Effects Of Aging Of Microplastics On Pollutant Adsorption Behavior

Microplastics,as a new type of pollutant,exist widely in the environment and have attracted extensive attention because of their carrying effect on organic pollutants.Microplastics in the natural environment are subject to mechanical wear,solar radiation,chemical oxidation and other effects of aging,their physical and chemical properties will change,and then affect their environmental behavior.In this paper,two non-degradable microplastics polyamide（PA）,polyvinyl chloride（PVC）and a degradable microplastic poly（lactic acid）（PLA）were used as adsorbents,and two organic pollutants bisphenol A and phenanthrene with different properties and structures were used as adsorbents to study the changes in the adsorption behavior of pollutants before and after aging of microplastics.In order to explore the influence of different water environmental conditions on the aging of microplastics,the aging conditions were set as follows:microplastics were placed in two different medium solutions（p H 6 and sodium nitrate solution）and irradiated continuously for 60 h under 500 W mercury lamp.By the aging of the original and micro plastic microscopic surface morphology,elemental composition,surface functional groups,crystallinity and amorphous polymer domain characterization of experiment,the contrast before and after aging micro plastic changes in the chemical and physical properties,found increased aging are three kinds of micro plastic surface roughness,and between different micro plastic or in different media solution ageing of the same kind of micro plastic,The changes of surface polarity,functional groups,crystallinity and glass transition temperature are different.In this paper,the effects of aging on the adsorption of pollutants by microplastics were studied by adsorption thermodynamic experiments and adsorption kinetics experiments.The results showed that the adsorption thermodynamic behavior could be fitted by Frendlich and Langmiur models,and the adsorption kinetic behavior could be fitted by quasi-second-order kinetic equation.Combined with model fitting parameters and the adsorption isotherm and adsorption kinetics curve,found that different microplastics ageing of the same kind of pollutants adsorption performance,the same microplastic ageing adsorption performance of different pollutants are present diversity,after this is attributable to the aging characteristics,such as specific surface area,hydrophobic,oxygen containing functional groups,such as the degree of crystallinity of different changes.At the same time,this paper explored the influence of nitrate ions on the adsorption of organic pollutants after aging of microplastics.The experiment found that nitrate ions can promote the photohydrolysis reaction of phenolic organic matter in water,and reduce the content of bisphenol A in the mixed solution with microplastics.As a result,the adsorption capacity of the microplastics aged in sodium nitrate solution to bisphenol A is lower than that of the original microplastics and the microplastics aged in the solution with p H 6.