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Swarnakar, PrakashDEVELOPMENT OF NOVEL SUSTAINABLE AND ENERGY EFFICIENT NANOTECHNOLOGY FOR WATER TREATMENT
Master of Science, Miami University, 2012, Environmental Sciences
Developing an energy efficient water treatment technology is a big challenge. This study investigated the catalytic activity of silver and gold modified nanoparticle (Ag-TiO2 and Au-TiO2) and unmodified nanoparticle TiO2 thin films towards photo degradation of methyl orange (MO) under illumination of natural sunlight and UV light. The degradation of MO was ~ 15 % greater in the presence of the Ag-TiO2 film than the TiO2 film, and there was negligible degradation of MO in the absence of film under sunlight. The catalytic activity of the Ag-TiO2 and TiO2 thin films to degrade MO in batch experiments diminished 9 % and 7%, respectively over five repetitions. All the experiments conducted under sunlight had better results as compared to UV light with all the film types. This novel application of silver modified nanoparticles may be useful for the efficient destruction of dissolved organic contaminants.

Committee:

Jonathan Levy, PhD (Advisor); Lei Kerr, PhD (Committee Member); John Rakovan, PhD (Committee Member); Sushil R. Kanel, PhD (Committee Member)

Subjects:

Environmental Science

Keywords:

Sunlight; UV light; TiO2 films; Photocatalysis; Ag-TiO2; Au-TiO2; Methyl Orange; water treatment

Pan, JieMATERIAL PROPERTY STUDY ON DYE SENSITIZED SOLAR CELLS AND CU(GA,IN)SE2 SOLAR CELLS
Master of Science, Miami University, 2009, Paper Science and Engineering
This thesis focuses on four different aspects. 1) Use hybrid TiO2 electrode instead of doctor bladed TiO2 for dye sensitized solar cells (DSSCs) and observed an increase in efficiency from 1.6% to 2.11%. 2) We investigated the post annealing treatment on the CdS sensitized ZnO and TiO2 nanocrystalline solar cells. It was found that the annealing will increase the cell efficiency on ZnO and TiO2 with porous structures. 3) We studied the degradation mechanism using damp heat based on ZnO and Al:ZnO. We found that the Al dopant would enhance the moisture capture ability in ZnO, causing degradation under damp heat and annealing treatment.4) we have compared the differences between Zn1-xMgxO and Al: Zn1-xMgxO and concluded that the existing of Al in the film would vary the film performance.

Committee:

Dr.Lei Kerr, PhD (Advisor); Dr. Shashi Lalvani, PhD (Committee Member); Dr.Coffin Douglas, PhD (Committee Member); Dr.Catherine Almquist, PhD (Committee Member)

Subjects:

Chemical Engineering

Keywords:

DSSC solar cells; CdS sensitized ZnO; CdS zensitized TiO2; Electrospinning; ZnO; TiO2; CIGS solar cells; stability; damp heat; efficiency

Chen, XiaoboSynthesis and Investigation of Novel Nanomaterials for Improved Photocatalysis
Doctor of Philosophy, Case Western Reserve University, 2005, Chemistry

Since the discovery of the photocatalytic splitting of water on TiO2 electrode by Fujishima and Honda in 1972, enormous effort has been spent on the study of TiO2 under light illumination, due to its various potential applications, such as photovoltaics and photocatalysis. The optical properties, in particular the absorption, of TiO2 are essential to its photon-driven applications. Typically, TiO2 absorbs in the UV regime, which is only a small fraction of the sun’s energy (< 10%). The performance of TiO2 can be enhanced by shifting the onset of its absorption from the UV to the visible region. Metals have been employed to tune the electronic structure of TiO2-based material. The photocatalytic reactivity of metal-doped TiO2 depends on many factors, and metal doping can result in thermal instability and increased carrier trapping. The desired visible-light absorption of TiO2 can be also achieved by using main group dopants.

In this dissertation, different non-metal elements, C, N and S, are incorporated to the lattice of TiO2 to induce the absorption in the visible-light regime. Both bottom-up and top-down methods are used to synthesize these doped TiO2 nanoparticles. The optical, physical, electronic and photocatalytic properties of these doped TiO2 nanoparticles are explored with different techniques. The relationship between the optical, electronic and photocatalytic properties are elucidated. The photocatalytic performance of the doped TiO2 nanoparticles is applied not only to the model photodegradation of methylene blue, but also on other industrial dyes under natural sun-light illumination. The non-metal-doped TiO2 nanoparticles demonstrated improved photocatalytic performance over the non-doped TiO2 nanoparticles, i.e. in the visible-light regime.

On the other hand, as the size of nanoparticles decreases, the surface-to-volume ratio increases dramatically (~ 1/r), so does the surface area (1/r2). The high surface area brought by the small size of nanoparticles becomes more important for the optical and electronic properties of nanomaterials, compared to the bulk materials. Besides the well-know quantum-confinement effect, the surface effect should be taken into account for small nanoparticles. Thus in this dissertation, the synthesis and properties of II-VI (CdSe, CdSe/CdS) semiconductor nanoparticles are investigated to elucidate the surface effect on the properties of nanoparticles, which helps to understand the photocatalytic property of TiO2 nanomaterials, since the main catalytic reactions occur on the surface. The gradual crystallization of small nanoparticles, as well as its effect on the optical properties is elucidated. The interface strain/stress in the CdSe/CdS core/shell system is explored on their optical properties, as well as the hot carrier relaxation dynamics in CdSe nanoparticles.

Committee:

Clemens Burda (Advisor)

Keywords:

TiO2; CdSe; Nanoparticles; doped TiO2; eV; Nanocrystals

Pelaez, MiguelDevelopment of Novel Visible and Solar Light-Activated Nanostructured Nitrogen-Fluorine Titanium Dioxide Photocatalyst for the Removal of Cyanotoxins in Water
PhD, University of Cincinnati, 2012, Engineering and Applied Science: Environmental Engineering
The prevalent and increasing occurrence of cyanobacteria and their toxins, known as cyanotoxins, in drinking water sources have become a potential health risk to humans. Physical treatment methods in conventional drinking water treatment have the capacity to remove cyanotoxins but are limited to a merely physical separation, where further treatment is required. Cyanotoxins are susceptible to chemical oxidation and recently advanced oxidation technologies (AOTs) and nanotechnologies (AONs), such as titanium dioxide (TiO2) photocatalysis, have been proven an effective alternative technology to chemically transform cyanotoxins in water. However, conventional TiO2 is restricted to UV light photoactivation for the generation of highly reactive oxygen species (i.e., hydroxyl radicals) representing an economical and technological limitation for the use of renewable energy sources such as solar light, since UV radiation accounts only for 5% of the total solar spectrum compared to the visible spectrum (~45%). This dissertation explored the development of nanostructured nitrogen and fluorine co-doped TiO2 (NF-TiO2) that can be activated under visible and solar light for the photocatalytic degradation of cyanotoxins in water. This work aimed to develop highly efficient NF-TiO2 nanoparticles and films to evaluate the environmental fate of microcystins, the most widespread and highly persistent group of cyanotoxins found in surface waters, and cylindrospermopsin which has emerged as the most significant toxin in freshwater sources. Specific attention was given to 1) the fundamental aspects on the synthesis method that influenced the physicochemical properties of NF-TiO2, such as the incorporation of nitrogen and fluorine in the structure of TiO2 and the synergistic effects induced by both dopants, 2) the surface interaction between the cyanotoxins and NF-TiO2 in different water matrix, 3) the reactivity and degradation kinetics of microcystins and cylindrospermopsin with NF-TiO2 and 4) the mechanism of radical formation with NF-TiO2 under visible and solar light. The existence of interstitial nitrogen and substitutional fluorine in the NF-TiO2 lattice was determined and the formation of localized intra-gap states was established implying that fluorine promotes nitrogen incorporation in TiO2. A shift in the absorbance capacity of NF-TiO2 in the visible range was also observed. Anatase/brookite heterojunctions, which promote photocatalytic efficiency, were found in NF-TiO2. High initial degradation rates for microcystin-LR (MC-LR) were obtained with NF-TiO2 nanoparticles and films in synthetic water under visible light. The effect of pH indicated that attractive forces at acidic conditions between the oppositely charged NF-TiO2 and MC-LR contributed to higher MC-LR initial degradation rates. The presence of alkalinity and natural organic matter had a scavenging effect since the initial MC-LR degradation rates decreased. Modifications to NF-TiO2 with Evonik Aeroxide¿¿¿¿ P25-TiO2 (P25) nanoparticles lead to composite NF-TiO2-P25 with improved photocatalytic activity towards MC-LR, MC-RR, MC-YR, MC-LA and cylindrospermopsin under visible and UV-vis light. The general reactivity was MC-LA>MC-LR>MC-YR>MC-RR. Finally, results using selected scavengers indicate that the main mechanism of NF-TiO2 radical formation under visible light irradiation differed from UV-mediated TiO2 photocatalysis since no evidence of hydroxyl radical production from the surface holes was observed. It was suggested that under visible light, surface oxygen reduction of NF-TiO2 occurred to form superoxide radical anion as main radical specie. The affinity of the scavenger with NF-TiO2 and MC-LR in terms of pH was established as an important parameter to determine the radicals formed in this study.

Committee:

Dionysios Dionysiou, PhD (Committee Chair); George Sorial, PhD (Committee Member); Margaret Kupferle, PhD (Committee Chair); Armah de la Cruz, PhD (Committee Chair)

Subjects:

Environmental Engineering

Keywords:

TiO2; water treatment; visible light; cyanotoxins; sustainability; UV light; nitrogen; fluorine; NF-TiO2

Yu, Cheng-LunTitanium dioxide thick film printing paste for dye sensitized solar cell
Master of Sciences (Engineering), Case Western Reserve University, 2011, Materials Science and Engineering
Comparing to the narrow band gap material, dye sensitized solar cells (DSSC) provide a less expensive manufacturing method. TiO2 nano-crystalline anode material highly improves the DSSC efficiency as Gratzel reported in 1991. Today the DSSC efficiency is about 12% based on TiO2 and ruthenium compound sensitizer. The development of a thick film screen printable paste for the DSSC TiO2 anode is the objective of this study, since thick film printing technique is appropriate for lowering the manufacturing cost of DSSC via mass production. An ideal TiO2 electrode has to achieve moderate thickness, good light transmittance, high degree of roughness and good electrical connection between the dyes and the TiO2 layer. Thick film printing pastes for the TiO2 layer are prepared tested and evaluated in this study, and their properties are experimentally examined. Experimental methods and experimental protocols for the characterization of the TiO2 thick film printable paste are established which can be useful in the advancement of the manufacturing of DSSC.

Committee:

Chung-Chiun Liu (Advisor); Mark R. De Guire (Committee Member); Gerhard E. Welsch (Committee Member)

Subjects:

Materials Science

Keywords:

TiO2; DSSC; paste; electrode

Patha, Venu GopalCharacterization of TiO2 Photoelectrodes Fabricated via a Low Temperature Sintering Process
Master of Science in Chemistry, Youngstown State University, 2011, Department of Chemistry
TiO2 photoanodes used for water-splitting solar cells or dye-sensitized solar cells (DSSC) have to meet the following properties to assure high efficiency: good connection between TiO2 grains and a large inner surface area, TiO2 grain shape and film conductivity. Nanocrystalline TiO2 films are usually prepared by adding an organic binder to TiO2 paste on glass substrates, and followed by heating at temperatures ranging from 450 to 500 °C. The organic binder is used to increase viscosity, enabling the formation of uniform TiO2 films. Heat treatment is used to sinter the nanoparticles, as well as burn out the organic binder. In the case of composite formulations involving organic polymer electrolyte membranes, the conventional preparation technology is not suitable, because of the low temperature resistance of the polymer, on order of 150 °C. Therefore, to make thick TiO2 films with good interconnection between the nanoparticles at low temperature, it is essential to enhance the viscosity of TiO2 colloidal solution without using an organic binder. Possible approaches are developed by using acid-base chemistry, where the viscosity of acidic TiO2 colloidal solution is monitored while adding ammonia solution which acts as a base. Thus the processed TiO2 photoanode was assembled into a photoelectrochemical cell and tested by measuring I-V characteristics under illumination by white light from a solar simulator. TGA, DSC, IR, XRF, XRD and SEM analyses were performed to characterize the films. The low temperature process yielded titania films that were comparable to the conventional high temperature method.

Committee:

Clovis Linkous, PhD (Advisor); Timothy Wagner, PhD (Committee Member); Larry Curtin, PhD (Committee Member); Howard Mettee, PhD (Committee Member)

Subjects:

Chemistry; Materials Science; Nanoscience

Keywords:

Characterization; TiO2; Photoelectrodes

Stinson, Jelynn A.The Electroanalytical Performance of Sonogel Carbon Titanium (IV) Oxide Electrodes versus Conducting Polymer Electrodes in the Electrochemical Detection of Biological Molecules
Master of Science (MS), Wright State University, 2007, Chemistry
Stinson, Jelynn Anneula. M.S., Department of Chemistry, Wright State University, 2007. The Electroanalytical Performance of Sonogel Carbon Titanium (IV) Oxide Electrodes versus Conducting Polymer Electrodes in the Electrochemical Detection of Biological Molecules. The electrochemical performance of a newly developed sonogel carbon titanium (IV) oxide (SGC/TiO2 ) electrode against poly(3-methylthiophene) (P3MT) and poly(2,2’-bithiophene) (PBTP) modified electrodes in the electrochemical detection of biological molecules is reported. The stability of the Titanium (IV) Oxide coating on the sonogel carbon electrode was shown to be greater than the P3MT coating on the conventional size glassy carbon electrode. After 10 consecutive scans, there was a 21% loss of the initial signal at the P3MT modified electrode and a 5% loss of the initial signal at the SGC/TiO2 electrode. The influence of NAD+ on NADH response was tested. The PBTP modified electrode and bare electrode demonstrated the inability to stabilize the interference due to NAD+. The SGC/TiO2 electrode was able to detour the susceptibility to interfering NAD+. The response potential was improved by 141 mV. Response time for 5mM catechol (CAT) and 5mM ascorbic acid (AA) in 0.01M sulfuric acid was determined. Specificity for CAT detection was measured using a 5mM CAT + 5mM AA mixture in 0.01M sulfuric acid. The SGC/TiO2 electrode permits a shorter response time and improved selectivity for CAT. NADH was irreversible in all electrolytes. Highest anodic peak potential, at the PBTP modified electrode, was measured in sodium nitrate. Highest anodic peak potential at the SGC/TiO2 electrode was recorded in sulfuric acid.

Committee:

Suzanne Lunsford (Advisor)

Subjects:

Chemistry, Analytical

Keywords:

SGC/TiO2; Electrodes; GCE; NADH; PBTP; P3MT; Scan Rate

Guzman Montanez, FelipeElectrochemical and Photocatalytic Oxidation of Carbon and Hydrocarbons
Doctor of Philosophy, University of Akron, 2009, Chemical Engineering

Development of novel technologies for the conversion and storage of energy has been actively investigated in recent years. The use of a combined approach consisting of direct electrochemical and photocatalytic oxidation reactions could allow the efficient utilization of energy resources. Direct electrochemical oxidation in a fuel cell could offer significant advantages over conventional combustion technologies, in light of their increased energy efficiency, reduction in emission of toxic pollutants, and overall process simplicity. The majority of fuel cell research has focused on the use of hydrogen, an environmentally friendly fuel characterized by high energy density and production of H2O byproduct. Despite these advantages, commercialization of hydrogen powered fuel cells is currently limited by difficulties in hydrogen production and storage.

The high operation temperature of the solid oxide fuel cell (700-1000 °C) facilitates the direct use of hydrocarbon and carbon fuels, avoiding the complex and expensive reforming processes for the generation of concentrated H2 fuel. Exposure of gaseous hydrocarbons to the fuel cell at these high temperatures provides a thermodynamically favorable pathway for formation of carbon deposits (i.e., coking) which can lead to rapid and irreversible anode electrode degradation. This dissertation presents a study of the use of a novel Cu/Ni-YSZ anode electrode that reduces the formation of coke deposits and allows the energy efficient operation of the solid oxide fuel cell in hydrocarbon and carbon fuels. The microstructure of the Cu/Ni-YSZ anode electrode is extensively characterized by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The performance of the Cu/Ni-YSZ anode and the energy efficiency during the operation on carbon (i.e., coke, a devolatized form of coal) is experimentally measured with the aid of in situ electrochemical analysis and, mass spectrometry (MS) and gas chromatograph (GC), demonstrating higher energy efficiencies compared with combustion technologies.

Photocatalytic reactions over semiconductor catalysts such as TiO2 have received significant attention due to their potential applications for conversion and storage of solar energy to chemicals and the degradation of harmful pollutants present in air streams and wastewaters. Excitation of photocatalysts by exposure to light of appropriate energy causes promotion of electrons from the valence band to the conduction band, resulting in the generation of electron/ hole pairs that can initiate redox reactions with species adsorbed on the surface of the photocatalyst. Hydrogen can be produced by the photocatalytic reduction of water (i.e. splitting reaction). Addition of alcohol molecules have been shown to improve the photocatalytic evolution of H2 from H2O due to hole scavenging oxidation reactions that limit electron/hole recombination. Detail knowledge of the mechanisms governing the photocatalytic oxidation of alcohols could facilitate the development of highly efficient photocatalysts for water splitting and degradation of volatile organic compounds (VOC).

The photocatalytic evolution of H2 from aqueous solutions containing methanol (CH3OH) hole scavenging reagents was studied by tracing the reaction of D2O over a Cu/S-TiO2 catalyst under UV illumination. Use of D2O/CH3OH produced higher formation rates of HD and D2 than that of H2. The low H2 formation rates indicate that the direct reaction of CH3OH with photogenerated holes does not proceed to an appreciable extent in the presence of high concentrations of D2O. The role of CH3OH in accelerating hydrogen formation can be attributed to its ability to produce an electron donor, injecting its electrons to the conduction band.

The photocatalytic oxidation of alcohols was further studied at 30 °C and 1 atm by in situ infrared methods, using ethanol as a model compound. Results from these studies have shown ethanol adsorbs on TiO2 in the presence of high contents of water as molecularly adsorbed ethanol (CH3CH2OHad), which exhibit a lower initial C-H scission and CO2 formation rate than ethoxy CH3CH2Oad produced from ethanol adsorbed low water content TiO2 catalysts. CH3CH2OHad photooxidation produced formic acid (HCOOHad) and formate (HCOO-ad) species, whereas CH3CH2Oad reactions proceed via formation of acetaldehyde (CH3CHOad) and acetate (CH3COO-ad). CH3CHOad was found to react on TiO2 via hydrogen abstraction of the -Carbon producing CH3COO-ad which can be further oxidized to HCOO-ad and CO2. The rate of ethanol photooxidation was found to decrease due to the accumulation of CH3COO-ad species on the TiO2 surface. In the presence of excess H2O, weakly adsorbed species (i.e., acetic acid CH3COOHad) can be redistributed in the surface and dissociated producing acetate.

Committee:

Steven S. Chuang, PhD (Advisor)

Subjects:

Chemical Engineering

Keywords:

fuel cell; fuel; TiO2; PHOTOCATALYTIC; anode; PHOTOCATALYTIC OXIDATION; H2O

Dinan, Benjamin J.Growth of Titania Nanowires by Thermal Oxidation
Doctor of Philosophy, The Ohio State University, 2012, Materials Science and Engineering

Due to the unique properties of nanostructured metal-oxides, derived from their extremely small size scale in at least one dimension, several techniques have been developed for their production. However many of these techniques involve the use of chemical additives which could impact device performance, require costly processing equipment and highly trained personnel, or are difficult to scale up for mass production. In this dissertation a novel technique for the production of nanostructured titanium dioxide (TiO2) by thermal oxidation of titanium and several of its alloys is presented. Two separate oxidation processes are described for the production of nanowires on titanium alloys and on commercially pure titanium (CPTi). The first involves oxidation in an oxygen deficient environment to promote the growth of 1-D nanowires. It was found that the oxidation temperature as well as the oxygen concentration play an important role in nanowire formation. A brief discussion is offered to explain the transition from planar oxide growth to highly anisotropic 1-D nanowires on the titanium alloy samples. Oxidation in an oxygen deficient environment was less successful at producing nanowires on CPTi. Thus, an alternative method of oxidation in a humid environment is presented as a means of increasing nanowire yield on CPTi substrates.

Several applications for the nanostructures produced by these methods are presented and future research directions are suggested. For example oxidation of Ti-6%Al-4%V (Ti64) alloy, widely used for biomedical applications, to produce nanostructures has been investigated as a means of improving cell adhesion and proliferation on medical implants. The nanowires grown on CPTi have been used as a precursor for hydrothermal conversion to barium titanate, a perovskite structure exhibiting ferroelectric behavior at room temperature. The unique morphology of the nanostructured TiO2 precursor results in the formation of dendritic barium titanate, a unique structure seldom reported for this material. These and other exciting applications have been explored demonstrating the potential for industrial application of the low-cost methods to produce nanowires. Both oxidation processes for the production of TiO2 nanowires on titanium substrates are low cost and are easily scalable for mass production of TiO2 nanowires giving them a distinct advantage over other nanowire production methods.

Committee:

Sheikh Akbar, PhD (Advisor); Suliman Dregia, PhD (Advisor); Michael Mills, PhD (Committee Member); John Morral, PhD (Committee Member); William Brantley, PhD (Committee Member)

Subjects:

Alternative Energy; Biomedical Engineering; Biomedical Research; Energy; Engineering; Materials Science; Mechanical Engineering; Nanoscience; Nanotechnology; Physical Chemistry

Keywords:

nanowires;nano;oxidation;titanium;tio2;titania;barium titanate;nanotechnology;nanoscience;sensors;

Nguyen, QuynhGiao N.High Temperature Volatility and Oxidation Measurements of Titanium and Silicon Containing Ceramic Materials
Doctor of Philosophy in Clinical-Bioanalytical Chemistry, Cleveland State University, 2008, College of Science
Titanium (Ti) and silicon (Si) containing materials are of high interest to the aerospace industry due to its high temperature capability, strength, and light weight. A continuous exterior oxide layer is desirable to reduce the oxidation rate of these two materials. At high temperatures, water vapor plays a key role in the volatility of materials including oxide surfaces. This study first evaluated several hot-pressed Ti and Si-containing compositions at high temperatures as a function of oxidation resistance. This study also evaluated cold pressed titanium dioxide (TiO2) powder pellets at a temperature range of 1400°C - 1200°C in water containing environments to determine the volatile hydoxyl species using the transpiration method. The water content ranged from 0-76 mole % and the oxygen content range was 0-100 mole % during the 20-250 hour exposure times. Results indicate that oxygen is not a key contributor at these temperatures and a volatile Ti-O-H species has been identified.

Committee:

Lily M. Ng, PhD (Committee Chair); James L. Smialek, PhD (Advisor); Kang N. Lee, PhD (Committee Member); John F. Turner II, PhD (Committee Member); Mary V. Zeller, PhD (Committee Member)

Subjects:

Aerospace Materials; Chemistry; Materials Science

Keywords:

aerospace; ceramic; combustion environment; high temperature; hydroxyl species; oxidation; materials; Si; silicon; titanium dioxide; TiO2; Ti-O-H; transpiration method; transpiration technique; volatility; water vapor

Su, LushengFormation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures
Doctor of Philosophy in Engineering, University of Toledo, 2013, College of Engineering
This research focused on the formation mechanism of TiO2 nanotubes on pure Ti foil and the development and improvement in performance of thermoelectric multi-components. For the formation mechanism, based on our experiments and observations, oxygen formed on the anode determines the final dimension of the TiO2 nanotubes. The length of the TiO2 nanotubes achieved was 15 µm in the electrolyte containing ethylene glycol and water (98:2 vol. %) + 0.3 wt. % NH4F for 24 hours. Bent anode was employed to show that there were no nanotubes formed on the bent part. Different anodization times were used to examine the action of fluorine ions. We also used different types of Ti foils, cold rolled and hot-rolled, to evaluate the effect of preprocess condition on the oxygen formation at their surfaces. Electrochemically and chemically treated Ti foils with exposed grain boundaries were used to reveal that the nanotubes grow along the grains of the Ti substrate. Finally, a dissolution model was established to calculate the dissolved TiO2 mass. The primary strategy to improve the performance of thermoelectric materials was employing low-dimensional materials to reduce the lattice thermal conductivity as described by the Wiedemann-Franz law. Rattling structures, point defects, vacancies and multi-components were used to efficiently scatter phonons within or between the unit cell crystals. And complex crystalline structures were used to decouple the electrical conductivity and thermal conductivity to achieve this goal. Based on such considerations, we developed TiO2 nanotubes/polyaniline, TiO2 nanotubes/Te-Bi-Pb nanoparticles and TiO2 nanotubes/CoO coaxial nanocables. Firstly, TiO2 nanotubes/polyaniline (PANI) multi-components were synthesized. The experiments of how the time, voltage, concentration of F- ions and concentration of H3PO4 were associated with the formation of TiO2 nanotubes were conducted. The formation of polyaniline was confirmed by both Raman Spectroscopy and FTIR. The results showed that the optimum conditions for the formation of well aligned TiO2 nanotubes are at 20 V for 60 minutes in the electrolyte containing 0.2 M fluorine ions. The TiO2 nanotubes with the wall thickness of 20 nm and length of 3 µm were obtained in the electrolyte containing 0.2 M F-. Nanotubes with wall thickness of 10 nm and length of 600 nm formed in the solution containing 0.1 M F-. The highest absolute value of the Seebeck coefficient obtained was 123.75 µV/K. The measurement was performed at 30°C. The Seebeck coefficients of TiO2 nanotubes and TiO2 nanotubes/polyaniline multi-components were investigated. Secondly, Te-Bi-Pb nanoparticles were grown on the surface of the TiO2 nanotubes via electrochemical method. The purpose of the nanoparticles was to further enhance the performance of the thermoelectricity, specifically in our case, to increase the Seebeck coefficient. From the results obtained, the best Seebeck coefficient for pure TiO2 nanotubes was around -90 µV/K; while the best Seebeck coefficient for TiO2 nanotubes covered with scattered Te-Bi-Pb nanoparticles was about -155 µV/K. This significant improvement could be explained by the quantum confinement in such a peculiar nanostructure. Lastly, TiO2 nanotubes and TiO2-CoO coaxial nanocables were prepared by liquid phase deposition into the pores of anodic aluminum oxide (AAO) templates to form TiO2 nanotubes and TiO2-CoO coaxial nanocables. Morphological studies of the TiO2 nanotubes and TiO2-CoO coaxial nanocables were performed using scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Elemental analysis of the composites was conducted by energy dispersive X-ray (EDX) spectroscopy. In addition, the Seebeck coefficients of the composites were measured. It was found that the highest absolute value of Seebeck coefficient was 393 µV/K for the TiO2 nanotube-filled AAO. The TiO2-CoO coaxial nanocable-filled AAO had the slightly lower value of 300 µV/K. Both composites showed n-type behavior.

Committee:

Yong X. Gan, Dr. (Advisor); Maria Coleman, Dr. (Committee Member); Matthew Franchetti, Dr. (Committee Member); Joseph Lawrence, Dr. (Committee Member); Arunan Nadarajah, Dr. (Committee Member)

Subjects:

Energy; Engineering; Materials Science

Keywords:

Thermoelectricity; Formation mechanism; TiO2 nanotube; Nanoparticle; Nanocable; PANI; Seebeck coefficient

Yoo, SehoonOriented arrays of single crystal TiO2 nanofibers by gas-phase etching: processing and characterization
Doctor of Philosophy, The Ohio State University, 2005, Materials Science and Engineering

A novel method to produce arrays of single crystal TiO2 nanofibers by one step heat treatment in a non-combustive H2/N2 atmosphere has been developed. The dimension of the nanofibers was ranged between 15 – 50 nm in diameter and 1 – 5 ìm in length. The nanofibers were formed by selective and anisotropic etching and it is dubbed “nano-carving”. Although nanocarving utilizes H2/N2 gas during treatment, N2 did not affect the nanofiber formation. Major impurities on disk surfaces were Al, Si, Ni, Fe, and C. Nanoparticles composed of metallic Fe and Ni were observed by TEM and it was likely to have formed on end tips of nanofibers. From XRD, XPS and TEM SAD analyses, the phase of nanofibers was rutile TiO2, and not a suboxide although the nanofibers were generated by a heat treatment in H2/N2. From TEM analyses, it was determined that the preferred direction of etching for the nanofiber formation was the <001> direction.

The rate of nanocarving of polycrystalline TiO2 increased as the sintering temperature and time decreased. The optimum H2/N2 heat treatment temperature ranged from 680 – 740 °C. Below 680 °C, the etching process was not active and above 740 °C, anisotropic etching disappeared because etching in other directions became comparable. Nanowhiskers were grown on nanofiber formed surface by reoxidation at 700 °C for 8 hrs in air. Heat treatment of TiO2 in a H2O atmosphere also created tiny nanofibers on the surface via an apparent deposition process. TiO2 nanofibers showed enhanced sensitivity as a sensor of H2(g), relative to sintered material without nanofibers.

TGA analyses indicated that excess Ti cations from gas phase reaction with H2 should also have been removed from the surface during nanocarving. The excess Ti cations from H2/N2 heat treatment were moved to the bulk by diffusion of Ti interstitials. Weight loss during H2/N2 heat treatment was also dependent on the grain size, which indicated that grain boundary diffusion was an important mode of Ti interstitial diffusion.

Committee:

Sheikh Akbar (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

Nanofibers; Nanowires; TiO2; H2; Etching

De Silva, Chamara L.Removal of Phenol from Oil/Gas Wastewater by Catalytic Supercritical Water Treatment
Master of Science (MS), Ohio University, 2016, Chemical Engineering (Engineering and Technology)
The U.S. oil/gas industry generates over 21 billion barrels of produced water annually. This wastewater stream contains a host of components including suspended solids, dissolved solids, and hydrocarbons. This waste stream represents a significant beneficial resource if reused to offset other water consumption demands. However, many beneficial reuse applications have strict hydrocarbon limits. Oxidation of hydrocarbons in supercritical water media provides an effective removal technique allowing wastewater reuse. In order to quickly and effectively remove hydrocarbons in supercritical water a heterogeneous catalyst is needed. In this study, an MnO2 catalyst on a TiO2 support was synthesized and evaluated for removal of phenol in supercritical water. Synthesized catalysts were characterized using temperature programmed reduction, pulse chemisorptions and X-ray powder diffraction. Catalyst activity for phenol conversion was evaluated in a continuous packed bed reactor at supercritical water conditions, while analyzing vapor and liquid products. Evaluated process variables included free O2 concentration and the catalyst Mn loading. Both variables had positive effects on phenol conversion. The process reached complete destruction of phenol at an O2 level of 500% of the stoichiometric O2 for complete oxidation. Increase in catalyst Mn loading increased its active sites concentration enhancing the contribution of heterogeneous reaction kinetics for phenol supercritical water oxidation (SCWO); however a saturation limit appeared to be reached as Mn loading is further increased. A part of the Mn composition appeared to be unable to create active sites on the catalyst due to interactions with TiO2. A phenol conversion of 70% was reached at 12% (w/w) Mn in the catalyst with 100% excess O2.

Committee:

Jason Trembly, PhD (Advisor); David Young, PhD (Committee Member); Marc Singer, PhD (Committee Member); Natalie Kruse, PhD (Committee Member)

Subjects:

Chemical Engineering; Energy; Engineering; Environmental Engineering

Keywords:

Supercritical; produced water; catalyst; MnO2; TiO2; phenol

Pattanapanishsawat, PiyapongStudy of Surface Modification and Effect of Temperature on Charge Carrier Generation and Recombination
Master of Science in Engineering, University of Akron, 2010, Chemical Engineering

Heterogeneous photocatalytic oxidation allows many applications in industry use. Titanium dioxide (TiO2) is one of the most efficient photocatalysts due to its chemical stability, non-toxicity and low cost. Many studies on photocatalytic activity have been done on various types of surface-modified TiO2 catalysts but not on SiH4 modified TiO2.

In this study, TiO2 (P25, Degussa) was treated with SiH4 and its photocatalytic activity has been observed and compared with that of non-treated TiO2. In order to understand some of the observations, various techniques such as introduction of varied ratio of EtOH/O2 pulses, variation of temperature, H2 and O2 exposure, phasing exposure of TiO2 to UV illumination and dark have been incorporated.

From the results, the increase on the absorbance intensity at 2000 cm-1 (i.e. I2000, background shift), was observed on SiH4-treated TiO2. This could be due to inhibition of electron-hole recombination process by blockage/removal of electron hole recombination centers such as surface hydroxyl groups and adsorbed water. Excessive coverage of SiO2 on TiO2 surface lowered the photocatalytic oxidation rate due to blockage of oxidation sites.

Quick drops followed by rises of the intensity of the background shift after EtOH/O2 pulses indicated faster consumption rate of photogenerated electrons by O2 comparing to the rate of accumulation of photogenerated electrons caused by the reaction of CH3CH2OHad and CH3CH2Oad with holes. This suggests that surface holes are more readily active than electrons and the majority of the photogenerated electrons are in the bulk. Increasing the ratio of O2 resulted in increased CO2 from different path of reactions. The background shift under abundant O2 was low due to electron scavenging. H2 can cause generation of trapped Ti atom as Ti3+. The trapped Ti3+ atoms can be exited resulting in separation of electron and hole and, in turn, causing higher background shift.

The density of photogenerated electrons was higher during the first UV illumination phase at 80°C than that at 30°C and the opposite could be observed during the third UV illumination phase. The extent of the background shift can be correlated with the photocatalytic oxidation rate of ethanol. Dark exposure caused faster background shift decay at 80 °C comparing to that at 30 °C indicating a faster electron-hole recombination process.

Committee:

Steven Chuang, Dr. (Advisor)

Subjects:

Chemical Engineering

Keywords:

tio2; sih4; background shift; temperature; photocatalytic activity; surface modification; UV; photocatalytic oxidation

Wang, Zhong-MinSynthesis of Nanostructured Catalyst Powders and Thin Film Reactors by Flame Aerosol Deposition and Their Applications in Partial Oxidation
PhD, University of Cincinnati, 2004, Engineering : Environmental Engineering
This is a study of the gas phase synthesis of nanostructured titania particles, doped titania and titania thin film coatings using flame aerosol reactors and their selected applications in green chemistry. The synthesized semiconductor particles and thin films have been used as photocatalysts and applied to the partial oxidation of organic compounds to produce highly desired oxygenates. A new flame synthesis technology has been developed to synthesize nanostructured titania powders, doped titania, and thin film coatings. The obtained catalyst powders and thin films have been characterized by various techniques, such as Raman spectroscopy, SEM, TEM, BET surface area, UV-VIS, ICP spectroscopy, Mössbauer spectroscopy and X-ray diffraction. The optimized catalysts were used in the organic synthesis. In order to lower the activation energy of titanium dioxide and increase the usable fraction of solar energy, metal-doped titanium dioxide was synthesized to increase the energy efficiency. The doping materials used in this study include vanadium and iron. The doped nanosize catalyst powders were evaluated with respect to crystal structure, atomic composition, band gap energy, light absorption wavelength shift and the performance in liquid phase photocatalytic partial oxidation of 1-phenylethanol to acetophenone. At the optimal doping concentration the doped titanium dioxide synthesized from the flame aerosol process showed higher conversion compared to the neat titania. The solvent effect on the photocatalytic reaction was studied using water and acetonitrile as the reaction solution. In order to overcome the shortcoming of powder titania in application, we developed a unique flame coating technique to synthesize catalyst thin film. The substrates being coated include ceramic mat, glass, and stainless steel sheet. The catalyst thin films synthesized in this study showed higher photocatalytic activity and more durable mechanic properties compared to the thin films coated by other methods, such as sol-gel process. To optimize the thin film coating, different coating parameters, like the coating temperature, coating composition, anatase to rutile ratio, different coating configuration and coating thickness were studied. Partial oxidation of cyclohexane to produce cyclohexanol and cyclohexanone in gas phase was used as a model of the photocatalytic reaction to test the coated thin films.

Committee:

Dr. Pratim Biswas (Advisor)

Subjects:

Engineering, Environmental

Keywords:

Nanostructured Catalyst; Nanosize Particle; Thin Film Coating; Aerosol Deposition; Green Chemistry; Partial Oxidation; Photocatalyst; Photooxidation; TiO2; Flame Aerosol; Semiconductor

Tilly, TrevorDISPERSION OF GEOMETRIC TITANIUM DIOXIDE NANOMATERIALS AND THEIR BIOLOGIC EFFECT
Master of Science, Miami University, 2013, Chemical, Paper & Biomedical Engineering
Tunable chemical and physical properties of engineered nanomaterials are achievable by changing their geometry and morphology. Titanium dioxide (TiO2) based nanofilaments-nanotube, nanowire, nanorod-have gained interest in industrial, energy, and as of recent, medical applications due to their superior performance over TiO2 nanoparticles. Safety assessment of these nanomaterials is critical to protect workers, patients, and bystanders as these technologies become widely implemented. Additionally, TiO2 based nanofilaments can easily be inhaled by humans and their high aspect ratio may make them toxic in the air passageway, like asbestos fibers. The tendency of TiO2 nanofilaments to aggregate makes their nanotoxicity assessment difficult and the results controversial because incomplete dispersion results in larger particle size exposure that is no longer at the nanoscale. In this study, a microfluidic device was utilized to produce stable dosing solutions necessary to evaluate the toxicity of TiO2 nanomaterials by eliminating any toxicity caused by aggregated TiO2 nanomaterials. The toxicity results could then be directly correlated to the TiO2 nanostructure itself. Well dispersed TiO2 based nanomaterials were nontoxic to cells. Whereas, aggregated 100 ug/ml concentrations of nanowires and nanotubes reduced viability up to 27%, indicating that in vitro toxicity results may be controlled by the dispersion of dosing solutions.

Committee:

Lei Kerr, PhD (Advisor); Saber Hussain, PhD (Advisor); Catherine Almquist, PhD (Committee Member); Justin Saul, PhD (Committee Member)

Subjects:

Biology; Chemical Engineering; Toxicology

Keywords:

Titanium Dioxide; TiO2; Nanotube; Nanofilament; toxicity; nanotoxicity

Guttman, JeremyPolymer-based Tunnel Diodes Fabricated using Ultra-thin, ALD Deposited, Interfacial Films
Master of Science, The Ohio State University, 2016, Electrical and Computer Engineering
Conjugated p-p bonded polymers offer a wide range of new electronic devices which have developed as a unique niche in the marketplace with an ever-growing need for integration. In particular, polymer-based tunnel diodes (PTDs) which exhibit negative differential resistance (NDR) at room temperature can be integrated with other novel components to realize memory and logic cells for highly manufacturable, roll-to-roll (R2R) printed electronics. The research presented here focuses primarily on the fabrication and operating principles behind PTDs. By incorporating an ultra-thin TiO2 interfacial tunneling barrier into a modified organic light emitting diode (OLED) structure, reproducible NDR can be realized. By varying the properties of the interfacial tunneling oxide, characteristics of NDR such as the peak-valley-current-ratio (PVCR), peak current density (J_peak), and the voltage at the peak density (V_peak) can be improved for memory and logic. This work successfully demonstrates room temperature NDR in PTDs using ultra-thin TiO2 interfacial tunneling barriers grown via atomic layer deposition (ALD). The intention of this work is to present a viable prototype PTD using ALD to deposit the tunneling barrier. By taking a look at the physical and electrical behavior behind the ALD deposited films, a better understanding can be gained on the nature of interfacial layer. It is suggested that localized defect states caused by oxygen vacancies induced during oxide growth is behind the tunneling behavior observed in the PTDs. By controlling the oxide growth, the crystal structure can be altered in order modify the oxygen vacancy concentration and therefore improve PVCR. Therefore, a key aspect of this thesis will be to observe how morphology, realized through varying temperature of ALD growth, can affect device characteristics. Additionally, to fully classify these devices, the physics behind the electrical operation needs to be further evaluated. Mapping the properties of the various materials through experimentation and modeling will serve as the starting place for future work to come. Finally, this thesis is part of an ongoing exploration for low-power, low-cost printed electronics. Therefore, a key aspect of this work is to present an argument for a printable process on a flexible, plastic substrate, and as such the requirement for a low temperature deposition is imperative. Low temperature ALD can come in the form of alternative precursors or alternative tunneling oxides. Moreover, by choosing to use alternative oxides, lower power NDR appearing at lower voltages may be realized. This study begins the work on finding alternative tunneling oxides that demonstrate similar oxygen vacancies observed in TiO2 films. In this case, Ta2O5 replaces TiO2 as the tunneling barrier. The initial data is promising, demonstrating a drop in the NDR voltage by approximately half compared to its TiO2 counterpart. Moreover, this work bolsters the claim that NDR is the result of a trap-based tunneling event through a defined defect band in the ALD deposited tunneling oxides. Though this thesis focuses solely on PTDs, the materials and processes demonstrated can be applied towards research interested in the conductivity properties of metal-oxides in addition to being useful for further work performed in the field of plastic electronics.

Committee:

Paul Berger (Advisor); George Valco (Committee Member)

Subjects:

Chemistry; Electrical Engineering; Engineering; Nanoscience; Nanotechnology; Organic Chemistry; Physical Chemistry; Physics; Plastics; Polymer Chemistry; Solid State Physics; Technology

Keywords:

polymer; organic; NDR; Negative Differential Resistance; Tunneling; IoT; Internet of Things; ALD; Atomic Layer Deposition; TiO2; Ta2O5; Memory; Logic; Low-power; flexible; printable; disposable; thin-film; oxygen vacancy; metal-oxide; defect; solid-state

Rismanchian, AzadehElectrochemical and Photocatalytic Oxidation of Hydrocarbons
Doctor of Philosophy, University of Akron, 2014, Polymer Science
This study demonstrates the development of a stable anode for electrochemical oxidation of hydrocarbons in solid oxide fuel cell (SOFC) and a highly active TiO2 based catalyst for photocatalytic reactions. The Ni/YSZ anode of SOFC was modified by Cu electroless plating. The catalytic activity toward H2 and CH4 oxidation were compared by the Faraday resistance (RF) obtained from the impedance spectroscopy. The RF ratio of Cu-Ni/YSZ in CH4 to H2 was greater than that of Ni/YSZ, indicating low catalytic activity of Cu-Ni/YSZ toward CH4 oxidation. The addition of Cu decreased the catalytic activity, but increased stability to 138 h in dry CH4. Characterization of the carbon type with Raman spectroscopy and temperature programmed oxidation showed that Cu formed disordered carbon rather than graphitic carbon which is the precursor to coking. Addition of CO2 to CH4 was studied as another approach to prevent coking. Electrochemical performance and mass spectrometry of the reactor effluent showed that the CH4-CO2 SOFC generated electricity from CO and H2, products of dry reforming reaction, with CO as the major contributor to current generation. CH4-CO2 decreased the activation polarization but showed a limiting current due to the fuel depletion at the interlayer-electrolyte interface. Anode interlayer was modified by reducing the particle size to 2 µm. The fine microstructure increased the three phase boundary length and reduced the activation polarization. The pore loss in the fine microstructure resulted in diffusion limitation and a limiting current in CH4 which was eliminated by adding 4 wt% of pore former at interlayer. Further addition of pore former lowered the performance by creating discontinuity at electrolyte-interlayer interface. The photocatalytic oxidation of ethanol on TiO2 and TiO2 modified with Ag and Au nanoparticles was studied by in-situ IR spectroscopy. Au and Ag increased the surface hydroxyl groups, which further served as active species to oxidize ethanol. Higher rate of electron transfer to Au than to Ag, evidenced by IR spectroscopy, resulted in higher rate of oxidation in Au-TiO2. This resulted in formation of formate (HCOO) on Au-TiO2 and acetate (CH3COO) on Ag-TiO2 as the major intermediate during the initial period of the photocatalytic oxidation.

Committee:

Steven Chuang, Dr (Advisor); Darrell Reneker, Dr (Committee Member); Yu Zhu, Dr (Committee Member); Xiong Gong, Dr (Committee Member); Homero Castaneda-Lopez, Dr (Committee Member)

Subjects:

Chemical Engineering; Energy

Keywords:

SOFC; Cu electroless plating; Raman spectroscopy; carbon type in CH4-SOFC; impedance spectroscopy;Faraday resistance; limiting current in CH4-CO2; interlayer microstructure; Photocatalytic oxidation on TiO2; in-situ IR spectroscopy; Au and Ag co-catalyst

Miller, DerekAdvancing electronic structure characterization of semiconducting oxide nano-heterostructures for gas sensing
Doctor of Philosophy, The Ohio State University, 2017, Materials Science and Engineering
The last decade has seen a rapid progression of newly-synthesized nano-heterostructures of many shapes, sizes, and compositions in an attempt to improve the properties and performance of gas sensors. Most studies published show improved or otherwise unique performance attributes when combining multiple compositions finely dispersed on the nano-scale. However, these novel structures are created faster than their electronic properties can be understood, leading many to a trial-and-error approach toward finding the right combinations of materials for a specific application. The performance of these materials is highly dependent on the defect states and charge carrier movement at the surfaces and interfaces. The fraction of studies that do attempt to explain the mechanisms behind the improvements often rely on literature values of important properties such as resistivity, band gap, defect state energies and Fermi level, which may or may not be accurate in their nanomaterials. In order to properly develop models to explain the charge carrier movement phenomena at the surfaces and interfaces, these structures must be understood and characterized in their most basic units. Unfortunately, the size and dispersion of these nanomaterials are beyond the spatial resolution limits of the best optical measurement techniques, leading to measurements averaged over several particles. Variations in synthesis and processing between samples and research groups adds additional uncertainty. Furthermore, measuring films of many particles necessitates interpreting results based on the expected average particle size, shape, or composition, rather than the variations actually present. In this work, single-nanowire devices were fabricated in order to assess the sensor properties without many of the confounding variables present in a film of randomly dispersed nanostructures. It was found that the current path through the nano-heterostructures can completely change the response type behavior in core-shell n-p materials. Impedance spectroscopy on single-nanowires helped to show that the resistance modulation of the junctions between nanowires are more sensitive to oxygen content than depletion of the internal or “bulk” region of the nanowires. Furthermore, high-resolution STEM techniques such as valence EELS and cathodoluminescence measured small spatial variations in the band gap and mid-gap defect states in SnO2 nanowires, ZnO nanowires, and TiO2 nanoparticles. In SnO2 and TiO2, emission peaks were designated to specific surface and bulk defects. Additionally, optical and dielectric properties were measured in individual nanostructures as well as spatially across nano-heterostructure interfaces. These direct measurements will help to build better mechanistic models than when relying on literature values from bulk versions of these materials. The photocatalytic ability of these materials to degrade a test dye in an aqueous environment was also investigated and showed the most promising results in ZnO nanowires. Furthermore, the creation of a new open-access database is described which will enable researchers in the field to rapidly analyze relationships between several test variables and performance attributes of resistive-type gas sensor materials utilizing individual data points pulled from published papers. The demonstration of these advanced characterization techniques should inform and encourage future research to deconstruct their mechanistic explanations to the most fundamental scale. Future studies should systematically test variations of these nano-heterostructures in carefully controlled ways to find the optimal morphology and composition for each test environment. These results should be paired with direct measurements of the electronic structure and properties of the primary and secondary materials in order to build a complete framework for explaining the mechanisms for improved performance. Insights gained from these studies will inform bottom-up design of new nano-heterostructures optimized toward specific sensing applications.

Committee:

Sheikh Akbar (Advisor); Patricia Morris (Advisor); David McComb (Committee Member)

Subjects:

Materials Science

Keywords:

nanowires; sensor; heterostructure; semiconductor; oxide; SnO2; TiO2; ZnO; VLS; nanomaterial; EELS; cathodoluminescence

CHEN, YONGJUNTHE ROLE OF PREPARATION CONDITIONS IN SOL-GEL METHODS ON THE SYTHESIS OF NANOSTRUCTURED PHOTOCATALYTIC FILMS FOR WATER TREATMENT
PhD, University of Cincinnati, 2007, Engineering : Environmental Engineering
Synthesis of high performance titania photocatalytic films with good structural integrity is an important aspect in the design of high-efficiency photocatalytic reactors for water purification. One aspect of this dissertation deals with employing new approaches based on template-assisted Degussa P25 TiO2 powder modified sol gel processes for the synthesis of tailor-designed porous TiO2-P25 composite films with good structural integrity for water purification. A relatively low Degussa P25 loading (i.e., 10 g/L in the sol) is employed, which can avoid crack formation in the films. High porosity induced by the combined effect of template such as polyethylene glycol (PEG 2000) or polyoxyethylene (20) sorbitan monolaurate (Tween 20) with Degussa P25 can be beneficial to the exposure of the maximum number of high active Degussa P25 nanocrystallites in the inner layers to the solid-liquid interface. Moreover, the formation of P25 associated larger pores (i.e., macropores or larger mesopores) is beneficial to fast mass transfer of the treated contaminants in the larger pore channels. As a result, the enhancement in photocatalytic activity induced by low loading P25 is high. For the TiO2-P25 composite films prepared by a PEG-assisted P25 modified sol gel method (i.e., PPMSGF-PEG), the optimum calcination temperature is 500&degC under which improved BET surface area/ porosity and a bimodal macro-mesoporous structure can be formed. For mesoporous TiO2-P25 composite films prepared by a Tween 20-assisted P25 powder modified sol gel method, the optimum Tween 20 loading is 50% (v/v) in the sol under which high BET surface area (74 m²/g) / porosity (50.6%), bimodal mesoporous structure and larger film thickness can be obtained. On the other hand, the pore structure of photocatalytic films prepared by a P25 powder modified sol gel method (i.e., PPMSGFs) and in the absence of templates can be improved and the amount of surface foreign metal ions (i.e., Cr³+) diffused from the stainless steel support during heat treatment can be decreased by increasing P25 loading from 0 to 50g/L in the sol or decreasing calcination temperature from 600 to 500-400&degC. However, crack formation cannot be avoided for the PPMSGFs with high P25 loading (i.e., 50 g/L in the sol) in this study. Another aspect of this dissertation is to address some challenging issues in the formation of unique structures of TiO2 films using various sol gel methods without Degussa P25 TiO2 nanoparticles addition. By decreasing calcination temperature from 600 to 500&degC, a crack free and thick TiO2 film with optimum film thickness (10 µm) as well as low porosity (~5%) and narrow pore size distribution (2-10 nm) was successfully prepared. Moreover, the macro-mesoporous texture of thick TiO2 films without crack formation was obtained by optimizing the PEG 2000 loading in the sol (i.e., 20 g/L PEG 2000). Tween 20 was found to be an effective template in a non-acidic sol gel system. Optimization of Tween 20 loading (i.e., Tween 20: final sol = 50%, (v/v)) in the sol) resulted in the formation of relatively ordered mesoporous structure of TiO2 films with anatase nanocrystallites of ultrafine size (~7 nm), high BET surface area (~120 m² /g) and high pore volume (~0.155 cm³/g). The advantages of the above unique structures of the as-prepared TiO2 films in the application of various water purification systems are emphasized.

Committee:

Dr. Dionysios Dionysiou (Advisor)

Subjects:

Engineering, Environmental

Keywords:

TiO2; photocatalysis; films; sol-gel; nanostructure; water treatment

Lee, HuyongTitanium Oxide Nanowire Growth by Oxidation Under a Limited Supply of Oxygen: Processing and Characterization
Doctor of Philosophy, The Ohio State University, 2009, Materials Science and Engineering

Instead of using expensive and complex methods to produce 1D structures, a simple direct oxidation method has been developed to produce either pure TiO2 nanowire or heterogeneous nanowires under a limited supply of oxygen. The dimension of the nanofibers ranged from 30 to 60 nm in diameter and their length were between 500 nm to several μm depending on Ti alloy samples. Experimental parameters such as flow rate, heat treatment temperature, and gas constituent have effects on the surface morphology of the samples. Based on studies under various conditions, pure TiO2 nanowires were only grown on pure Ti samples at the heat treatment temperature of 600 °C with an Ar flow rate of 200 ml/min. As the heat treatment temperature increased, well faceted crystals were formed and connected to each other to form a continuous oxide scale. As the flow rate increased, the formation of nanowires were hindered and an oxide layer was formed rather than the formation of nanowires. The phase of nanowires was determined to be rutile based on SAED pattern from TEM analyses.

For Ti alloy samples, the growth of nanowires was accelerated in terms of the density and length. The effects of the heat treatment temperature on the surface morphology were similar to those of pure Ti samples. However, the effect of the flow rate was not prominent as those of pure Ti samples. Consequently, the growth processing window for Ti alloys is larger than that of pure Ti samples with respect to the flow rate. The phase characterization of nanowires by XRD and TEM analyses indicated that the inner rutile core was covered by an Al rich outer layer.

While the growth mechanism for nanowire formation is not well understood, it is established that the growth occurs at the tip and that the rate limiting step is the transport of oxygen through the gas boundary layer. Additionally, 1D growth implies surface reaction anisotropy that disappears at high temperature promoting oxide cale growth. the Based on experimental observations, a four-stage mechanism is proposed as a function of time. In stage I, a cracked oxide scale grows followed by the formation of bumps in stage II that act as nucleation sites for nanowires. In stage III, nanowires continue to grow along with nucleation and growth of new nanowires leading to the increase in density. In stage IV, the density of nanowires is so large that the accessibility of oxygen to the base becomes difficult and nanowires continue to grow at the tip.

Committee:

Sheikh Akbar, Dr (Advisor); Suliman Dregia, Dr (Advisor); Patricia Morris, Dr (Committee Member); Nittin Padture, Dr (Committee Member)

Subjects:

Materials Science

Keywords:

Nanowire; oxidation; TiO2

Shahreen, LailaPalladium Doped Titanium Dioxide Nanofiber Based Catalytic Support To Reduce Nitric Oxide Over Carbon Monoxide Gas
Doctor of Philosophy, University of Akron, 2013, Chemical Engineering
NOx and CO are two most hazardous gases among the exhaust gases stream from automotive vehicles, power plants, coal and mine industries, reactors, smelters etc.These gases cause severe damage to vegetation, plant and aquatic life by photochemical reaction resulting smog and acid rain. Particulate matter less than 2.5&#xb5;m is another substance to be removed from these sources. Serious health hazards are also likely to happen such as cardiovascular and respiratory problem even at the lower concentration of these noxious gases. Conventional method of eradicating NOx and CO is catalytic converter with ceramic substrate which is wash-coated by noble metal. Platinum, Palladium and Rhodium are three common active catalyst impregnated in Al2O3 based substrate although being expensive. According to US EPA total NOx emission in the world per year is 165 million tons of which 70-80% comes from automotive vehicles. To meet the requirement of EPA and preventing air pollution, highly cost effective and reliable functional material is in need. Ceramic nanofiber is a unique substitute as it is thermally stable, light weight and has high aspect ratio of diameter to volume compared to traditional one. In this work, Pd incorporated TiO2 ceramic nanofiber has been fabricated through electrospinning process followed by calcination at 600&#xba;C. Catalytic nanofiber was characterized using SEM, TEM, BET, XRD, XEDS to analyze fiber diameter, morphology, specific surface area, crystallization phases of TiO2 and PdO, atomic percentage of elements in fiber respectively. 0.5%, 1.7% and 2.7% Pd on TiO2 surface were loaded during electrospinning process. Proper optimization of electrospinning process parameters was done and elimination of beads on fiber was ensured observing the solution properties such as viscosity, surface tension and electrical conductivity with change of polymeric concentration. Among 8%, 10%, 12% and 13% PVP (W/W), 12% PVP offered beadless catalytic fiber for three different catalyst loading. Average fiber diameter is 180-280nm. Catalytic nanofiber was incorporated into a micro fibrous media and placed inside a reactor to see the NO ad CO conversion at different temperature from 25&#xba;C, 100&#xba;C, 200&#xba;C, 250&#xba;C, 300&#xba;C, 350&#xba;C, 400&#xba;C and 450&#xba;C. 2.7% Pd loaded catalytic filter showed complete conversion of gases at 300&#xba;C. As the amount of catalyst loading increased, the decomposition temperature decreased. Filter media was also tested in a TSI automated filter tester to see NaCl aerosol particle loading efficiency and then retested in the reactor to observe its effect on reactivity. A moderate change in decomposition temperature was observed after loading. TiO2 and PdO/TiO2 nanofiber was calcined at different temperature such as 200&#xba;C, 300&#xba;C, 400&#xba;C, 500&#xba;C and 600&#xba;C to find out anatase phase content and filter media was prepared out of these samples. To test the photocatalytic activity of TiO2 nanofiber based filter media UV light was irradiated on the filter surface but no significant reaction was seen.

Committee:

George Chase, Dr. (Advisor); Edward A. Evans, Dr. (Committee Member); Steven S. Chuang, Dr. (Committee Member); Shing-Chung Josh Wong, Dr. (Committee Member); Rex D. Ramsier, Dr. (Committee Member)

Subjects:

Chemical Engineering

Keywords:

Electrospinning, TiO2 nanofiber, NOx, catalysis, particulate filtration, anatase, rutile, pohotocatalyis

Miller, Duane DIn Situ Infrared Spectroscopy Study of Gold Oxidation Catalysis
Master of Science, University of Akron, 2006, Chemical Engineering

Infrared spectroscopy has been extensively applied in catalysis and the structural determination of adsorbed molecules. Its application to surface chemistry has provided one of the most direct means of observing the interactions that occur at the surface during chemisorption as well as helping in elucidation of reaction mechanisms. Among infrared spectroscopy extensive use, the catalytic oxidation of CO with O2 has been investigated most extensively and intensively in heterogeneous catalysis because of the simplicity of the CO/O2 oxidation reaction resulting in CO2 being a gaseous product. CO is a hazardous gas which is a concern in environmental protection. Pollutants in automobile exhaust gases, indoor air quality control, and the selective removal of trace CO concentrations in hydrogen fuel demonstrates the importance of the CO oxidation reaction finding many applications today. CO oxidation at low temperatures from room temperature to 160 °C has become a subject of study of great importance.

Gold catalysts prepared by coprecipitation, deposition-precipitation, and homogeneous deposition-precipitation (HDP) have been prepared for CO oxidation at room temperature. Gold catalyst activity is very sensitive to preparation method; ideal preparation methods should provide a well dispersed particle diameters below 5 nm. The result of this study demonstrates HDP method was the best preparation method for high catalytic activity in the CO oxidation reaction.

Understanding the reaction mechanism and kinetics under transient conditions can lead to approach for preparation of highly active catalyst. This study used a transient pulse technique which introduced the reactants into inert gas to determine the reactivity of adsorbed oxygen in CO and CH3CH2OH oxidation reaction. Use of this technique and infrared spectroscopy of CO and CH3CH2OH found H2O2 promotes total oxidation. The result of this study demonstrated hydrogen peroxide promotes both CO and CH3CH2OH oxidation.

One hypothesis investigated reduced gold, Au0-1 is the active intermediate for CO oxidation. In situ infrared spectroscopy technique demonstrated nitric oxide coordinates the Au sites preventing room temperature CO oxidation. At higher temperatures, nitrite and nitrate species desorbed providing more Au0 sites for CO oxidation showing Au0 is the active site for CO oxidation reaction. The result of this study demonstrates AuM+1 and Au+3 were not active for CO oxidation and Au0 is active for CO oxidation.

One of the biggest problems with gold catalysts is the sintering of the small Au particles into larger particles. Bulk gold melting temperature is 1336 K but as the gold particles gets smaller the melting temperature lowers to 537 K. Au particle mobility is a major problem thus future study should be directed towards locking in the particle size while reducing particle mobility to prevent sintering while maintaining high catalytic activity.

Committee:

Steven Chuang (Advisor)

Subjects:

Engineering, Chemical

Keywords:

gold titania; Au/TiO2; gold catalysis; CO oxidation

Andersen, Joel MSolar- and visible light-activated titania for removal of pesticides and emerging contaminants: Synergies, intermediates, and reusability
MS, University of Cincinnati, 2013, Engineering and Applied Science: Environmental Engineering
The importance of sustainable environmental remediation techniques continues to grow each year. To this end, many researchers have emphasized titania (TiO2)-based photocatalysis since its discovery in the 1970s. Conventionally, titania requires ultraviolet light for activation. However, doping with non-metals such as nitrogen and fluorine allowed the activation of the photocatalyst by visible light. As such, a more significant portion of the solar spectrum became available. With this in mind, it is pertinent to explore numerous factors of NF-TiO2. These factors are explored in two sections. Section I: In order to investigate sustainable alternatives to current water treatment methods, the effect of NF-titania film thickness and subsequent photocatalysis in combination with oxidants was examined under simulated solar light. Such a combination presents a theoretical possibility for a synergistic interaction between the photocatalyst and the oxidant (activation of an oxidant by the catalyst under conditions under which it may not conventionally be activated). To investigate, peroxymonosulfate (PMS) and persulfate (PS) were used as oxidants, and two pesticides, amitrole and atrazine, were used as target contaminants. In the absence of a film, activation of PMS under simulated solar conditions is demonstrated by removal of atrazine, whereas PS provided minimal removal, suggesting inefficient activation. Combining photocatalytic films with PMS and PS manifested synergies for both oxidants. The effect was most pronounced for PS since PMS already underwent significant activation without the photocatalyst. Amitrole degradation results indicated a lack of removal of amitrole by activated persulfate alone, suggesting that this sulfate radical-based treatment technology may be ineffective for the removal of amitrole. The NF-TiO2 films demonstrated reusability under solar light both with and without oxidants. Finally, the degradation intermediates are described, and a new intermediate appeared upon incorporating oxidants into the system. Section II: Titanium dioxide-based photocatalysis using visible light has previously been explored by numerous research groups in an effort to increase the utilization of solar light for the destruction of environmental contaminants in water. Conventionally, UV light is required for TiO2 photocatalysis, but through the use of dopants, such as nitrogen and fluorine, activation of TiO2 by visible light has been observed. However, doping may also change the catalyst’s degradation mechanisms (e.g., oxidative mechanisms, such as electron holes and reactive oxygen species or reductive mechanisms, such as reduction by mobile electrons in the conduction band). As a result, the intermediate degradation products may be altered. The present work explores this possiblity. To investigate this possibility, microcystin-LR, which is a cyanotoxin of emerging concern, was chosen as the target contaminant. The results of LC/MS2 (and in one case LC/MS3) indicated that the intermediates are not drastically altered compared to traditional TiO2 photocatalysis using UV light. Most importantly, visible light-induced photocatalysis using NF-TiO2 degrades the portion of MC-LR that is responsible for biological toxicity. As a result of this, it was concluded that doping TiO2 with nitrogen and fluorine is an effective method for increasing utilization of visible light while degrading MC-LR in water.

Committee:

Dionysios Dionysiou, Ph.D. (Committee Chair); Mallikarjuna Nadagouda, Ph.D. (Committee Member); Pablo Campo-Moreno, Ph.D. (Committee Member)

Subjects:

Environmental Engineering

Keywords:

nf-tio2;photocatalysis;microcystin-lr;visible light

Yung, Matthew MauriceOxidation catalysis in environmental applications: nitric oxide and carbon monoxide oxidation for the reduction of combustion emissions and purification of hydrogen streams
Doctor of Philosophy, The Ohio State University, 2007, Chemical Engineering
The environmental applications of oxidation catalysis were examined as part of a two-stage strategy for the reduction of nitrogen oxides (NOx) and also for the removal of carbon monoxide from hydrogen streams. Cobalt-based catalysts were examined. Reduction of NOx, Co/TiO2 and Co/ZrO2 were studied for the oxidation of NO to NO2 in excess oxygen. NO oxidation was studied as the first step in a two-step catalytic scheme where NO is oxidized to NO2 and, in turn, NO2 is reduced with CH4 to N2 under lean conditions. Catalysts were prepared by sol-gel and incipient-wetness impregnation techniques. It was found that increasing the calcination temperature had an adverse effect on the activity of the IWI catalysts. Catalyst characterization showed higher activity for NO oxidation on Co/ZrO2 than on Co/TiO2 which was observed to correlate with the formation of the Co3O4 phase. For the preferential oxidation of CO, cobalt on several metal oxide supports were investigated and showed the highest activity on Co/ZrO2. A variety of reaction experiments were performed to examine the effects of reactant concentrations, residence time, and temperature on the CO conversion and O2 selectivity to CO2.

Committee:

Umit Ozkan (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Catalyst; NO oxidation; CO oxidation; NOx reduction; Cobalt; Cobalt oxide; ZrO2; TiO2; PROX

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