Density Functional Theory (DFT) studies for the ring opening mechanism of tetraethyl 2-aryl-1,2-epoxygembisphosphonates
- Authors: Marondedze, Epraim F.
- Date: 2016
- Subjects: Density functionals , Molecular structure , Molecules - Models - Data processing
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/84634 , uj:19246
- Description: Abstract: The study reported in this thesis was aimed at investigating the ring opening mechanism(s) associated with the breaking of the carbon-oxygen oxirane bond of tetraethyl 2-aryl-1,2-epoxygembisphosphonate. Density Functional Theory (DFT) was employed to theoretically determine the mechanism(s) of the oxirane ring opening for tetraethyl 2-aryl-1,2-epoxy-2-phenylbisphosphonate. Simulations were carried out using the Gaussian09 version D01 software whereas visualisations were performed in GaussView 5.0.8, a graphic user interface compatible and part of the Gaussian software packages. The generalized gradient approximation functional BP86 in combination with the 6-31+G(d,p) and aug-cc-pVTZ basis sets was used for investigating the proposed reaction pathways. The method was selected after comparing energies and geometries obtained at both the BP86 and B3LYP functionals on selected local minima. Two transition states were obtained and found to be associated with opening on carbon 1 and 2 of the oxirane ring. These transition states were verified by running a frequency calculation and an intrinsic reaction coordinate (IRC) calculation at the same level of theory. Solvent effects were incorporated implicitly using the conductor-like polarised continuum model (CPCM) to investigate the effects on the energy and structures involved in the proposed mechanistic pathways. The effect of both electron donating and electron withdrawing groups on the transition state energies was also investigated. The ring opening at C2 was found to be the most favoured pathway both in vacuum and in the selected solvents. , M.Sc. (Chemistry)
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- Authors: Marondedze, Epraim F.
- Date: 2016
- Subjects: Density functionals , Molecular structure , Molecules - Models - Data processing
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/84634 , uj:19246
- Description: Abstract: The study reported in this thesis was aimed at investigating the ring opening mechanism(s) associated with the breaking of the carbon-oxygen oxirane bond of tetraethyl 2-aryl-1,2-epoxygembisphosphonate. Density Functional Theory (DFT) was employed to theoretically determine the mechanism(s) of the oxirane ring opening for tetraethyl 2-aryl-1,2-epoxy-2-phenylbisphosphonate. Simulations were carried out using the Gaussian09 version D01 software whereas visualisations were performed in GaussView 5.0.8, a graphic user interface compatible and part of the Gaussian software packages. The generalized gradient approximation functional BP86 in combination with the 6-31+G(d,p) and aug-cc-pVTZ basis sets was used for investigating the proposed reaction pathways. The method was selected after comparing energies and geometries obtained at both the BP86 and B3LYP functionals on selected local minima. Two transition states were obtained and found to be associated with opening on carbon 1 and 2 of the oxirane ring. These transition states were verified by running a frequency calculation and an intrinsic reaction coordinate (IRC) calculation at the same level of theory. Solvent effects were incorporated implicitly using the conductor-like polarised continuum model (CPCM) to investigate the effects on the energy and structures involved in the proposed mechanistic pathways. The effect of both electron donating and electron withdrawing groups on the transition state energies was also investigated. The ring opening at C2 was found to be the most favoured pathway both in vacuum and in the selected solvents. , M.Sc. (Chemistry)
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Development and application of molecularly imprinted polymers for selective separation and recovery of gold and silver from industrial wastewaters
- Ahamed, Mohammed Elbushra Hassan
- Authors: Ahamed, Mohammed Elbushra Hassan
- Date: 2018
- Subjects: Extraction (Chemistry) , Heavy metals , Polymers - Separation , Polymers - Analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/261571 , uj:27582
- Description: Ph.D. (Chemistry) , Abstract: Due to the continued global demand for silver and gold, there is constantly a need for more efficient and cost-effective methods to recover these precious metals from industrial aqueous solutions. The recovery of these metals is not easy owing to their presence in complex matrices. As selective recognition elements materials, molecularly imprinted polymers (MIPs) have been attracting great attention for their application in metals extraction. In this research, the performance of imprinted polymers as an adsorbent for the selective recovery of precious metal ions from mining and metallurgical wastewaters was investigated. The imprinted polymers were prepared using various functional monomers (vinylated monomers) and modified chitosan-biopolymers. Various techniques were used to characterize the prepared polymers and to elucidate their interaction mechanisms with the studied precious metal ion. The study also investigated the adsorption behavior of these materials in single and co-adsorption metal ions systems. In the first part of the study, ion-imprinted polymers (IIPs) were prepared by bulk polymerization method using three coordinating monomers namely: 4-vinyl pyridine (4-VP), N-(4-vinyl benzyl) ethylenediamine (EDA) and N-(allyl)-N-diethylthiophosphate (ADT), and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. Comparative studies on the adsorption performance of these IIPs for gold ion were conducted. The results obtained indicated that IIPs containing 4-VP had superior adsorption capability and selectivity towards gold compared to the other IIPs. Molecular modeling, using a Gaussian software package, was used to understand this difference in the adsorption ability. The results obtained indicated that the interaction between gold ion and 4-VP monomer is the strongest (ΔG = -4143.75 kcal mol-1) than its interaction with the other two monomers, suggesting that the adsorption process is more feasible for the IIP derived from 4-VP. FTIR and XRD analysis were done in order to understand and elucidate the adsorption mechanisms. It was proposed that gold ion adsorbed onto IIPs 4-VP and EDA by coordination and ion exchange mechanisms, while complexation – reduction mechanism was the one that accounted for its adsorption onto ADT produced polymeric material. In another attempt, IIPs synthesized from two functional monomers, 4-VP and 1-vinyl imidazole (1-VID), and N, N-ethylene bisacrylamide (EBAm) as the crosslinker via a precipitation polymerization method were found to be suitable for Ag(I) extraction...
- Full Text:
- Authors: Ahamed, Mohammed Elbushra Hassan
- Date: 2018
- Subjects: Extraction (Chemistry) , Heavy metals , Polymers - Separation , Polymers - Analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/261571 , uj:27582
- Description: Ph.D. (Chemistry) , Abstract: Due to the continued global demand for silver and gold, there is constantly a need for more efficient and cost-effective methods to recover these precious metals from industrial aqueous solutions. The recovery of these metals is not easy owing to their presence in complex matrices. As selective recognition elements materials, molecularly imprinted polymers (MIPs) have been attracting great attention for their application in metals extraction. In this research, the performance of imprinted polymers as an adsorbent for the selective recovery of precious metal ions from mining and metallurgical wastewaters was investigated. The imprinted polymers were prepared using various functional monomers (vinylated monomers) and modified chitosan-biopolymers. Various techniques were used to characterize the prepared polymers and to elucidate their interaction mechanisms with the studied precious metal ion. The study also investigated the adsorption behavior of these materials in single and co-adsorption metal ions systems. In the first part of the study, ion-imprinted polymers (IIPs) were prepared by bulk polymerization method using three coordinating monomers namely: 4-vinyl pyridine (4-VP), N-(4-vinyl benzyl) ethylenediamine (EDA) and N-(allyl)-N-diethylthiophosphate (ADT), and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. Comparative studies on the adsorption performance of these IIPs for gold ion were conducted. The results obtained indicated that IIPs containing 4-VP had superior adsorption capability and selectivity towards gold compared to the other IIPs. Molecular modeling, using a Gaussian software package, was used to understand this difference in the adsorption ability. The results obtained indicated that the interaction between gold ion and 4-VP monomer is the strongest (ΔG = -4143.75 kcal mol-1) than its interaction with the other two monomers, suggesting that the adsorption process is more feasible for the IIP derived from 4-VP. FTIR and XRD analysis were done in order to understand and elucidate the adsorption mechanisms. It was proposed that gold ion adsorbed onto IIPs 4-VP and EDA by coordination and ion exchange mechanisms, while complexation – reduction mechanism was the one that accounted for its adsorption onto ADT produced polymeric material. In another attempt, IIPs synthesized from two functional monomers, 4-VP and 1-vinyl imidazole (1-VID), and N, N-ethylene bisacrylamide (EBAm) as the crosslinker via a precipitation polymerization method were found to be suitable for Ag(I) extraction...
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Evaluation of selected oxidising reagents, as an attempt to replace FeCl3 in the mirror face cleaning process
- Authors: Motsogi, Gladness
- Date: 2019
- Subjects: Oxidizing agents , Mirrors
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/418350 , uj:35466
- Description: Abstract: The necessity of a clean face of a mirror goes as far as ensuring that its reflection abilities are not questioned. Reflection is what attracts people to a mirror. During mirror manufacturing, silver, copper and other chemicals overlap to the reflection side of a mirror, making a mirror have metals on both sides. In order to remove the copper and silver metals on the wrong side, we report the comparison of Na2FeO4 and prepared copper chloride (or a mixture of CuSO4.5H2O and NaCl) in cleaning the mirror face by oxidation reaction as a substitute to the currently used FeCl3. We report on the comparison of the three reagents, in terms, of the effluent plant contamination using XRD and XRF to analyse precipitates that formed because of their use. The comparison of equipment corrosion by determining the corrosion rate (gravimetric weight loss method) is also reported. We report the comparison of corrosion resistance of the final mirror using the CASS test or salt spray test. We also tested a much better stainless, steel duplex 2205, using the two reagents to see if it can be used in future, for mirror making equipment to overcome the challenge of equipment corrosion caused by inorganic oxidants. When compared by time parameter, the prepared CuCl2 solution is the fastest; removing 95.63 % copper and 62.83 % silver, and outdoing the currently used FeCl3 which only removed 12.45 % of the deposited silver on the glass within 20 seconds. The prepared CuCl2 did not cause more toxicity to the effluent water generated after its use. The use of Na2FeO4 did not result in mirror corrosion because it passed the CASS test. , M.Sc. (Chemistry)
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- Authors: Motsogi, Gladness
- Date: 2019
- Subjects: Oxidizing agents , Mirrors
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/418350 , uj:35466
- Description: Abstract: The necessity of a clean face of a mirror goes as far as ensuring that its reflection abilities are not questioned. Reflection is what attracts people to a mirror. During mirror manufacturing, silver, copper and other chemicals overlap to the reflection side of a mirror, making a mirror have metals on both sides. In order to remove the copper and silver metals on the wrong side, we report the comparison of Na2FeO4 and prepared copper chloride (or a mixture of CuSO4.5H2O and NaCl) in cleaning the mirror face by oxidation reaction as a substitute to the currently used FeCl3. We report on the comparison of the three reagents, in terms, of the effluent plant contamination using XRD and XRF to analyse precipitates that formed because of their use. The comparison of equipment corrosion by determining the corrosion rate (gravimetric weight loss method) is also reported. We report the comparison of corrosion resistance of the final mirror using the CASS test or salt spray test. We also tested a much better stainless, steel duplex 2205, using the two reagents to see if it can be used in future, for mirror making equipment to overcome the challenge of equipment corrosion caused by inorganic oxidants. When compared by time parameter, the prepared CuCl2 solution is the fastest; removing 95.63 % copper and 62.83 % silver, and outdoing the currently used FeCl3 which only removed 12.45 % of the deposited silver on the glass within 20 seconds. The prepared CuCl2 did not cause more toxicity to the effluent water generated after its use. The use of Na2FeO4 did not result in mirror corrosion because it passed the CASS test. , M.Sc. (Chemistry)
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Phosphorylated carbon nanotube-cyclodextrin/silver-doped titania nanobiocomposites for water purification
- Authors: Leudjo Taka, Anny
- Date: 2018
- Subjects: Water - Purification , Cyclodextrins , Titanium dioxide , Carbon nanotubes , Nanobiotechnology
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/278734 , uj:29917
- Description: Ph.D. (Chemistry) , Abstract: Nowadays, the shortage of water resources is the major concern around the world and especially in Southern Africa. The challenge is to develop an effective method to recycle wastewater through adequate treatment. That is to design a water treatment material able to remove the pollutants from wastewater effectively and efficiently to the accepted levels. In this regard, the aim of this research project was to develop a new nanomaterial which was used as adsorbent and disinfectant to remove all the three classes of water pollutants (inorganic, organic and pathogenic microorganism) from wastewater. In this study, phosphorylated multiwalled carbon nanotube-cyclodextrin/silver doped titania (pMWCNT-βCD/TiO2-Ag) was synthesized, using a combined process of amidation reaction, cross-linking polymerization and the sol-gel method. For a better evaluation of the target material, the insoluble nanosponges β-cyclodextrin (βCD) polymer and pMWCNT-βCD composite polymer were also synthesized for comparison purposes. The prepared nanostructured materials were fully characterized using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), Brunauer-Emmett-Teller (BET) method, electron microscopy, and spectroscopy techniques. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of functional groups on the surface of modified MWCNTs, and the polymerization reaction. X-ray photoelectron spectroscopy (XPS) was employed to further confirm the presence of functional groups on the surface of the nanomaterials synthesized and to provide the percentage elemental composition with binding energies. Laser Raman showed the presence of MWCNT, βCD, and TiO2 in the nanocomposite. The anatase crystalline form of TiO2 in the samples synthesized was confirmed by X-ray diffraction (XRD) spectroscopy analysis. Transmission electron microscopy (TEM) analysis confirmed the structural morphology of the new biopolymer nanocomposite (pMWCNT-βCD/TiO2-Ag) as a sponge-like structure which showed a good dispersion of Ag nanoparticles. The BET surface area of the newly developed pMWCNT-βCD/TiO2-Ag was very high (352.55 m2/g), and this favored the use of this new nanomaterial as an adsorbent for the effective removal of pollutants from synthetic i.e. model wastewater and mine effluent samples...
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- Authors: Leudjo Taka, Anny
- Date: 2018
- Subjects: Water - Purification , Cyclodextrins , Titanium dioxide , Carbon nanotubes , Nanobiotechnology
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/278734 , uj:29917
- Description: Ph.D. (Chemistry) , Abstract: Nowadays, the shortage of water resources is the major concern around the world and especially in Southern Africa. The challenge is to develop an effective method to recycle wastewater through adequate treatment. That is to design a water treatment material able to remove the pollutants from wastewater effectively and efficiently to the accepted levels. In this regard, the aim of this research project was to develop a new nanomaterial which was used as adsorbent and disinfectant to remove all the three classes of water pollutants (inorganic, organic and pathogenic microorganism) from wastewater. In this study, phosphorylated multiwalled carbon nanotube-cyclodextrin/silver doped titania (pMWCNT-βCD/TiO2-Ag) was synthesized, using a combined process of amidation reaction, cross-linking polymerization and the sol-gel method. For a better evaluation of the target material, the insoluble nanosponges β-cyclodextrin (βCD) polymer and pMWCNT-βCD composite polymer were also synthesized for comparison purposes. The prepared nanostructured materials were fully characterized using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), Brunauer-Emmett-Teller (BET) method, electron microscopy, and spectroscopy techniques. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of functional groups on the surface of modified MWCNTs, and the polymerization reaction. X-ray photoelectron spectroscopy (XPS) was employed to further confirm the presence of functional groups on the surface of the nanomaterials synthesized and to provide the percentage elemental composition with binding energies. Laser Raman showed the presence of MWCNT, βCD, and TiO2 in the nanocomposite. The anatase crystalline form of TiO2 in the samples synthesized was confirmed by X-ray diffraction (XRD) spectroscopy analysis. Transmission electron microscopy (TEM) analysis confirmed the structural morphology of the new biopolymer nanocomposite (pMWCNT-βCD/TiO2-Ag) as a sponge-like structure which showed a good dispersion of Ag nanoparticles. The BET surface area of the newly developed pMWCNT-βCD/TiO2-Ag was very high (352.55 m2/g), and this favored the use of this new nanomaterial as an adsorbent for the effective removal of pollutants from synthetic i.e. model wastewater and mine effluent samples...
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Synthesis and characterization of 2-phenyl-1,3,2-dioxaphosphoalkyl-2-oxides and their sulphide analogues
- Authors: Mamatela, Tuma Gabriel
- Date: 2017
- Subjects: Alkylation , Organic compounds - Synthesis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/244041 , uj:25233
- Description: M.Tech. (Chemistry) , Abstract: Please refer to full text to view abstract
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- Authors: Mamatela, Tuma Gabriel
- Date: 2017
- Subjects: Alkylation , Organic compounds - Synthesis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/244041 , uj:25233
- Description: M.Tech. (Chemistry) , Abstract: Please refer to full text to view abstract
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Synthesis and characterization of carbon nanospheres and carbon nanotubes conjugated bisphosphonates as potential drugs for the treatment of secondary bone cancer
- Authors: Dlamini, Njabuliso Lucia
- Date: 2019
- Subjects: Carbon , Carbon nanotubes , Nanostructured materials , Bone - Cancer - Radiotherapy , Bone - Cancer - Chemotherapy , Diphosphonates - Therapeutic use
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/417240 , uj:35327
- Description: Abstract: The statistical proof that most of the different forms of cancer metastasize to bone tissue from other body organs has seen to the development of several treatment regimes. These include surgery, radiotherapy, hormonal therapy and chemotherapy. The latter was established to be an effective form of treatment for secondary bone cancer. This is due to that drugs administered into the body system can reach most areas where the cancerous cells have metastasized... , Ph.D. (Chemistry)
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- Authors: Dlamini, Njabuliso Lucia
- Date: 2019
- Subjects: Carbon , Carbon nanotubes , Nanostructured materials , Bone - Cancer - Radiotherapy , Bone - Cancer - Chemotherapy , Diphosphonates - Therapeutic use
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/417240 , uj:35327
- Description: Abstract: The statistical proof that most of the different forms of cancer metastasize to bone tissue from other body organs has seen to the development of several treatment regimes. These include surgery, radiotherapy, hormonal therapy and chemotherapy. The latter was established to be an effective form of treatment for secondary bone cancer. This is due to that drugs administered into the body system can reach most areas where the cancerous cells have metastasized... , Ph.D. (Chemistry)
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Synthesis of disubstituted vinyl bisphosphonates using the Michaelis-Becker reaction
- Authors: Donga, Cabangani
- Date: 2017
- Subjects: Phosphonates , Phosphonates - Structure-activity relationships , Palladium catalysts
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235704 , uj:24109
- Description: M.Sc. (Chemistry) , Abstract: A novel work on the synthesis of a series of disubstituted vinyl gembisphosphonates from 1-iodo-vinyl phosphonates through a tetrakis (triphenylphosphine) palladium (0) catalyzed Michaelis-Becker reaction is reported.In this study, the Michaelis-Becker reaction involves attack of a diethyl phosphite anion on a 1-iodo vinyl phosphonatecontaining a phenyl substituent to yield disubstituted vinyl gembisphosphonates by nucleophilic substitution. Characterization of all the synthesised compounds was done by Fourier Transmission Infrared (FT-IR),1H, 13C and 31P Nuclear Magnetic Resonance (NMR) spectroscopy.
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- Authors: Donga, Cabangani
- Date: 2017
- Subjects: Phosphonates , Phosphonates - Structure-activity relationships , Palladium catalysts
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235704 , uj:24109
- Description: M.Sc. (Chemistry) , Abstract: A novel work on the synthesis of a series of disubstituted vinyl gembisphosphonates from 1-iodo-vinyl phosphonates through a tetrakis (triphenylphosphine) palladium (0) catalyzed Michaelis-Becker reaction is reported.In this study, the Michaelis-Becker reaction involves attack of a diethyl phosphite anion on a 1-iodo vinyl phosphonatecontaining a phenyl substituent to yield disubstituted vinyl gembisphosphonates by nucleophilic substitution. Characterization of all the synthesised compounds was done by Fourier Transmission Infrared (FT-IR),1H, 13C and 31P Nuclear Magnetic Resonance (NMR) spectroscopy.
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