CAS-MNP: Molecular Probing Surface Reactivity Dynamics of Native versus Photo-Oxidized Microplastics and Nanoplastics in Environmental Aqueous Media

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This award from the Environmental Chemical Sciences Program in the Division of Chemistry and the Environmental Engineering Program in the Division of Chemical, Biological, Environmental, and Transport Systems is supporting Dr. Ludmilla Aristilde at Northwestern University for research on microplastics and nanoplastics, which are important end-products in the environmental fate of plastics in oceans, lakes, and rivers. These remnant plastic materials are reported to trap various organic contaminants in different environmental aqueous media. Through photo-oxidation due to exposure to sunlight in the presence of reactive particles, the fragmented plastic surfaces can develop different chemical characteristics. This project focuses on unraveling these different chemical characteristics and their role in facilitating contaminant adsorption on the polyethylene, polypropylene, and polystyrene plastic types. The outreach and educational broader impacts aim to implement undergraduate students into the research activities, foster the engagement of high school students, and increase public literacy regarding the environmental fates of plastic wastes.This project applies several spectroscopic investigations coupled with molecular simulations to unravel the surface chemistry and chemical dynamics at native versus photo-oxidized structures of microplastics and nanoplastics in relation to their selective interactions with specific contaminant classes. The adsorbent role of plastics relies on favorable nanoscale to molecular-scale interactions at the water-plastic interfaces. However, a mechanistic understanding of these interactions, especially within the context of the different surface chemistries of native versus photo-oxidized plastics, remains a critical knowledge gap. Atomistic-scale experimental probing at the water-plastic interfacial environments is performed to elucidate changes in molecular reactivity in different media composition representing freshwater versus seawater of varying chemistries. These experimental results are coupled with molecular modeling simulations of solvated systems to determine the structural factors that control favorable versus unfavorable contaminant affinity to native versus photo-aged nanoplastic surfaces. The research is expected to provide new mechanistic insights on how structural and chemical changes at the microplastic and nanoplastic surfaces influence the trapping dynamics of organic contaminants of different classes at the water-plastic interface. These findings will be important in the quest to develop predictive models for the role of microplastics and nanoplastics in the fate of organic contaminants in freshwater and marine waters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.