CAS-MNP: Microplastic Surface Chemistry at the Nanoscale: Single Molecule Studies of Organic Micropollutant Adsorption and Transport

About This Grant

With support from the Environmental Chemical Sciences (ECS) program in the Division of Chemistry, Professor Daniel Higgins at Kansas State University and his students will study the accumulation of hazardous organic micropollutants on the surfaces of secondary microplastics. Microplastics are plastic fragments that form when larger objects are subjected to mechanical and chemical weathering. It is now well known that microplastics accumulate, concentrate, and transport organic pollutants into new environments, where they may pose risks to both aquatic and terrestrial life. Unfortunately, the mechanisms by which micropollutants interact with microplastics are not well understood. Prior studies have relied mostly on averaged measurements that neglect the possibility of nonuniform surface chemistry. Many have employed micropollutant concentrations that far exceed those found in the environment. These limitations will be overcome by employing super-resolved single-molecule detection methods. These methods afford nanometer-scale spatial resolution and allow for studies at environmentally relevant concentrations. The results will reveal the mechanisms by which organic micropollutants accumulate on microplastic surfaces, and how these evolve in space and time, as the plastics are weathered, pointing to micropollutant-microplastic interactions of greatest environmental concern. The team will incorporate related concepts into public science outreach activities hosted annually in western Kansas. Synthetic microplastics will be prepared from pristine polyethylene terephthalate sheets widely used in food and beverage containers commonly found in the environment. They will be artificially aged in a weathering chamber by exposure to UV light, water spray, and elevated temperatures. Changes in surface chemistry will be followed by water contact angle measurements, X-ray photoelectron spectroscopy, and vibrational spectroscopy. Surface morphology will be characterized by atomic force microscopy. Super-resolved single molecule detection methods will be used to follow the accumulation of fluorescent organic dyes on the plastic surfaces as models for organic micropollutants, revealing the strengths and mechanisms of relevant molecular level interactions on relevant nanometer length scales. The local isotherms associated with dye adsorption will be deduced and the mechanisms by which weakly associated molecules diffuse on the microplastics will be elucidated. An improved understanding of how microplastic surface chemistry evolves on nanometer length scales under weathering, and how these changes contribute to micropollutant adsorption, diffusion, and release will be important outcomes of this work. 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.