none

Chitosan films are an excellent media for binding metal ions due to the electrostatic nature of the chitosan molecules. Addition of cross-linking or plasticizing agents alters texture of the films, but their effect on metal-binding capacity has not been fully characterized. The objective of this research was to determine effects of plasticizers and cross-linkers on physical and metal-binding properties of chitosan films and coatings prepared by casting and by spincoating. Chitosan films were prepared using 1% w/w chitosan in 1% acetic acid with or without (control) additives. Plasticizing agents were tetraethylene glycol (TEG) and glycerol while citric acid, ethylenediamine tetraacetic acid (EDTA), and tetraethylene glycol diacrylate (TEGDA) were used as cross-linkers. The additives were applied in concentrations of 0.10%, 0.25%, and 0.50% w/w of film-forming solution. The films were prepared by casting and by spincoating. Films were cast at ambient conditions for tests within one week (fresh films) and eight weeks (aged) after casting. The cast films were evaluated for thickness, residual moisture (by the Karl Fischer method), Cr(VI) binding capacity, puncture strength, and puncture deformation while the chitosan coatings were tested for thickness, Cr(VI) binding capacity, solubility in aqueous solution, and surface morphology (using atomic force microscopy). Cast films with cross-linkers showed an increase in resistance to puncture while plasticized films become more elastomeric. Control films bound 97.2% Cr(VI) ions from solution (0.56 mg Cr(VI)/g film), and addition of plasticizers did not affect chromium binding, tying up to 96.7% Cr(VI) ions from solution (0.56 mg Cr(VI)/g film). Films containing cross-linkers yielded binding capabilities ranging from 42.3% to 94.3% bound Cr(VI) ions (0.26-0.52 mg Cr(VI)/g film). Ultrathin coatings also possess the ability to bind Cr(VI) from solution, though only a maximum of 7.4% of Cr(VI) ions could be bound from solution, the thin films had the ability to bind up to 224 mg Cr(VI)/g ultrathin film. These coatings use less chitosan, but they display greater binding per mass. Overall, plasticizers do not alter, while cross-linkers may reduce, the binding capacity of chitosan films, but physical properties of the films can be controlled by inclusion of additives.

Thesis (Ph. D.)--University of California, San Diego, 2004. / Vita. Includes bibliographical references.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 58-59). Also available in electronic version. Access restricted to campus users.

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

D. Tech. Chemical Engineering / Aims of this research project was to add value to largely wasted South African sawdust by development of low-cost AC of high efficiency for removal of toxic Cr (VI), phenol and glutaraldehyde from dilute aqueous media. The main objectives of the research project were: a) To develop low-cost AC based on South African P. patula sawdust using economical physical superheated steam activation.Characterization of carbon samples for selection of optimum preparation conditions for development of low-cost AC of effective microporosity mesoporosity and surface functionality for enhanced adsorption capacity of Cr (VI) and/or phenol and/or glutaraldehyde from dilute aqueous solution. Acid-amine surface groups modification of optimally developed AC for further enhancement of adsorption capacity for mixed polarized glutaraldehyde molecules from aqueous solution. b) To evaluate the aqueous phase batch adsorption properties of developed AC for Cr (VI) and phenol and, of acid-amine modified developed AC for glutaraldehyde. Determination of optimum pH for adsorption; accurate adsorption isotherm modelling for determination of maximum adsorption capacity, comparison of maximum adsorption capacities for Cr (VI) and phenol of developed AC with commercial AC and literature ACs, and attempt to establish average micropore size for enhanced capacity for Cr (VI) and phenol from dilute aqueous solution.Kinetics reaction and diffusion modelling for determination of adsorption rate constants and diffusion parameters; and determination of adsorption thermodynamic parameters.Evaluation of equilibrium selectivity of developed AC for Cr (VI) and/or phenol in binary aqueous solutions. c) To evaluate aqueous phase fixed-bed adsorption characteristics of developed AC for single Cr (VI) and mixed solution using Rapid Small Scale column Tests (RSSCTs). Generation of breakthrough curves at optimum adsorption conditions for evaluation of column performance indicators at different process conditions, bed regeneration-reusability potential, and dynamic adsorption selectivity of developed AC for Cr (VI) from solution of base metals. Determination of column diffusion parameters; accurate mass transfer and empirical modelling of breakthrough data; determination of applicable RSSCT scaling equation; and optimization of breakthrough data for accurate RSSCT scale-up.

M. Tech. Chemistry. / The aim of this study was to develop and evaluate an analytical method for the determination of Cr(VI) in ferrochrome dusts and to apply the method in the analysis of environmental samples (grass, soil and tree bark) for Cr(VI) content (that might be caused by dust emissions originating from the smelter). Both the public and Xstrata Wonderkop ferrochrome plant will benefit from data of Cr(VI) determination generated from the study. The information can potentially be incorporated into health risk assessments of the affected geographical areas. The results of the investigation showed that ferrochrome smelter dust emissions were the source of contamination of the environment with Cr(VI). With time, Cr(VI) could accumulate in soil to unacceptable levels, thereby endangering both plants and animals.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

Increasing attention has been given to the preparation and study of compounds with linear chains of metal atoms surrounded by four ligands. The majority of linear trimetal complexes are supported by dpa, the anion of dipyridylamine, having the general formula M3(dpa)4X2, where X is typically a monoanion. It has been shown that the behavior of the trinuclear system is far more complicated than might have been expected. Specifically, both symmetrical and unsymmetrical chains can occur and the interpretation of the magnetic properties of certain compounds has been a challenging task. Present in this dissertation is the bulk of work completed on an exploration of syntheses and characterizations of linear trichromium and trinickel compounds with different types of tridentate ligands. These ligands include 2,6-bis(phenylamino)pyridine,H2BPAP, (the corresponding dianion of this is denoted by BPAP) and a set of five unsymmetrical formamidines with different organic substituents ranging from strong electron-donating groups, such as -OCH3, to electron-withdrawing groups, e.g., F. Ligands impact on the trimetal chain in various ways. In the case of the M3(BPAP)42- ions, there are no axial interactions because these anionic species do not attract electron donating ligands. Thus they have properties which are different from those of M3(dpa)4X2 molecules. Most notably, the Ni3(BPAP)42- ion is diamagnetic and all three nickel ions can be described as square-planar, low-spin NiII centers. ivWhen unsymmetrical formamidines are used to support linear trichromium chains with a Cl anion at each end, the separation between terminal chromium atoms is significantly longer (ca. 0.15 - 0.25) than those in trichromium compounds reported earlier. Moreover, the unsymmetrical formamidinates tend to support symmetrical trichromium chains, while the rest of the known tridentate ligands typically yield unsymmetrical Cr36+ chains. The synthesis and structural studies of trinickel compounds with unsymmetrical formamidines are also presented.