| Since the emergence of genetically modified herbicide-resistant crops,humans have increased the use of various pesticides in order to increase the yield of crops.Among them,glyphosate has become one of the most commonly used herbicides in the world due to its safety,high efficiency and economic advantages.However,it has recently been discovered that glyphosate is a potentially carcinogenic substance.During toxicological experiments,it has been found that glyphosate not only has oxidative toxicity effects on organisms,but also affects zebrafish brain and morphological development abnormalities and reproduction.Effects but also affects zebrafish brain and morphological development and reproductive functions such as decreased sperm quality and ovarian dysfunction.The production and use of glyphosate will pollute the environment.The concentration of glyphosate in the wastewater of the glyphosate production factories can reach 2560 mg/L.Therefore,it is necessary to obtain a kind of material that can effectively adsorb and degrade the organophosphorus pesticide.The purpose of this experiment is to use pure water instead of N,N-dimethylformamide(DMF),a solvent harmful to the environment and the human body,to hydrothermally synthesize flexible metal frame MIL-8 8A.Because of it has large specific surface area in water,stable performance and can be suitable for degradation reactions,it can be used for adsorb and degrade glyphosate.In the process of synthesis,the factors affecting the morphology and size of MIL-88A were explored by changing the ratio of ferric chloride and fumaric acid,synthesis time,synthesis temperature and other conditions.The final synthesis conditions of MIL-88 A with a size of 7.47μm are:ferric chloride:fumaric acid=1:1,synthesis temperature 100℃,synthesis time 2 h.The MIL-88A synthesized under this condition was used for subsequent degradation experiments,and it was found that the adsorption of glyphosate by MIL-88A was mainly affected by pH.At room temperature,0.1 g/L MIL-88A was used to adsorb 100 mg/L glyphosate(pH=3.28),the maximum adsorption capacity is 287.38 mg/g,and the adsorption reaction can be completed within 16 min.During the degradation process,pH,the dosage of MIL-88A,and the initial concentration of glyphosate have little effect on the degradation efficiency.The main factor affecting the degradation efficiency is H2O2 dosage.Under the irradiation of a Xe-lamp light source,the initial concentration of the glyphosate solution is 100 mg/L,and the H2O2 dosage is 1 mL/L.The glyphosate degradation efficiency is about 98%within 30 min of the Xe-lamp light.During the degradation process of glyphosate,the C-N bond is rapidly broken to generate aminomethyl phosphate and glycine.In this process,not only glyphosate will be degraded,the degradation products will also be degraded to a lower concentration.The free radical scavenger is used to analyze the free radicals that may play a role in the degradation process.Through the analysis,it is found that the main role in the degradation process is ·OH and ·O2-.In order to determine whether light sources can be used to degrade glyphosate by this method,through the comparison of Xe-lamp light and sunshine it was found that the method still has a good degradation effect under sunlight and has the potential for large-scale use.A big disadvantage of the Fenton reaction is that it is easy to form sludge during the degradation process,and the degraded materials cannot be reused.In this experiment,the heterogeneous Fenton reaction is used.After the glyphosate is degraded,MIL-88A can be recycled and reused.And through experiments,it is found that the degradation effect can still be maintained after three times of recycling. |
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