Adsorotion Behavior And Mechanism Of Two Microplastics For Flusilazole And Epoxiconazole

Pesticides are important agricultural material products,but unscientific and unstandardized application will cause pollution to soil,water bodies and other environments.Plastic agricultural films play a key role in water and moisture retention during the cultivation of agricultural products.However,they could degrade to micron-sized plastic particles when exposed to the natural environment.In recent years,large amounts of microplastics have been detected in water bodies and soils around the world,with polyethylene,polypropylene and polystyrene being the most common types.Due to their small particle size,large specific surface area and high hydrophobicity,micro plastics could adsorb pesticide molecules in the environment,making it easier for pesticide contamination to persist and spread in the ecosystem.Therefore,it is crucial to investigate the adsorption behaviors and mechanisms of microplastics towards pesticide molecules.In this thesis,the adsorption behavior and adsorption mechanism of flusilazole(FLU)and epoxiconazole(EPO),which are commonly used in film-covered crops maize,on two microplastics polyethylene(PE)and polystyrene(PS)were investigated and the main conclusions were obtained as follows.(1)The adsorption of pesticides on microplastics was influenced by the properties of microplastics and pesticides.For the same type of plastic,microplastics with smaller particle size had a higher adsorption capacity for pesticide molecules(100μm PS<10μm PS;100μm PE<10μm PE)(p<0.05).For the different types of plastics,10μm PE(FLU:171.5μg/g and EPO:153.4μg/g)had a higher adsorption capacity for both pesticides than 10μm PS(FLU:142.6μg/g and EPO:99.8μg/g)(p<0.05),probably due to the lower crystallinity of PE than PS and the rougher surface of PE.In addition,the adsorption of both pesticides by PE after high temperature aging was significantly lower compared to the pristine microplastics(FLU:138.39μg/g<171.5μg/g;EPO:111.6μg/g<153.4μg/g)(p<0.01).For the different pesticides,two microplastics both showed higher adsorption capacity to FLU than EPO,which may be due to the stronger hydrophobicity of FLU than EPO.(2)The adsorption of pesticides by microplastics was influenced by environmental factors.As the solution p H increased from 6.0 to 9.0,the adsorption of pesticides on microplastics gradually increased;the ionic strength added with 0.05%Na Cl increased the adsorption capacity of pesticides on microplastics,while the higher ionic strength decreased the adsorption capacity;dissolved organic matter(DOM)decreased the adsorption of pesticides on microplastics,and DOM had a stronger inhibitory effect on the adsorption of EPO compared to FLU.Compared with the single pesticide system,the adsorption of microplastics on two pesticides in the binary pesticides system decreased significantly(p<0.01),and competitive adsorption occurred between the both systems,and the adsorption of microplastics on FLU was consistently higher than that on EPO in both systems.(3)Study of the adsorption mechanisms of pesticide onto microplastics.The adsorption kinetic study showed that the adsorption process was more in accordance with the pseudo-second-order kinetics(R~2=0.9920-0.9983),and surface adsorption,mass transfer and intraparticle diffusion may occur.The adsorption isotherm study showed that the adsorption of pesticide molecules by microplastics was more consistent with the Freundlich model(R~2=0.9856-0.9970),indicating multilayer adsorption on inhomogeneous surfaces.The Q_e values calculated by the pseudo-second-order kinetics and the K_F values calculated by the Freundlich model all followed the order of PE>PS and FLU>EPO,which were consistent with the actual adsorption results.The adsorption thermodynamic study indicated that adsorption is a spontaneous,heat-absorbing process;PE for FLU exhibited the lowestΔG value at the same temperature(-12.0355 k J/mol--11.1485 k J/mol),which explained the highest adsorption capacity of FLU on PE.FT-IR analysis showed that physical adsorption played a key role in the adsorption process.XPS analysis further confirmed the existence of adsorption of both MPs on the target agents and that hydrogen and halogen bonds may facilitate the adsorption process.Considering the factors affecting the ability of MPs to adsorb pesticides,it is presumed that the adsorption mainly relies on hydrophobic interaction.In addition,the adsorption may haveπ-πinteractions due to the presence of benzene rings in the PS structure.