The work presented in this thesis involves the application of room temperature ionic liquids (RTILs) as solvents for use in electrochemical experiments. Initially, the fundamentals of electrochemistry is presented, followed by a comprehensive overview of RTILs in terms of their properties, applications and their behaviour as electrochemical solvents compared to conventional aprotic solvents. The results of 8 original studies are then presented as follows: X-Ray photoelectron spectroscopy is used to quantify the concentration of bromide ions in an ionic liquid, and is independently confirmed by potential-step chronoamperometry. The reaction mechanisms and kinetics for the electrochemical reduction of some aromatic nitro compounds (namely nitrobenzene and 4-nitrophenol) are determined. The electrochemistry of phosphorus trichloride and phosphorus oxychloride is studied in detail for the first time, due to the unusual stability of these highly reactive compounds in RTILs. The reductions and oxidations of sodium and potassium nitrate are studied, giving rise to 'melt'-like behaviour. The electrodeposition of sodium oxide on platinum is also demonstrated. The electrochemical oxidation of nitrite and the oxidation and reduction of the toxic gas, nitrogen dioxide, is presented. The oxidation of hydrogen gas is studied in ten RTILs with a range of different cations and anions, and contrasting interactions with the RTIL anions are seen. The electrochemical oxidation of ammonia gas is studied in five RTILs with different anions and a general reaction mechanism is suggested. The reduction of benzoic acid is studied in six RTILs, and the kinetics of the dissociation step are found to be very fast. The first five studies are all carried out in one particular ionic liquid, and the reactions and mechanisms are compared to that observed in conventional aprotic solvents. The last three studies employ several RTILs with different cations and anions to look at the contrasting interaction of protons with the RTIL cation/anion and ultimately help to understand the pH properties of the solvent. The overall findings from the work in this thesis are that some reactions and mechanisms (e.g bromide, nitro derivatives and ammonia) are generally the same in RTILs as in conventional aprotic solvents, but other species (e.g. nitrates, phosphorus derivatives) show remarkably different behaviour. It has also been demonstrated that RTILs are suitable media for the detection of nitrogen dioxide, hydrogen and ammonia gases. This suggests that RTILs could potentially offer many advantages when employed as solvents in electrochemical reactions and in amperometric gas sensors.

Ionic liquids (IL) are salts which are liquid at low temperatures, typically with melting points under 100 °C. In recent years ILs have been treated as novel solvents and used in a wide variety of applications such as analytical and separation processes, electrochemical devices and chemical syntheses. The properties of many ILs have been extensively studied; these studies have primarily focused on the investigation of key physical properties including viscosity, density and solubility. This thesis presents mass spectrometry (MS) and computational data to investigate the intrinsic interactions between a small number of IL ions and also their interactions with contaminants. MS was used to study gas-phase aggregates of three ILs based on the 1-butyl-3- methylimidazolium (C4mim+) cation. The influence of different ion sources was investigated on C4mimCl. Conventional electrospray ionisation (ESI) and nano-ESI techniques were compared with recently developed sonic-spray ionisation (SSI) and plasma assisted desorption ionisation (PADI). SSI was found to be beneficial to the formation of larger aggregates while PADI was significantly less efficient. Gas-phase structures of the singly charged cationic aggregates of C4mimCl were characterised with the aid of collision induced dissociation (CID) and density functional theory (DFT) calculations. Additionally, CID and DFT gave consistent results for the relative stability of the C4mimCl aggregates, showing a good agreement between experiment and theory. Mixed solutions of C4mimCl with a range of metal chloride salts were used to form aggregates incorporating both IL and metal chlorides. LiCl, NaCl, KCl, CsCl, MgCl2 and ZnCl2 were all combined with C4mimCl. Magic number characteristics were observed for a number of pure IL and mixed aggregates. Many of the mixed species were characterised using MS and DFT calculations. In particular, the relative stabilities were determined and the structures of the aggregates were calculated. It was found that the metal ions would normally act as a core for the aggregates with the stability determined by the metal-chlorine binding strength and the steric hindrance of the aggregates. It was necessary to exploit pseudopotentials as opposed to all-electron basis sets for the larger aggregates and aggregates containing heavy atoms. While water is a very effective contaminant for ILs it was not possible to observe gas-phase IL aggregates incorporating this despite using multiple methods. Additionally the presence of protonated aggregates was likewise not observed throughout the range of experiments. Possible structures where these features would be incorporated were studied with DFT to obtain some insight into their lack of formation.

Submitted in fulfillment of the academic requirements for the Masters of Applied Science (Chemistry), Durban University of Technology, Durban, South Africa, 2016. / In this work, the thermodynamic properties for the binary mixtures containing the ionic liquid (IL): 1-ethyl-3-methylimidazolium ethyl sulphate ([EMIM] [EtSO4]) were calculated. The binary systems studied were {pyridine (Py) or ethyl acetoacetate (EAA) or thiophene (TS) + [EMIM] [EtSO4]}. The results were interpreted in terms of the intermolecular interactions between the (pyridine + IL), (ethyl acetoacetate + IL), and (thiophene + IL) molecules. The physical properties: density, speed of sound, and refractive index were measured for the binary mixtures over the complete mole fraction range using an Anton Paar DSA 5000 M vibrating U- tube densimeter and an Anton Paar RXA 156 refractometer, respectively. The measurements were done at T = (298.15, 303.15, 308.15, 313.15, and 318.15) K and at p = 0.1 MPa. The experimental data was used to calculate the derived properties for the binary mixtures namely:- excess molar volume (V E ), isentropic compressibility (ks), molar refractions (R) and deviation in refractive index (Δn). For the binary mixtures, (Py or EAA or TS + IL), V E was negative throughout the whole composition range which indicates the existence of attractive intermolecular interaction between (pyridine + IL) and (ethyl acetoacetate + IL) for (thiophene + IL), V E was negative at low mole fraction of thiophene and became positive at high mole fraction of thiophene. For the binary mixtures (pyridine + IL), (ethyl acetoacetate + IL), ks was positive indicating that the binary mixtures were more compressible than the ideal mixture. For the binary mixture (thiophene + IL) ks was negative at low thiophene composition and positive at high composition indicating that the binary mixture was less compressible than the ideal mixture at low thiophene composition and more compressible at high composition of thiophene. The molar refraction, R, is positive for the (Py or EAA or TS + IL) binary systems at T = (298.15 – 318.15) K, molar refraction decreases as the organic solvent composition increases. For the binary mixture (pyridine + [EMIM] [EtSO4]), Δn is negative at mole fractions < 0.75 of pyridine and positive at mole fractions >0.75 at all temperatures and decreases with an increase in temperature. For the binary system (ethyl acetoacetate + [EMIM] [EtSO4]), Δn values are positive over the entire composition range and at all temperatures and increases with an increase in temperature. Δn values for the (thiophene + IL) system are negative for mole fractions of thiophene < 0.62 and becomes positive for mole fractions of thiophene > 0.62 and Δn increases with an increase in temperature. The Redlich-Kister smoothing equation was used successfully for the correlation of V E and Δn data. The Lorentz- Lorenz equation gave a poor prediction of V E , but a good prediction of density or refractive index. / M

Six polyamine anthracene conjugates (Ants) were studied that take advantage of the polyamine transporter system (PTS) to target specific cancer. The structural features of the Ants involve planar aromatic anthracene that has highly cytotoxicity properties and a polyamine chain similar to natural polyamine, which is taken up by eukaryote cells expressing the PTS actively. Experimental data show that Ants with di-substituted polyamine chains have significantly higher DNA binding affinities than the mono-substituted anthracene conjugates. The high ionic conditions (~150 mM NaCl and 260 mM KCl) in the eukaryote cell nucleus extensively impair the apparent DNA binding of the Ants, but may further reinforce DNA structural stability. Combining the published cytotoxicity of the PTS data with the DNA interaction data reported here, the di-substituted polyamine anthracene conjugates have the highest potential to, after cellular uptake via PTS, bind to DNA.

The silicon based sensor is able to detect part per trillion ionic silver in 0.0098% hydrofluoric acid based on the open circuit potential (OCP) measurement. The OCP jump of 100 ppt ionic silver solution is up to 120 mV. The complex agent can effectively suppress the ionic silver concentration and suppress the OCP signal. The ability of complex agent to suppress the OCP signal depends on the formation constant of the complex with silver. The complex adsorbed on the sensor surface induces a second OCP jump, the height of the second jump depends on the formation constant of the complex. The MINEQL chemical equilibrium modeling program is used to calculate the ionic silver concentration when complex agent presents, a discrepancy is found between the MINEQL simulation result and the OCP signal of the silicon based sensor. The toxicity of ionic silver to C. dubia is studied parallel to the OCP signal of silicon based sensor. Less toxicity is found when the complex agent is present similar to the OCP signal. Another discrepancy is found between the MINEQL simulation and the toxicity test when MINEQL simulation is used to predict and control the ionic silver concentration. The data from both biosensor C. dubia and silicon based sensor support each other and both are not in agreement with MINEQL simulation prediction.

No description available.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2016 / The use of fuels (from crude oil) in vehicles is responsible for one of the biggest environmental challenges; SO2 emission. As a result most countries regulate their sulfur emissions, with the goal of getting to the use of 10 ppm sulfur fuels. These stringent fuel sulfur content requirements have resulted in intensive research being directed at alternative desulfurization technologies which will ensure the treatment of fuels to acceptable sulfur levels. Extractive desulfurization using ionic liquids (IL) may be considered as one of the most promising of these technologies and is the subject of the study presented in this work. This study served two major purposes: (1) to investigate the capacity as well as key parameters which affect the extraction efficiency of the IL; 1-butyl-3-methylimidazolium octylsulfate as a solvent for deep extractive desulfurization of real Fluid Catalytic Cracking Unit (FCCU) diesel fuel samples collected from a typical South African Refinery, (2) to study/find suitable solvents for the regeneration of sulfur-loaded 1-butyl-3-methylimidazolium octylsulfate and the efficiency and effectiveness of the regenerated IL in the desulfurization of diesel fuel. 1-butyl-3-methylimidazolium octylsulfate was selected due to its properties i.e. good extractive ability for S-compounds and insolubility in fuel oils. A 22.1% sulfur removal was achieved in the desulfurization of FCCU feed stream diesel fuel, while 96% sulfur removal was achieved for FCCU product stream diesel fuel. These results show that the IL is more effective in the selective removal of sulfur (S) from FCCU diesel product than from FCCU feed stream, suggesting that fuel sulfur content and stream composition affects the extraction efficiency and effectiveness of the IL. Based on thermodynamic considerations, hexane was selected as the most suitable solvent for the re-extraction of sulfur from spent IL. Regenerated IL was used for desulfurization of diesel and achieved highest sulfur removal of 95% and the IL was regenerated up to four times without appreciable decrease in efficiency. The results obtained herein show that ILs are effective in the desulfurization of real diesel oil samples when the sulfur concentration is not very high. Further studies on the recoverability of ILs as well as their environmental impact need to be done to support findings in this study. / GR2016

Significant improvements in power conversion efficiency (>10%) of emerging thin-film photovoltaics have been achieved in the last 5 years. High efficiencies would not be possible without the development of new selective interfacial layers. However, a complete understanding of how interfacial layers function to improve the selectivity of charge extracting contacts in thin-film photovoltaics is still being sought. The goal of this work is to contribute to the understanding of the operation of selective interfacial layers based on the study of ionically functionalized fullerenes. Just as other ionically functionalized materials have shown promise as electron-selective interfacial layers in organic photovoltaics and mixed organic-inorganic halide perovskites, Chapter II demonstrates the utility of ionically functionalized fullerenes. High performing solar cells necessitate the use of conductive interfacial layers; anomalously high conductivity in ionically functionalized materials, which have been used as interfacial layers, has been ascribed to self-doping. This work demonstrates that less than 1% of an ionically functionalized fullerene is reduced in its highly conductive pristine state and is concurrent with the presence of distinct chemical species. These studies describe how the chemical origin of the high conductivity of ionically functionalized fullerenes does not require the invocation of direct anion reduction or significant chemical transformations such as Hofmann-like elimination reactions occurring to a stoichiometric degree. This work also addresses the question of how the selectivity of a charge extracting contact is improved by the presence of an interfacial layer. The quantification of energy barrier reduction, which is often discussed in terms of work function modification or energy-level alignment, is demonstrated using metal|semiconductor junctions modified with an ionically functionalized fullerene. The barrier height of high work function electrodes was reduced significantly, by as much as 0.45 V, and was correlated to thin (2–5 nm) portions of the film rather than fullerene aggregates. The studies that comprise this work form a coherent model for understanding the key factors that have resulted in the continued use of ionically functionalized interfacial layers, their high conductivity, and energy barrier modification of the charge extracting electrodes. This dissertation contains coauthored, previously published, and unpublished work. / 10000-01-01

A novel application of ionic liquid as a charge carrier for the analysis and detection of neutral organometallic complexes using a mass spectrometer has been presented. The mass spectrometer detects only charged compounds which raise a difficulty in analyzing a neutral molecule that lacks a basic site to associate with charge. Therefore, an effective way of providing charge has always been an area of keen interest in the field of mass spectrometry. Ionic liquids have a very fascinating property of forming a cation-? interaction with other molecules to give a charged complex. In order to take advantage of this, it is important to know the geometric structure of the complex. Advanced methodologies like hydrogen-deuterium exchange and computational calculations have been used assisting in better understanding of the structure of the ionic liquid complexes.

Silver nanoparticles (sub 10 nm), supported on, or in, cellulose, have been demonstrated to be well stabilised and immobilised during application in a model continuous reaction: the reduction of 4-nitrophenol (4-NP) to 4-aminophenol with sodium borohydride. The production of these silver nanoparticles (NP), within the cellulose supports, was carried out by either in situ reduction of silver precursors absorbed into the preformed cellulose supports, or, by inclusion of ex situ synthesised NPs (prepared in DMSO solutions) in the dissolution of cellulose and trapping upon subsequent coagulation of cellulose. The effects of NP synthesis method (affecting particle size and agglomeration) and the cellulose morphology and porous structure were examined with respect to the catalytic activity of the materials. The in situ reduction of a silver salt with aqueous NaBH4 solutions (0.03 to 1.0 wt. %) led to tuneable Ag NP sizes with mean diameters of 5 to 11 nm (TEM) and metal loadings of 0.5-1.0 wt. %. The catalytic activity of these samples in the 4-NP reduction reaction (0.05 mM, 0.167 M NaBH4, 30 °C) was demonstrated to increase upon decreasing NP size: TOF values of 22–356 h-1, consistent with a Langmuir-Hinshelwood mechanism. The porous structure of these Ag-cellulose materials (0.2 to 294 m2 g-1) was demonstrated to be variable and dependent on drying treatments of the regenerated cellulose hydrogel. Thermal drying, freeze-drying and critical point drying resulted in materials with different bulk structure and porosity. In turn the different porosities resulted in extremely different catalyst activities, e.g. Ag-cellulose catalyst (0.3 mm disks) thin film, hydrogel and cryogel phases exhibited TOF values of 2, 12 and 178 h-1, respectively. In addition, the NP synthesis could be carried out in either the cellulose hydrogel or cryogel, which led to different extents of Ag NP catalyst stabilisation against agglomeration during the 4-NP reaction and catalyst recovery and recycling. The Ag NPs synthesised in the cryogel cellulose disks were observed to undergo agglomeration (TEM) after use in 4 repeat batch reductions, whilst those NPs synthesised in the hydrogel cellulose, prior to freeze-drying to the final cryogel catalyst material, did not exhibit any agglomeration upon 4 repeat reduction reactions. The ex situ reduction of Ag and Au NPs was carried out by the reduction of AgOAc and Au(OAc)3 by DMSO and variation of the NP synthesis parameters, such as time (10 min – 1h) and temperature (50 – 80 °C), allowed for control of the NP sizes (3 to 6 nm Ag NPs and 4 to 11 nm Au NPs, TEM). It was demonstrated that the addition of the polysaccharide starch (0.42 wt. % in DMSO) allowed for consistent Ag NP size (ca. 4 nm) to be achieved throughout the 8 h synthesis, the starch acting as both the reducing and capping agent, maintaining the small sizes and narrow particle size distributions of the NPs upon aging (72 h). A kinetic model with a bimolecular nucleation step was developed to describe this reduction of the silver acetate by the starch/DMSO system. However, contact of the NPs with solutions of imidazolium ILs, 1-Ethyl-3-methylimidazolium acetate (EmimOAc) and 1-Butyl-3-methylimidazolium chloride (BmimCl) in DMSO, used in the dissolution of cellulose, led to the oxidation of the Ag(0) and Au(0) NPs. Thus, when these NP solutions were mixed in cellulose solutions regeneration by phase inversion with the aim of preparing cellulose/NP composites led to materials with negligible metal loadings (AAS). This oxidation, of the metal NPS, was partially overcome by stabilisation of the starch capped Ag NPs by pre-treatment with cellulose (1:1 mixture of α and MC cellulose). However, the activity of the resulting Ag-cellulose catalyst (0.5 wt. % AAS, 6.7 nm TEM) was much lower than the Ag-cellulose catalysts prepared by in situ reduction of silver in the cellulose hydrogel, despite the comparable NP sizes. This was presumed to be a result of encapsulation of the Ag NPs by the cellulose, leading to a decrease in the accessible surface of the NPs. Finally, the use of Ag NP / cellulose composites, prepared by in situ reduction of silver in cellulose hydrogel beads (0.19 wt. %, 6.4 nm), were demonstrated in the continuous reduction of 4-NP in a packed bed reactor (τ’ 100 g s dm-3). The activation energies of the reactions of 4-NP catalysed by the Ag-cellulose catalyst materials were determined (3.2 to 9.4 kJ mol-1) from Arrhenius plots, which demonstrated that above 20 °C the reaction was likely subject to diffusion limitations in the cellulose beads. The high degree of stabilisation of the Ag NPs against agglomeration imparted by the cellulose support was demonstrated: the rate of reaction was observed to be constant over 120 h, treating 45 L of 4-NP solution, with the catalyst material after use demonstrating no significant leaching of silver, or agglomeration, of NPs (AAS, TEM).