This collaborative research between teams at the University of Oklahoma (OU) and North Carolina State University (NCSU) intends to achieve controlled synthesis of transition-metal-oxide (TMO) nanoforms and to develop a scientific understanding of the underlying mechanisms. Flames have been successfully applied for the synthesis of high-demand nanomaterials such as metal and ceramic nanopowders, carbon fibers, carbon nanotubes, and fullerenes. As a nearly unexplored research area, the flame-gradient synthesis of TMO nanostructures is of fundamental and practical interest due to the potential variety and multifunctionality of the formed nanoforms, their unique properties, morphology and prospective applications. The team will use a flame-gradient method based on the interaction of a bulk metal support with a flame environment of varying temperature and chemical composition, a method they had pioneered. The successful preliminary experiments proved the applicability of this method for the synthesis of unique TMO nanostructures that have never been generated using flames or other traditional synthesis methods. The new research will extend the method to various important transition metals, such as molybdenum, tungsten, iron, cobalt, tantalum, chromium, vanadium, and zinc, to produce an experimental database on generated nanoforms and corresponding synthesis conditions. The focus of the proposed studies will be the confirmation of the key hypothesis that various 1-D TMO nanostructures can be generated in flames by a synergetic action of a highly reactive flame environment possessing strong thermal and chemical gradients. Within this collaborated research, the OU team will study the structure and morphology of generated nanoforms that will be analyzed using advanced material diagnostic techniques, and the NCSU group will conduct flame diagnostics and modeling to uncover the mechanisms. Flame chemistry, the nature of flame interaction with the metal surfaces, and the mechanism of the synthesis process will be closely studied. Broader impacts are both technological and educational. This research will serve as a fundamental basis for the development of novel technologies for flame synthesis of advanced TMO nanostructures with potential applications in electronics, medicine, chemistry, optics, sensors, recording and imaging media. The advantages of flame synthesis over other synthesis methods involve reduced cost, shorter processing times, improved scalability and quality. The method to be studied suggests essential economic and technological advances over current synthesis methods. Graduate and undergraduate students at OU and NCSU working on this interdisciplinary project will gain expertise in the fields of combustion, nanotechnology, and material synthesis. Underrepresented minority students will be encouraged and aided to start graduate school studies by providing them with a supportive and stimulating research experience during their junior and senior years. Additionally, the educational program involves high school teachers and students of North Carolina and Oklahoma communities by exposing them to the field of modern science via lectures, laboratory demonstrations, and hands-on experience.
Researchers at the University of Oklahoma (OU) and North Carolina State University (NCSU) demonstrated a breakthrough in accelerating the process for synthesizing 1-D and 3-D transition metal oxide (TMO) nanostructures. The growth of similar structures can take from hours to days in other processes; however, in the flame it can be accomplished nearly instantaneously. Background: A variety of uses propels the development of novel synthesis methods for the generation of transition metal oxide nanomaterials with desirable structure, chemical activity, and physical properties. Most of the presently used methods are considered expensive since they involve multi-step processes resulting in laborious and time consuming tasks. It is important to be able to synthesize the components on a large-scale to meet the demands of future applications. The growing need for these unique materials and the absence of a robust method to produce them have led the research teams from OU and NCSU to consider using flames for the single step synthesis of metal-oxide nanostructures. Results: The main objective of this collaborative research proposal between OU and NCSU teams was to achieve controlled synthesis of TMO nanoforms and to develop a scientific understanding of the underlying mechanisms. Following successful preliminary experiments, this NSF-funded research extended the method to various important transition metals, such as molybdenum, tungsten, iron, cobalt, tantalum, chromium, vanadium, and zinc, producing an experimental database of generated nanoforms and corresponding synthesis conditions. The research confirmed a key hypothesis that various 1-D and 3-D TMO nanostructures can be generated directly in flames by the synergetic action of a probe-flame interaction in the highly reactive flame environment possessing strong thermal and chemical gradients. Strategic Outcome Goals Discovery: A number of unique nanoforms were prepared using molybdenum, niobium, zinc, vanadium, tungsten and iron oxides. The synthesized nanoforms include hybrid metal oxide/carbon nanostructures. A scientific understanding of the underlying mechanisms has also been developed. Learning: This NSF-funded project provided an opportunity for training and research for one PhD student, three MS students, and four undergraduate students at OU and for one PhD student and one MS student at NCSU. In addition, a team of high school students worked on the project "Enhancing solar cell efficiency through coating by flame-synthesized transition metal-oxide nanoparticles." Transformative Research: The synthesis of a variety of novel nanoforms and the developed scientific understanding of the underlying synthesis mechanisms open new pathways in developing approaches to generate novel multifunctional nanomaterials. Intellectual Merit: Spherical, faceted and one-dimensional transition metal-oxide nanostructures were grown in the high temperature environment of an oxy-fuel flame using a flame gradient method. Experiments conducted using various flame and probe parameters revealed the sequence of the morphological changes. The variation of probe temperature resulted in different supersaturation levels of evaporated oxides. Low probe temperatures resulted in the synthesis of well-defined convex polyhedron nanocrystals and nanorods. High probe temperatures produced mainly spherical nanomaterials agglomerated in soot-like fractal structures. A common generic mechanism controlling the growth of 1-D nanostructures in the gas phase was studied numerically. This mechanism involves interaction of the probe material with the flame possessing strong temperature and chemical gradients. The numerical model of the flame synthesis for spherical, faceted and one dimensional nanoparticles has been developed. The model involves nucleation and multidimensional growth kinetics of nanostructures in flames. Broader Impacts Benefits to society: The experimental and theoretical studies provide a fundamental basis for the development of novel technologies for flame synthesis of advanced nanostructures with potential applications in electronics, medicine, chemistry, and optics. Broadening participation of underrepresented groups: Overviews of this research were presented to prospective freshmen as one of the exciting new areas of engineering. A non-technical description of this research and potential applications of carbon nanotubes were made available to outreach presentations to high school students. Advancing discovery and understanding while promoting teaching, training, and learning: A team of high school students worked on the project "Enhancing solar cell efficiency through coating by flame-synthesized transition metal-oxide nanoparticles." The team prepared solar cells coated with various nanomaterials. The results were presented at the International Sustainable World Energy, Engineering and Environment Project Olympiad in Houston, Texas. The students earned a silver medal in the Engineering category for their project. The results were also presented at the North Carolina State Science Fair. The students earned first place for Outstanding Nanotechnology Prize for their project. Enhancing the infrastructure for research and education: Experimental systems for flame synthesis, flame diagnostics, and materials characterization have been developed at OU and NCSU. Results disseminated broadly to enhance scientific and technological understanding: The results of this research have been published in 9 journal articles and presented at 12 national and international conferences. Furthermore, the findings of this research supported by this grant received national and international media coverage, including the "New.science360" at NSF, Nano Werk, Eureka Alert, Phys.org, and American Chemical Society, among others.
