Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 196-214).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvii, 161 p.; also includes graphics (some col.) Includes bibliographical references (p. 144-161). Available online via OhioLINK's ETD Center

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed April 27, 2010). Thesis advisor: Dr. Kent S. Gates. Vita. Includes bibliographical references.

Darmstadt, Techn. Univ., Diss., 2001. / Dateiformat: tar.gz, Dateien im PDF-Format

University, Diss., 2000--Heidelberg.

Universiẗat, Diss., 2002--Heidelberg.

É urgente o desenvolvimento de novas tecnologias para o tratamento de água nos dias atuais. Neste contexto, os processos oxidativos avançados (POA) tem sido bem-sucedido no tratamento de contaminantes presentes em efluentes industriais e na rede de esgoto doméstico. Neste trabalho, estudamos um dos POA, a fotocatáliseheterogênea por meio da síntese de fotocatalisadores mistos de nióbio e titânio utilizando-se o método Pechini, com uma temperatura de calcinação de 470 oC. Foram sintetizados os fotocatalisadores PNB000, PNB018, PNB030, PNB070, PNB099 e PNB100, onde os números mostram aporcentagem em mols de pentóxido de nióbio presente em cada um deles. Estes fotocatalisadores foram submetidos a um segundo tratamento térmico a 800oC, durante 6 horas, e obtivemoso PNB000_01, PNB018_01, PNB030_01, PNB070_01 e PNB100_01. A caracterização dos fotocatalisadores foi feita por: análise de espectroscopia de energia dispersiva (EDS); área superficial determinadas por isotermas de adsorção e dessorção de nitrogênio, BET; imagens de microscopiaeletrônica de varredura (MEV); difração de raios-X; análises térmicas (termogravimetria e análise térmica diferencial), determinação de band gap por reflectância difusa. O potencial para serem usados como fotocatalisadores heterogêneos para degradação de compostos orgânicos foi avaliado pela eficiência fotônica de geração de radicais hidroxilas(OH)sob radiação de lâmpada UVA (15 W). A análise de EDS confirmou acomposiçãoem mol de TiO2 e Nb2O5presentes nosfotocatalisadoressintetizados. A área superficial obtida por isotermas (BET) do PNB018 (161,7 m²/g), PNB030 (130,8 m²/g), PNB070 (150,5 m²/g) mostraram-se maiores do que ado TiO2 P25 (52,68 m²/g). As imagens de MEV mostrou que estes fotocatalisadoressão constituídos de partículas manométricas. Outra característica dos óxidos com quantidade intermediária de mols de Nb2O5 (18, 30 e 70%) foi a estrutura amorfa determinada por difração de raios-X. Por sua vez, os óxidos tratados a 800oC apresentaram estruturas cristalinas edifratogramas de raios-X completamente diferentes do TiO2 e do Nb2O5, comprovando-se que são novos materiais.As medidas de energia de band gapmostrou diferenças significativas quando comparamos o TiO2 P25 (Egap 3,22eV) e o PNB000 (Egap 2,90eV). Isso leva a concluir que estes fotocatalisadores sintetizados pelo método Pechini necessitam de uma energia menor para que ocorram as transições eletrônicas. O fotocatalisador PNB070, que apresenta 70% em mols de pentóxido de nióbio, apresentouOH de 0,104 da mesma ordem de grandeza do TiO2 P25 (OH 0,134) e ligeiramente menor do que o OH do Nb2O5.nH2O (OH 0,164). Dessa maneira, supõe-se que o PNB070 tenha o mesmo potencial de eficiência que o TiO2 P25 para fotodegradações. Por sua vez, os fotocatalisadores que passaram por um segundo tratamento térmico a 800 oC mostraram valores de rendimento quântico de produção de radicais hidroxilas bem inferiores aos seus originais. Por exemplo, o PNB070_01 teve OH de 0,003. Esses resultados sugerem que o aumento da cristalinidade pode diminuir a atividade fotocatalítica, ou, que o estado amorfo dos fotocatalisadores deste trabalho favorece o aumento da velocidade de transferência de elétrons e a da fotocatálise. / Nowadays, the development of new technologies for the treatment of water is urgent. In this context, the advanced oxidative processes (AOP) has been successful in the treatment of contaminants foundin industrial effluents and domestic sewage. In this work, we have studied an AOP, the heterogenousphotocatalysis, by means the synthesis of niobium and titanium mixedphotocatalysts, employing calcination temperature of 470 oC.The PNB000, PNB018, PNB030, PNB070, PNB099 and PNB100photocatalysts were synthetized, where the numbers show the percentage in mol of Nb2O5content in each of them. These photocatalytswere submitted to a second heat treatment to 800oC during 6 hours, and PNB000_01, PNB018_01, PNB030_01, PNB070_01 and PNB100_01 were obtained. The characterization of the photocatalysts was made by: analysis of the energy dispersive spectroscopy (EDS); the surface area determined by adsorption and desorption isotherms of nitrogen, BET; images of scanning electron microscopy (SEM); X-ray diffraction; thermal analysis (thermogravimetry and differential thermal analysis), determination of the band gap by diffuse reflectance.Their potential to be used as heterogeneous photocatalystsfor degradation of organic compounds was evaluated by means the determination of the photonic efficiency for hydroxyl radical production (OH)under radiation of UV-A lamp (15 W). The EDS analysis confirmed the composition in mol of TiO2 and Nb2O5 present in the synthesizedphotocatalysts. Surface area obtained by isotherms (BET) of PNB018 (161.7 m ²/g), PNB030 (130.8 m ²/g), PNB070 (150.5 m ²/g) were higher than TiO2 P25 (52.68 m ²/g). SEM images showed that these photocatalysts consist of nanoparticles. Another feature of the oxides with intermediate amount of moles of Nb2O5 (18, 30 and 70%) was the amorphous structure determined by X-ray diffraction. On the other hand, the oxides treated to 800 oC showed crystalline structures and X-ray patternscompletely different from TiO2 and Nb2O5, proving that the synthetized oxides are new materials.The band gap energy measurements showed significant differences when we compare TiO2 P25 (Egap 3.22 eV) and the PNB000 (Egap 2.90 eV). This allow us to conclude that thephotocatalysts synthesized by Pechini method require lower energy in order to have electronic transitions. The PNB070 photocatalyst, which has 70% in mols of niobium pentoxide, showed OHof 0.104 of the same order of magnitude of TiO2 P25 (OH0.134) and slightly smaller than the OH of Nb2O5.nH2O (OH 0.164). For this reason, we can assume that PNB070 has the same potential of the TiO2 P25 for organic compound photodegradation. The photocatalyststhat were submittedthrough a second heat treatment at 800 oC showed quantum efficiency of hydroxyl radical production values well below their original. For instance, PNB070_01 showed OHof 0.003. These results suggest that increased crystallinity can reduce the photocatalytic activity, or the amorphous structures of the photocatalysts of this work improve the electron transfer rates and the photocatalysis.

Atmospheric aerosols play an important role in climate by scattering and absorbing radiation and by serving as cloud condensation nuclei. An aerosol’s optical or nucleation properties are driven by its chemical composition. Chemical aging of aerosols by atmospheric oxidants, such as ozone, alters the physiochemical properties of aerosol to become more hygroscopic, light absorbing, and viscous during transport. However the mechanism of these transformations is poorly understood. While ozone is a protective and beneficial atmospheric gas in the stratosphere, it is a potent greenhouse gas in the troposphere that traps heat near the Earth’s surface. It also impacts human heath by irritating the respiratory tract and exacerbating cardiovascular diseases. Additionally, ozone can alter the ecosystem through oxidizing plant foliage which can lead to deforestation and crop losses as well. Both gases and aerosols in the troposphere can react with ozone directly and indirectly with hydroxyl radicals. While daytime aging is thought to be primarily driven by photochemical processes and hydroxyl radicals, ozone is thought to be a key player in nighttime or dark aging processes that can alter the physicochemical properties of aerosols. Measured concentrations of trace gases and aged aerosol components in the field are higher than values predicted based on laboratory studies and computer simulations. Consequently, new experimental approaches are needed to narrow the gaps between observations and mechanistic understandings. In this dissertation, a plume of microdroplets was generated by pneumatically assisted aerosolization and then exposed to a flow of ozone before entering a mass spectrometer. This surface-specific technique allowed for the real-time analysis of reaction products and intermediates at the air-water interface. This work explores the in situ oxidation of iodide, a component of sea spray aerosols, by 0.05 – 13.00 ppmv ozone to explore how heterogeneous oxidation could enhance the production of reactive iodide species. Methods to study the reaction channels and intermediates were also established to not only determine a mechanism of iodide oxidation by ozone, but to enable the study of more complex systems. The developed approach was then applied to examine the oxidation of catechol and its substituted cousins, a family of compounds selected to model biomass burning and combustion emissions, at the air-water interface. While literature suggested that the primary mechanism of catechol oxidation by ozone would be the cleavage of the C1-C2 bond, it was determined that this was only a minor pathway. An indirect oxidation channel dominated heterogeneous processes at the air-water interface, giving rise to hydroxyl and semiquinone radicals that recombine to produce polyhydroxylated aromatics and quinones. This new mechanism of aging represents an overlooked channel by which brown, light-absorbing carbon aerosols are produced in the atmosphere. In addition, the work investigates how reactions on solid particulate aerosols proceed under variable relative humidity. Thin films were developed alongside a novel flow-through reactor to study of how aerosols are transformed by ozone and hydroxyl radicals when exposed to 50 ppbv - 800 ppmv of ozone. This system was employed to probe how catechol reacts with ozone under variable relative humidity. Further work was undertaken to model the adsorption process at the air-solid interface under variable humidity, permitting the estimation of the reactive uptake of ozone by the film at concentrations (50-200 ppbv) seen in rural and urban areas. Together, these results provide an increased understanding of how heterogeneous oxidation of aerosols contributes to aerosol aging processes as well as free radical production in the troposphere.

No description available.

The photosensitized processes significantly enhance photolysis of various chemicals in the aqueous system with dissolved organic matter (DOM) as sensitizer. The excitation of chromophores on the DOM molecule further generates reactive species as triplet states DOM, singlet oxygen, hydroxyl radical, carbonate radical etc. We investigated the photosensitization properties of Beaufort Fulvic Acid, Suwannee River Fulvic Acid, South Platte River Fulvic Acid, and Jeddah wastewater treatment plant effluent organic matter with a sunlight simulator. DOM photochemical properties were characterized by observing their performances in 3DOM*, singlet oxygen, hydroxyl radical production with indirect probing protocols. Sensitized degradation of 0.1 μM and 0.02 μM 2, 4, 6- Trimethylphenol exhibited higher pseudo-first-order rate constant than that of 10 μM. Pre-irradiated DOMs were found to be depressed in photochemical properties. Photolysis of 5 different contaminants: ibuprofen, bisphenol A, acetaminophen, cimetidine, and caffeine were found to be enhanced in the presence of sensitizers. The possible reaction pathways were revealed. Long time irradiance induced change in contaminants degradation kinetics in some DOM solutions, which was proposed to be due to the irradiation initiated indirect transformation of DOMs. Key Words: Photolysis Dissolved Organic Matter, Triplet State DOM, Singlet Oxygen, Hydroxyl Radical, Contaminants Degradation.