Carbon nanotubes (CNT) have gained interest for wide use as both support and catalyst due to the ease of uniquely tunable surface chemistry. Increasingly severe greenhouse effects have attracted attention to novel materials and technologies capable of capturing carbon dioxide (CO2). In this context, we develop a CNT based solid state amine for the CO2 capture. CNT are functionalized under various methods as a support for polymeric amines. Polyethyleneimine are physically adsorbed on CNT and are further characterized and studied for reversible CO2 capture. We obtain a high CO2 capture capacity (6.78 mmol∙g-1) for linear polyethyleneimine (LPEI) and 6.18 mmol∙g-1 for branched polyethyleneimine (BPEI). Based on the study of pore structure, we also demonstrate that in a steam post-combustion environment, supported polymeric amines on CNT show higher stability than traditional metal oxides. Besides the increased stability of the support in steam, we also improve the stability of amines under steam conditions by developing a covalent modification method. The CO2 capture capacity of the covalent bonded materials under steam conditions improved by 14% compared to dry conditions. In addition, the loading, chemical properties of PEI, and the surface chemistry of CNT remained stable under steam conditions compared to physically adsorbed PEI on CNT. These results suggest that covalent bonded PEI on CNT can be more suitable for CO2 capture in post-combustion processes. A different CNT application is as a catalyst for oxidative dehydrogenation (ODH) of ethane, and herein we develop a new processing technique for tuning the surface chemistry of the CNT-based catalyst. A one-step, gas-phase hydrogen (H2) surface modification is used to reduce carboxylic groups to phenolic groups on carbon nanotube (CNT) materials. This technique is greener and more facile for large-scale industrial catalysts than what has previously been reported. This method uses fundamental principles of CNT surface chemistry to efficiently reduce the unselective oxidation sites and enhances the active sites used for alkane oxidative dehydrogenation. The resulting catalyst improves the ethylene selectivity and yield by at most 81% and 28% respectively compared to the non-modified catalyst. A clear linear correlation between the functional groups and catalytic activity reveals the effect of specific oxygen species on performance. As the catalyst surface area increases, pretreatments generate more selective active sites instead of over-oxidation sites, providing a guideline for catalyst optimization. We suggest that the gas-phase H2 method is general for reducing carbon catalysts to increase selective oxidation sites for gas phase reactions.

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Carbon nanotube forests are vertically grown tubular formations of graphene. Samples were grown with an injection chemical vapor deposition method on substrates of silicon with various deposited layers and bare fused silica. The morphology of the forest is characterized by the height, density, and presence of defects. Total diffuse reflectance and transmittance measurements were taken in the 2-16 �m spectral range and correlated to the forest’s specific morphology. From these correlations, the conditions necessary to maximize the absorption of the forest were found and exploited to cater sample growth for specific substrates to make ideal absorbers. From the transmittance data, the absorption coefficient is found via Beer-Lambert’s Law and also correlated to sample morphology, giving us an indication of the height of the forest needed for ideal absorption. Two models were used to attempt to reproduce the experimental absorption coefficient: an effective medium theory using a Maxwell Garnett approximation and by treating the carbon nanotube forest as an effective cylindrical waveguide with walls of graphite. Each model leads to a set of fitting parameters providing a better physical understanding of the forests. It was found that the effective medium theory gave results loosely corroborated with electron microscopy, but had trouble fitting the experimental data, and the index of refraction it provides does not behave like a unified medium. The waveguide model fits the data well, but it requires more experimental evidence to be more conclusive. The theoretical models need more work, but fabrication of ideal absorbers has been achieved on various substrates providing framework for their usage in radiometry and spectroscopy.

Thermal interface materials (TIMs) are used as an aid in transporting heat away from a circuit or electronic module. Composite materials are a popular research area for TIMs because they allow the desired properties from the individual constituents to be combined. The composite selected for this study uses carbon nanotubes (CNT) as the filler and an elastomeric polymer for the matrix, specifically a multiwalled carbon nanotube (MWCNT) / polydimethylsiloxane (PDMS) composite. Additionally, functionalization of the CNT may affect the composites’ thermal conductivity because of its effect on the CNT dispersion in the polymer matrix and its effect on the CNT-polymer interface. The objective of this study was to determine the effect CNT functionalization has on the effective thermal conductivity of a MWCNT/PDMS composite. The three functionalization’s used in this study are unfunctionalized, functionalized with a carboxyl group, and functionalized with a hydroxyl group. Secondary objectives were to develop the initial stages of a carbon-polymer composite database and to perform an uncertainty analysis on the stepped bar apparatus used in this study. The database is to be used for visualization of data found in literature to promote data driven research. The uncertainty analysis on the stepped bar apparatus is to qualify the instrument for thermal measurements in this study Initial results showed some increase in thermal properties of the composite, but there was little difference between the thermal conductivity of the three functionalization’s because of the high level of uncertainty used early on in this study. Later results showed an increase in mechanical properties of the composite which offset any thermal advantage with use as a TIM. A stronger composite means less compression under a similar load, resulting in a thicker TIM and higher resistance. However, the mechanical and thermal properties compound to show that -OH functionalized MWCNT present better properties for a TIM than unfunctionalized and -COOH functionalized; none show better results than the polymer by itself.

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Electrically conductive membranes (ECMs) are of significant research interest for their ability to mitigate fouling, enhance separation capacity, and induce electrochemical degradation of contaminants. Most ECM development has been in flat sheet format suitable for laboratory studies; in industrial applications, formats such as hollow fiber (HF) are preferred for their high packing density. While ECMs in HF format are emerging in research, these techniques typically employ the same methods proven for flat sheet, often involving direct deposition of conductive material onto a support membrane with no further investigation into how the deposition process affects ECM properties. This is a significant challenge for long (~1 m) HF membranes where coating uniformity is essential to ensure consistent performance. The goal of this project was to fabricate conductive HF membranes, ensuring uniform performance along the fiber. In this work, we have developed a “crossflow deposition” technique to deposit a uniform layer of single walled/ double walled carbon nanotubes (SW/DWCNTs) onto the interior surface of commercial polyether sulfone HF membranes. In a design-of-experiments model, feed pressure and crossflow velocity were shown to directly impact composite membrane conductivity and permeability. The highest permeability (~2900 LMH/bar) and conductivity (~670 S/m) were both achieved at the high pressure (0.2 bar) and high crossflow velocity (1.06 cm/s) condition. An inverse relationship was identified between conductivity and permeability for 29 different HF membranes coated under various flow and particle loading conditions. Similar trends were evident in ECM literature when comparing 80 membranes across 38 papers, covering various conductive materials, separation types, configurations, and applications. Metallic-based ECMs outperformed graphitic nanomaterial or conductive polymer-based ECMs with conductivities three orders of magnitude higher. This review also revealed a wide variation in performance testing with 35 unique pollutants in 63 total tests, indicating a need for standardization to accurately compare ECMs and a need for testing with more realistic feed sources. Finally, electrochemical degradation of methyl orange using the CNT-coated HF membranes was evaluated in batch and continuous removal experiments. Although no significant MO removal was detected in either configuration, these modules can be used for further optimization in terms of targeted conductivity, contact time, and electrochemical parameters such as applied voltage. This work highlights the existence of a conductivity/ permeability trade-off in ECM development and how manipulation of flow parameters during deposition can impact this trade-off in HF membrane development. / Thesis / Master of Applied Science (MASc) / Membrane separation technologies are a common purification strategy in many fields due to their simplicity and low energy requirements. Membranes operate by rejecting particles from feed water based on their chemical or physical properties such as size or charge. Long-term membrane operations are limited by fouling, incurring large operating costs for frequent cleaning cycles and downtime. Furthermore, traditional membrane separations only physically remove particles, presenting a risk for contaminant re-introduction into the environment. Electrically conductive membranes are an emerging strategy for addressing these concerns due to their demonstrated antifouling, enhanced selectivity, and redox capabilities. To date, these membranes have almost exclusively been developed as flat sheets with limited research into other membrane formats. Hollow fiber membranes resemble thin tubes ~1 mm in diameter and up to ~1 m in length where filtration occurs through the tubular wall of the fiber; the small diameter allows for hundreds of fibers to pack into an individual module, thus maximizing throughput. In this thesis, several issues with hollow fiber conductive membrane fabrication are addressed to ensure consistent performance along the length of the fiber. A key trade-off between membrane surface conductivity and throughput was found to exist universally in the conductive membrane field. This knowledge can be used to select fabrication methods and parameters to target certain performance ranges.

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