Browsing by Subject "Titanium dioxide"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Design of a Real-Time Scanning Electrical Mobility Spectrometer and its Application in Study of Nanoparticle Aerosol Generation(2012-07-16) Singh, GaganA real-time, mobile Scanning Electrical Mobility Spectrometer (SEMS) was designed using a Condensation Particle Counter (CPC) and Differential Mobility Analyzer (DMA) to measure the size distribution of nanoparticles. The SEMS was calibrated using monodisperse Polystyrene Latex (PSL) particles, and was then applied to study the size distribution of TiO2 nanoparticle aerosols generated by spray drying water suspensions of the nanoparticles. The nanoparticle aerosol size distribution, the effect of surfactant, and the effect of residual solvent droplets were determined. The SEMS system was designed by integrating the Electrical System, the Fluid Flow System, and the SEMS Software. It was calibrated using aerosolized Polystyrene Latex (PSL) spheres with nominal diameters of 99 nm and 204 nm. TiO2 nanoparticle aerosols were generated by atomizing water suspensions of TiO2 nanoparticles using a Collison nebulizer. Size distribution of the TiO2 aerosol was measured by the SEMS, as well as by TEM. Furthermore, the effect of surfactant, Tween 20 at four different concentrations between 0.01mM and 0.80mM, and stability of aerosol concentration with time were studied. It was hypothesized that residual particles in DI water observed during the calibration process were a mixture of impurities in water and unevaporated droplets. Solid impurities were captured on TEM grids using a point-to-plane Electrostatic Precipitator (ESP) and analyzed by Energy Dispersive Spectroscopy (EDS) while the contribution of unevaporated liquid droplets to residual particles was confirmed by size distribution measurements of aerosolized DI water in different humidity conditions. The calibration indicated that the mode diameter was found to be at 92.5nm by TEM and 95.8nm by the SEMS for 99nm nominal diameter particles, a difference of 3.6%. Similarly, the mode diameter for 204nm nominal diameter particles was found to be 194.9nm by TEM and 191nm by SEMS, a difference of 2.0%. Measurements by SEMS for TiO2 aerosol generated by Collison nebulizer indicated the mode diameters of 3mM, 6mM, and 9mM concentrations of TiO2 suspension to be 197.5nm, 200.0nm and 195.2nm respectively. On the other hand, the mode diameter was found to be approximately 95nm from TEM analysis of TiO2 powder. Additionally, concentration of particles generated decreased with time. Dynamic Light Scattering (DLS) measurements indicated agglomeration of particles in the suspension. Furthermore, the emulation of single particle distribution was not possible even after using Tween 20 in concentrations between 0.01mM and 0.80mM. From the study of residual particles in DI water, it was found that residual particles observed during the aerosolization of suspensions of DI water were composed of impurities present in DI water and unevaporated droplets of DI water. Although it was possible to observe solid residual particles on the TEM grid, EDS was not able to determine the chemical composition of these particles.Item Effects of photocatalysis on concrete surfaces(2012-05) Terpeluk, Alexandra Lee; Juenger, Maria C. G.; Fowler, David W.Highway air pollution is a significant environmental threat that has staggering implications for human health worldwide. Photocatalytic materials have the potential to reduce air pollution levels near major highways using ultraviolet radiation. This project, funded by the Texas Department of Transportation, evaluated photocatalytic efficiency and durability of several commercially-available photocatalytic coatings for use on concrete structures near highways. The research presented in this thesis involved obtaining concrete highway barriers and creating concrete slabs for outdoor testing and laboratory chamber testing. Three commercially-available coatings were applied to the specimens for testing: Keim Soldalit ME paint, TxActive Stucco Cement, and Pureti Clean. Field sites were set up near major highways in Houston and Austin, Texas. Durability and photocatalytic efficiency were regularly monitored at the field sites using ion chromatography and spectrophotometry. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted on samples from each of the specimens taken before and after placement at the field sites in order to understand durability of the photocatalytic materials that were exposed outdoors. SEM results from this research project revealed that the photocatalytic material in the TxActive stucco and Keim paint remained in their original distribution after the exposure period, while the photocatalytic material in the Pureti Clean product appeared to decrease. XRD results remained fundamentally consistent for all coatings. Ion chromatography results showed that TxActive specimens had the highest surface levels of nitrates and nitrites between rainfall events, which indicates photocatalytic activity. Spectrophotometry results revealed a decrease in brightness for the Keim paint-coated specimens and no change or an increase in brightness for the TxActive stucco over time. The spectrophotometry results indicate how many surface contaminants are accumulating on the surface of a specimen, and thereby how efficiently sunlight is reaching the surface and activating the photocatalytic process. Results obtained from this research project may be influential in the selection of a means for reducing highway pollution in Texas.Item Thermodynamic analysis and sustainability improvement of nanoparticles synthesis processes with application to titanium dioxide(2012-05) Li, Bingbing; Zhang, Hong-Chao; Fan, Zhaoyang; Rivero, Iris V.; Tate, Derrick; Wang, ShirenIncreasing world population, dwindling resources, and the degradation of natural ecosystems make thermodynamics and sustainability improvement of manufacturing processes a prominent goal for the engineering community for the foreseeable future. Although nanomanufacturing is expected to generate major economic impacts estimated in the billions of dollars, little is known about the energy consumption, potential environmental health and safety risks associated with public exposure of nanoparticles synthesis processes. The overarching objective of this research is to present a complete thermodynamic (including energy consumption and exergy losses) analysis and sustainability improvement for the nanoparticles synthesis processes. Firstly, the introductions of sustainable manufacturing, industrial ecology, energy consumption and nanotechnology are introduced briefly in Chapter 1. Then problem statement, research objective and contribution are clearly stated. Secondly, the literature review on data collection (top-down and bottom-up), thermodynamic model, mechanical model, finite element analysis and manufacturing processes are summarized in Chapter 2. Thirdly, the energy consumption and exergy losses general model for nanoparticles synthesis processes (divided into two main processes: precursor transport and chemical reaction) based on thermodynamics and kinetics is created in Chapter 3, which includes all the assumptions, boundaries, conditions and equations of model. Both first law and second law of thermodynamics were used for energy consumption and exergy losses of nanoparticles synthesis processes which are considered as steady state, steady flow open system. A simplified exergy model was also created for nanoparticles synthesis process. A two dimensional kinetic differential equations describing the conservation of mass, momentum and energy with appropriate boundary conditions was modeled for precursor transport process (convection and diffusion). The NPs chemical reaction process was modeled by thermodynamic model. Fourthly, the created model was applied to titanium dioxide nanoparticles (TiO2 NPs) synthesis processes. Background, crystal structure and route of TiO2 NPs are introduced in first section. Then the experimental setup, calculation and analysis for electrochemical annodization process (including five main processes: formation of oxide layer, chemical diffusion, physical diffusion, infiltration and crystallization) of TiO2 NPs are placed in detail. Based on results from experimental data and discussions, the energy consumption and exergy losses for the specific electrochemical annodization process are clearly demonstrated and the identification of sustainability improvement potential is also given. The thermodynamic model about size dependence of nanoparticles on electrical voltage is also discussed and validated by both experimental data and literature data. Fifthly, conclusion is given that the created model is validated by the electrochemical annodization process of TiO2 NPs and can also be applied to other nanoparticles synthesis processes, which is really essential and fundamental for sustainability development and life cycle assessment of manufacturing process. Future work is indicated in the end.Item Titanium dioxide photocatalytic inactivation of bacteria on remote surfaces and air in a closed system reactor(2009-05) Bayliss, Desiree M.; Zak, John; Francisco, Michael J. D. S.; Jeter, Randall M.Today it is estimated people spend 90% of their time indoors, increasing their exposure to potentially dangerous indoor pollutants. Titanium dioxide photocatalytic technology represents a new method for controlling these pollutants and has been proven to inactivate bacteria within close range. However, there is no evidence of such activity occurring distant to the photocatalytic reactor. Understanding the effects of photocatalytic oxidation at remote distances from the reactor can improve the application of such technology to improving indoor air quality measures. Two bacterial species, Gram negative Escherichia coli and Gram positive Staphylococcus aureus, were chosen to evaluate the impact of photocatalytic oxidation on different cell structures at remote distances. The extent of inactivation was evaluated using traditional colony count techniques and chemical based assays. The thiobarbituric acid assay has recently been applied as a method of quantifying the effects of titanium dioxide photocatalysis. This approach is used to measure the extent of lipid peroxidation in the exposed bacterial cells. Treatment of bacterial cells with photocatalysis results in an increase in lipid peroxidation and degradation of the cell membrane. Photocatalytic oxidation is dependent on the production of reactive oxygen species such as superoxide radicals, hydroxyl radicals and hydrogen peroxide. Superoxide radicals are known to form in gas phase photocatalysis and are hypothesized to cause any inactivation effects observed in this investigation’s reactor configuration. The presence of superoxide can be assayed for using a superoxide dismutase assay. In this study, the thiobarbituric acid assay and superoxide dismutase assay were applied to investigate the effects and extent of photocatalytic oxidation on bacteria placed distant to a photocatalytic reactor. Inactivation of bacterial cells occurred in remote aqueous solutions for Gram negative species and on remote surfaces for Gram positive species. The effects of photocatalytic oxidation were exhibited for both species on remote surfaces. The differences in inactivation was attributed to varying reactivities of reactive oxygen species, production of additional reactive oxygen species in each of the treatment configurations and to the different cell structures of each species. Superoxide anion was shown to be present at remote surfaces, but most likely did not solely produce the inactivation effect.