Browsing by Subject "Nitrogen doping"

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Effect of nitrogen doping on the electronic and catalytic properties of carbon nanotube electrode materials
(2011-05) Wiggins-Camacho, Jaclyn Dawn; Stevenson, Keith J.; Crooks, Richard M.; Vanden Bout, David A.; Webb, Lauren J.; Manthiram, Arumugam
This dissertation discusses the influence of nitrogen doping (N-doping) on the electronic and catalytic properties of carbon nanotubes (CNTs). These properties have been studied using a variety of techniques, in order to both qualitatively and quantitatively analyze the relationship between the nitrogen concentration and observed properties. Chapter 1 provides a general overview of CNTs and N-doping and details some of the previous research from our group. Chapter 2 discusses the assembly and characterization of free-standing electrode mats, which are used in order to understand the intrinsic physicochemical properties of the material without relying on the secondary influence of another conductive support. Raman microscopy, X-Ray photoelectron spectroscopy, scanning and scanning-tunneling electron microscopy, as well as electrochemical methods were all used to demonstrate the viability of the mat electrodes for further experiments. Chapter 3 addresses the examination of a range of nitrogen concentrations in order to better understand the effects of nitrogen concentration on the electrochemical and electrical properties such as the differential capacitance, density of states at the Fermi level (D(E[subscript F])), bulk conductivity and work function. These properties were studied using a variety of techniques, including UV-photoelectron spectroscopy, electrochemical impedance spectroscopy and conductive four point probe. Chapter 4 investigates the inherent catalysis of the nitrogen doped CNTs (N-CNTs) with respect to O2 reduction, and a complex mechanism is proposed. Electrochemical methods such as cyclic and linear sweep voltammetries as well as thermo-gravimetric analysis and gasometric analysis were all employed to determine heterogeneous decomposition rates as well as to detect intermediates of the O₂ reduction reaction. Chapter 5 discusses the electrocatalytic degradation of free cyanide (CN⁻) at the N-CNT mat electrodes. These results both provide further support for the mechanism discussed in Chapter 4, and present the opportunity for a potential application of N-CNTs for environmental purposes. Specifically, spectroscopic and electrochemical methods, in conjunction with theoretical models show both that the presence of CN⁻ does not inhibit O2 reduction, and that it can be effectively converted to cyanate (OCN⁻) at the N-CNT electrodes. Future work involving the assembly and characterization of transparent N-CNT films is discussed in Chapter 6.
Removal of formaldehyde from indoor air : enhancing surface-mediated reactions on activated carbon
(2013-08) Carter, Ellison Milne; Katz, Lynn E.; Speitel, Gerald E.
Formaldehyde is a ubiquitous and hazardous indoor air pollutant and reducing concentrations in indoor environments is a public health priority. The goals of this doctoral work were to advance analytical methods for continuous monitoring of formaldehyde at very low concentrations (sub-20 ppb[subscript v]) and to improve fundamental, mechanistic understanding of how structural and chemical properties of activated carbon influence removal of formaldehyde from indoor environments. To achieve these goals, emerging sensor-based technology was evaluated for its ability to detect and quantify ppb[subscript v]-level formaldehyde concentrations on a continuous basis at relative humidity levels characteristic of residential indoor environments. Also, a combination of spectroscopic and selective titration techniques was employed to characterize molecular-level structural and chemical properties of traditional and chemically treated granular activated carbon (GAC). In addition to selecting two different commercially available GACs for study, design and preparation of a laboratory-prepared, chemically treated GAC was pursued to create nitrogen-doped GAC with desirable surface chemical properties. Performance of all GACs was evaluated with respect to formaldehyde removal through a series of packed bed column studies. With respect to continuous formaldehyde monitoring, a method detection limit for emerging sensor technology was determined to be approximately 2 ppb[subscript v], and for relative humidity levels characteristic of indoor environments (> 40%), quantitative, continuous formaldehyde measurements less than 10 ppb[subscript v] were robust. The two commercially available GACs tested were both capable of removing formaldehyde; however, the GAC with greater density of basic surface functional groups and greater electron-donating potential (Centaur) removed twice as much formaldehyde (on a GAC mass basis) as the less basic GAC (BPL). A laboratory-prepared GAC (BPL-N) was successfully created to contain pyridinic and pyrrolic nitrogen, which was associated with increased surface density of basic functional groups, as well as with increased electron-donating potential. BPL-N exhibited better removal capacity for formaldehyde than BPL and Centaur. Furthermore, packed bed column studies of BPL-N and BPL formaldehyde removal performance yielded evidence to support the hypothesis that electron-donating potential, especially nitrogen functional groups at the BPL-N surface, promote catalytic removal of gas-phase formaldehyde via oxidation.