Sorption Mechanism Of Typical Pollutants By Microplastics

Antibiotics and heavy metal pollution have always been the focus of attention.In recent years,scholars in various countries have conducted extensive research on the adsorption of antibiotics and heavy metals on environmental media,but most of them are concentrated on soil,water,sediments and other environmental media for the sorption of antibiotics and heavy metals.It has been reported that a large amount of plastics in the environment will adsorb organic pollutants and heavy metals,which has a non-negligible impact on the transfer and conversion of pollutants.At present,the research on the sorption mechanism of pollutants by plastics is not systematic.Therefore,the sorption mechanisms of tylosin(TYL)and Cd2+ on polyethylene(PE),polypropylene(PP),polystyrene(PS)and polyvinyl chloride(PVC)and effect of Cd2+on adsorption of TYL on PS were studied in this paper.The following results are obtained:1.Sorption of TYL on the four micro-plastics can be well fitted by the two-stage kinetics model and the particle diffusion model.Sorption reaches a dynamic equilibrium after adsorption for 36 h.Sorption isotherms can be well fitted by Henry model and Freundlich model.The value of n in Freundlich model is less than 1 and adsorption is nonlinear.The sorption capacity of four microplastics is PVC>PP>PS>PE.Sorption thermodynamic models were used to show that the sorption endothermic process was spontaneous and the spontaneous tendency was greater with increasing temperature.The amount of sorption decreases with increasing pH of the solution,increases first and then decreases with increasing K+ intensity.The sorption process is dominated by hydrophobic distribution,electrostatic interaction and surface complexation.2.Sorption data of Cd2+ on the four micro-plastics can be well fitted with the second-order kinetics model and particle diffusion.Sorption reaches equilibrium at 36 h.Sorption data of Cd2+ on PE,PP,PS and PVC can be well fitted by three models.Among them,the Freundlich model has the best fitting effect.n is less than 1 and the sorption process was nonlinearity.The sorption capacity of the four microplastics follows PE<PP<PS<PVC.The amount of sorption decreased with increasing pH value,decreased with increasing K+ concentration,and increased with increasing concentration of fulvic acid(FA)in the solution.Sorption process is dominated by electrostatic attraction,chelation,complexation and ion exchange.3.The sorption of TYL in the composite system can be fitted by Henry model and Freundlich model.n is close to 1 and the sorption process was nonlinearity.In the composite system,Cd2+ will reduce the sorption of TYL by PS.The sorption of TYL in the composite system increases with the increase of pH and decreases with the increase of K+ intensity.The sorption process is dominated by the distribution coefficient of the solid-liquid two phases,and the electrostatic attraction exists on the adsorption.The microplastics adsorbed Cd2+ first and then adsorbed TYL.The sorption data of TYL can be well fitted by using the Henry model and the Freundlich model.The value of n is less than 1,indicating that the sorption is a multi-layer dominated physical sorption,accompanied by chemical sorption.The sorption of TYL increases with the increase of pH and decreases with the increase of K+ intensity.Sorption of TYL is mainly affected by hydrophobicity distribution,bond-bridge interaction,electrostatic interaction and complexation.