NO2 is one of six priority air pollutants regulated by the US Environmental Protection Agency and has been linked to health problems (lung diseases, strokes, ischemic heart disease, and cancer), formation of ground-level ozone, and fine-particle pollution. Under ultraviolet (UV) light, titanium dioxide (TiO2) oxidizes low-level NOx (~1 ppm or below) in air to harmless nitrates. This project will provide the framework for the coupling of carbon nanotubes (CNTs) and TiO2 with the goal of enabling low-cost and large-area CNT-based/TiO2 coatings for efficient outdoor pollution control. This technology is expected to provide significant improvement in urban air quality and combat ozone at the source. The educational plan will simultaneously advance scientific discovery and increase the science, technology, engineering, and mathematics (STEM) pipeline, as well as equip engineering students at Kansas State University (KSU) with skillsets for innovative and successful careers in nanotechnology.
The objective of this project is to integrate nanotechnology and heterogeneous catalysis to fabricate well-tailored and multifunctional CNT-based composites for environmental remediation. The PI will test the broad hypothesis that photocatalytic activity and photoresponse of CNT-supported TiO2 nanocomposites (CNT/TiO2) are enhanced by the properties of CNTs and resulting interfacial charge transfer properties. The research goal will be achieved by pursuing the following specific tasks: 1) scalable synthesis of highly uniform CNTs [metallic single-walled CNTs (m-SWCNTs), semiconducting SWCNTs (s-SWCNTs), and multiwalled CNTs (MWCNTs)] using an industrial waste gas from Fischer-Tropsch synthesis as a feedstock; 2) controlled CNT functionalization and coupling of CNTs and TiO2 using UV light and a green solvent (H2O2); 3) elucidation of the coupling mechanisms between CNTs and TiO2; and 4) evaluation of the photocatalytic activity of CNT/TiO2 in the oxidation of NOx under various environmental and material variables. This study will illuminate the coupling mechanisms between TiO2 and CNTs and establish structure-property-function relationships. The work is a novel means for maximizing charge-separation efficiency of TiO2 and extending its photoresponse to the visible-light region. The resulting s-SWCNT/TiO2 photocatalyst will provide a transformative pathway for the synthesis of visible-light-active, low-cost, efficient, and large-area CNT-based/TiO2 coatings for the photocatalytic oxidation of NOx. Creation of a scalable and controlled CVD synthesis approach for s-SWCNTs and m-SWCNTs that are orders-of-magnitude higher than conventional post-purification methods will be transformative, as it is a necessary first step for scalable synthesis of well-tailored SWCNT/TiO2 photocatalysts. The use of UV/H2O2 for CNT functionalization during TiO2 deposition will ensure that electrons are freely shuttled along the CNTs; this approach differs from conventional approaches, which largely involve the use of aggressive acid treatment that imparts significant defects on CNTs. The resulting structure-property-function correlations of CNT/TiO2 photocatalysts will substantially improve understanding of the coupling mechanisms and lay a solid foundation for the adoption of the nanocomposites in a number of photocatalytic applications including water splitting, air purification, CO2 reduction, water purification, and microbial inactivation. The international exchange program will benefit both research and education at KSU, as US students will gain valuable global perspective--a critical skill for an engineer in the 21st century.
