Publication Date
2015
Document Type
Dissertation
Committee Members
Amir Farajian (Committee Member), Mark Goltz (Committee Member), Hong Huang (Committee Member), Sharmila Mukhopadhyay (Advisor), Mallikarjuna Nadagouda (Committee Member)
Degree Name
Doctor of Philosophy (PhD)
Abstract
The overall goal of this study is two-fold: synthesis of multiscale nanostructures by growing aligned carbon nanotubes on porous foam substrates and investigation of their applicability as adsorbents and catalyst supports for environmental remediation applications. High purity, vertically-aligned arrays of carbon nanotubes (CNT) are grown on open-cell interconnected porous carbon foams by pre-activating them with an oxide buffer layer followed by chemical vapor deposition (CVD). This type of hierarchical morphology provides the capability of increasing surface area by several orders of magnitude, while tuning its morphology for targeted applications. Analytical models are also proposed in this study for specific surface area calculations, those agree well with the experimental measurements. These hierarchical carbon materials are seen to be powerful adsorbents of aqueous pollutants such as methylene blue dye. Their monolayer adsorption capacities correlate very well with the total CNT surface area determined from analytical models and with BET measurements, indicating full utilization of the nanotube surfaces. The hierarchical structures can also serve as base supports for attachment of metal nanoparticle catalysts. The catalysts investigated in this study are metallic palladium (Pd), oxidized palladium (PdO), and silver-palladium (Ag-Pd) nanoparticles combination. These are suitable for a variety of industrial applications such as hydrocarbon conversion, hydrogen storage, fuel cell electrodes and pollutant degradation. The current architecture allows synthesis of highly active catalyst structures utilizing very small quantities of precious metal that make the catalyst component significantly lighter and more compact than conventional systems. Detailed characterization of structure and surface chemical states of these nano-catalysts have been performed and their catalytic activities are tested by measuring the degradation kinetics of organic contaminants via bench-scale experiments. Catalytic degradation of atrazine, an emerging problematic contaminant, was quantified using high-performance liquid chromatography. Among Pd, PdO, and Ag-Pd nanoparticles, PdO in the presence of hydrogen was seen to provide the most rapid reaction rate. These nanocatalysts also enable rapid degradation of chlorinated hydrocarbons such as trichloroethylene and trichloroethane quantified using head-space gas chromatography, with PdO providing the fastest kinetic route. Durability tests indicated that the nano-particles and nanotubes are robust, and remain attached to the base support after long periods of rapid rotation in water. These results imply that such materials can provide compact and powerful surface active materials in future applications such as adsorbents, catalysts, porous electrodes, and energy storage devices.
Page Count
225
Department or Program
Ph.D. in Engineering
Year Degree Awarded
2015
Copyright
Copyright 2015, all rights reserved. This open access ETD is published by Wright State University and OhioLINK.
