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- Genre: Masters Thesis
Description
Hexavalant chromium (Cr(VI)) poses an emerging concern in drinking water treatment with stricter regulations on the horizon. Photocatalytic reduction of Cr(VI) was investigated as an engineering scale option to remove hexavalent chromium from drinking or industrial waters via a UV/titanium dioxide (TiO2) process. Using an integrated UV lamp/ceramic membrane system to recirculate TiO2, both hexavalent and total chromium levels were reduced through photocatalytic processes without additional chemicals. Cr(VI) removal increased as a function of higher energy input and TiO2 dosage, achieving above 90% removal for a 1g/L dose of TiO2. Surface analysis of effluent TiO2 confirmed the presence of chromium species.
ContributorsStancl, Heather O'Neal (Author) / Westerhoff, Paul K (Thesis advisor) / Chan, Candace (Committee member) / Hristovski, Kiril (Committee member) / Arizona State University (Publisher)
Created2013
Description
Lithium-ion batteries can fail and catch fire when overcharged, exposed to high temperatures or short-circuited due to the highly flammable organic liquid used in the electrolyte. Using inorganic solid electrolyte materials can potentially improve the safety factor. Additionally, nanostructured electrolyte materials may further enhanced performance by taking advantage of their large aspect ratio. In this work, the synthesis of two promising nanostructured solid electrolyte materials was explored. Amorphous lithium niobate nanowires were synthesized through the decomposition of a niobium-containing complex in a structure-directing solvent using a reflux method. Lithium lanthanum titanate was obtained via solid state reaction with titanium oxide nanowires as the titanium precursor, but the nanowire morphology could not be preserved due to high temperature sintering. Hyperbranched potassium lanthanum titanate was synthesized through hydrothermal route. This was the first time that hyperbranched nanowires with perovskite structure were made without any catalyst or substrate. This result has the potential to be applied to other perovskite materials.
ContributorsYang, Ting (Author) / Chan, Candace K. (Thesis advisor) / Crozier, Peter A. (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2012
Description
A system for illuminating a sample in situ with visible and UV light inside a transmission electron microscope was devised to study photocatalysts. There are many factors which must be considered when designing and building such a system. These include both mechanical, optical, and electron optical considerations. Some of the restrictions posed by the electron microscope column are significant, and care must be taken not to degrade the microscope's electron optical performance, or to unduly restrict the other current capabilities of the microscope. The nature of these various design considerations is discussed in detail. A description of the system that has been added to the microscope at ASU, an FEI Tecnai F20 environmental transmission electron microscope is also given. The system includes a high brightness broadband light source with optical filters, a fiber to guide the light to the sample, and a system for precisely aligning the fiber tip. The spatial distribution and spectrum of the light reaching the sample has been characterized, and is described in detail.
ContributorsMiller, Benjamin (Author) / Crozier, Peter A. (Thesis advisor) / McCartney, Martha (Committee member) / Rez, Peter (Committee member) / Arizona State University (Publisher)
Created2012
Description
Topological insulators with conducting surface states yet insulating bulk states have generated a lot of interest amongst the physics community due to their varied characteristics and possible applications. Doped topological insulators have presented newer physical states of matter where topological order co&ndashexists; with other physical properties (like magnetic order). The electronic states of these materials are very intriguing and pose problems and the possible solutions to understanding their unique behaviors. In this work, we use Electron Energy Loss Spectroscopy (EELS) – an analytical TEM tool to study both core&ndashlevel; and valence&ndashlevel; excitations in Bi2Se3 and Cu(doped)Bi2Se3 topological insulators. We use this technique to retrieve information on the valence, bonding nature, co-ordination and lattice site occupancy of the undoped and the doped systems. Using the reference materials Cu(I)Se and Cu(II)Se we try to compare and understand the nature of doping that copper assumes in the lattice. And lastly we utilize the state of the art monochromated Nion UltraSTEM 100 to study electronic/vibrational excitations at a record energy resolution from sub-nm regions in the sample.
ContributorsSubramanian, Ganesh (Author) / Spence, John (Thesis advisor) / Jiang, Nan (Committee member) / Chen, Tingyong (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2013
Description
Lithium nickel manganese cobalt oxides (NMCs) are layered oxide cathode materials which are becoming increasingly popular as the demand for lithium-ion batteries increases. Lithium-ion batteries are used to power modern vehicles and for other battery applications. To better understand the structure and energetics of NMCs, various molar ratios of these compounds were synthesized via a sol-gel method and characterized with powder X-ray diffraction profile fitting. Lattice constants for the nickel, manganese, and cobalt solid solutions were determined. High temperature oxide melt solution calorimetry was used to determine the enthalpies of formation and mixing. All but Li2MnO3 had the same space group as LiCoO2 (R-3m). The lattice constants approximately followed a linear fit with cobalt mole fraction (R2average= 0.973) for the cobalt series. As the molar ratio of cobalt increased the lattice constants decreased. The nickel series was less linear (R2average=0.733) and had an opposite lattice constant trend to cobalt. The manganese series possessed a roughly linear trend when excluding the outlier Li2MnO3 (R2average=0.282). The formation enthalpy of the cobalt series becomes more negative as more cobalt is added. A second order polynomial fit could be used to model the enthalpies of mixing for the series. NMC2.5,2.5,5 exhibited the most stable energetics. A third order polynomial fit could be used to model the enthalpy of mixing for the nickel and manganese series with NMC811 and NMC181 exhibiting the most stable energetics.
ContributorsKanitz, William James (Author) / Navrotsky, Alexandra (Thesis advisor) / Chan, Candace (Committee member) / Xu, Hongwu (Committee member) / Arizona State University (Publisher)
Created2023
Description
This paper aims to analyze and estimate the factors affecting the State of Health (SoH) of lithium-ion batteries by leveraging advanced evaluation of electrical and chemo-mechanical processes contributing to degradation. The focus was on characterization and collection of empirical battery cycling data investigating the impact of different input variables on SoH prediction to enable predictions for capacity and degradation to validate reliability for second-life applications. The methodology involves collecting cycling data alongside Electrochemical Impedance Spectroscopy (EIS) using a custom test protocol under varied temperatures and charging rates to simulate real-world conditions. The alterations in capacity and the variation of the open circuit voltage with increasing cycles across different temperatures and c rates are also analyzed. The proposed method facilitates a better understanding of the interplay between temperature and C rates on the capacity, open circuit voltage, nominal voltage and EIS response to help estimate the SoH of lithium-ion batteries.
ContributorsMargoschis, Selva Seelan (Author) / Rolston, Nicholas (Thesis advisor) / Chan, Candace (Committee member) / Hwa, Yoon (Committee member) / Arizona State University (Publisher)
Created2024
Description
In this research work, the process optimization of silver iodide-silver meta phosphate ionic glass molding for solid state super ionic stamping was performed. Solid state super ionic stamping is a process of all solid ambient condition electrochemical nano patterning technique. In solid state super ionic stamping, anodic dissolution on a solid electrolyte –metal interface and subsequent charge-mass transport in the solid electrolyte is used for obtaining nanometer features on the metallic surface. The solid electrolyte referred to as the stamp is pre-patterned with features to be obtained on the metallic surface. This research developed the process for obtaining stamp with specific dimensions by making use of compression molding. The compression molding process was optimized by varying the five process parameters-temperature, pressure, holding time, pressing time and cooling time. The objective of the process optimization was to obtain best geometrical features for the stamp including flatness and surface roughness and by optimizing the compression molding process, stamp with minimum flatness and surface roughness was obtained. After the experimental optimization of the process was completed, statistical analysis was performed to understand the relative significance of the process parameters and the interaction of the process parameters on the flatness and surface roughness values of the molded stamp. Structural characterization was performed to obtain the variation of average domain size of ionic glass particles within the molded glass disk by varying the process parameters of holding time, pressing time and cooling time.
ContributorsPanikkar, Gautam (Author) / Hsu, Keng H (Thesis advisor) / Chan, Candace (Committee member) / Jiang, Hanqing (Committee member) / Arizona State University (Publisher)
Created2015
Description
Titanium oxide (TiO2), an abundant material with high photocatalytic activity and chemical stability is an important candidate for photocatalytic applications. The photocatalytic activity of the TiO2 varies with its phase. In the current project, phase and morphology changes in TiO2 nanotubes were studied using ex-situ and in-situ transmission electron microscopy (TEM). X-ray diffraction and scanning electron microscopy studies were also performed to understand the phase and morphology of the nanotubes. As prepared TiO2 nanotubes supported on Ti metal substrate were amorphous, during the heat treatment in the ex-situ furnace nanotubes transform to anatase at 450 oC and transformed to rutile when heated to 800 oC. TiO2 nanotubes that were heat treated in an in-situ environmental TEM, transformed to anatase at 400 oC and remain anatase even up to 800 oC. In both ex-situ an in-situ case, the morphology of the nanotubes drastically changed from a continuous tubular structure to aggregates of individual nanoparticles. The difference between the ex-situ an in-situ treatments and their effect on the phase transformation is discussed. Metal doping is one of the effective ways to improve the photocatalytic performance. Several approaches were performed to get metal loading on to the TiO2 nanotubes. Mono-dispersed platinum nanoparticles were deposited on the TiO2 nanopowder and nanotubes using photoreduction method. Photo reduction for Ag and Pt bimetallic nanoparticles were also performed on the TiO2 powders.
ContributorsSantra, Sanjitarani (Author) / Crozier, Peter A. (Thesis advisor) / Carpenter, Ray (Committee member) / Buttry, Daniel (Committee member) / Arizona State University (Publisher)
Created2014
Description
Tin (Sn) has a high-specific capacity (993 mAhg-1) as an anode material for Li-ion batteries. To overcome the poor cycling performance issue caused by its large volume expansion and pulverization during the charging and discharging process, many researchers put efforts into it. Most of the strategies are through nanostructured material design and introducing conductive polymer binders that serve as matrix of the active material in anode. This thesis aims for developing a novel method for preparing the anode to improve the capacity retention rate. This would require the anode to have high electrical conductivity, high ionic conductivity, and good mechanical properties, especially elasticity. Here the incorporation of a conducting polymer and a conductive hydrogel in Sn-based anodes using a one-step electrochemical deposition via a 3-electrode cell method is reported: the Sn particles and conductive component can be electrochemically synthesized and simultaneously deposited into a hybrid thin film onto the working electrode directly forming the anode. A well-defined three dimensional network structure consisting of Sn nanoparticles coated by conducting polymers is achieved. Such a conductive polymer-hydrogel network has multiple advantageous features: meshporous polymeric structure can offer the pathway for lithium ion transfer between the anode and electrolyte; the continuous electrically conductive polypyrrole network, with the electrostatic interaction with elastic, porous hydrogel, poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) (PAMPS) as both the crosslinker and doping anion for polypyrrole (PPy) can decrease the volume expansion by creating porous scaffold and softening the system itself. Furthermore, by increasing the amount of PAMPS and creating an interval can improve the cycling performance, resulting in improved capacity retention about 80% after 20 cycles, compared with only 54% of that of the control sample without PAMPS. The cycle is performed under current of 0.1 C.
ContributorsGao, Tianxiang (Author) / He, Ximin (Thesis advisor) / Sieradzki, Karl (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2015
Description
Lithium ion batteries prepared with a ceramic separator, have proven to possess improved safety, reliability as well as performance characteristics when compared to those with polymer separators which are prone to thermal runaway. Purely inorganic separators are highly brittle and expensive. The electrode-supported ceramic separator permits thinner separators which are a lot more flexible in comparison. In this work, it was observed that not any α-alumina could be used by the blade coating process to get a good quality separator on Li4Ti5O12 (LTO) electrode. In this work specifically, the effect of particle size of α-alumina, on processability of slurry was investigated. The effect of the particle size variations on quality of separator formation was also studied. Most importantly, the effect of alumina particle size and its distribution on the performance of LTO/Li half cells is examined in detail. Large-sized particles were found to severely limit the ability to fabricate such separators. The α-alumina slurry was coated onto electrode substrate, leading to possible interaction between α-alumina and LTO substrate. The interaction between submicron sized particles of α-alumina with the substrate electrode pores, was found to affect the performance and the stability of the separator. Utilizing a bimodal distribution of submicron sized particles with micron sized particles of α-alumina to prepare the separator, improved cell performance was observed. Yet only a specific ratio of bimodal distribution achieved good results both in terms of separator formation and resulting cell performance. The interaction of α-alumina and binder in the separator, and its effect on the performance of substrate electrode was investigated, to understand the need for bimodal distribution of powder forming the separator.
ContributorsKanhere, Narayan Vishnu (Author) / Lin, Jerry Y. S. (Thesis advisor) / Kannan, Arunachala (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2017