Effects of Surface-Adsorbed Biomolecules and Geomolecules on the Photoreactivity of Metal Oxide Nanomaterials

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Recently, new nanomaterials that can degrade organic pollutants under sunlight irradiation (photoreaction or photocatalysis) have been identified and developed. This unique photoreactivity makes them attractive for applications in diverse water treatment technologies. On the other hand, this property can also correlate to the toxicological hazard of nanomaterials in natural environments. Predicting nanomaterial photoreactivity is challenging in aqueous environments since the surface of the nanomaterial can become coated with a complex mixture of biomolecules and natural organic matter. The interactions of these complex surface coatings with the irradiated nanomaterial and the resulting impact on the effective photoreactivity of the nanomaterial are not yet well understood. A further challenge is to generalize the coating effects across a variety of photocatalytic nanomaterials currently being investigated. Examples of photocatalytic nanomaterials include titanium dioxide, which is activated by ultraviolet light, and novel visible light active nanomaterials, such as molybdenum oxide that could show improved viability for water treatment applications. This research will investigate the mechanisms underlying the formation of complex surface coatings and their effects on the photoreactivity of various metal oxide nanomaterials. The fundamental knowledge and models developed in this research will facilitate the development of effective and safe photocatalytic nanomaterials for environmental applications and alleviate the burden on industry and regulatory agencies for large-scale testing of nanomaterials. The results of this research will be disseminated to the public through a joint program between the University of Houston and local museums called "Unveiling the World of Nanomaterials." This program aims to expose and recruit K-12 students, particularly from underrepresented groups, to careers in science and engineering. This research will also be incorporated into hands-on modules for high school teachers to disseminate knowledge to high school students in the Houston area, demonstrate impacts of nanotechnology on society, and recruit teachers to conduct research in the field of nanotechnology. Finally, the results will be incorporated into undergraduate and graduate environmental engineering courses on water quality and environmental modeling at the University of Houston. The overarching goal of this research is to develop a model that is capable of predicting the effects of surface coatings on photoreactivity across a variety of photocatalytic, metal oxide nanomaterials, including titanium dioxide and molybdenum oxide. The effect of the coating is hypothesized to be predictable from the composition of the surface coating, which will dictate the type and extent of coating interactions with the photoreactive nanomaterials. Novel approaches and analytical tools will be incorporated in this research to enable a mechanistic understanding of the coating effects, including (1) direct characterization and control of surface coating formation onto photocatalytic nanomaterials from heterogeneous mixtures of biomolecules and natural organic matter, (2) validation and refinement of complementary biological and chemical assays to quantify photoreactivity, and (3) application of in situ spectroscopic methods to identify and monitor the reactions of specific coating components on the nanomaterial surface. The detailed surface chemistry and reactivity data obtained in this research will ultimately be used to develop quantitative models expressing the fundamental mechanisms by which organic surface coatings modify the effective photoreactivity of nanomaterials.