The Study On Adsorption Behavior Of Sulfadiazine And Ciprofloxacin Onto Microplastics

In recent years,microplastics and antibiotics as new pollutants have caused a series of environmental and ecological pollution problems.Microplastics are ubiquitous.Because of their small particle size,they are easy to be swallowed by marine organisms and do harm to marine organisms.Microplastics can be transmitted along the food chain,which poses a greater potential threat to the ecological environment.The extensive use of antibiotics also causes serious pollution to the water environment.In addition,microplastics have large specific surface area and are easy to absorb pollutants and become a carrier for the migration and diffusion of pollutants in the marine environment.Therefore,the study on adsorption and enrichment of pollutants onto microplastics has important significance to explore the mechanism of marine ecological pollution by microplastics.In this work,two kinds of plastics and two kinds of antibiotics were selected as study objects,including polyethylene(PE),polypropylene(PP),sulfadiazine(SDZ)and ciprofloxacin(CIP).High performance liquid chromatography and micro-fourier transform infrared spectrometer were used to analyze the adsorption behavior and adsorption mechanism of antibiotics onto microplastics in seawater or purewater,and then to investigate the influence factors on antibiotic adsorption onto microplastics.(1)In the background of different solutions such as seawater and pure water,PP and PE had different adsorption capacities for two antibiotics.The adsorption capacities of PP or PE for each antibiotic was in descending order:PP in pure water>PE in pure water>PP in seawater>PE in seawater.The strength of antibiotics absorbed was also different,the amounts of SDZ absorbed onto microplastics in seawater was far less than that in pure water,and CIP was hardly adsorbed.The amount of CIP absorbed was greater than that of SDZ in pure water.Antibiotics adsorbed in different media was in descending order:CIP in pure water>SDZ in pure water>SDZ in seawater>CIP in seawater.(2)The isothermal adsorption models and the kinetic adsorption models were used to fit the experimental data.The Freundlich model had a good fitting effect on microplastics adsorption,this indicated that the adsorption sites are heterogeneous.The fitting effect of SDZ adsorption onto PE in seawater was in accordance with the pseudo-first order kinetic model,which showed that the main adsorption pattern was diffusion.The fitting effect of SDZ adsorption onto PP in seawater,SDZ or CIP adsorption onto PP or PE in pure water were all in accordance with the pseudo-second order kinetic model.This indicated that the adsorption process was jointly controlled by multiple adsorption stages.(3)FTIR was used to explore the adsorption mechanism between microplastics and antibiotics.Comparing FTIR spectra between PP and PE before and after adsorption,it was known that no new chemical functional groups were formed during the adsorption,this implied that the chemical adsorption can be neglected in the adsorption process.Combining the results of this work with those of others,the structure characteristics or the changes of microplastics before and after adsorption,the physicochemical properties of antibiotics,and the effects of different background solutions were analyzed.The mechanisms of adsorption mainly included electrostatic forces,hydrogen bonds,Van Der Waals forces,and hydrophobic interactions.