Preparation And Performance Of Pretilachlor And AD-67 Nano Controlled Release Formulation Based On ZIF-67

Pretilachlor（Pre）is an efficient and broad-spectrum pre-emergence herbicide,but it is easy to remain in the environment,and the field dosage is large,which is easy to cause phytotoxicity to Oryza sativa seedlings.When used in large quantities as a soil treatment agent,it will adversely affect soil organisms.The formulation is single and the organic solvent in the preparation is easy to cause pollution to the environment.Benzamide（AD-67）is a herbicide safener,which can reduce the phytotoxicity of herbicides to plants.Although it has no negative effect on plants,it is actually a kind of biologically active compound for other organisms in the environment and has ecological risks.Zeolitic imidazolate frameworks（ZIFs）are a subclass of metal-organic frameworks（MOFs）,which have the advantages of large specific surface area,high stability and moderate porosity as carriers.And some ZIFs structures collapse rapidly under acidic conditions,which can respond to changes in the micro-ecological environment,thereby accurately releasing necessary and sufficient active ingredients through a controlled release mechanism.Therefore,in this study,AD-67@Pre@ZIF-67was prepared by using acidolysis material ZIF-67 as the carrier,internal loading of Pre and surface self-assembly safener AD-67,aiming to reduce the frequency of pesticide application and improve the safety of non-target organisms.In this paper,AD-67@Pre@ZIF-67 was studied from five aspects.The main research contents and results are as follows:1.The preparation of ZIF-67,Pre@ZIF-67,AD-67@Pre@ZIF-67Used cobalt nitrate hexahydrate and 2-methylimidazole as raw materials,the preparation methods of ZIF-67 were screened by aqueous phase method,aqueous alcohol phase method and alcohol phase method.Through the single variable method,the synthesis conditions with methanol as the solvent and the ratio of 1:8 were determined:4.00 g（48.72 mmol）of 2-methylimidazole and 1.78 g（6.12 mmol）of cobalt nitrate hexahydrate were dissolved in methanol,respectively.The cobalt nitrate hexahydrate solution was added to the 2-methylimidazole solution to obtain ZIF-67.Pre@ZIF-67 was prepared by dissolving Pre in methanol,adding 800 mg ZIF-67 and stirring.AD-67@Pre@ZIF-67 was prepared by adding the obtained Pre@ZIF-67 to AD-67 methanol solution,stirring at 200 r/min for 8 h,standing for 12 h,centrifugal washing and drying.2.The characterization of ZIF-67,Pre@ZIF-67,AD-67@Pre@ZIF-67Fourier transform infrared spectroscopy（FTIR）results showed that AD-67@Pre@ZIF-67 had a new absorption peak near 3000 cm^-1,which corresponded to the characteristic absorption peaks of AD-67 and Pre,indicating that AD-67@Pre@ZIF-67was successfully prepared.Through scanning electron microscopy（SEM）and transmission electron microscopy（TEM）,it is shown that ZIF-67,Pre@ZIF-67 and AD-67@Pre@ZIF-67 are evenly distributed,regular in shape,and dodecahedron crystals.The results of dynamic laser light scattering（DLS）showed that the average particle size of ZIF-67 was about 470 nm,and the average particle size of AD-67@Pre@ZIF-67 was about 490 nm.The surface of ZIF-67 is electronegative,and the surface of Pre@ZIF-67loaded with Pre is positively charged.When the surface self-assembly potential value is negative AD-67,the positive potential value of AD-67@Pre@ZIF-67 decreases.The specific surface area of ZIF-67 was 1038.0769 m² g^-1,and the specific surface area of AD-67@Pre@ZIF-67 was 386.7254 m² g^-1.The results of the thermogravimetric analyzer（TGA）showed that the total drug loading of AD-67@Pre@ZIF-67 was about28%,Pre was about 23%,and AD-67 was about 5%.3.The sustained release properties of AD-67@Pre@ZIF-67Simulated the p H of the paddy field environment,200 mg AD-67@Pre@ZIF-67was weighed and placed in a dialysis bag,dispersed in 200 m L PBS buffer medium,and stirred at a rate of 200 rpm at room temperature.The contents of Pre and AD-67 in the solution were determined at certain intervals.The results showed that the release behavior of Pre and AD-67 was divided into two stages,and the release rate increased with the decrease in p H value.The system not only has the effect of p H-responsive drug release but also has the effect of drug-sustained release.4.Herbicidal efficacy of AD-67@Pre@ZIF-67The herbicidal activity of AD-67@Pre@ZIF-67 against Echinochloa crusgalli was determined by a greenhouse pot experiment.The results showed that the fresh weight inhibition rate of AD-67@Pre@ZIF-67 on barnyard grass for 18 d was 77.5%-89.6%.The fresh weight inhibition rate of Pre@ZIF-67 was 77.9%-90.3%.The fresh weight inhibition rate of Pre+AD-67 was 39.3%-89.6%.The fresh weight inhibition rate of Pre was 41.6%-80.8%.AD-67@Pre@ZIF-67 has the same inhibitory effect as Pre@ZIF-67.Compared with Pre and Pre+AD-67,AD-67@Pre@ZIF-67 has stronger herbicidal activity,which can reduce the dosage of Pre by 50%to achieve the same herbicidal effect.5.Environmental safety evaluationThe safety of AD-67@Pre@ZIF-67 in rice was studied by an indoor pot experiment.The results showed that the inhibitory effect of Pre@ZIF-67 on rice was more obvious than that of Pre,indicating that Pre after ZIF-67 nanocrystallization was easier to enter plants.Compared with the single application of Pre,the relative root length of rice treated with Pre and AD-67 was 10%higher,indicating that the simple combination of AD-67 and Pre could slightly alleviate the phytotoxicity of Pre to rice,but the effect was not good.The relative root length,relative plant height and relative fresh weight of rice seedlings treated with AD-67@Pre@ZIF-67 increased by 50%,40%and 62%,respectively.AD-67@Pre@ZIF-67 can increase the activity of GST and the content of GSH in rice,thereby reducing the phytotoxicity of Pre to rice.The acute toxicity of AD-67@Pre@ZIF-67 to earthworm Eisenia foetida was determined by the filter paper method.The results showed that the LC₅₀ value of AD-67@Pre@ZIF-67was the largest,indicating that it could reduce the toxicity of Pre to earthworms and improve the application safety.