Adsorption Behavior And Mechanism Of Antibiotics In Water By Microplastics

Rivers are regarded as the main way for the transportation of microplastics from land to marine ecosystems.Microplastics have good environmental mobility due to their small size and light density.More and more evidences show that as an ideal carrier and medium for organic pollutants,microplastics can be attached to a large number of pollutants on its surface.At present,the adsorption research of microplastics is mainly focused on the original microplastics.The physical and chemical properties of the aging microplastics will change,which makes the aging microplastics may have completely different adsorption behaviors.Biodegradable plastics have developed rapidly in recent years.Their good degradation performance is based on the conclusions drawn in an ideal industrial stacking system.Facts have proved that compared with traditional plastics,biodegradable plastics produce more plastic particles in the environment.The carrier function of the aging and degradable microplastics is still unclear.Based on this,this project targets microplastics with polylactic acid（PLA）,polyethylene terephthalate（PET）and polypropylene（PP）particles,and uses sulfamethoxazole（SMX）and promise Flefloxacin（NOR）and tetracycline（TC）are the target antibiotics,and the advanced oxidation process-thermally activated K₂S₂O₈ method is used to simulate the aging conditions of microplastics in the environment to study the adsorption effect and influencing factors of microplastics on antibiotics before and after aging.The adsorption behavior of microplastics was analyzed by SEM,BET,FT-IR,Zeta potential,adsorption kinetics and isotherms,and the effects of different initial p H values,salinity and dissolved organic matter（DOM）on the adsorption behavior of microplastics were compared.To provide a reference for further exploring the environmental risks of microplastics as antibiotic carriers,the following conclusions are drawn:（1）Three different types of microplastics were aged by the thermal activation K₂S₂O₈ method,and the morphology and functional groups of the microplastics before and after adsorption were characterized.As the aging time increases,the adsorption capacity of the microplastics also increases significantly.Persulfate aging causes pitting,cracks,peeling,and chipping on the surface of the three types of microplastics,as well as gullies that penetrate before and after.The aging process changes the surface morphology and structure of the microplastics.The dissolved oxygen in the solution will enter the pores of the microplastics and replace the original functional groups,so that the peak intensity of the oxygen-containing functional groups of the microplastics after aging is strengthened,and the original hydrophobicity of the microplastics surface is weakened.（2）PLA has the highest adsorption capacity in the original or aged microplastics.The original microplastics conform to the quasi-first-order kinetic model,and the aging microplastics conform to the quasi-second-order kinetic model,which means that the aging microplastics The adsorption of SMX involves multiple processes.The Freundlich adsorption isotherm model can better describe the adsorption of microplastics to SMX,which belongs to multilayer adsorption.NOR exhibits a high degree of linearity in the isothermal model,and the distribution coefficient may play a major role.The adsorption behavior of TC on PET and PP after aging conforms to the quasi-first order adsorption kinetic model;the PP before and after aging is more in line with Linear.The fitting results show that the maximum adsorption capacity of PLA and PET for TC after aging reaches2.293 mg/g and 3.617 mg/g.（3）p H has a greater influence on the adsorption capacity of microplastics and has a similar trend.Among them,SMX has the largest adsorption capacity under acidic conditions,and the adsorption capacity of NOR and TC reaches the maximum at p H=6 and 7,and then gradually decreases.The presence of salinity inhibits the adsorption of SMX on PET and PP,but when the salinity is greater than 10‰,the adsorption capacity of PLA increases;the increase in salinity inhibits the adsorption of NOR by microplastics,but has no significant effect on TC It is speculated that the hydrogen bonds in the TC molecule are not sensitive to salinity.Humic acid（HA）inhibits the adsorption of SMX on PET and PP,but promotes PLA.It has a significant inhibitory effect on the adsorption of NOR by PLA and PP.Similarly,the change of HA has no significant effect on the adsorption of TC by microplastics.（4）The results of this study show that aging can significantly change the adsorption behavior of microplastics on antibiotics.The analysis shows that the adsorption is dominated by electrostatic force.After aging,the specific surface area of the microplastics increases and the oxygen-containing functional groups increase,which enhances its adsorption capacity,indicating that hydrogen bonding is its main effect.Microplastics can be used as effective carriers of organic pollutants,and after aging,the effect of microplastics on antibiotics is stronger than that of original microplastics,which may increase the migration and toxicity of water.Studies have shown that the microplastics after the aging process have a stronger effect on the carrier of antibiotics than the original microplastics,which aggravates the migration and toxicity of the water.