The rapid development of novel nanomaterials and their incorporation into consumer products has not been paralleled with an equal effort investigating the possible environmental implications. Increasingly, the properties of engineered nanoparticles (ENPs) are tailored for specific applications through the use of organic capping agents. The properties imparted by the capping agents are also likely to influence the transport, toxicity and fate of these materials in the environment. In addition to the purposeful tailoring of ENPs, it is well established that natural organic matter (NOM), which is ubiquitous in surface water, will interact with natural colloids and ENPs, influencing their environmental behavior. To date, little research has focused on systematically investigating the roles that engineered capping agents play in controlling the environmental behavior of ENPs. Although preliminary studies have focused on the interactions between NOM and ENPs, many questions remain about the mechanisms controlling these interactions. Furthermore, none of the existing efforts have attempted to correlate environmental behavior and mechanisms of NOM-ENP interactions with the properties of the ENPs, NOM, and aqueous chemical composition. With the staggering number of new products being developed, it is essential that a fundamental framework be developed for predicting environmental behavior based on these properties. Intellectual Merit: The overarching objective of this work is to develop an improved understanding of the roles of synthetic capping agents and NOM in controlling the homogeneous and heterogeneous aggregation of ENPs in aquatic environmental systems. Using a suite of ligand-stabilized gold nanoparticles (AuNPs) and various NOM isolates, the specific aims of the project are to: (1) Correlate the physicochemical properties of capping agents with interactions between capped ENPs in aquatic systems; (2) Correlate the physicochemical properties of capping agents and NOM with interactions between capped ENPs and NOM in aquatic systems; and (3) Correlate the physicochemical properties of capping agents, NOM and suspended particulate matter with the interactions between capped ENPs and suspended particulates in aquatic systems. ENP stability with respect to homo-aggregation will be assessed using the zeta potential and aggregation rates measured using time-resolved dynamic light scattering. NOM-AuNP interactions will be probed using fluorescence and surface enhanced Raman spectroscopy. Finally, the interactions between AuNPs and suspended colloids will be quantified through a novel application of instrumental neutron activation analysis. By using a group of well-characterized ENPs that vary only with respect to their surface functionality, environmental behavior can be correlated with ENP properties in structure-activity type relationships. This work will provide an improved ability to predict environmental fate based on NP characteristics and yield the feedback necessary for the design of safer nanomaterials. Broader Impacts: The proposed work is transformational in that it aims to move the field away from assessing the environmental implications of nanomaterials on a case-by-case basis and towards the development of structure-activity type relationships correlating environmental behavior with nanoparticle characteristics. It is anticipated that such a framework will be extendable to other classes of nanoparticles and environmental processes like deposition, redox and dissolution. The larger body of work made possible by the project, both by this team and others, will likely facilitate the development of improved models for predicting environmental fate and assessing risk. The work supports the aims of the Safer Nanomaterials and Nanomanufacturing Initiative, of which the PI is a member, and will spur collaborations with colleagues at OSU and other institutions. Other broader impacts will result from the formation of human capital from the education of a Ph.D. student in environmental engineering. Outreach, undergraduate education and opportunities for undergraduate research will be an integral part of the proposed work. The PI has a history of supporting undergraduate research through existing programs at OSU that focus on the recruitment of women and minority students. The PI will continue to mentor undergraduate researchers through hosting senior project teams, Johnson scholars (college freshmen) and SESEY (high school) students in the laboratory. These students will become an integral part of the research team on the work in question. In addition, the PI will develop an educational module focused on particle filtration for water treatment that is appropriate for K-12 and freshmen engineering students as a tool for engaging students in the field of environmental engineering.
