Graduation date: 1995

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (M.S.)--Oregon Graduate Center, 1972.

M.S. / Chemistry / The present investigation concerns itself with the study of the pressure dependence of hydrogen adsorption on a platinum electrode in acid media. The specific intent of this work is to find whether additional hydrogen adsorbs onto a platinum electrode when the system pressure is increased. Through this means it is possible to prove or disprove the assumption usually made that hydrogen forms a monolayer on a platinum electrode at one atmosphere pressure. Secondary aspects of this study are the effects of diffusion of hydrogen atoms into the electrode bulk, and the desorption and diffusion of hydrogen molecules into the solution layer surrounding the electrode.

Although the impacts of foreign species on aqueous transformations and arsenic adsorption by 2-line ferrihydrite (FH2) have been extensively studied, much less is known about the impact of transformation inhibitors on solid-state transformation of FH2 and arsenic adsorption. In this study, the influence of inhibitors (Si(IV), Mg(II), Al(III), Ti(IV), and Ci(citrate)), aging time, and heat treatment on FH2 transformation and arsenic adsorption was investigated. The FH2s were synthesized by mixing Fe(III) salts with an inhibitor at pH 7.5 and air drying for 2 d. With increases in Al/Fe molar ratio, FH2, poorly crystalline Al hydroxide, gibbsite, and bayerite were formed in the FH2-Al series, whereas FH2 was formed in the other FH2s. Heat treatment had a more considerable impact on the transformation, structure, and PZC of FH2 than aging at RT for 235 d. Upon heating the FH2s at 360 oC, most of the amorphous Fe oxide was transformed into hematite, whereas Si and Al had stronger retarding effects on transformation than the other inhibitors. Hematite and FH2 were identified with increases in Si/Fe molar ratio, whereas with increasing Al/Fe molar ratio, FH2 remained, gibbsite and bayerite were decomposed, and boehmite appeared as a trace component. However, the effect of Si was much more pronounced than that of Al in retarding the transformation. The adsorption density for As(III) on the FH2s (at pH 7) decreased in the order: FH2-Mg-2 > FH2 > FH2-Al-1, whereas As(V) followed the order: FH2-Al-1 > FH2-Mg-2 > FH2. Compared to aging at RT for 235 d, heat treatment at 360 oC resulted in significantly reduced arsenic adsorption. The heated FH2 showed a smaller adsorption capacity for arsenic compare to that of the other FH2s. In contrast, the heated FH2-Al and FH2-Si series showed much higher adsorption capacities for As(V) than any other FH2, whereas the heated FH2-Mg series exhibited the largest adsorption capacity of As(III) among the heated FH2s. It is concluded that the use of the FH2-Al, FH2-Mg, or FH2-Si series instead of pure FH2 as filter media in water treatment might achieve more efficient arsenic removal and enhance arsenic retention at waste-disposal sites.

Ce travail de thèse est consacré à la réalisation et à la prédiction des données d’adsorption physique sous pression sur différents adsorbants carbonés poreux comme les charbons actifs ou les tamis moléculaires carbonés. Le choix de ces adsorbants tient compte de la nécessité de disposer d’échantilons microporeux suffisamment différenciés. Ce travail a été réalisé dans le but d’apporter une contribution à la compréhension des mécanismes d’adsorption en corps pur et en mélanges dans des conditions hautement non- idéales et pour des matériaux hétérogènes en prenant essentiellement en compte les paramètres de la texture poreuse et les paramètres del’adsorbat en phase gazeuse et en phase adsorbée. Cette démarche nous permet en suite d’étudier le degré del’hétérogénéité structurale des adsorbants carbonés. Un appareillage volumétrique en mode statique a été mis au point dans le but de collecter des mesuresd’adsorptionencorps purs. Une étude rigoureuse des incertitudes sur cet appareillage a permis la quantification des erreurs sur chaque paramètre expérimental afin d’estimer l’erreur totale sur la masse adsorbée. Une étude comparative avec un autre appareillage gravimétrique en mode statique a permis de mettre en évidence les performances de nos outils de mesure dans ce travail. Les isothermes d’adsorption de l’azote,de l’argon, du méthane et del’oxygène à haute pression ont été obtenues sur cinq différents adsorbants carbonés. Les isothermes ont été collectées à différentes températures permettant la détermination des chaleurs isostériques par application de l’équationde Clausius-Clapeyron. Les résultats obtenus sont en parfait accord avec les résultats de caractérisation. Nous avons ensuite proposé de confronterl’ensemble de ces mesures à notre modèle de thermodynamique statistique basé sur la notion d’équation intégrale d’adsorption. Nous avons proposé d’étudier l’influence du choix du potentiel d’énergie d’adsorption sur les performances du modèle en corps pur. Cette confrontation expérience théorie a permis d’extraire les paramètres de la fonction de distribution du volume des pores de chaque adsorbant ainsi que les paramètres relatifs au comportement de l’adsorbat en phase adsorbée. Nous proposons l’extension directe du modèle à l’étude des équilibres en mélanges sans détermination de paramètre supplémentaire. Enfin des mesures en mélanges binaires sur un appareillage en mode statique, couplant volumétrie et chromatographie, ont été réalisées pour étudier les performances de notre modèle. Nous proposons par analogie à l’étude des corps purs une analyse rigoureuse des incertitudes sur cet appareillage. L’ensemble de ce travaila permis de mettre en évidence les performances de notre modèle basé sur les caractéristiques structurales des adsorbants pour étudier les équilibres en corps purs et en mélanges, et cela dans de larges gammes de conditions non-idéales qui sont les conditions requises dans la plupart des applications industrielles (procèdes de séparation (PSA), stockage en phase adsorbée à haute pre sion du gaz naturel et de l’hydrogène,etc

No description available.

Aflatoxins are toxic organic compounds produced by fungi in grains. Moderately contaminated grains that cannot be used as food are often directed to animal feed. Economically-feasible detoxification measures for contaminated feeds are needed. The objectives of this research were to identify effective bentonites as aflatoxin adsorbents and to evaluate the performance of the clays as aflatoxin amendments in feed for broiler chickens. Five bentonite samples from Gonzales, Texas, USA were collected and analyzed against the published selection criteria for aflatoxin adsorbents: aflatoxin adsorption capacity, pH, cation exchange capacity (CEC), organic carbon, particle size distribution, and mineralogical and structural compositions. Two bentonites were identified as potentially good aflatoxin adsorbents based on the analyses. These two bentonites were selected for an in vivo poultry experiment where chickens were fed with aflatoxin-contaminated corn (1400 ppb) to test the detoxification efficacy of the clays. Detailed mineralogy analyses were conducted on these two samples (4TX and 1TX) after size fractionation. Clay 4TX and 1TX contained 87 percent and 65 percent clay, respectively. Smectite was the dominant mineral phase in both clay fractions. Quartz and feldspars were also present in both samples. These minerals are unlikely to cause harmful effects on the chickens. The presence of pyrite and heavy metals in 1TX raised concerns about its use in animal feed. The clays were introduced into feed by mixing the dry bentonite powder with the feed for twelve minutes in a mechanical mixer. The body weight was increased by 21 percent with clay 4TX and 14 percent with clay 1TX in the aflatoxin diet. The concentration of total aflatoxins in liver was reduced by 36 percent with the addition of clays. Liver visual appearance was also improved from pale red to a more reddish color resembling the healthy red liver. All chickens fed clean feed had significantly higher body weights than those fed with highly contaminated feed, suggesting that the clays did not completely eliminate aflatoxin toxicity. The published aflatoxin binder selection criteria were useful for screening bentonites as aflatoxin amendments. The selected bentonites based on the criteria could effectively sequester aflatoxins in vivo. Yet direct mixing of bentonite as dry powder to highly contaminated poultry feed could not eliminate the toxicity of aflatoxins.

Ellipsometry was used to study the effects of surface energetics and temperature on the equilibrium adsorptive behavior exhibited by β-lactoglobulin. β-Lactoglobulin isotherms at 25, 37, and 55°C were constructed for this purpose. The surfaces of acrylic, polycarbonate, polyester, glass, and #304 stainless steel were contacted with protein solutions of varying concentration, buffered at pH 6.7 with mono- and dibasic sodium phosphate. After three hours, the surfaces were mildly rinsed with deionized water and dried overnight. Optical properties of each film were ellipsometrically measured and the adsorbed mass was calculated as a function of film thickness and refractive index. Contact angle methods were used to measure the hydrophobicity exhibited by each of the five solid surfaces. However, interpretation of protein adsorption results based solely on solid surface hydrophobicity proved unworkable. For polymers (low-energy surfaces), the adsorbed mass of protein was explained with reference to the degree of extensibility of molecular structure. Glass (a high-energy surface) was observed to adsorb the greatest mass of β-lactoglobulin. Stainless steel was observed to adsorb the least mass of β-lactoglobulin and the plateau values of protein adsorption were found to be consistent with those reported elsewhere, and to lie within the range of adsorbed mass on metal surfaces in general. The temperature dependence of β-lactoglobulin adsorption could not be clearly quantified. Apparently, any differences in adsorbed mass were too small to be detected by the instrument. In any event, other investigators have not detected any significant difference in adsorbed mass as long as the temperature was below the denaturation temperature of the protein. / Graduation date: 1991

The adsorption equilibrium and kinetic behavior exhibited by β-lactoglobulin at silanized silicon surfaces of varying hydrophobicity were examined using ellipsometry. Adsorption equilibrium results were used to construct adsorption isotherms; the adsorbed mass of β-lactoglobulin was observed to increase with increasing surface hydrophobicity, within a defined range of hydrophobicity. Adsorption kinetics recorded for β-lactoglobulin on each surface were compared to the kinetic behavior predicted by a simple model for protein adsorption. The model described the data well in all cases, enabling interpretation of the kinetic behavior in terms of contact surface hydrophobicity influences on rate constants affecting protein attachment and unfolding at the interface. In particular, both experimental and simulation results seem to be in support of a hypothesis that rate constants defining protein arrival and conversion to an irreversibly adsorbed state increase with increasing surface hydrophobicity, while the rate constant defining desorption of protein from a reversibly adsorbed state decreases with increasing surface hydrophobicity. Contact surface hydrophobicity was quantified using contact angle analysis to determine the polar component of the work required to remove water from unit area of surface. Quantitative consideration of possible mass transfer influences on the observed adsorption rates supports the notion that the experiments were not conducted in a transport-limited regime; i.e., true kinetics were measured. / Graduation date: 1992