With a unique blend of power and energy densities, as well as long cycling lives, electrochemical supercapacitors are finding greater application in energy storage solutions. Among candidate materials for supercapacitors, MnO2 has garnered a great deal of attention. However, its low intrinsic electrical conductivity has proven to be a serious hindrance on performance when used in supercapacitor electrodes. Efficient use of conductive additives is a demonstrated, effective method to combat this problem, however there is still a great need for improvement. Two new colloidal processing techniques have been developed to mix chemically synthesized MnO2 and conductive multi-walled carbon nanotubes (MWCNT). The first strategy involved the linking of MnO2 and MWCNT through the formation of a Schiff base. 3,4-dihydroxybenzaldehyde (DB) was used to modify MnO2, while MWCNT were dispersed with the dye New Fuchsin (NF). These compounds were selected due to the presence of molecular features previously identified as conducive to strong adsorption and good colloidal dispersion, as well as the necessary functional groups required to form a Schiff base. The second involved the use of liquid-liquid extraction, primarily in an attempt to prevent post synthesis MnO2 particle agglomeration. Lauryl gallate (LG) was used as an extracting and dispersing agent for MnO2 synthesized via the reaction between aqueous potassium permanganate (KMnO4) and 1-butanol. LG facilitated the co-dispersion and mixing of both MnO2 and MWCNT in the 1-butanol phase. V2O3 was also investigated as a replacement for MnO2, as its high intrinsic electrical conductivity gives it a potential advantage over MnO2. In each of these three projects, electrodes were produced with exceptionally high areal normalized capacitances at high active mass loadings. The MnO2-MWCNT composites were used to fabricate full asymmetric supercapacitor devices that were able to deliver a useable amount of energy. / Thesis / Master of Applied Science (MASc) / The modern world has an insatiable appetite for energy and must have access to it for stationary and mobile applications. To meet this demand, it is of paramount importance to develop new, high performance energy storage technologies. The energy requirements for different applications, however, necessitate storage devices that have suitable properties. The energy stored in a large pool of hot water is not in a suitable form to power a cellphone. The key goal of this work was to further develop one particular energy storage technology, called electrochemical supercapacitors. Novel processing techniques were developed and new materials investigated with the aim of producing supercapacitor electrodes that would exceed the performance of what is already available today. The materials that were produced exhibited very high performance and offered new insight and direction for further research in this exciting field.

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Yes / The effect of extruder screw configuration on the dispersion and properties of compatibilised polypropylene (PP)/multi‐walled carbon nanotube (MCNT) composite is investigated. Three principle screw designs with mainly conveying elements (medium intensity), kneading elements (high intensity), and folding elements (chaotic mixing) were used to prepare polypropylene nanocomposites containing 4wt% of maleic anhydride grafted polypropylene (MAH‐g‐PP) compatibilizer and different nanotube loadings. The effect of each screw configuration and nanotube loading on the tensile, rheological, and electrical properties of the nanocomposites were studied. The screw configurations were found to have a strong influence on the electrical resistivity while only slightly affected the tensile properties of the nanocomposites. Scanning electron microscopy examinations showed that the use of screw configuration consisting of kneading elements promoted the dispersion of nanotubes and resulted in a low electrical percolation at 2wt% of MCNT.

Global urbanization has resulted in rapidly increased urban land. Soils are the foundation that supports plant growth and human activities in urban areas. Furthermore, urban soils have potential to provide a carbon sink to mitigate greenhouse gas emission and climate change. However, typical urban land development practices including vegetation clearing, topsoil removal, stockpiling, compaction, grading and building result in degraded soils. In this work, we evaluated an urban soil rehabilitation technique that includes compost incorporation to a 60-cm depth via deep tillage followed by more typical topsoil replacement. Our objectives were to assess the change in soil physical characteristics, soil carbon sequestration, greenhouse gas emissions, and stormwater mitigation after both typical urban land development practices and post-development rehabilitation. We found typical urban land development practices altered soil properties dramatically including increasing bulk density, decreasing aggregation and decreasing soil permeability. In the surface soils, construction activities broke macroaggregates into smaller fractions leading to carbon loss, even in the most stable mineral-bound carbon pool. We evaluated the effects of the soil rehabilitation technique under study, profile rebuilding, on soils exposed to these typical land development practices. Profile rebuilding incorporates compost amendment and deep tillage to address subsoil compaction. In the subsurface soils, profile rebuilding increased carbon storage in available and aggregate-protected carbon pools and microbial biomass which could partially offset soil carbon loss resulting from land development. Yet, urban soil rehabilitation increased greenhouse gas emissions while typical land development resulted in similar greenhouse gas emissions compared to undisturbed soils. Additionally, rehabilitated soils had higher saturated soil hydraulic conductivity in subsurface soils compared to other practices which could help mitigate stormwater runoff in urban areas. In our study, we found urban soil management practices can have a significant impact on urban ecosystem service provision. However, broader study integrating urban soil management practices with other ecosystem elements, such as vegetation, will help further develop effective strategies for sustainable cities. / Ph. D.

Nitrification, the chemoautotrophic process via which ammonium-nitrogen (NH₄-N) is converted to nitrate-nitrogen (NO₃-N), is an important nitrogen (N) transformation in stream ecosystems. Experimental addition of dissolved organic carbon (DOC) has been shown to inhibit rates of nitrification, and rates have been stimulated by NH4-N addition. Insights regarding the role of particulate organic matter (POM) in this scenario could further enhance our understanding of linkages between ecosystem carbon (C) and N cycles. Hugh White Creek, a headwater stream located in the southern Appalachian mountains of North Carolina, USA, receives large amounts of allochthonous POM inputs each fall. To address the effects of these inputs on nitrification, I conducted a seasonal survey of organic matter standing stocks and nitrification rates along with experimental manipulation of dissolved C and N supplies in stream sediment microcosms to determine: 1) how rates of nitrification compare across seasons, and 2) to what extent nitrification rates are influenced by seasonal changes in standing stocks and relative abundances of both sedimentary and dissolved forms of C and N. Rates of nitrification were most closely and positively related to rates of ammonification, which, in turn were negatively related to C:N of fine benthic organic matter (FBOM). Uniform additions of C and N throughout the year had different effects on rates of nitrification and ammonification due to their changing relative importance as sediment organic matter stocks were depleted and underwent changes in quality. Slow rates of nitrification for much of the year could be attributed to large quantities of C relative to N in stream sediments. To the extent that changes in OM stocks dictate change in C and N availability, seasonal patterns in OM dynamics represent changes in ecosystem structure relevant to rates of nitrification, emphasizing the importance of terrestrial/aquatic linkages for predicting rates of N transformation in aquatic ecosystems. / Master of Science

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Yes / Owing to their small size, good wettability, uniform dispersion ability and high thermal properties, the nickel-plated carbon nanotubes (Ni-CNTs) with different aspect ratios are used to reinforce reactive powder concrete (RPC) through modifying the nano/micro- structural units of concrete. Incorporating only 0.075 vol% of Ni-CNTs (0.03 vol% of CNTs) can significantly increase mechanical properties of RPC. The enhancement effect on compressive strength caused by the incorporation of Ni-CNTs with aspect ratio of 1000 reaches 26.8%/23.0 MPa, mainly benefiting from the high polymerization C-S-H gels, low porosity, and refined pore structure. The 33.5%/1.92 MPa increases of flexural strength can be attributed to the decrease of large pore, original cracks, molar ratio of CaO to SiO2, and gel water content when Ni-CNTs with aspect ratio of 125 are added. Ni-CNTs with aspect ratio of 1500 have the largest utilization rate of being pulled-out, resulting from the improvement of dispersibility and the pining effect of nickel coating and then leading to the increased toughness. Therefore, incorporating Ni-CNTs can fundamentally modify the nano/micro- scale structural nature of RPC, providing a bottom-up approach for controlling the properties of RPC. / Funding supported from the National Science Foundation of China (51908103 and 51978127) and the China Postdoctoral Science Foundation (2019M651116).

The unique electronic, mechanical and physical properties led Carbon nanotubes (CNTs) to be potential candidate for field emitter, hydrogen storage, sensors, nano electronic devices, nano electromechanical systems, polymer composites. In order to make them in the industrial scale we need large quantity production of CNTs with low cost. The present thesis work deals with the preparation of CNTs by pyrolysis method from xylene and further studies on the grown CNTs. Magnetic characterization of CNTs has been done using SQUID. The interaction of CNTs with the microwave irradiation is studied and it was found for the first time that there is light emission from the CNTs apart from direct electric field. In this process we also observed that the static charge develops on the CNTs. A composite of CNTs/DNA has been prepared with varying CNT content and the electrical conductivity measurements have been done. The first chapter of the thesis provides an introduction to carbon family. Carbon nanotubes, which are potential candidates from carbon family, is a growing field for research in science and technology. A glimpse of various methods of preparation of CNTs like arc-discharge, laser ablation, chemical vapour deposition (CVD), hot-filament CVD, plasma enhanced chemical vapor deposition (PECVD), electron cyclotron resonance (ECR PECVD), high-pressure catalytic decomposition of carbon monoxide (HiPCO), pyrolysis are discussed. Some applications of CNTs are also included in this chapter. The second chapter deals with the experimental techniques employed for the preparation of CNTs and their characteristics studied by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Raman Spectroscopy (RS). The preparation of CNTs from xylene as carbon source and ferrocene as catalyst in pyrolysis method is described in detail. Well aligned CNTs with a length of several tens of micrometers and diameter of 40 to 80 nanometers were obtained as confirmed by SEM. TEM and XRD confirms the graphitic crystal structure of the CNTs. RS also confirms the information about the crystal structure. The third chapter discusses the magnetic studies on CNTs using Superconducting Quantum Interference Device (SQUID) as a function of magnetic field and temperature. In the random mixture of parallel, perpendicular and oblique nanotubes, the applied field produces diamagnetic behavior, although the sample possess different kinds of tubes with various chirality and radii. Paramagnetic deviation was observed on the diamagnetic susceptibility at weak fields and low temperature, confirming qualitatively with the Aharonov-Bhom effect on the energy gap for the magnetic field parallel to the tube axis Chapter four presents the light emission from the CNTs. It describes the light emission from different processes reported in the literature. Here we have observed a new process to generate light from CNTs through microwave irradiation. Along with the light emission some of the tubes get charged and some tubes are physically broken. We provide a simple approach as to why the tubes break and the nature of the breakage is also discussed. The fifth chapter discusses the preparation of CNTs/DNA composites. The conductivity increases with increasing carbon nanotube weight percentage. The increase in conductivity as a function of the CNTs weight percent is attributed to the introduction of conducting CNTs path in the DNA matrix. A summary of the results obtained and the scope for future work are included in the chapter six of the thesis.