The Interaction Mechanism Between Polystyrene Nanoplastic And Minerals In Aqueous Phase

With the extensive use and discard of plastic products,they continue to release microplastic particles,including nanoplastics,under multiple actions in the environment,Micro（nano）plastics pollution becomes an increasing global problem.When micro（nano）plastics enter the environment,they will interact with the active substances in the environment to change their environmental behavior.At present,some scholars have studied the interaction between micro（nano）plastics and active substances such as humus and microorganisms in the environment.Minerals are active substances that exist widely in soil and sediments.However,the interaction between microplastics and minerals is rarely studied,especially from the perspective of nanoplastics.In addition,micro（nano）plastics exposed to the environment will undergo aging,such as light,wind,mechanical action,and so on,and aging will significantly change the physical and chemical properties of micro（nano）plastics,so that their microstructure and surface properties will change.Therefore,the study of the aging process and characteristics of micro（nano）plastics in the environment and the micro-interaction mechanism with minerals is very important for the scientific assessment of the environmental behavior and ecological risk of micro（nano）plastics.In this study,the widely used polystyrene nanoplastic（PSNP）was selected as the research object.The interaction between PSNP and four typical minerals（goethite,magnetite,kaolinite and montmorillonite）was systematically studied,and three other materials with different surface charges（MnO₂,Al₂O₃ and SiO₂）were tested for comparison.In addition,considering the aging behavior of nanoplastics under physical and chemical action in the environment,light was selected as an important way of aging nanoplastics.By studying the distribution kinetics and isotherm of aged PSNP on minerals,combined with the influence of different hydrochemical conditions（p H,ionic strength）on the distribution of PSNP,the interaction process between minerals and aged PSNP was discussed.The interaction mechanism between aged PSNP and minerals was revealed by two-dimensional infrared correlation spectroscopy（2D-FTIR-COS）and analysis of the surface morphology and microstructure before and after the interaction.The main research results of this paper are as follows:（1）The stability of negatively charged PSNP colloidal suspensions decreased in the presence of positively charged goethite and magnetite,while it was not affected in the presence of negatively charged montmorillonite and kaolinite,indicating that electrostatic interaction would affect the interaction between PSNP and minerals.The importance of electrostatic interaction on the stability of PSNP suspension was confirmed by the reaction of PSNP with other three metal oxides MnO₂,Al₂O₃ and SiO₂ with different surface charges.Transmission electron microscope（TEM）analysis and batch adsorption experiments show that goethite and magnetite have strong electrostatic attraction to PSNP,and can effectively adsorb PSNP.The Fourier transform infrared spectra（FTIR）and two-dimensional correlation spectroscopy（2D-COS）analyses indicated that there was strong hydrogen bonding between the-OH（γ-Fe OOH）of goethite and PSNP,contributing to the higher adsorption of PSNP on goethite than magnetite.（2）After aging,the surface of PSNP was rough and the oxygen-containing functional groups increased.It was found by adsorption experiments with minerals:Compared with the pristine PSNP,iron oxides（goethite,magnetite）showed a stronger adsorption ability to aged PSNP,and adherence of aged PSNP was also found on the surface of clay minerals.The higher adsorption capacity of aged PSNP on mineral surface may be related to electrostatic attraction and ligand exchange.The FTIR spectra of the adsorption of aged PSNP on minerals showed that the adsorption affinity between functional groups was different.2D-COS for the aged PSNP further showed that preferential adsorption occurred on minerals in the sequential order of Oxygen-containing functional groups（OFGs）.In conclusion,nanoplastics entering the environment will interact with minerals,which will affect the environmental behavior of nanoplastics.Aging effects of nanoplastics in the environment also affect their interaction with minerals.The study provides a theoretical basis for scientific evaluation of the ecological risk of nano-plastics in the environment.