Aerosol Route Synthesis and Applications of Doped Nanostructured Materials

Manoranjan Sahu
2011
of Dissertation Aerosol Route Synthesis and Applications of Doped Nanostructured Materials by Manoranjan Sahu Doctor of Philosophy in Energy, Environmental and Chemical Engineering Washington University in St. Louis, 2011 Professor Pratim Biswas, Chairperson Nanotechnology presents an attractive opportunity to address various challenges in air and water purification, energy, and other environment issues. Thus, the development of new nanoscale materials in low-cost scalable synthesis processes
more » ... nthesis processes is important. Furthermore, the ability to independently manipulate the material properties as well as characterize the material at different steps along the synthesis route will aide in product optimization. In addition, to ensure safe and sustainable development of nanotechnology applications, potential impacts need to be evaluated. In this study, nanomaterial synthesis in a single-step gas phase reactor to continuously produce doped metal oxides was demonstrated. Copper-doped TiO 2 nanomaterial properties (composition, size, and crystal phase) were independently controlled based on nanoparticle formation and growth mechanisms dictated by process control parameters. Copper dopant found to significantly affect TiO 2 properties such as particle size, crystal phase, stability in the suspension, and absorption spectrum (shift from UV to visible light absorption). The insitu charge distribution characterization of the synthesized nanomaterials was carried out ii by integrating a tandem differential mobility analyzer ( TDMA) set up with the flame reactor synthesis system. Both singly-and doubly-charged nanoparticles were measured, with the charged fractions dependent on particle mobility and dopant concentration. A theoretical calculation was conducted to evaluate the relative importance of the two charging mechanisms, diffusion and thermo-ionization, in the flame. Nanoparticle exposure characterization was conducted during synthesis as a function of operating condition, product recovery and handling technique, and during maintenance of the reactors. Strategies were then indentified to minimize the exposure risk. The nanoparticle exposure potential varied depending on the operating conditions such as precursor feed rate, working conditions of the fume hood, ventilation system, and distance from the reactors. Nanoparticle exposure varied during product recovery and handling depending on the quantity of nanomaterial handled. Most nanomaterial applications require nanomaterials to be in solution. Thus, the role of nanomaterial physio-chemical properties (size, crystal phase, dopant types and concentrations) on dispersion properties was investigated based on hydrodynamic size and surface charge. Dopant type and concentration were found to significantly affect iso-electric point (IEP)shifting the IEP to a high or lower pH value compared to pristine TiO 2 based on the oxidation state of the dopant. The microbial inactivation effectiveness of as-synthesized nanomaterials was investigated under different light irradiation conditions. Microbial inactivation was found to strongly depend on the light irradiation condition as well as on material properties such chemical composition, crystal phase, and particle size. The potential interaction mechanisms of copper-doped TiO 2 nanomaterial with microbes were iii also explored. The studies conducted as part of this dissertation addressed issues in nanomaterial synthesis, characterization and their potential environmental applications. iv Acknowledgements
doi:10.7936/k7vt1q44 fatcat:mr5ehjsfc5esnaafql6e53aqaa