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

Microplastics and nanoplastics represent an important class of end-products in the life cycle of plastics in oceans, lakes, and rivers. Plastic remnant materials are reported to trap various organic contaminants in these different environmental aqueous media. 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. The three most common plastics types found in natural surface waters are derivatives of polyethylene, polypropylene, and polystyrene. It is well documented that nanoscale pellets of these hydrophobic plastic types accumulate legacy hydrophobic contaminants such as polychlorinated biphenyls and polyaromatic hydrocarbons. However, through photo-oxidation due to sunlight exposure with or without mineral and organic particles as photosensitizers, the hydrophobic plastic surfaces can develop functionalized surfaces with hydrophilic keto, hydroxyl, and ionizable groups. It remains largely unknown the implications of these alterations in compromising the trapping of hydrophobic contaminants versus providing an attractive adsorbent surface for polar aquatic contaminants (such as cyanotoxins, pharmaceuticals, and herbicides). To address this knowledge gap, the proposed research will integrate spectroscopic analyses with molecular dynamics simulations to investigate the fundamental surface chemistry and chemical dynamics that will prescribe the adsorption reactivity towards hydrophobic contaminants and polar contaminants of concerns on native versus photo-oxidized nanoplastics of the polyethylene, polypropylene, and polystyrene types. The specific research objectives are to (1) characterize particle size and surface chemistry of native versus photo-aged plastics in solution of varying chemistries, (2) determine the dynamics of polar and electrostatic interactions of the structurally different plastic structures, and (3) investigate theoretically and experimentally mechanisms of selective contaminant adsorption. In addition to providing new opportunities for undergraduate researchers, educational outreach programs will be implemented to engage diverse students from a local high school.