Thesis (Ph. D.)--Columbia University, 1940. / Vita. Bibliography: p. [19].

Thesis--Wisconsin. / Includes bibliographical references (leaves 93-95).

Thesis (M.S.)--University of Wisconsin--Madison, 1980. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 79-84).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis--Göteborg. / Includes reprints of author's articles.

Inaug.-Diss. - Breslau. / Vita.

The International Agency for Research on Cancer (IARC) stated that chromium in the form of Cr(VI) has been deemed to be a class-A human carcinogen. It has been a major contaminant associated with wastewater. Moreover, the existence of heavy metals in aquatic systems is a critical concern for the environment as well as industries that manufacture or consume these particular elements. In order to remove these particular toxic metals, several well-known conventional methods including ion-exchange, filtration and adsorption are used. Amongst these methods, adsorption offers significant advantages such as the low-cost materials, ease of operation and efficiency in comparison to the other conventional methods. The aim of this work was to develop nanomaterials (particles and fibers) to address some critical issues for the treatment of heavy metals, especially chromium in aqueous systems. Furthermore, the use of nanomaterials and how they relate to nanoscale operations at the biological level has generated considerable concerns in spite of their novel properties. The first part of this thesis deals with the synthesis and characterizations of Fe3O4, magnetite, as nanoparticles which were further coated with surfactants bis(2,4,4-trimethylpentyl)dithiophosphinic acid, Cyanex-301, and 3-Mercaptopropionic acid with the active compound being the thiol (SH) groups, that will suffice as a viable material for Cr(VI) removal from aqueous solutions. The proposed mechanism was the complexation between the thiol group on Cyanex-301 and 3-Mercaptopropionic acid, respectively. The effect of different parameters on the adsorption including contact time, initial and final Cr(VI) ion concentration and solution pH was investigated. The second part of this thesis encompassed the fabrication of flexible nanocomposite materials, with a large surface area and architecture for the removal of Cr(VI) in batch and continuous flow mode. A technique known as electrospinning was used to produce the nanofibers. The flexible yet functional materials architecture has been achieved by growing ZnO nanorod arrays through chemical bath deposition on synthesized electrospun poly-L-lactide nanofibers. Moreover, polyacrylonitrile nanofibers (PAN) were synthesized and adapted by the addition of hydroxylamine hydrochloride to produce amidoxime polyacrylonitrile nanofibers (A-PAN). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify the morphologies and particle sizes whereas Fourier-Transform Infrared spectroscopy (FT-IR) was used to identify either the presence or absence of functional groups for the formation of PAN and A-PAN nanofibers. The optimization of functionalized nanoadsorbents to adsorb Cr(VI) was also carried out to investigate the effect of experimental parameters: contact time, solution pH, initial, final and other metal ion concentration. Commercially manufactured pristine engineered (TiO2, ZnO and SiO2) nanoparticles and lab-made functionalized (Fe3O4 and CeO2) nanoparticles were studied while the powders were suspended in appropriate media by Dynamic Light Scattering (DLS) to identify their cytotoxicity effects. / <p>QC 20160111</p>

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A critical evaluation of the published data for chromium levels in serum and urine shows major discrepancies, indicating that further work to establish normal values for these parameters is necessary. Methods have been developed for the determination of total protein-bound, and alpha-2-globulin-bound, chromium in serum, and chromium in urine. The sample pretreatment for serum is based on concurrent protein precipitation and dehydration using propan-2-ol for the total protein-bound chromium, and 0.5M hydrochloric acid in propan-2-ol for the alpha-2-globulin-bound metal. The precipitates are washed in propan-2-ol, then in toluene. Urine aliquots equivalent to 20 umol creatinine are dried at 75&deg; C. Acetic acid (plus 7.5% v.v. sulphuric acid) and 1,1,1,5,5,5-hexafluoropenta-2,4-dione are added to the serum precipitates and urine residues. The chromium in the specimens is converted to the beta-diketonate at 75&deg; C, and the complex extracted with petroleum spirit. The excess diketone is removed by washing with phosphate buffer. The chromium is back-extracted with ammonia in EDTA solution and, after an evaporation step, dissolved in ammonium acetate solution. Atomic absorption spectrometry with electrothermal atomisation is used to measure the chromium, and because of the matrix simplification achieved, background correction is not necessary. The mean results on serum from normal subjects were 0.11 ug/L for total protein-bound chromium, and 0.07 ug/L for alpha-2-globulin-bound chromium. The detection limit was 0.03 ug Cr/L for both serum parameters. The mean normal value for urinary chromium was 0.44 ug/ 10 mmol creatinine, with a detection limit of 0.05 ug Cr/10 mmol creatinine. The analytical relative standard deviations for the three parameters at the above levels were: 7%, 9% and 13%respectively. The serum chromium parameters did not show a significant response to a glucose challenge. Precautions against sample contamination were taken, and techniques for reagent purification, and equipment cleaning to a high standard were developed.

Orientador: Assis Vicente Benedetti / Banca: Koshum Iha / Banca: Paulo Olivi / Banca: Sérgio Machado Espíndola / Banca: Nelson Ramos Stradiotto / Resumo: O crômio é o principal elemento de liga, responsável pela alta resistência à corrosão dos aços inoxidáveis. Esta resistência está relacionada com a formação de óxidos e/ou hidróxidos de Cr3+ na superfície. A literatura reporta muitos trabalhos sobre a comportamento eletroquímico do crômio em meio de ácido sulfúrico. Entretanto pouco se conhece sobre o crômio em soluções contendo cloreto. Este conhecimento pode ser muito importante para entender o mecanismo de formação dos filmes e passivação da superfície do crômio e dos aços inoxidáveis. Neste trabalho estudou-se o comportamento eletroquímico do crômio em soluções contento íons cloreto, utilizando-se técnicas eletroquímicas convencionais. Espectroscopia fotoeletrônica e Uv-visível foram também empregadas para analisar, respectivamente, a superfície e espécies de crômio em solução. As curvas de polarização do crômio em soluções mostram três regiões de potenciais: ativa, passiva e transpassiva. Na região ativa verificou-se que o crômio se dissolve como Cr2+ junto com geração de hidrogênio. Para soluções com pH<3 a formação do filme passivo deve ocorrer via dissolução/precipitação enquanto que para soluções com pH>3 o mecanismo deve ser via formação direta do filme. As medidas de espectroscopia de impedância eletroquímica mostraram um circuito equivalente para a interface em solução com pH=0,3 e outro diferente para a interface em soluções com 0,3<pH. As análises por XPS revelaram que o filme é constituído basicamente por Cr2O3. Os resultados das medidas eletroquímicas e de espectroscopia UVvisível mostraram que o crômio e o filme passivante se dissolvem como dicromato na região de transpassivação. / Abstract: Chromium is the main alloying element for stainless steels responsible for their high corrosion resistance. This is due to the formation of Cr3+ surface oxides and/or hydroxides at the chromium surface. In the literature there are many papers reporting studies on the electrochemical behavior of chromium in sulfuric acid. Nevertheless, there is still a lack of knowledge about electrochemical in chloride ions medium. This knowledge can be useful to understand the film formation and passivation mechanisms of chromium and stainless steels. This work reports the influence of the pH dependence on the electrochemical behavior of chromium in aqueous Cl--containing solutions using conventional electrochemical techniques. X-ray Photoelectron and UV-vis Spectroscopies were used to analyze the surface composition and chromium species in solution, respectively. The polarization curves of chromium in acid solutions showed three potential regions: active, passive and the transpassive region. In the active region chromium dissolve as Cr2+ and hydrogen evolution was also observed. It seems that for solutions with pH<3 the formation of a passive layer occurs via a dissolution/precipitation process while for pH>3 the mechanism changes to direct film formation. The electrochemical impedance spectroscopy measurements, performed in the passive region agree with a circuit equivalent at pH=0.3 and another for 0.3< pH. XPS analysis revealed that the passive layer is basically constituted by Cr2O3. For the transpassive region the electrochemical results and UV-vis spectroscopy measurements indicated that both chromium and the passivating film dissolved as dichromate ions. / Doutor