algal toxicity.Under the same conditions,there were also great differences with the algal species.For common chlorella,the growth inhibition rate of SMX and SMT photodegradation was no more than 6%under both aerobic and anoxic conditions,and the photodegradation solution assisted the growth of chlorella in most time.For S2,the inhibition rate of SMX raw materials was low under both aerobic and hypoxia conditions,while a great growth inhibition was showed during the degradation process.At the degradation time of 10min and 3040min,the inhibition rate of SMX degradation products on S2 could reach30%40%.The photodegradation toxicity of SMX under aerobic conditions was slightly greater than that under hypoxia conditions.Under both aerobic and anoxic conditions,the inhibition rate of SMT to S2 was nearly 20%.For S3,the inhibition of the growth by SMX photodegradation products under hypoxia was significantly enhanced compared with that under aerobic conditions.Under anaerobic conditions,the inhibition rate of the growth by SMX photodegradation was nearly 100%at the 40min illumination time,showing a very high toxicity.The inhibitory trend of SMT on S3 in the process of photodegradation under aerobic and anoxic conditions was almost the same,and the inhibitory effect on S3 decreased after about 4 hours of degradation.The results showed that light source and dissolved oxygen had a great effect on the toxicity of luminescent bacteria during the photodegradation of sulfonamide antibiotics.For SMX,the effects of halogen lamp and ultraviolet photodegradation solution on the toxicity of luminescent bacteria showed similar change rules under hypoxia conditions.With the increase of light time,the toxicity of luminescent bacteria gradually decreased.Under aerobic conditions,the toxicity of some light-emitting bacteria was slightly enhanced,but compared with SMX,the toxicity during degradation was not significantly increased.The photodegradation to the overall toxicity of luminescent bacteria is stable under anoxic conditions.However,under aerobic conditions,the mortality of halogen lamps and ultraviolet light degradation solutions to luminescent bacteria increases from about 10%to 45%and 56%,respectively,in a given light time range.4.Structure and reactivity analysis of sulfonamide antibioticsAccording to the density functional theory,the MPW1K method was used to calculate the molecular reactivity indices,such as hardness,softness,electrophile,electronegativity and frontier orbital energy of five kinds of sulfonamide antibiotics containing five-membered ring substituents and five kinds of sulfonamide antibiotics containing six-membered ring at MPW1K/6-311G?d,p?level.The stability was determined according to the activation energy index AEI and the stability index fH/L.Taking SMX as the representative of 5-membered ring substituents and SMT as the representative of 6-membered ring substituents,the differences in the reactivity of SMX and SMT were calculated in different configurations.By calculating the local softness of SMX and Fukui function,the attack position of hydroxyl radical in photo reaction is predicted.The results showed that the orders of the chemical stability of five kinds of five-component ring sulfonamide antibiotics from strong to weak were:sulfathiazole?STZ?,sulfamethylthiazine?SMZ?,sulfamethoxazole?SXZ?,sulfamethoxazine?SFX?,sulfamethoxazole?SMX?.The stabilities of sulfadiazine?SFD?and sulfachlorpyridazine?SCD?among 5 sulfonamide antibiotics with six-membered ring substituents were higher.The stability of SMX is the best in anion state and the worst in neutral molecular state.Under anionic morphology,the stability of SMT is the most unstable,while under cationic condition,it is the most stable.When hydroxyl radical attacks SMX and all sulfonamide with six-membered ring,the main active sites of attack are S,N,benzene ring,and substituents in the sulfonamide molecule,and there is no significant difference among various sulfonamides antibiotics. |
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