RUI: CAS-MNP: Molecular Behavior at Colloidal/Aqueous Interfaces of Heterogeneous Nano- and Micro-Plastics - Binding Interactions and Effect of Aging

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With support from the Environmental Chemical Sciences Program in the Division of Chemistry, Mahamud Subir and his team of graduate and undergraduate students at Ball State University will perform surface-selective second harmonic generation (SHG) spectroscopy and quartz crystal microbalance technology with the aim of determining the adsorption parameters pertaining to various types of micro- and nano-plastics (MNPs). Plastic pollution has become a major environmental concern. In the aquatic environment, plastics can break down and form small fragments ranging from a few nanometers to hundreds of micrometers in size. These micro- and nano-plastic (MNP) particles offer a large surface area, which allows other organic contaminants dissolved in water, to interact with the MNP surfaces. Understanding these binding interactions is important as they determine the fate and transport properties of both MNPs and organic pollutants. Moreover, elucidating the surface affinities of MNPs is critical in developing effective adsorption techniques to remove microplastics. In this project, surface interactions of different types of organic compounds with MNPs of various compositions and surface properties will be investigated. The project will not only generate new knowledge on the binding behavior of MNPs in the presence of organic molecules, but also train future scientists in tackling persistent challenges associated with plastics pollution. MNPs are heterogeneous and their interfacial chemistry is complex. Therefore, a systematic investigation using surface-selective second harmonic generation (SHG) spectroscopy and quartz crystal microbalance technology will be performed to determine the adsorption thermodynamic and kinetic parameters pertaining to various types of MNPs. The adsorption studies will be conducted using charged and neutral SHG probe molecules. Temperature-dependent adsorption studies are expected to reveal the binding strengths and mechanisms of their interaction with MNP/aqueous interfaces. Together, these experiments have the potential to help establish relationships between surface functional groups of MNPs and binding interactions. The role of non-specific vs. specific binding interactions will be examined. Additional objectives include investigating the impact of MNP ageing and of their size and shape on molecular binding. Determining a correlation between organic compound adsorption strength and chemical characteristics of MNPs has the potential, in the longer term, is expected to provide a foundation for improved modeling of the fate and transport of these emerging aquatic contaminants.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.