Formation of Environmentally Persistent Free Radicals on Engineered Nanomaterials During Thermal Treatmen

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

Environmentally persistent free radicals, a new class of environmental pollutants, are formed during the thermal treatment of wastes and hazardous materials. Environmentally persistent free radicals are present at sufficiently high levels in diverse environments such as atmospheric particulate matter. Unlike previously identified atmospheric free radicals that exhibit lifetimes of less than a second, environmentally persistent free radicals exist for hours to months, lifetimes which are long enough for them to be transported over long distances from their source. Despite pioneering studies on environmentally persistent free radicals that have significantly improved our understanding of their environmental and human health effects, fundamental questions remain unanswered. This project will assess the impact of engineered nanomaterials on the formation of environmentally persistent free radicals during thermal treatment of wastes. Results will: 1) improve understanding of the interaction of engineered nanomaterial in forming environmentally persistent free radicals during thermal treatment of wastes; 2) improve understanding of the behavior, fate, transformation of and human and environmental exposures to engineered nanomaterials and environmentally persistent free radicals; and 3) support the nanotechnology revolution by informing the development of disposal strategies suitable for engineered nanomaterials. Results will assist in mitigating adverse impacts of engineered nanomaterials and environmentally persistent free radicals and will facilitate the development of potentially safer applications of engineered nanomaterials that can lead to enhanced economic opportunities. In addition, underrepresented students will be trained in science and engineering topics through their participation in the research project. The project will also involve the promotion of teaching and learning by integrating project concepts, methods, and results in the development of new curriculum Previous studies have simulated experimentally the formation of environmentally persistent free radicals on nano-sized transition metal oxides that are supported on surfaces of large micron-sized particles. The prevailing thought on the formation of environmentally persistent free radical assumes that the transition metal is a key component, serving as the electron donor to an organic molecule. This view explains environmentally persistent free radicals that are formed over some transition metal oxides, but it is inconsistent with those formed over a zinc oxide surface in which an electron transfers to the organic molecule instead. Hence, the current mechanism cannot be generalized, and environmentally persistent free radicals may form via other pathways. Answers to these questions hinge on the hypothesis that since band gap energy for engineered nanomaterials exhibits size-dependence and thermally excited electrons may cross this band gap easily, some engineered nanomaterials, depending on size and electronic and chemical properties, may form and stabilize aromatic organic species forming environmentally persistent free radicals. Extending this hypothesis, engineered nanomaterials, other than those composed of transition metals that survive incineration, may form environmentally persistent free radicals. Experimental studies will determine if: (1) engineered nanomaterials and engineered nanomaterials, other than transition metals, can form and stabilize environmentally persistent free radicals; (2) changes in the physicochemical properties of engineered nanomaterials during thermal treatment impact environmentally persistent free radicals formation; or (3) environmentally persistent free radicals can form on engineered nanomaterials at temperatures lower than those that occur during combustion. Experimental methods will use these analytical techniques: electron paramagnetic resonance spectroscopy to measure and characterize environmentally persistent free radicals; mass spectroscopy to determine the nature of chemical species formed when persistent free radicals recombine, and electron microscopy and other surface-sensitive techniques to characterize changes in the nanomaterials. The results of this study are expected to transform the current understanding on environmentally persistent free radicals. First, if environmentally persistent free radicals can form on non-metallic engineered nanomaterials, it will challenge the existing thought that environmentally persistent free radicals form exclusively on transition metal oxide nanoparticles. Second, if environmentally persistent free radicals can form at a lower temperature on engineered nanomaterials, it suggests that environmentally persistent free radicals can form easily and are thus more prevalent. 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.