Theses and dissertations (Applied Sciences)
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Item Molecular interactions of binary mixtures of deep eutectic solvents with organic solutes(2024-05) Molefi, Reitumetse Precious; Kabane, Bakusele; Deenadayalu, NirmalaDeep eutectic solvents are the new emerging solvents formed by the combination of hydrogen bond acceptor and hydrogen bond donor. This type of solvent is still under development for possible industrial application including in chemistry, biotechnology, and pharmaceutical processes. The deep eutectic solvents have attracted much attention because they are characterized as greener solvents when compared to the currently used volatile organic solvents. Deep eutectic solvents are to replace the ionic liquids, which are posed as green solvents, however, their toxic nature has turned to be its drawbacks. The deep eutectic solvents attracted great interest due to their unique properties such as biodegradability, thermal stability, less toxicity, easy and cheap to prepare. This work explores the activity coefficients at infinite dilution of deep eutectic solvents. The deep eutectic solvents under investigation were carefully synthesized using hydrogen bond donors (HBD) and hydrogen acceptors (HBA) at a specific ratio. The analysis of these prepared deep eutectic solvents were analysed using spectroscopic techniques (FTIR and NMR) to confirm the formation of deep eutectic solvents and the type of interaction occurring between the HBD and the HBA. Additionally, thermal stability of the prepared deep eutectic solvents was investigated. The DESs were then used to measure the activity coefficients at infinite dilution for volatile organic compounds (alkanes, alkene, alkynes, aromatic hydrocarbons, ketones, acetonitrile, tetrahydrofuran, alcohols and thiophene) using the chromatography technique. The activity coefficients at infinite dilutions were conducted over a range of temperature (313.15 - 353.15) K. The prepared deep eutectic solvents for this include. DES1 {1- butyl-2,3-dimethylimidazolium chloride + ethylene glycol (1:3)} DES2 {1-butyl-2,3-dimethylimidazolium chloride + diethylene glycol (1:2)} DES3 {1-butyl-2,3-dimethylimidazolium tetrafluoroborate + ethylene glycol (1:3)} DES4 {1 -butyl-2,3-dimethylImidazolium tetrafluoroborate + diethylene glycol (1:3)) The study also focuses on understanding the behaviour of these DES through a comprehensive analysis of their thermophysical characteristics and their ability to dissolve solutes at infinite dilution. The investigation revealed intriguing trends in the solvation behaviour of different classes of solutes within the DES. Alkanes exhibited higher activity coefficients, with a clear dependence on the alkyl chain length. Cyclic hydrocarbons showed distinct behaviour due to stronger interactions with the imidazolium ring. Alkynes demonstrated the lowest activity coefficients, attributed to the presence of triple bonds influencing solute-solvent interactions. Aromatic hydrocarbons exhibited unique solvation behaviour influenced by the delocalized pi- π- electrons on the benzene ring. To use the deep eutectic solvents at an industrial level, it is highly imperative to understand the intermolecular interactions and properties of the pure deep eutectic solvents and their mixtures with volatile organic solutes. The prepared deep eutectic solvents for thermophysical properties include. DES5 (1-butyl-1-methylpyrrolidinium bromide + ethylene glycol) DES6 (1-butyl-3-methylimidazolium chloride + ethylene glycol) Thermophysical properties, such as densities, speed of sound, and refractive indices were measured as a function of temperature. The study investigated the binary mixtures containing (DES5 + acetic acid or ethanol) and (DES 6 + acetic acid or ethanol). These were investigated at temperatures ranging between (293.15 and 313.15) K and at atmospheric pressure (0.1MPa) over a range of mole fraction (𝑥1= 0 to 1) as a function of DES. The measured property values were used to compute the excess properties such as excess molar volumes, isentropic compressibilities, deviation in refractive indices, deviation in isentropic compressibilities and intermolecular free length. The data obtained provides insights into the molecular interactions within the DESs, shedding light on their structural arrangements and overall stability. This study contributes to the fundamental understanding of deep eutectic solvents, offering a detailed exploration of their thermophysical properties and their solvation behaviour at infinite dilution. The findings have implications for the design and optimization of DESs for various applications, including their use as green solvents in chemical processes and separations.Item Thermodynamic properties at infinite dilution of deep eutectic solvents with organic solutes at different temperatures(2023) Manyoni, Lindokuhle; Redhi, Gan G.Many industrial processes in the chemical industry require surge amounts of energy to separate organic mixtures. While numerous separating substances used for this purpose are volatile and have closely related boiling points to the mixtures, they are environmentally harmful. As a result, new separation substances in the space of these solvents should be researched. The latest group of solvents known as deep eutectic solvents (DESs), classified as Type (III), were studied in the space of conventional organic solvents, which are currently used in industrial processes for extraction or separation purposes. In the forecast, deep eutectic solvents have gained significant interest as part of the low melting temperature solvents with many other attractive and unique properties. This includes their physical, thermophysical, and thermodynamic properties. These properties were investigated in this study in order to better understand the intermolecular interactions of 1-ethyl-1-methylpyrrolidinium bromide + glycerol [(EMPYR) Br + Gly] or 1-ethyl1-methylpyrrolidinium bromide + ethylene glycol [(EMPYR) Br + EG], with methanol or ethanol. Hence, the first section of the study investigated the physical properties, including density and sound velocity, of deep eutectic solvents and their binary mixtures, as a function of temperature. The obtained physical properties were used to compute the thermophysical properties, i.e., excess molar volume (Vm E ), intermolecular free length (Lf), variation in isentropic compressibility (∆Ks), and isentropic compressibility (Ks ), to advance the study of the intermolecular interactions of the selected deep eutectic solvents and their binary mixtures. Furthermore, the second section of this study investigated the infinite dilution activity coefficients of five different deep eutectic solvents, including (1) 1-ethyl-1-methylpyrrolidinium bromide + glycerol [(EMPYR) Br + Gly], (2) 1-ethyl-1-methylpyrrolidinium bromide + ethylene glycol [(EMPYR) Br + EG], (3) 1-ethyl-1-methylpyrrolidinium bromide + 1-pentanediol [(EMPYR) Br + 1.5-PDO], (4) 1-ethyl-1-methylpyrrolidinium bromide + 1-hexanediol [(EMPYR) Br + 1.6- HDO], and (5) trihexyltetradecylphosphonium decanoate + ethylene glycol [(THTDP) Dc + EG], with various solutes at different temperatures. The obtained infinite dilution activity coefficients (γ13 ∞ ) were utilized to compute the other thermodynamic properties, viz., enthalpy (∆H1 E,∞), entropy (∆S1 E,∞), and Gibbs free energy (∆G1 E,∞) as well as the selectivity (Sij ∞) and capacity (kj ∞), of the selected organic solutes. The separation was possible with the investigated solvents. As is known, the accurate and precise analysis of the thermodynamic properties of liquid substances such as deep eutectic solvents is of significant interest to the chemical industry as it would help ascertain the implementation of these solvents on a large scale for industrial separation processes.Item Synthesis, characterization and application of novel ionic liquids(2018) Arumugam, Vasanthakumar; Redhi, Gyanasivan Govindsamy; Gengan, Robert MoonsamyIonic liquids (ILs) or molten salts at room temperature presently experience significant attention in many areas of chemistry. The most attractive property is the “tenability” of the physical and chemical properties of ILs by varying structure. The use of ILs in solvents demands information about their behaviour in the presence of other compounds including organic solvents such as alcohols or carboxylic acids or water, commonly used for products extraction. In addition, the efficiency of chemical processes (synthesis, extractions and separations) is strongly influenced by the nature of ILs. In this study describes the synthesis and characterization of novel epoxy propyl substituted ionic liquids (ILs). The thermophysical properties of ILs and their binary mixtures with either water, alcohol or carboxylic acids were investigated and the results are discussed in terms of interactions through thermodynamic properties. Furthermore, 2-oxopyrrolidine (Pyr), 2-aminopicoline (Apic) and 1,4-diazabicyclo [2.2.2] octane (DABCO)-based dihydroxypropyl substituted ILs are synthesised and characterised successfully. These ILs were then used to synthesize and characterize a novel 4 th -generation multi-ionic IL. A significant application of this IL is the synthesis of a unique nanomaterial using magnetic iron nanoparticles, h-boron nitride and titanium dioxide. The nanomaterial was strategically used to reduce selected dyes and series of nitroanilines (NAs). The chapter 1 to 4 explains about the introduction, literature review, synthesis and thermophysical properties of ILs as well as thermodynamic properties of ILs. The fifth chapter of this study describe the synthesis, characterization and thermophysical properties of a novel 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium chloride IL and its binary mixtures, with either water or ethanol. The density (ρ), and speed of sound (u), were measured for the above IL and its corresponding binary systems with either water or ethanol at different temperatures ranging from (293.15 to 313.15) K. The derived thermodynamic properties for instance excess molar volumes (V mE ), isentropic compressibility (k s ) deviation in isentropic compressibility (∆k s ) and intermolecular free length (L f ) were investigated from the ρ and u data, respectively. It is noted that V mE , k s ∆k s and L f values increase with increasing temperature. Derived properties such as V mE , and ∆k s data were fitted to the Redlich-Kister polynomial equation. The measured and calculated data were interpreted in terms of intermolecular interfaces and structural effects between similar and dissimilar molecules upon mixing (Paper: I) The chapter six describes the synthesis and characterization of 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium salicylate and 2′, 3′-epoxypropyl-N-methyl-2-oxopyrrolidinium acetate ILs. These ILs and their binary mixtures with either water or methanol were then studied to determine their thermophysical properties. The temperature dependent ρ and u for IL, methanol, water, and their corresponding binary mixtures of {IL (1) + methanol or water (2)} were measured over the entire range of mole fractions at temperatures from T = (293.15 to 313.15) K in intervals of 5 K, under atmospheric pressure. The calculated thermodynamic properties such as V mE , k s ∆k s andL f , were derived from the investigated ρ and u data. The resulting experimental data for V mE , L f , and ∆k s , were well fitted to the Redlich-Kister polynomial equation. (Paper: II & III) The chapter seven reports the thermophysical properties of binary mixtures for the combination of 2′, 3′- epoxypropyl-N-methyl-2-oxopyrrolidinium chloride with carboxylic acids either ethanoic or propionic acids. The novel IL [EPMpyr] + [Cl] − was synthesized, and it has been mixed with ethanoic or propanoic acids. The influence of an epoxy group in this IL was more strongly affected with the acids, and their thermophysical properties at varied temperatures are discussed in term of density (ρ), viscosity (η), speed of sound (u), and refractive index (n) measurements. The ρ, u, η, and n of the IL, ethanoic acid, propanoic acid, and their corresponding binary mixtures {[EPMpyr] + [Cl] − (1) + ethanoic or propanoic acid (2)} were measured at T = (293.15-313.15) K and at P = 0.1 MPa. The theoretical thermodynamic properties of V mE , k s , ∆k s , and L f are calculated using experimental ρ and u data. The V mE and ∆k s values for both binary mixtures were found to be negative over the entire mole fraction range of compositions at all the investigated temperatures. These results suggest the existence of specific interactions between components in the molecules. The experimental data could be helpful to understand the molecular interactions between the IL and carboxylic acid combinations. The experimental data were fitted to the Redlich-Kister polynomial equation. This study is very important for industries because most of the ILs are viscous and have high pH values, so making their applications in industries are difficult. Hence these main disadvantages could be addressed and rectified simultaneously without drastically altering the nature of the IL by using various carboxylic acid combinations. Moreover, the thermophysical data and information about acid and IL mixtures will provide insight into the use of these ILs in acidic conditions, thereby enabling the development of processes for future industries. Additionally, the measurements of thermophysical properties were used to calculate thermodynamic properties, which lead to a better understanding of the interactions amongst unlike molecules and hydrogen bonds in binary mixtures. (Paper: IV) In summary, the first four publications describes the synthesis, characterization and thermophysical properties of 2′,3′-epoxypropyl substituted 2-oxopyrrolidinium cation-based novel ILs with various anions such as chloride, acetate and salicylate. These ILs were characterized by FTIR, 1 H NMR, 13 C NMR and elemental analysis to confirm the chemical structure of the ILs. The binary mixtures of ILs with either water or methanol or ethanol were carefully prepared. Experimental measurements of the thermophysical properties of ρ, u, η and n, selected solvents, and their binary mixtures at various temperatures, across the entire mole fraction ranges of ILs, were determine. Thermodynamic properties of V mE , k s , ∆k s and L f were calculated from ρ, and u data. These thermodynamic properties were correlated using the Redlich-Kister polynomial equation. Molecular interactions, especially H-bonding and other interaction effects that occur between ILs and molecular solvents were discussed. The chapter eight discusses the synthesis and characterization of novel 4 th generation amino trismethyl phosphonate (ATMP) based IL such as [DABCO, PYR, APIC-PDO] + [ATMP] - and their application to the synthesis and characterization of partially oxidized h-boron nitride modified nanomaterial with copper ferrite magnetic nanoparticles (NPs). This nanomaterial was characterized through various spectroscopic, microscopic and surface morphological techniques. Thereafter it was used as environmentally friendly heterogeneous catalyst for the reduction of a series of NAs and dyes such as 2-nitroaniline (2-NA), 3-nitroaniline (3-NA), 4-nitroaniline (4-NA), 4-nitro-1,2-phenylenediamine (4-NPD), methylene blue and allura red to their corresponding amino analogues. The rate constant, order of reaction, activation energy and constant ratio were calculated for each substrate. The order of reduction, was 4-NPD > 4-NA > 3-NA > 2-NA. Kinetic studies indicated either zero or pseudo-first order reactions. Furthermore, kinetic studies at various temperatures such as 25, 30, 40, 50 and 60 o C as well as the range of various quantities of catalyst such as 0.015, 0.030 and 0.045 ml (0.2mg/ml concentration) showed that either an increase in temperature or the amount of catalyst increased the rate of the reaction. It was found that the nanomaterial is an efficient catalyst in aqueous solution at ambient temperature, and the processes for recovery were simple. It was re-used more than seven times with negligible loss of its catalytic activity. It is envisaged that new industrial applications of the ILs and their nanomaterials will emanate in the future. (Paper: V) The chapter nine describes the synthesis, characterization and application to the reduction of NAs which were made using 2′,3′- epoxypropyl-N-methyl-2-oxopyrrolidinium salicylate IL, NiFe 2 O 4 NPs and titanium dioxide (TiO 2 ). Here IL was used as a bonding or capping agent to synthesize NiFe 2 O 4 NPs doped TiO 2 nanocomposite. This nanocomposite was characterized by various microscopic and surface morphological studies. The nanocomposite displayed a good catalytic activity for the reduction of 2-NA to 2-aminoaniline and can be recovered as well as recycled easily. (Paper: VI)