| Chlorotheconil is a highly effective,low toxic,broad-spectrum fungicide pesticide used to protect vegetables,crops and turf from fungal pathogens.Because chlorothalonil is widely used in the environment,the degradation is slow,and its metabolite 4-hydroxyl chlorothalonil is more toxic than its parent,it has attracted extensive attention.In order to degrade chlorothalonil in water safely and efficiently,anthocyanins and fenton reagents were selected to study the photodegradation of chlorothalonil in ultrapure water,providing technology for the pollution treatment of chlorothalonil in wastewater from pesticide enterprises and dehydrated farmland.The experimental results are mainly as follows:1.Under the light of sunlight,high-pressure mercury lamp,ultraviolet lamp and xenon lamp,the droppingrate of chlorothalonil in ultrapure water is different at different light sources.Anthocyanins significantly promoted the photodegradation of chlorothalonil solution,and the photodegradation rate and photosensitization efficiency of chlorothalonil gradually increased with the increase of anthocyanin concentration within the set concentration range.However,under mercury lamps and sunlight,the photolysis rate and photosensitization rate of chlorothalonil first increased and then decreased due to the saturation effect.Under high pressure mercury lamps,the photodegradation efficiency of chlorothalonil increased by 9.56 times when the molar ratio of anthocyanin to chlorothalonil was 9.0:1.Under the light of sunlight,ultraviolet light and xenon lamp,the photodegradation efficiency of chlorothalonil increased by 19.36 times,26.11 times and9.42 times respectively.2.Under light conditions,when anthocyanin was added to chlorothalonil aqueous solution,the determination results of chloride ion and hydroxyl radical showed that chloride ion content increased significantly and hydroxyl radical was not generated,indicating that this reaction was a reductive dechlorination reaction.Meanwhile,the highly toxic metabolite 4-hydroxychlorothalonil was not produced.The degradation pathway of chlorothalonil in ultrapure water is chlorothalonil?2,4,5-trichloro-1,3-isophthalene?2,5-dichloro-1,3-isophthalene?5-chloro-1,3-isophthalene,but anthocyanin cannot degrade 5-chloro-1,3-isophthalene,anits dechlorination reaction is not complete enough.3.Under the illumination of high-eprssure mercury lamp,anthocyanin will undergo photodegradation reaction in aqueous solution itself.After adding anthocyanin to thesolution with chlorothalonil under illumination,anthocyanin will also consume with the reaction system in addition to photodegradation consumption itself,and the consumption of anthocyanin is about 2.85 times of the degradation amount of chlorothalonil,which indicates that only some phenolic hydroxyl groups play a role in the reaction process.4.Under the illumination of high-pressure mercury lamp,diacaronitrile did not degrade under dark conditions,and the photolysis half-life of diacaronitrile itself in pure water was266.54 min.The photodegradation half-life of difenitrile was 61.88 min after adding 9times molal concentration of anthocyanin.The photodegradation efficiency of dioxin was4.31 times that of dioxin without anthocyanin.Anthocyanins can promote the photodegradation of dioxitrile in ultra-pure water,indicating that anthocyanins may have photodegradation of chlorothalonil similar structure of pesticides.5.Under the strong oxidation of Fenton reagent,5-chloro-1,3-dicyanobenzene was degraded under illumination,and 5-hydroxyisophthalonitrile was presumed to be formed until mineralization.By simulating the stepwise photodegradation experiment of chlorothalonil,it is found that adding anthocyanin with a certain concentration to react under light and then adding Fenton reagent can effectively promote the degradation of chlorothalonil and degradation products until the degradation products completely disappear,indicating that anthocyanin and Fenton reagent have synergistic effect on the photodegradation of chlorothalonil. |
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