Adsorption Of Fluoroquinolones By Microplastics

In recent years,microplastics have been frequently detected in the environment.Microplastics in waters will adsorb the coexisting organic pollutants,thereby affect their environmental fate and ecotoxicity.Therefore,the study of the adsorption behavior between microplastics and organic pollutants is of great significance for assessing their environmental risks and revealing the toxicity mechanism of microplastics.Since the research on microplastics is still at the initial stage,the current research on the adsorption of microplastics mainly focuses on non-ionizable organic pollutants,and there are only a few researches on ionizable organic pollutants,such as antibiotics.Under natural water p H conditions,the adsorption capacity and mechanism between microplastics and antibiotics need to be revealed.Therefore,in this study,we prepared widely used microplastics of polyethylene(PE),polyethylene terephthalate(PET)and polyamide-6(PA-6),and investigated their adsorption towards 2 frequently detected fluoroquinolone antibiotics(Gatifloxacin,GAT and Norfloxacin,NOR).The purpose is to explore the adsorption mechanism and influencing factors.The main research contents and results are as follows:PE,PET and PA-6 type microplastics with particle sizes of 300-600 ?m,100-300 ?m and<100 ?m were prepared.Structural characterization found that the prepared PE type microplastic is white powdery particles in appearance,and is spherical,loose and porous microscopically;PET type microplastic is needle-shaped sphere with foaming bulges on the surface,and is a crystalline polyhedron microscopically;the PA-6 type microplastic is irregularly scaly in appearance and ellipsoid in the microscopic view;the particle size show no significant effect on the surface structure of the three types of microplastics.The specific surface area(BET)test results show that PET shows the largest specific surface area and pore volume under the same particle size range,followed by PE and PA-6.The order of the pore size followed by: PA-6> PE>PET.Zeta potential test results show that the three types of microplastics are all negatively charged.Under the same p H and the same type of microplastics,the electronegativity decreases with the increase of the particle size.The adsorption of GAT and NOR on the surface of three kinds of microplastics(particle size:100-300 ?m)were analyzed by kinetic model fitting.The adsorption kinetics results shoed that the adsorption process between microplastics and antibiotics can be divided into three stages:rapid adsorption,slow adsorption and adsorption saturation.The adsorption capacity of three microplastics for GAT is greater than NOR,and the maximum adsorption capacity for two antibiotics is in accordance with the order: PET > PE > PA-6.All the studied adsorption processes are more in line with the Lagrangian second-order model,indicating that the adsorption of fluoroquinolone antibiotics by microplastics is a complex heterogeneous adsorption process.As the collision probability among molecules increases,the adsorption rate decreases with the increasing of the initial antibiotic concentration.The particle diffusion model fitting found that surface adsorption and intra-particle diffusion play a leading role in adsorption.Henry,Langmuir and Freundlich models were used to fit the adsorption isotherms of three microplastics in different particle size ranges towards two antibiotics.The results showed that the adsorption curve of antibiotics on microplastics mainly showed a trend that firstly increased and then decreased with the concentration.The adsorption isotherms of Langmuir and Freundlich models showed better fitting results,indicating that the adsorption process was mainly monolayer adsorption.For microplastics with the same composition,the specific surface area of the microplastic increase with the particle size decreasing.Then the larger microplastic with smaller size will contain more adsorption sites,and show stronger adsorption capacity.Within the same particle size range,the adsorption capacity of PET is the strongest,followed by PE,and the adsorption capacity of PA-6 is relatively weakest.The adsorption capacity of the same kind of microplastics to GAT is stronger than that of NOR.The p H condition mainly affects the dissociation form of antibiotics and the surface chargeability of microplastics,and then influences their adsorption capacity by the combined effects of electrostatic repulsion,electrostatic adsorption and hydrophobic interaction.In summary,this study explored the adsorption interaction mechanism between the prepared microplastics and typical antibiotics through batch adsorption equilibrium experiments,and revealed the influencing low of microplastics composition,microplastics particle size,antibiotic type,antibiotic concentration and p H on the adsorption process and capacity.The research results can provide basic data for accurately assessing the environmental risks of microplastics and antibiotics under the combined pollution conditions,and for the further research of the adsorption effects on their ecological toxicity.