The modification of electrodes is always an important task in electrochemical detection of electroactive and biological molecules. Chemically modified electrodes can offer improved selectivity and sensitivity for the target analyte, which greatly enhance the electrode performance. Various materials such as conducting polymers, metal nanoparticles and carbon nanomaterials have been exploited and widely used for the modification of electrodes. Electrochemical or spontaneous deposition, electrostatic adsorption, layer-by-layer self assembly and covalent binding have also been developed for electrode modification and offer improved performance. Both Prussian blue (PB) and toluidine blue O (TBO) are excellent redox mediators and very popular in electrode modification. PB has shown strong catalytic property for the reduction of hydrogen peroxide, but the application in biosensor fabrication is limited for its instability at neutral pH. Graphene, as a single-atom-thick carbon material, is considered an ideal platform for designing composite nanomaterials for high-performance electrochemical or electrocatalytic devices. The combination of PB with reduced graphene oxide (RGO) and poly(toluidine blue O) (PTBO) will greatly improve the stability of PB. An amperometric biosensor based on glassy carbon (GC) electrode modified with reduced graphene oxide, PB and poly(toluidine blue O) was developed. Experimental results showed that the GC/RGO/PB/PTBO modified electrode offered an excellent electrocatalytic activity toward the reduction of hydrogen peroxide due to the possible synergistic effects of the PB-PTBO composite material. After codeposition of glucose oxidase (GOD) and chitosan (CHIT) coating, the resulting GC/RGO/PB/ PTBO/CHIT-GOD electrode exhibited excellent response to glucose with a sensitivity of 59 mA M1 cm2, a low detection limit of 8.4 μM and a linear range from 0.02 to 1.09 mM at a detection potential of +0.2 V vs. Ag.

M.Tech. (Chemical Technology) / Please refer to full text to view abstract

Composite structures for aerospace and wind turbine applications are subjected to high acoustic and vibrational loading and exhibit very high amplitude displacements and thus premature failure. Materials with high damping or absorbing properties are crucially important to extend the life of structures. Traditional damping treatments are based on the combinations of viscoelastic, elastomeric, magnetic, and piezoelectric materials. In this work, the use of carbon nanofibers (CNFs) in the form of interconnected self-supportive paper as reinforcement can significantly improve damping performance. The interfacial friction is the primary source of energy dissipation in CNF paper based nanocomposites. The approach entailed making CNF paper by filtration of well-dispersed nanofibers under controlled processing conditions. The CNF paper was integrated into composite laminates using modified liquid composite molding processes including Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM). The rheological and curing behaviors of the CNF-modified polymer resin were characterized with Viscometry and Differential Scanning Calorimetry (DSC). The process analysis in mold filling and pressure distribution was conducted using Control Volume Finite Element Method (CVFEM) in an attempt to optimize the quality of multifunctional nanocomposites. The mold filling simulation was validated with flow visualization in a transparent mold. Several tests were performed to study the damping properties of the fabricated composites including Dynamic Mechanical Analysis (DMA) and piezoceramic patch based vibration tests. It was found that the damping performance was significantly enhanced with the incorporation of carbon nanofibers into the composite structures.

School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa August 2017 / Global warming, resulting from emission of greenhouse gases (GHGs), is the cause of drastic climate changes that threatens the economy and living conditions on the planet. Currently, recovery and mitigation of these greenhouse gases remains a technological and scientific challenge. Various recovery processes for the mitigation of GHGs have been reported including among others carbon capture and storage (CCS). The most mature and applied technology in CCS process involves the absorption of carbon dioxide on amine based solvents. However, studies have shown that this process has several drawbacks that include low stability and high energy required to strip off the absorbed CO2 and regenerate the solvent. This presents an opportunity for the development of new materials for CO2 capture such as zeolite membranes. Previous studies have shown that the separation of CO2 can be achieved with high selectivity at low temperatures using thin-film SAPO-34 membranes (thin layers on supports). This is because CO2 adsorbs strongly on the membranes compared to other gases found in flue gas. In the thin-film membranes supported on ceramic or sintered stainless steel, thermal expansion mismatch may occur at higher operating temperatures resulting in loss of membrane selectivity due to the formation of cracks. A new method is required to overcome the aforementioned problems, thereby enhancing the separation application of the membranes at higher temperatures. The effective separation and capture of CO2 from the coal-fired power plant flue gas is an essential part in the CCS process (Figueroa et al., 2016; Yang et al., 2008). Currently, the capture stage is a huge contributor to the overall cost of CCS (Yang et al., 2008). This is due to the high-energy intensity and inefficient thermal processes applied in the separation and capture in various industrial applications (Yang et al., 2008). This work presents the use of nanocomposite SAPO-34 zeolite membranes synthesized via the pore-plugging hydrothermal method for the separation of CO2 during post-combustion CO2 capture. The SAPO-34 membranes used were supported on asymmetric α-alumina as membrane supports. The membranes were characterized with a combination of dynamic and static physicochemical techniques such as Basic Desorption Quality Test (BDQT), X-ray diffraction (XRD) spectroscopy, Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The characteristic peaks at 2θ = 21°, 26°, and 32° on the XRD pattern confirmed the presence of SAPO-34 with a rhombohedral crystalline structure. The SEM images showed the formation of the cubic crystalline which were consistent with the reported morphology of SAPO-34. FTIR spectra showed the presence of the essential double-6 membered rings (D6R) and TO4 structural groups in surface chemistry of crystalline materials further confirming the presence SAPO-34. The TGA confirmed that the membranes possessed high thermal stability. To assess the feasibility of the synthesis process, the nanocomposite zeolites were grown within the tubular supports. The SEM images of the cross-section of the membrane confirmed the presence of the zeolites within the pores of the support confirming the fabrication of nanocomposite membranes by the pore-plugging synthesis method. The permeation tests used a dead-end filtration mode to measure the single gas permeance and the ideal selectivity of CO2 and N2 were calculated. The BDQT was essential in the study of the quality of the as-synthesized nanocomposite membranes. The quality of the membranes increased with an increase in the synthesis layers of the membranes. However, with an increase in synthesis layers, the membrane thickness also increases. The membrane thickness affected the gas permeance for CO2 and N2 significantly. The permeance of the N2 gas decreased from 10.73 x10-7 mol.s-1.m2Pa-1 after the first synthesis to 0.31 x10-7 mol.s-1.m2Pa-1 after seven synthesis layers. Alternatively, the more adsorbing gas CO2 decreased from 12.85 x10-7 mol.s-1.m2Pa-1 to 2.44 x10-7 mol.s-1.m2Pa-1. The performance of these zeolite membranes depends significantly on the operating conditions. Hence, we studied extensively the influence of the various operating conditions such as temperature, feed pressure and feed flowrate in this work. Results indicated that the membrane separation performance in this study is largely dependent on the temperature. In addition, the ideal selectivity decreased significantly with an increase in temperature. High temperatures results in less adsorption of the highly adsorbing CO2 gas, the permeance reduces significantly, while the permeance of the less adsorbing N2 increased slightly. The feed flow rate has less effect on the adsorbing gas while the non-absorbing gas increased resulting in a decrease in the ideal selectivity as well. The nanocomposite membranes in this study have a low flux compared to their thin film counterparts. An increase in feed pressure significantly increased the flux significantly as well as the ideal selectivity. Maxwell-Stefan model simulation was done in this study to describe the permeance of pure CO2 single gas permeance as a function of temperature. This model considered explicitly the adsorption-diffusion mechanism, which is the transport phenomenon, involved in the transport of CO2 through the zeolite membrane. The description of the support material was included in the model as well. However, the model was only applied to the CO2 gas permeation well within the experimental data. We then compared the model was with the experimental results and a good correlation was observed. In conclusion, SAPO-34 nanocomposite zeolite membranes were obtained at low temperatures (150 °C) with a short synthesis time (6 h). In addition, the high thermal stability of the as-synthesized SAPO-34 membranes makes them ideal for high temperature CO2 separation such as the intended post-combustion carbon capture. The BDQT revealed that the quality of the membranes was related to the thickness of the membranes. Therefore, better membrane quality was obtained with relatively thicker membranes. The separation performance evaluation was conducted on the membrane with the greatest quality. Our findings demonstrate that the performance of the membranes depends extensively on the operating conditions. / MT2018

Siu, King Sang = 網狀合金的白鑄鐵的退火處理 / 蕭健生. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / Siu, King Sang = Wang zhuang he jin de bai zhu tie de tui huo chu li / Xiao, Jiansheng. / Abstract --- p.i / 摘要 --- p.iv / Acknowledgments --- p.v / Table of contents --- p.vi / List of table captions --- p.viii / List of figure captions --- p.ix / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Composite Materials --- p.1 / Chapter 1.2 --- Nanostructured Material --- p.2 / Chapter 1.3 --- Typical Methods of Fabrication of Nanostructure Material --- p.3 / Chapter 1.4 --- Combination of the Ideas of Nanostructure and Composite --- p.4 / Chapter 1.5 --- Phase Separation --- p.5 / Chapter 1.6 --- Nucleation and Growth --- p.6 / Chapter 1.7 --- Spinodal Decomposition --- p.8 / Chapter 1.7.1 --- The Initiation of Spinodal Decomposition --- p.8 / Chapter 1.7.2 --- Dynamics of Spinodal Decomposition --- p.9 / Chapter 1.7.2.1 --- Classical Equation of Diffusion --- p.9 / Chapter 1.7.2.2 --- Factors Deterring Spinodal Decomposition and Formation of Spinodal Network --- p.10 / Chapter 1.7.3 --- Relationship between Wavelength of Spinodal Network and Undercooling --- p.11 / Chapter 1.7.4 --- "Comparing Nucleation and Growth, and Spinodal Decomposition" --- p.11 / Chapter 1.8 --- How to achieve large undercooling --- p.12 / Chapter 1.9 --- Thermal annealing --- p.12 / Chapter 1.9.1 --- Recovery --- p.13 / Chapter 1.9.2 --- Recrystallization --- p.13 / Chapter 1.9.3 --- Grain Growth --- p.14 / Chapter 1.9.4 --- Equation of Ideal Grain Growth --- p.14 / Chapter 1.9.5 --- Factor that slow down grain growth --- p.15 / Chapter 1.10 --- Prospect of this Thesis Project --- p.16 / References --- p.17 / Figures --- p.19 / Chapter Chapter 2 --- Experimental Method / Chapter 2.1 --- Introduction --- p.26 / Chapter 2.2 --- Sample Fabrication --- p.26 / Chapter 2.3 --- Procedures for Preparing Thermal Annealing --- p.26 / Chapter 2.3.1 --- Preparation of Vacuum Environment --- p.26 / Chapter 2.3.2 --- Sealing Silica Tube --- p.27 / Chapter 2.4 --- Furnance --- p.27 / Chapter 2.5 --- Samples Analysis --- p.27 / Chapter 2.5.1 --- Optical Microscope --- p.27 / Chapter 2.5.2 --- Scanning Electron Microscope (SEM) Analysis --- p.27 / Chapter 2.5.3 --- Transmission Electron Microscope (TEM) Analysis --- p.28 / Chapter 2.5.3.1 --- Sample Preparation --- p.28 / Chapter 2.5.3.1.1 --- "Grinding, Polishing and Pouching" --- p.28 / Chapter 2.5.3.1.2 --- Dimpling --- p.29 / Chapter 2.5.3.1.3 --- I on Milling --- p.29 / Chapter 2.5.3.2 --- Phase Identification --- p.30 / References --- p.31 / Figures --- p.31 / Chapter Chapter 3 --- Grain Growth in Fe81C17Si5 / Chapter 3.1 --- Abstract --- p.34 / Chapter 3.2 --- Introduction --- p.35 / Chapter 3.3 --- Experimental --- p.36 / Chapter 3.4 --- Result --- p.37 / Chapter 3.5 --- Discussion --- p.44 / References --- p.48 / Figures --- p.49 / Chapter Chapter 4 --- High temperature thermal annealing of Fe81C14Si5 network alloys / Chapter 4.1 --- Abstract --- p.74 / Chapter 4.2 --- Introduction --- p.75 / Chapter 4.3 --- Experimental --- p.76 / Chapter 4.4 --- Result --- p.77 / Chapter 4.5 --- Discussion --- p.83 / References --- p.86 / Figures --- p.87

Includes bibliographical references (p. 149-179).

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Massachusetts Amherst, 2009. / Includes bibliographical references (p. 126-135). Print copy also available.

Thesis (Ph. D.)--University of North Texas, Aug., 2009. / Title from title page display. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 51-53). Also available on the World Wide Web.