The synthesis of functionalized carbon nanomaterial from waste tyre sourced carbon for chemosensing during purification processes
- Authors: Du Plessis, Jacolien
- Date: 2018
- Subjects: Nanostructured materials , Nanotechnology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/29925 , vital:30794
- Description: The short lifetime of tyres causes great environmental harm due to their non-biodegradable nature resulting in land and water pollution. Exploration of novel uses for recycled tyres is therefore imperative. The use of recycled waste tyres as carbon source for the synthesis of fluorescent chemosensing carbon nanomaterial for the detection of harmful chemicals in water is proposed in this work. Three key problems are addressed in this study: i) re-using of waste tyre products, ii) synthesis of low-cost carbon nanomaterial, iii) detection of harmful compounds within environment systems. The fluorescent triazolyl-coumarin compound, 7-(diethylamino)-3-(4-(1-hydroxyethyl)-1H-1,2,3-triazol-1-yl)-2H-chromen-2-one, was synthesized in multiple steps from 4-diethylamino salicylaldehyde. The last step included the use of Cu(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition (“click-reaction”) to form a triazole ring. Carbon spheres were synthesized through catalytic chemical vapour deposition (CVD) from waste tyre pyrolysis oil (WTPO), as the carbon source, in the presence of a catalytic amount of ferrocene. The quality and quantity of the carbon spheres had an overall improvement as the synthesis temperatures increased from 800 oC to 950 oC. The diameter of the carbon spheres reduced from 1017 nm to 577 nm as seen in TEM and SEM imaging. TGA and XRD analysis indicated a direct relationship between an increase in synthesis temperatures with an increase in the crystallinity of the carbon spheres. Commercially available naphthenic oil was used as a reference to compare the impact of the starting carbon precursor on the morphology of the carbon nanomaterial under the same reaction conditions. Multi-walled carbon nanotubes were synthesized at the lower temperatures of 800-850 oC. Carbon fibres and carbon spheres were observed at the synthesis temperatures of 900-950 oC. The carbon source played a role in the morphology of the carbon nanomaterial as it could be seen between the complex natured WTPO and the pure naphthenic oil. The purified carbon spheres synthesized at 950 oC from WTPO were functionalized with the triazolyl-coumarin units on the surface through Steglich esterification using DCC/DMAP to yield fluorescent carbon spheres. Complexation studies of the functionalized carbon spheres were done using UV/Vis spectroscopy and fluorescence with a wide range of ions; Ag+, Al3+, Co2+, Cr3+, Cu2+, Fe3+, ii Hg2+, Li+, Ni2+, Pb2+ and Zn2+. The triazolyl-coumarin carbon spheres showed reasonable sensitivity and selectivity towards Fe3+ in water with a quenching effect in fluorescence. Titration studies with Fe3+ indicating an exponential decay of quenching in the fluorescence up to 68% with detection limit at 2.73 x 10-5 M.
- Full Text:
- Date Issued: 2018
- Authors: Du Plessis, Jacolien
- Date: 2018
- Subjects: Nanostructured materials , Nanotechnology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/29925 , vital:30794
- Description: The short lifetime of tyres causes great environmental harm due to their non-biodegradable nature resulting in land and water pollution. Exploration of novel uses for recycled tyres is therefore imperative. The use of recycled waste tyres as carbon source for the synthesis of fluorescent chemosensing carbon nanomaterial for the detection of harmful chemicals in water is proposed in this work. Three key problems are addressed in this study: i) re-using of waste tyre products, ii) synthesis of low-cost carbon nanomaterial, iii) detection of harmful compounds within environment systems. The fluorescent triazolyl-coumarin compound, 7-(diethylamino)-3-(4-(1-hydroxyethyl)-1H-1,2,3-triazol-1-yl)-2H-chromen-2-one, was synthesized in multiple steps from 4-diethylamino salicylaldehyde. The last step included the use of Cu(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition (“click-reaction”) to form a triazole ring. Carbon spheres were synthesized through catalytic chemical vapour deposition (CVD) from waste tyre pyrolysis oil (WTPO), as the carbon source, in the presence of a catalytic amount of ferrocene. The quality and quantity of the carbon spheres had an overall improvement as the synthesis temperatures increased from 800 oC to 950 oC. The diameter of the carbon spheres reduced from 1017 nm to 577 nm as seen in TEM and SEM imaging. TGA and XRD analysis indicated a direct relationship between an increase in synthesis temperatures with an increase in the crystallinity of the carbon spheres. Commercially available naphthenic oil was used as a reference to compare the impact of the starting carbon precursor on the morphology of the carbon nanomaterial under the same reaction conditions. Multi-walled carbon nanotubes were synthesized at the lower temperatures of 800-850 oC. Carbon fibres and carbon spheres were observed at the synthesis temperatures of 900-950 oC. The carbon source played a role in the morphology of the carbon nanomaterial as it could be seen between the complex natured WTPO and the pure naphthenic oil. The purified carbon spheres synthesized at 950 oC from WTPO were functionalized with the triazolyl-coumarin units on the surface through Steglich esterification using DCC/DMAP to yield fluorescent carbon spheres. Complexation studies of the functionalized carbon spheres were done using UV/Vis spectroscopy and fluorescence with a wide range of ions; Ag+, Al3+, Co2+, Cr3+, Cu2+, Fe3+, ii Hg2+, Li+, Ni2+, Pb2+ and Zn2+. The triazolyl-coumarin carbon spheres showed reasonable sensitivity and selectivity towards Fe3+ in water with a quenching effect in fluorescence. Titration studies with Fe3+ indicating an exponential decay of quenching in the fluorescence up to 68% with detection limit at 2.73 x 10-5 M.
- Full Text:
- Date Issued: 2018
Synthesis of folate-conjugated palladium nanoparticles
- Authors: Xolo, Luthando
- Date: 2018
- Subjects: Nanotechnology , Nanostructured materials Complex compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/36442 , vital:33943
- Description: In this study, the synthesis of two new folate-conjugated palladium (Pd) nanoparticles was carried out. This was done via two steps; firstly, the synthesis of palladium nanoparticles (PdNPs) capped with 4-aminothiophenol (4-Atp) and secondly, they were conjugated to the folate to form Folate-4Atp-PdNPs. All the above were characterized by using Fourier Transform Infrared spectroscopy (FTIR) which confirmed the formation of the targeted product (PdNPs-4-Atp-folate) as well as the 2-Aet linked with folate product (2-Aet-folate). The optical properties of the products formed were characterized further by using UV-Vis spectroscopy and Photoluminescence (PL). The size and shape of the nanoparticles were obtained by Transmission Electron Microscopy (TEM). The FTIR confirmed the formation of desired nanoparticles (Fa-4Atp-PdNPs), with peak of C=O stretching vibration at 1659 cm-1. The UV-Vis showed absorption peaks at 236 nm and 285 nm which was due to n-π* and π-π* transitions. The nanoparticles also showed excitation and emission peaks at 360 nm and 455 nm from the PL when excitation wavelength was set at 270 nm. The methanol soluble nanoparticles had an average size of 36 nm while the water-soluble nanoparticles were 4 nm in size. The HRTEM also showed the methanol nanoparticles were amorphous while the water-soluble nanoparticles were crystalline. The work reports on comparison of the methanol-soluble and water-soluble nanoparticles size distribution and the effect of capping agent used on the nanoparticles.
- Full Text:
- Date Issued: 2018
- Authors: Xolo, Luthando
- Date: 2018
- Subjects: Nanotechnology , Nanostructured materials Complex compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/36442 , vital:33943
- Description: In this study, the synthesis of two new folate-conjugated palladium (Pd) nanoparticles was carried out. This was done via two steps; firstly, the synthesis of palladium nanoparticles (PdNPs) capped with 4-aminothiophenol (4-Atp) and secondly, they were conjugated to the folate to form Folate-4Atp-PdNPs. All the above were characterized by using Fourier Transform Infrared spectroscopy (FTIR) which confirmed the formation of the targeted product (PdNPs-4-Atp-folate) as well as the 2-Aet linked with folate product (2-Aet-folate). The optical properties of the products formed were characterized further by using UV-Vis spectroscopy and Photoluminescence (PL). The size and shape of the nanoparticles were obtained by Transmission Electron Microscopy (TEM). The FTIR confirmed the formation of desired nanoparticles (Fa-4Atp-PdNPs), with peak of C=O stretching vibration at 1659 cm-1. The UV-Vis showed absorption peaks at 236 nm and 285 nm which was due to n-π* and π-π* transitions. The nanoparticles also showed excitation and emission peaks at 360 nm and 455 nm from the PL when excitation wavelength was set at 270 nm. The methanol soluble nanoparticles had an average size of 36 nm while the water-soluble nanoparticles were 4 nm in size. The HRTEM also showed the methanol nanoparticles were amorphous while the water-soluble nanoparticles were crystalline. The work reports on comparison of the methanol-soluble and water-soluble nanoparticles size distribution and the effect of capping agent used on the nanoparticles.
- Full Text:
- Date Issued: 2018
Of science and small things: recollections of the past twenty(-)odd years
- Authors: Botha, J. R
- Subjects: Nanoscience , Nanotechnology , f-sa
- Language: English
- Type: text , Lectures
- Identifier: http://hdl.handle.net/10948/20867 , vital:29409
- Description: I will start, therefore, with an overview of achievements in a “new” field of endeavour, a science of small things, popularly called nanoscience, and its spin-off called nanotechnology. I will present a brief history, look at the approaches that have been followed by scientists and engineers to develop and understand small things, and summarise some of the benefits to society in terms of new materials and processes, energy storage and generation, electronics, environmental applications, medicine and transportation. Since our own research focuses on the development on semiconductors, I will conclude the scientific part of the presentation by considering the contribution of semiconductors to the development of nanotechnology and highlight a few examples from our own research during the past two decades on the development of nano-scale semiconductor structures, like nanorods, quantum wells and superlattices.
- Full Text:
- Authors: Botha, J. R
- Subjects: Nanoscience , Nanotechnology , f-sa
- Language: English
- Type: text , Lectures
- Identifier: http://hdl.handle.net/10948/20867 , vital:29409
- Description: I will start, therefore, with an overview of achievements in a “new” field of endeavour, a science of small things, popularly called nanoscience, and its spin-off called nanotechnology. I will present a brief history, look at the approaches that have been followed by scientists and engineers to develop and understand small things, and summarise some of the benefits to society in terms of new materials and processes, energy storage and generation, electronics, environmental applications, medicine and transportation. Since our own research focuses on the development on semiconductors, I will conclude the scientific part of the presentation by considering the contribution of semiconductors to the development of nanotechnology and highlight a few examples from our own research during the past two decades on the development of nano-scale semiconductor structures, like nanorods, quantum wells and superlattices.
- Full Text:
The development of palladium nanoparticles for radiopharmaceutical application
- Authors: Gandidzanwa, Sendibitiyosi
- Date: 2019
- Subjects: Nanotechnology , Nanostructures Nanofluids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42163 , vital:36631
- Description: The dissertation describes an in-depth synthesis and optimisation of palladium(0) nanoparticles of three distinct size ranges, respective capping agents, and cellular uptake studies using a non-toxic concentration (10 μM), laying a foundation for the design of palladium-based folate receptor-targeted theranostic nanoradiopharmaceutical. In the preliminary selection to determine the optimal diamines for the study, ethylenediamine, hexamethylenediamine, 1,10-diaminodecane, 1,12-diaminododecane, 1,4- diaminobenzene, 4,4’-ethylenedianiline, 1,2-diphenyl-1,2-diaminoethane, and tetraaminophthalocyanine were employed. The characterisation of the nanoparticles obtained from the in situ reduction of palladium(II) salt at room temperature by either 1,2,3- trihydroxybenze (pyrogallol), citric acid, sodium metabisulphite, sodium borohydride, hydrazine hydrate, or formaldehyde was performed. Ethylenediamine and sodium borohydride were found to be the best diamine capping and reducing agent, respectively. Systematic investigations determined that the nanoparticle synthesis was dependent on various reaction parameters: such as reaction temperature, time, reductant reducing power, and capping agents. The parameters effects on the nanoparticle size, morphology, shape, stability, crystallinity, and surface charge were investigated. The optical properties, elemental composition, functional group, concentration and molecular weight for the synthesised nanoparticles or conjugates were determined. These properties were analysed using Ultraviolet–visible spectroscopy (UV-Vis), high resolution transmission electron microscopy (HRTEM) coupled with selective area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), zeta potential (ZP), dynamic light scattering (DLS), elemental analysis (EA), 1H and 13C-nuclear magnetic resonance (1H- and 13CNMR), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and liquid chromatography-mass spectroscopy (LC-MS). The in vitro cytotoxicity, cell uptake, and internalisation studies of palladium nanoparticles (10 μM) ranging in size and different types of capping agent were performed using three breast cancer cell lines: MDA-MB-468 , MCF-7 and MDA-MB-231 , and a non-tumorigenic MCF-10A breast cell line. The cell uptake and internalisation were investigated using ICP-OES and TEM. A high dependence between reduction rate and concentration of palladium precursor was observed for the room temperature synthesis of palladium nanoparticles, and the employed synthesis procedure will be applied to the hot palladium isotope (109Pd). A facile, green, aqueous synthesis route for palladium nanoparticles at room temperature was developed, and the synthesised nanoparticles indicated narrow size distributions. A concentration dependence between cytotoxicity and palladium nanoparticles was observed, with lower concentrations (10 μM) exhibiting minimal cytotoxicity relative to higher concentrations (100 μM). The cellular uptake of palladium nanoparticles was found to be concentration, folate-receptor, capping agent, and cell line proliferation-dependent. Well-defined, monodispersed, and negatively charged folate-ethylenediamine and folate-phthalocyanine capped palladium nanoparticles were taken up by cells, with higher nanoparticle internalisation in folate receptor positive tumorigenic cells relative to folate receptor negative non-tumorigenic cells. It can be concluded that palladium(0) nanoparticles can be synthesised from the reduction of palladium(II) by sodium borohydride at room temperature. The folate-conjugated palladium nanoparticles are non-cytotoxic at 10 μM and were successfully optimised and selectively delivered to folate receptor-positive breast cancer cells (MDA-MB-231 and MCF-7) relative to non-tumorigenic breast cells (MCF-10A) and folate receptor negative cancer cells (MDA-MB-468).
- Full Text:
- Date Issued: 2019
- Authors: Gandidzanwa, Sendibitiyosi
- Date: 2019
- Subjects: Nanotechnology , Nanostructures Nanofluids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42163 , vital:36631
- Description: The dissertation describes an in-depth synthesis and optimisation of palladium(0) nanoparticles of three distinct size ranges, respective capping agents, and cellular uptake studies using a non-toxic concentration (10 μM), laying a foundation for the design of palladium-based folate receptor-targeted theranostic nanoradiopharmaceutical. In the preliminary selection to determine the optimal diamines for the study, ethylenediamine, hexamethylenediamine, 1,10-diaminodecane, 1,12-diaminododecane, 1,4- diaminobenzene, 4,4’-ethylenedianiline, 1,2-diphenyl-1,2-diaminoethane, and tetraaminophthalocyanine were employed. The characterisation of the nanoparticles obtained from the in situ reduction of palladium(II) salt at room temperature by either 1,2,3- trihydroxybenze (pyrogallol), citric acid, sodium metabisulphite, sodium borohydride, hydrazine hydrate, or formaldehyde was performed. Ethylenediamine and sodium borohydride were found to be the best diamine capping and reducing agent, respectively. Systematic investigations determined that the nanoparticle synthesis was dependent on various reaction parameters: such as reaction temperature, time, reductant reducing power, and capping agents. The parameters effects on the nanoparticle size, morphology, shape, stability, crystallinity, and surface charge were investigated. The optical properties, elemental composition, functional group, concentration and molecular weight for the synthesised nanoparticles or conjugates were determined. These properties were analysed using Ultraviolet–visible spectroscopy (UV-Vis), high resolution transmission electron microscopy (HRTEM) coupled with selective area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), zeta potential (ZP), dynamic light scattering (DLS), elemental analysis (EA), 1H and 13C-nuclear magnetic resonance (1H- and 13CNMR), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and liquid chromatography-mass spectroscopy (LC-MS). The in vitro cytotoxicity, cell uptake, and internalisation studies of palladium nanoparticles (10 μM) ranging in size and different types of capping agent were performed using three breast cancer cell lines: MDA-MB-468 , MCF-7 and MDA-MB-231 , and a non-tumorigenic MCF-10A breast cell line. The cell uptake and internalisation were investigated using ICP-OES and TEM. A high dependence between reduction rate and concentration of palladium precursor was observed for the room temperature synthesis of palladium nanoparticles, and the employed synthesis procedure will be applied to the hot palladium isotope (109Pd). A facile, green, aqueous synthesis route for palladium nanoparticles at room temperature was developed, and the synthesised nanoparticles indicated narrow size distributions. A concentration dependence between cytotoxicity and palladium nanoparticles was observed, with lower concentrations (10 μM) exhibiting minimal cytotoxicity relative to higher concentrations (100 μM). The cellular uptake of palladium nanoparticles was found to be concentration, folate-receptor, capping agent, and cell line proliferation-dependent. Well-defined, monodispersed, and negatively charged folate-ethylenediamine and folate-phthalocyanine capped palladium nanoparticles were taken up by cells, with higher nanoparticle internalisation in folate receptor positive tumorigenic cells relative to folate receptor negative non-tumorigenic cells. It can be concluded that palladium(0) nanoparticles can be synthesised from the reduction of palladium(II) by sodium borohydride at room temperature. The folate-conjugated palladium nanoparticles are non-cytotoxic at 10 μM and were successfully optimised and selectively delivered to folate receptor-positive breast cancer cells (MDA-MB-231 and MCF-7) relative to non-tumorigenic breast cells (MCF-10A) and folate receptor negative cancer cells (MDA-MB-468).
- Full Text:
- Date Issued: 2019
Block copolymer templates for metal oxide nanostructures
- Authors: Talla, Assane
- Date: 2019
- Subjects: Nanotechnology , Nanostructured materials Metal oxide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43889 , vital:37075
- Description: Recent advances in technology have increased the need for fabrication of devices with feature sizes of tens of nanometers, such as ultra-fine filters or membranes, and high density data storage media, to name a few. For this reason, research is now focused on block copolymer nanolithographic processes, particularly the fabrication of nanoscale templates with domains well below 100 nm. Block copolymers have the tendency to self-organise into various structures, such as lamellae, spheres or cylinders on a nanometer scale. Among these possible configurations, the perpendicular cylindrical structure is most desirable, because it can be used for templates or masks for feature development, in particular, oriented wires or rods. In this work, the aim is to create a nano-mask from a di-block copolymer thin film, for zinc oxide nanorods growth. For this purpose poly (styrene-block-methylmethacrylate) (PS-b-PMMA) was investigated as a potential nano-mask. Samples were characterized using X-ray reflectometry to determine the thicknesses of the PS-b-PMMA thin films, while scanning probe microscopy and scanning electron microscopy was used to investigate the surface morphology of the samples. PS-b-PMMA thin films were produced on a random copolymer (poly (styrene-random-methylmethacrylate) (PS-r-PMMA) coated onto a silicon substrate. The PS-r-PMMA permits a non-preferential interaction between the di-block constituents and the substrate. Thermal annealing in vacuum of PS-b-PMMA on PS-r-PMMA led to perpendicular cylinders of PMMA within a PS matrix in the di-block. The typical thicknesses measured for the di-block copolymer films ranged between 33 nm and 37 nm. During this study, a perpendicular orientation of the di-block components was also produced when PS-b-PMMA was spun onto a layer of zinc oxide nanoparticles and thermally annealed in vacuum. It was shown that the ZnO nanoparticles created a corrugated surface on silicon which induced perpendicular cylinders of PMMA within the PS matrix. This was possible for a specific surface roughness parameter and film thickness. In this case, the typical thickness determined for the di-block copolymer ranged between 33 and 35 nm and the surface roughness parameter was 0.07. For the fabrication of a di-block template or PS nano-mask, the vertically oriented PMMA cylindrical nanodomains in the PS matrix were removed by exposing the film to ultraviolet radiation at an adequate dose, followed successively by washing in acetic acid and de-ionized water. It was shown that ultraviolet exposure is necessary to ensure the degradation of PMMA. A subsequent rinse in glacial acetic acid and DI water of the film exposed to ultraviolet, left an array of ordered nanoscopic pores with sizes ranging between 10 nm and 20 nm. Finally, the growth of ZnO nanorods on the di-block template produced on zinc oxide nanoparticles, was attempted using an aqueous solution based-method, namely chemical bath deposition. The rods did not grow inside the nanopores, probably due to poor capillary action. In additional experiments, the di-block template was removed by toluene (a selective solvent for PS) followed by the growth of ZnO rods on the exposed nanoparticle surface. Vertical and well separated ZnO rods formed on this surface, in places where the underlying seed layer had been attacked by the acetic acid treatment during removal of the PMMA. The observed ZnO rod morphology can be used in applications such as solar cell.
- Full Text:
- Date Issued: 2019
- Authors: Talla, Assane
- Date: 2019
- Subjects: Nanotechnology , Nanostructured materials Metal oxide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43889 , vital:37075
- Description: Recent advances in technology have increased the need for fabrication of devices with feature sizes of tens of nanometers, such as ultra-fine filters or membranes, and high density data storage media, to name a few. For this reason, research is now focused on block copolymer nanolithographic processes, particularly the fabrication of nanoscale templates with domains well below 100 nm. Block copolymers have the tendency to self-organise into various structures, such as lamellae, spheres or cylinders on a nanometer scale. Among these possible configurations, the perpendicular cylindrical structure is most desirable, because it can be used for templates or masks for feature development, in particular, oriented wires or rods. In this work, the aim is to create a nano-mask from a di-block copolymer thin film, for zinc oxide nanorods growth. For this purpose poly (styrene-block-methylmethacrylate) (PS-b-PMMA) was investigated as a potential nano-mask. Samples were characterized using X-ray reflectometry to determine the thicknesses of the PS-b-PMMA thin films, while scanning probe microscopy and scanning electron microscopy was used to investigate the surface morphology of the samples. PS-b-PMMA thin films were produced on a random copolymer (poly (styrene-random-methylmethacrylate) (PS-r-PMMA) coated onto a silicon substrate. The PS-r-PMMA permits a non-preferential interaction between the di-block constituents and the substrate. Thermal annealing in vacuum of PS-b-PMMA on PS-r-PMMA led to perpendicular cylinders of PMMA within a PS matrix in the di-block. The typical thicknesses measured for the di-block copolymer films ranged between 33 nm and 37 nm. During this study, a perpendicular orientation of the di-block components was also produced when PS-b-PMMA was spun onto a layer of zinc oxide nanoparticles and thermally annealed in vacuum. It was shown that the ZnO nanoparticles created a corrugated surface on silicon which induced perpendicular cylinders of PMMA within the PS matrix. This was possible for a specific surface roughness parameter and film thickness. In this case, the typical thickness determined for the di-block copolymer ranged between 33 and 35 nm and the surface roughness parameter was 0.07. For the fabrication of a di-block template or PS nano-mask, the vertically oriented PMMA cylindrical nanodomains in the PS matrix were removed by exposing the film to ultraviolet radiation at an adequate dose, followed successively by washing in acetic acid and de-ionized water. It was shown that ultraviolet exposure is necessary to ensure the degradation of PMMA. A subsequent rinse in glacial acetic acid and DI water of the film exposed to ultraviolet, left an array of ordered nanoscopic pores with sizes ranging between 10 nm and 20 nm. Finally, the growth of ZnO nanorods on the di-block template produced on zinc oxide nanoparticles, was attempted using an aqueous solution based-method, namely chemical bath deposition. The rods did not grow inside the nanopores, probably due to poor capillary action. In additional experiments, the di-block template was removed by toluene (a selective solvent for PS) followed by the growth of ZnO rods on the exposed nanoparticle surface. Vertical and well separated ZnO rods formed on this surface, in places where the underlying seed layer had been attacked by the acetic acid treatment during removal of the PMMA. The observed ZnO rod morphology can be used in applications such as solar cell.
- Full Text:
- Date Issued: 2019
Photocatalytic reduction of CO2 by cobalt doped TiO2 and ZnO micro/nanostructured materials
- Authors: Mgolombane, Mvano
- Date: 2020
- Subjects: Nanostructures , Catalysis , Nanotechnology , Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49171 , vital:41607
- Description: Large emissions of carbon dioxide (CO2) in the atmosphere have caused many harmful effects on humans and the environment. Carbon dioxide is a good source C and is used in a number of applications such as synthesis of fossil fuels. Redox reaction of CO2 and H2O with photocatalysts such as TiO2 and ZnO to produce solar fuels is a promising approach in reducing the environmental impacts of greenhouse gasses. This dissertation describes an in-depth synthesis of four photochemical catalysts and their photocatalytic conversion of CO2 to methanol, thereby addressing the above-mentioned problems by applying synthesised nano-based catalysts. Prior to photocatalytic reduction studies, catalysts such as TiO2, Co-doped TiO2, Co-doped TiO2/rGO, ZnO, Co-doped ZnO and Co-doped ZnO/rGO were synthesized and characterized using various spectroscopic and imaging techniques such as Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Micrograph (TEM), X-ray Photoelectron Spectroscopy (XPS), Brunner- Emmet- Teller measurement (BET), Thermogravimetry Analysis (TGA) and UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis-DRS). The conversion yield of CO2 to methanol on TiO2, Co-doped TiO2 and Co-doped TiO2/rGO reached 32.3 μmol/gcat, 730 μmol/gcat and 936 μmol/gcat, respectively, after 7 h of irradiation. Theoretical studies via Density functional theory (DFT) revealed that doping TiO2 with Co ions facilitated the formation of adsorbed carbonate or CO2•- species, as CO2 adsorbs onto Co-doped TiO2 surface with binding energy (BE) of -18.12 KJ/mol. The photocatalytic activities of ZnO-based nanomaterials found that Co-doped ZnO/rGO with high ratio of Co, reduced graphene (rGO) and large surface area (10.62 m2g-1) possessed higher CH3OH (30.1 μmol/g) in comparison with Co-doped ZnO (27.3 μmol/g) and ZnO (7.5 μmol/g). The research will deepen the understanding that TiO2 based photocatalyst show higher activity and the mole ratio (Ti/Zn:Co) influences nanocomposites performance and provide new ideas for designing efficient photocatalysts.
- Full Text:
- Date Issued: 2020
- Authors: Mgolombane, Mvano
- Date: 2020
- Subjects: Nanostructures , Catalysis , Nanotechnology , Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49171 , vital:41607
- Description: Large emissions of carbon dioxide (CO2) in the atmosphere have caused many harmful effects on humans and the environment. Carbon dioxide is a good source C and is used in a number of applications such as synthesis of fossil fuels. Redox reaction of CO2 and H2O with photocatalysts such as TiO2 and ZnO to produce solar fuels is a promising approach in reducing the environmental impacts of greenhouse gasses. This dissertation describes an in-depth synthesis of four photochemical catalysts and their photocatalytic conversion of CO2 to methanol, thereby addressing the above-mentioned problems by applying synthesised nano-based catalysts. Prior to photocatalytic reduction studies, catalysts such as TiO2, Co-doped TiO2, Co-doped TiO2/rGO, ZnO, Co-doped ZnO and Co-doped ZnO/rGO were synthesized and characterized using various spectroscopic and imaging techniques such as Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Micrograph (TEM), X-ray Photoelectron Spectroscopy (XPS), Brunner- Emmet- Teller measurement (BET), Thermogravimetry Analysis (TGA) and UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis-DRS). The conversion yield of CO2 to methanol on TiO2, Co-doped TiO2 and Co-doped TiO2/rGO reached 32.3 μmol/gcat, 730 μmol/gcat and 936 μmol/gcat, respectively, after 7 h of irradiation. Theoretical studies via Density functional theory (DFT) revealed that doping TiO2 with Co ions facilitated the formation of adsorbed carbonate or CO2•- species, as CO2 adsorbs onto Co-doped TiO2 surface with binding energy (BE) of -18.12 KJ/mol. The photocatalytic activities of ZnO-based nanomaterials found that Co-doped ZnO/rGO with high ratio of Co, reduced graphene (rGO) and large surface area (10.62 m2g-1) possessed higher CH3OH (30.1 μmol/g) in comparison with Co-doped ZnO (27.3 μmol/g) and ZnO (7.5 μmol/g). The research will deepen the understanding that TiO2 based photocatalyst show higher activity and the mole ratio (Ti/Zn:Co) influences nanocomposites performance and provide new ideas for designing efficient photocatalysts.
- Full Text:
- Date Issued: 2020
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