A kinetic study was made of the reaction between cupric acetate and hydrogen in aqueous solution. The reaction was followed by determining the concentration of cupric acetate remaining in solution and was found to proceed in accordance with the equation 2CuAc₂ + H₂ + H₂O → Cu₂O + 4HAc The reaction was found to be second order kinetically, the rate being proportional to the concentrations of cupric acetate and molecular hydrogen. It was established that the reaction is homogeneous, both the stainless steel vessel and the cuprous oxide product being without effect. The rate increased slightly when sodium or ammonium acetate in concentrations of 0.25 moles per liter was added to the solution but remained unchanged with further addition of these salts. The rate was also independent of the concentration of acetic acid and the pH of the solution over a wide range. The activation energy was found to be 23,400 cal. per mole and the frequency factor 1.0 x 10¯¹²1.mole¯¹ sec.¯¹ corresponding to an entropy of activation of - 5.9 cal. mole¯¹ deg.¯¹. The following mechanism has been proposed to account for these kinetic results, the first step in the reaction sequence being rate determining 1. CuAc₂ + H₂ → CuAc₂ . H₂ slow 2. CuAc₂ . H₂ + CuAc₂ → 2CuAc + 2HAc fast 3. 2CuAc + H₂O → Cu₂O + 2HAc fast This appears to be the first established instance of a homogeneous hydrogenation reaction in aqueous solution. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Ph.D. (Physics) / Compounds of rare-earth (RE) elements (Ce, Yb, Eu) as well as actinide element U with partially filled 4f or 5f shells have been receiving considerable attention in the field of low temperature studies. This stems from the diversity of magnetic ground state exhibited by the compounds. These range from non-magnetic, metallic, ferromagnetic or antiferromagnetic ordered state. The nature of the ground state depends on the balance between the on-site Kondo interaction, which mostly favours a local non-magnetic singlet and also the indirect Rudderman-Kittel-Kasuya- Yosida (RKKY) exchange interactions. The interactions of the localized f moments with their environment result in the crystal electric field (CEF) effects at the rare-earth (RE) ion site which splits the free-ion ground-state multiplet. The competing energy scales of CEF splitting, Kondo and RKKY interaction cause the large variety of exceptional phenomena observed in rare earth systems, such as heavy-fermion (HF) behaviour, intermediate valence, unconventional superconductivity, and quantum criticality. Generally, the low-temperature properties of RE systems depend sensitively on the position of the undisturbed 4f state with respect to the Fermi level. Thus, the hybridization between the 4f and conduction-electron states may give rise to either an enhanced density of states (DOS) near the Fermi level in HF metals or to the formation of a gap at Fermi level in Kondo insulators. Recent considerable research interest in strongly correlated electron systems (SCES) studies has been the study of intermetallic compounds close to magnetic instability and the introduction of non-Fermi-liquid (NFL) state. NFL behaviour in f-electron systems is characterized by special power laws and logarithmic divergences in temperature of the physical properties of materials at low temperatures...

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017. / While bioleaching is a proven technology for the efficient recovery of base metals from sulphide minerals, its sustenance is dependent on the continuous availability of ferric ion, Fe3+, in soluble form, in the bioleach liquor. However, the solubility of ferric ion is low at higher pH that it tends to precipitate, resulting in the formation of ferric ion precipitates. The formation of ferric ion precipitates in bio-hydrometallurgy decreases the leaching efficiency by trapping the leached metals in solution through an adsorption mechanism which is not well understood. Although the surface properties of the precipitate could be linked to its metal adsorption properties, there has not been a detailed study that gives any indication or explanation of the adsorption mechanism. Therefore, the aim of this study was to investigate the effect of initial pH on the surface properties of ferric ion precipitate and relate this to the adsorption characteristics of the precipitate for desired metals. Biooxidation experiments catalysed by Leptospirillum ferriphilum were conducted in a CSTR with a working volume of 1L. The biooxidation experiments were conducted at pH values of 1.3, 1.5, 1.7, 1.9 and 2.2 at a constant temperature of 35 0C for 14 days. The recovered precipitates were characterized by X-ray diffraction, elemental analyses, SEM, particle size distribution (PSD) and zeta potential. Zeta potential measurements were conducted to investigate what role initial pH plays in modifying the precipitate surface charge and what role the surface charge of each precipitate plays in the nature of adsorption of copper ions onto the precipitate surface. The amount of copper adsorbed onto the precipitate was quantified by the magnitude of the change in surface charge after adsorption experiments. Quantification results showed that the amount of ferric ions precipitates formed increased from 4.31g to 13.26g with an increase in initial pH (from 1.3 to 2.2). The results also showed that significant precipitation of ferric ion occurred during the exponential phase while insignificant precipitation was observed during the stationary phase.

Metal-organic frameworks (MOFs) have been intensely researched over the past 20 years. In this dissertation, metal-inorganic frameworks (MIFs), a new class of porous and nonporous materials using inorganic complexes as linkers, in lieu of traditional organic linkers in MOFs is reported. Besides novel MIF regimes, the previously described fluorous MOF "FMOF-1", is re-categorized herein as "F-MIF1". F-MIF-1 is comprised of [Ag4Tz6]2- (Tz = 3,5-bis-trifluoromethyl-1,2,4-triazolate) inorganic clusters connected by 3-coordinate Ag+ metal centers. Chapter 2 describes isosteric heat of adsorption studies of F-MIF1 for CO2 at near ambient temperatures, suggesting promise for carbon capture and storage. We then successfully exchanged some of these Ag(I) centers with Au(I) to form an isostructural Au/F-MIF1. Other, nonporous MIFs have been synthesized using Ag2Tz2 clusters with bridging diamine linkers 4,4'-bipyridine, pyrazine, and a Pt(II) complex containing two oppositely-situated non-coordinating pyridines. This strategy attained luminescent products better-positioned for photonic devices than porous materials due to greater exciton density. Chapter 3 overviews work using an entirely inorganic luminescent complex, [Pt2(P2O5)4]4- (a.k.a. "PtPOP") to form new carbon-free MIFs. PtPOP is highly luminescent in solution, but as a solid shows poor quantum yield (QY ~0.02) and poor stability under ambient conditions. By complexing PtPOP to various metals, we have shown a dramatic enhancement in its solid-state luminescence (by an order of magnitude) and stability (from day to year scale). One embodiment (MIF-1) demonstrates microporous character. Chapter 4 overviews the design and application of new MIF linkers. Pt complexes based upon (pyridyl)azolates, functionalized with carboxylic acid groups, have been synthesized. These complexes, and their esterized precursors, show strong luminescence on their own. They have been used to generate new luminescent MIFs. Such new MIFs may be useful toward future inorganic (LEDs) or organic (OLEDs) light-emitting diodes, respectively. The electronic communication along their infinite coordination structures is desirable for color tuning and enhanced conductivity functions, compared to the small molecules used in such technologies, which rely on intermolecular interactions for these functions.

A plethora of novel scientific phenomena and practical applications, such as solid-state molecular solar cells and other optoelectronic devices for energy harvesting and lighting technologies, have catalyzed us to synthesize novel compounds with tunable properties. Synthetic routes, single crystal structures, and spectral and materials properties are described. Reactions of Ag(I) and Cu(I) precursors with various types of ligands -- including the azolates, diimines, and diiphosphines -- lead to the corresponding complexes in high yield. Varying the metal ions, ligands, synthetic methods, solvents, and/or stoichiometric ratio can change the properties including the molecular geometry or packing structure, reactivity, photophysical and photochemical properties, semiconducting behavior, and/or porosity of the functional coordination polymers obtained. For solar cells purposes, the absorption energy can be extended from the ultraviolet (UV) region, through the entire visible (Vis) region, onto a significant portion of the near-infrared (NIR) portion of the solar spectrum with high absorption coefficients due to the infinite conjugation of Cu(I) with diimine ligands. Twenty-eight crystal structures were obtained by conventional crystal growth methods from organic solvents, whereas their bulk product syntheses also included "green chemistry" approaches that precluded the use of hazardous organic solvents. The resulting products are characterized by powder x-ray diffraction (PXRD), Fouriertransform infrared (FTIR), nuclear magnetic resonance (NMR), UV/Vis/NIR absorption/diffuse reflectance/photoluminescence spectroscopies, and thermogravimetric analysis (TGA). Regarding the scientific phenomena investigated, the highlighting work in this dissertation is the discovery of novel bonding/photophysical/optoelectronic properties of the following materials: a black absorber with absorption from 200- 900 nm, a very stable compound with a bright green luminescence obtained by a solventless reaction, and a novel coordination polymer showing uncommon interaction of Ag(I) with three different types of diimine ligands simultaneously.