LD2668 .T4 1962 L67

LD2668 .T4 1962 R39

Call number: LD2668 .T4 1965 L78 / Master of Science

Submitted in fulfilment of the academic requirements for the Masters Degree in Technology: Chemistry, Durban University of Technology,2013. / The thermodynamic properties of binary liquid mixtures using an ionic liquid (IL) with alcohols were determined at different temperatures. The ionic liquid used was 1-butyl-3- methylimidazolium methylsulphate [BMIM]+[MeSO4]-. Densities, speed of sound, and refractive indices for the binary mixtures ([BMIM]+[MeSO4]- + methanol, or 1-propanol, or 2-propanol, or 1-butanol) were experimentally measured over the whole range of composition at T = (298.15, E 303.15, 308.15, and 313.15) K. From the experimental data, excess molar volumes, V m , E , deviations in refractive isentropic compressibilities, κ s , excess isentropic compressibilities, κ S indices, ∆n, and molar refractions, R, were calculated. The excess partial molar volumes were also calculated at T = 298.15 K. For the binary systems, ([BMIM]+[MeSO4]- + methanol, or 1-propanol, or 2-propanol, or E E E 1-butanol) V m and κ S are always negative and V m decrease slightly when the temperature increases. The refractive index deviation at T = (298.15, 303.15, 308.15, and 313.15) K is positive over the whole composition range. The measured negative values for excess molar volume of these mixtures ([BMIM]+[MeSO4]- + methanol, or 1-propanol, or 2-propanol, or 1-butanol) indicate strong ion-dipole interactions and packing between alcohols and IL are present. The Redlich-Kister smoothing polynomial equation was satisfactorily applied for the E E fitting of the V m , κ S , and ∆n data to give the fitting parameters and the root-mean-square deviations. The Lorentz-Lorenz (L-L) equation was also used to correlate the volumetric property and predict the density or refractive index of the binary mixtures of ionic liquid and the organic solvents. The Lorentz-Lorenz approximation gives a higher σ when used to correlate the iiiexcess molar volumes for the mixtures ([BMIM]+[MeSO4]- + methanol, or 1-propanol, or 2-propanol, or 1-butanol). The L-L equation gives good results for the prediction of density and refractive index. The results are discussed in terms of solute-solute, solute-solvent and solvent- solvent interactions. / National Research Foundation

Carbon is prepared from flax shive by treatment with sulphuric acid. The optimised conditions of preparation were based on metal sorption (Cd2+, Hg2+), carbon yield, and acid and energy consumption. The carbon product retains its fibrous woody texture and XRD indicates an amorphous structure which has a very low surface area determined by nitrogen adsorption. Elemental analysis of the sorbent shows a very low amount of sulphur (-1%), while FTIR shows the presence of carboxyl, carbonyl and hydroxyl (or phenolic) groups. Cadmium shows fast kinetics of sorption for this material reaching equilibrium within 3 hours and having a sorption capacity similar to the cation exchange capacity (CEC) and base neutralisation capacity data. On the other hand mercury shows slow kinetics with 120 hours equilibrium time. Sorption capacity for mercury was high compared to that of cadmium or the cation exchange capacity. Base neutralisation capacity shows that the sorbent prepared at 200°C (C200) possesses more carboxylic and hydroxyl groups than that prepared at 160°C (C 160) and agrees with the cation exchange capacity data and cadmium sorption. A comprehensive study for cadmium on C200 sorbent found that sorption increases with pH and decreases with the presence of other metal ions in the aqueous solution. Mechanism of sorption investigated by the ratio of [H+]/[Cd2+] on a molar basis gave a value -2 indicating an ion exchange mechanism. Other metals such as Coe+, Cri+, Cue+, Nie+, Pb2+ and Zn 2+ were found to behave in a similar way to cadmium. These metals show fast kinetics with C200 reaching equilibrium within 3 hours. The ratio of metal sorbed on C160 to that on C200 is similar to that of cadmium and also to the ratio of CEC C 160/CEC C200. Such results suggest that these metal ions are sorbed via an ion exchange mechanism onto sites such as carboxylic and hydroxyl groups. Sorption was found to fit the Langmuir equation with an insignificant increase with temperature. Column studies proved that C200 can be used several times to sorb Cd 2+ from aqueous solution and using 0.5 mol/dm3 sulphuric acid as a stripping solution. On the other hand, mercury behaves differently showing, in addition to slow kinetics, a much higher uptake. This suggests that mercury sorption is not only an ion exchange mechanism. Such slow kinetics were found to follow a first order rate equation and the sorption data also fits the Langmuir equation. Wet samples showed a higher sorption than one that had been previously dried. Other metals such as Au (III), Cr (VI), Pd (II), Ag (I), Pt (II) and Pt (IV) were found to behave similarly to Hg (II) following the Langmuir equation with higher uptake with increasing temperature and also showing slow kinetics. The kinetics of uptake of these metals follows the first order rate equation and during the sorption process these metals were reduced. In addition, Mn04_ was converted to Mn02 and Mn2+; Fe 3+ to Fee+and Cr6+ reduced to Cr3+ which was then sorbed via an ion exchange process. Also, and depending on the initial pH, the kinetics of sorption of Cr6+ was found to follow a second order rate equation at pH 4.5, while starting at pH 1.5, chromium reduction follows a first order rate equation. Sorption of this group of metals depends on the pH of the aqueous solution. Hg 2+ sorption shows maximum uptake in the pH range 6-7 while Cr6+ shows maximum sorption within pH range 2.2-2.6 depending on the sorbent state (wet, dry) and the concentration of Cr6+. Reduction of Hg2+ to Hg2CI2 and elemental mercury was confirmed with the observation of deposits on the carbon surface from SEM photographs. X-ray powder diffraction (XRD) showed that the crystals formed on the carbon surface are mercury (I) chloride. Some other metal species such as AuC14", PdC12,A gNO3 and PtC142"showedre duction on the carbon surface to their elemental forms as observed on the SEM photographs and confirmed by XRD. Reduction of the metals was followed by the formation of new carbon-oxygen groups on the surface and also evolution of carbon dioxide. PtC162' does not show any reduction on the carbon surface suggesting the possibility that the carbon reduction potential is perhaps very close to +0.7V. This material seems to be an efficient alternative for activated carbon sorbents to remove and recover heavy metals from waters, with added advantages for those metals which can be reduced to the elemental form.

Gas phase ultraviolet photoelectron spectroscopy was used to investigate the electronic structure of organometallic compounds. Acetylide ligands in (η⁵-C₅H₅)Fe(CO)₂CECR (R = H, ᵗBu, Ph, C=CH) compounds are found to be effective π donor ligands. There is extensive interaction between the filled acetylide π and filled dπ orbitals. The HOMO and SHOMO of the acetylide compounds are partially localized on the acetylide β carbon. Variation of the R group causes both the σ and π donor ability of the acetylide to change significantly. The dπ/pπ mixing is more extensive in the R = ᵗBu or Ph compounds than in the R = H compound. In the compound CpFe(CO)₂(C=C-C=CH), the butadiyne π system mixes extensively with the metal dπ electrons. The d1t electron density is extended across the C₄H chain. These findings explain the observed reactivity toward electrophiles and Metal/acetylide communication. The first photoelectron spectra of Rh(III) compounds were obtained. The electronic structure of (η⁵-C₅Me₅)Rh(PMe₃)(Cl)(R) compounds, where R = CI, CH₃ or C₆H₅, is sensitive to changes in the R ligand. The a donor ability of the methyl and phenyl ligands are similar, but the phenyl has an additional filled/filled interaction with a metal dn orbital. The PES of (η⁵-C₅Me₅)Rh(PMe₃)(R)₂ (R = H or CH₃) revealed an electronic structure that is not isolobal with other d⁶ organometallic compounds. The HOMO and SHOMO are ligand based, as a result of the metal orbitals mixing with the Cp ring and M-R a bond combinations. The PES spectra of the compounds (η⁵-C₅H₄X)Rh(CO)₂ (X = NO₂, CF₃, CI, H, NMe₂, CH₃) gave measures of σ (inductive) and π (resonance) effects of the X substituent. The ionization energies of the metal based orbitals correlate with the carbonyl stretching frequencies and with Hammett σ(p) parameters. The X = Cl and NMe₂ compounds have significant π overlap with the Cp ring, and also have accelerated rates of associative CO substitution. The measures of inductive and resonance effects were correlated to the rates of CO substitution. The 7t terms are crucial to the correlation and suggest stabilization of an η³-Cp slipped ring intermediate. The PES of the associative substitution products (η⁵-C₅H₅)Rh(CO)L (L = PMe₃ or PPh3) have analogous electronic structure to CpRh(CO)₂, except that the valence ionizations are destabilized due to donor properties of the phosphines. The PPh₃ ligand is a better donor than PMe₃.

A theoretical model has been developed to advance the study of the thermodynamics of highly concentrated binary polymer solutions. This statistical mechanical theory was developed to allow the modeling of the molar Gibbs and Helmholtz free energies of mixing as well as the standard derived functions, such as the solvent and solute activities, and the molar enthalpies and entropies of mixing. Three major results have been generated from this work: (1) The polymer/solvent interactions can be partitioned into a coordination term, which leads to a configurational entropy, and an interaction energy of mixing term, which leads to the standard enthalpy of mixing; (2) The temperature dependence of the enthalpy of mixing yields an interaction energy of mixing which incorporates an additional entropy of mixing which is present for all types of systems, even athermal mixtures; and (3) The theory enables the use of experimentally obtained enthalpies of mixing to be used directly in the prediction of solvent activities, and experimentally determined solvent activities to be used as a predictor of the enthalpies of mixing without differentiating the experimental data. The theory was tested on fifteen binary systems. These systems had a range of physical property characteristics, from mixtures which can be considered almost ideal, to highly non-ideal athermal polymer solutions, to aqueous polymer solutions. The studied systems were; benzene/cyclopentane, benzene/cyclohexane, benzene/biphenyl, benzene/diphenylmethane, benzene/1,2-diphenylethane, cyclohexane/bicyclohexyl, n-hexane/n-hexadecane, toluene/polystyrene, chloroform/polystyrene, methylethylketone/polystyrene, cyclohexane/polystyrene, benzene/polypropylene glycol, benzene/polyethylene glycol, water/glucose, and water/polyethylene glycol. Parameters for each of these systems and components are tabulated. The experimental solvent activity data are graphed with the regression lines, and the experimental enthalpy of mixing data are graphed with the curves predicted from the solvent activity parameters. The average relative error of fit for the regression of the solvent activity data up to a polymer volume fraction of about 0.85 is less than ±0.0035, while for the entire solvent activity data set it is ±0.025. The average relative error of fit for the molar enthalpy of mixing predictions (excluding the water/PEG data) is less than ±0.005.

1) species show a preference for the MJ = ±1 sub-levels. For these bands the electronic alignment is very similar to that observed in the dissociation of OCS, indicating a similar mechanism, at least in the exit channel, is responsible for the polarisation in both systems.

A dissertation submitted to the Faculty of Science, University of the Wtlwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science / This dissertation focusses on the deactivation of SAP0-34 and modified SAPOs during methanol conversion under various conditions, in comparison to H-ZSM-5. SAPO-34 was found to deactivate rapidly during methanol conversdon. This was shown by the decrease in activity, surface area and pore volume of the catalyst. The deposited "coke" was analysed by in situ diffuse reflectance infra-red Fourier Transform spectroscopy,solid-state magic angle spinning nuclear magnetic resonance, gas chromatography mass spectroscopy (GCMS) of the HF- and dichloromethane-extracted to "coke"; and GCMS of the organic specfes released during regeneration of the catalyst and trapped in resin capillary inlet tubes.The "coke" consisted of alkylated aromatics and naphthalenes which probably formed on the surface or in the large cavities of SAPO-34. The amount of "coke" deposited during methanol conversion increased with reaction temperature, decreased with dilution of the methanol with water or nitrogen. and decreased with increased pressure, Incorporation of Ni into the SAPO framework did not decrease the rate of deactivation, but the "coke" that Has deposited was less bulky than that deposited in SAPO-34. Modification of the SAPO-34 with trlmethyl silylchloride decreased the rate at deactivation of the catalyst. / AC 2018

Photon upconversion (UC) is a unique process that has garnered increased interest in the past decade as a way to harness lower energy photons and convert them to higher energy for use in a host of applications. In molecular UC, a sensitizer molecule absorbs low energy light and undergoes intersystem crossing to generate a triplet excited state. Subsequent sensitizer-to-acceptor triplet energy transfer (TET) yields acceptor molecules in the triplet excited state. Two triplet acceptor molecules in proximity can then undergo triplet−triplet annihilation (TTA), generating one excited singlet acceptor and one ground state acceptor. Emission from the resulting singlet excited state is hypsochromically shifted relative to the excitation light and thus the photon energy is upconverted during the process. Application of molecular TTA-UC into solar cell devices, where the conversion of photons of energy below the bandgap of typical absorbing materials to those of higher energy could yield higher efficiencies, is theoretically predicted to circumvent the theoretical efficiency limit of a standard solar cell device from ~33% to more than ~43%. One approach is the use of self-assembled bilayers of sensitizer and acceptor molecules electronically coupled into a dye-sensitized solar cell (DSSC) type device to facilitate TTA-UC and direct charge separation at the organic-inorganic hybrid interface of the self-assembled bilayer and the mesoporous nanoparticle semiconductor substrate. This dissertation explores the assembly of these bilayer structures onto films of zirconium dioxide (ZrO2) and titanium dioxide (TiO2) mesoporous nanoparticle substrates in order to study the enablement of photon upconverted emission and photocurrent generation, respectively. Herein it is experimentally outlined how self-assembled bilayers can be formed via a simple, stepwise soaking procedure to afford films with surface bound acceptors followed by linking of sensitizers to acceptors via metal ion coordination. These films are shown to facilitate TTA-UC on ZrO2 as well as allow direct charge separation of the upconverted singlet state from acceptor molecules on TiO2, even under solar intensity. These self-assembled bilayer films are compared to alternative solution based systems to show they are not limited by some of the common loss pathways. Finally, the role of the redox mediator in TTA-UC solar cell devices is explored in order to understand the impact of adding an additional component relative to the TTA-UC system and how they affect excited state species. Commentary on problems faced in the system will be given along with insights into optimizing key processes to maximize efficiency. / A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / March 27, 2018. / interface, photon upconversion, self-assembly, solar cell, solar energy, triplet-triplet annihilation / Includes bibliographical references. / Kenneth Hanson, Professor Directing Dissertation; William S. Oates, University Representative; Joseph B. Schlenoff, Committee Member; Michael Shatruk, Committee Member; A. Eugene DePrince, III, Committee Member.