In this research, in order to set up the ultimate approaches to determine the content of chromium(¢¾) in seawater, different pH values, the amount of chelating agent, chelating time and extraction time were investigated in two different solvent extraction systems, APDC-MIBK and Aliquat 336-MIBK. In APDC-MIBK system, the ultimate extracting condition is that 400 mL sample is adjusted to pH 3.0, added 4 % APDC 4 mL to chelate chromium(¢¾) for 60 minutes, and added 20 mL MIBK to partiton into two fractions for 5 minutes. The recovery in APDC-MIBK system is 68 %~ 123 %. The method detection limit is 0.2 ppb. In Aliquat 336-MIBK system, the ultimate extracting condition is that 400 mL sample is adjusted to pH 2.0, added 5 % Aliquat 336 4 mL to chelate chromium(¢¾), added 20 mL MIBK to be shaken for 2 minutes, and partitoned into two fractions for 5 minutes. The recovery in Aliquat 336-MIBK system is 80 %~ 120 %. The method detection limit is 0.1ppb. Although in APDC-MIBK system assorted metals can be extracted at same time, it is steadier in Aliquat 336-MIBK system than APDC-MIBK system. Therefore, it is a feasible extraction method to adopt Aliquat 336-MIBK system to determine the content of chromium(¢¾) in seawater.

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Immobilization and detoxification of chromium in the vadose zone is made possible by the existence of an effective reductant, SO2, that exists in a gaseous form at room temperature. Experimental studies were designed to characterize stoichiometry and kinetics of chromium reduction both in aqueous solutions at pH values near neutrality and in soil. First, batch experiments and elemental analyses were conducted to characterize the stoichiometry and kinetics of Cr(VI) reduction in water. The stoichiometric ratio of S(IV) removed to Cr(VI) removed ranged between 1.6 and 1.8. The overall reaction is believed to be the result of a linear combination of two reactions in which dithionate is an intermediate and sulfate is the stable oxidized product. The reaction was also rapid, with the half-time of about 45 minutes at pH 6 and about 16 hours at pH 7. A two-step kinetic model was developed to describe changes in concentrations of Cr(VI), S(IV), and S(V). Nonlinear regression was applied to obtain the kinetic parameters. The rate of reaction was assumed to be second-order with respect to [Cr(VI)] and first-order with respect to [S(IV)], and [S(V)]. The values for the rate coefficient for the first reaction (k1) were found to be 4.5 (?10%), 0.25 (?9.4%) (mM-2h-1) at pH 6 and 7, respectively. The values of the rate coefficient for the second reaction (k2) were 25 (?29%), 1.1 (? 30%) (mM-2h-1) at pH 6 and 7, respectively. The reaction rate decreased as pH increased. Experiments showed that the rate at pH 7 was lower than that at pH 6 by one order of magnitude. Second, batch experiments and elemental analyses were conducted to characterize the stoichiometry and kinetics of Cr(VI) reduction in soil. The stoichiometric ratio of S(IV) removed to Cr(VI) removed was almost 2, which is slightly higher than that for the reaction in water. This higher value may be due to S(IV) oxidation by soil-derived Fe(III). The reaction was rapid, with the half-time less than 2 minutes, which is faster than in water. The rate coefficients, k1 and k2, were 22 (?41%) and 13 (?77%) (M-2h-1), respectively.

The ability to utilize cheaper starting materials in the synthesis of commercially important materials has been a goal of scientists since the advent of the chemical industry. The ideal situation would be one in which by combining the correct proportions of hydrogen, nitrogen, carbon and oxygen that virtually anything from simple sugars to complex polymers could be produced. Unfortunately, such processes are flights of fancy often reserved for movies and television shows. On a more realistic level, the utilization of simple molecules and a transition metal catalyst has been a process that industry has exploited for many years. The most easily identifiable process is that for polyolefin production, that employs homopolymerization of simple monomers such as ethylene and catalysts ranging from Ziegler-Natta to metallocene type catalysts. On a more difficult level copolymerization reactions require a delicate balance between two competing reactions and as a result these reactions have been much less successful. For over a decade now the Darensbourg Research Laboratories have focused on utilizing another simple molecule: carbon dioxide. Carbon dioxide is a cheap, inert, nontoxic starting material that appears to be an ideal monomer. Although simplistic, CO2 is also very stable and its utilization in polymerization reactions have proven to be quite complex. In order for us to facilitate these reactions we employ both a transition metal catalyst and a comonomer. Epoxides act as an effective comonomer because the thermodynamic energy gained from breaking the strained three membered epoxide ring overcomes the stability of CO2 and allows the copolymerization reaction to occur. We have demonstrated a great deal of success with this process, most of which will be mentioned throughout this report. The majority of this dissertation will detail our use of salen complexes to optimize this copolymerization process, in order to further the use of CO2 as a viable source of C1 feedstock. Herein, I will illustrate how we have obtained more than a 100 fold increase in the rate of polymer formation as well as detailed mechanistic data that will provide a basis for future catalyst design studies.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.)--Brown University, 2008. / Source: Dissertation Abstracts International, Volume: 69-06, Section: B, page: 3556. Adviser: Anatoly Zhitkovich. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (M. Sc.)--University of Hong Kong, 1968. / Mimeographed.

published_or_final_version / Chemistry / Master / Master of Philosophy

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