Theses and Dissertations (Chemistry)

Permanent URI for this collection

https://hdl.handle.net/10352/165

Browse

Now showing 1 - 5 of 5

Modification of glassy carbon electrode (GCE) with prussian blue as a mediator on carbon nanotube materials through sequential deposition
(Vaal University of Technology, 2012-08) Farah, Abdullahi Mohamed ; Modise, S. J., Prof.; Dikio, E. D., Prof.
Prussian blue (PB) nanoparticles were synthesized from FeCl3.6H2O, K4[Fe(CN)6].3H2O, and from Fe(NO3)3.9H2O and K4[Fe(CN)6].3H2O, and then characterized by Fourier transform infrared (FT-IR), Ultraviolet-visible spectroscopy, X-ray diffraction (XRD), Energy dispersive spectroscopy (EDS), Scanning electron microscopy (SEM), Raman spectroscopy and thermogravimetric analysis. Graphene oxide and carbon nanotubes were also synthesized and characterized. PB nanoparticles, carbon nanotubes (CNT), graphene oxide (GO) and cetyltrimethylammonium bromide (CTAB) were sequentially deposited onto glassy carbon electrode surface to form chemically modified electrode for the detection of hydrogen peroxide (H2O2) and dopamine. The following electrodes were fabricated, GC-PB, GC-MWCNT, GCGO, GC-CTAB, GC-MWCNT-PB, GC-GO-PB and GC-CTAB-PB. Cyclic and Square wave voltammetric techniques were used to measure the hydrogen peroxide detectability of the electrodes at pH ranges of (3 - 7.4) in 0.1M phosphate buffer solution, in the absence or presence of 25 μL of H2O2. The GC-CNT-PB, GC-GO-PB,GC-CTAB-PB electrodes showed a good response for the detection of hydrogen peroxide in both acidic and neutral media while the GCPB electrode only showed good response in acidic media.
Synthesis and characterization of electrocatalytic graphene for electrochemical sensing and bioelectronics
(Vaal University of Technology, 2018-02) Osikoya, Adeniyi Olugbenga; Dikio, E. D., Prof.
In this study, few layer graphene (Gr) and heteroatom graphene (HGr) were synthesized by chemical vapour deposition (CVD) method. Acetylene gas was used as carbon source for the synthesis of graphene, while a mixture of nitrobenzene and dichloromethane (ratio 1:1) were used as both carbon and dopant sources for the synthesis of the heteroatom graphene (HGr). A mixture of argon and nitrogen gases were carefully combined and used as carrier gasses and purge for both the synthesis of graphene and the synthesis of heteroatom graphene. X-ray diffraction (XRD) characterized showed that the as synthesized materials were crystalline materials, Raman spectroscopy indicated that the synthesized materials consist of sp2 hybridized carbon atoms, while scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that the synthesized materials possess regions of 2 to 7 nm of thickness. Transmission electron microscopy (TEM) characterization also showed that the synthesized heteroatom graphene possesses about 5 to 7 layers with about 2 nm thickness, and x-ray photoelectron spectroscopy (XPS) result showed the presence of nitrogen, oxygen and chlorine in the lattice of the synthesized heteroatom graphene while the synthesized material still retained about 80% sp2 hybridization. The synthesized materials were used in the fabrication of modified bioelectrodes for electrobiocatalytic biosensing of glucose and hydroquinone. The fabricated bioelectrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV characterization showed a diffusion-controlled electrode processes in al modified electrodes, while the EIS characterization showed the presence of both diffusion controlled and kinetic controlled impedance at the electrode-electrolyte interface. The fabricated GC/PEDOT-PSS/HGr/Lac modified bioelectrode exhibited a kinetic controlled impedance of 3150 Ω, while the fabricated GC/PEDOT-PSS/Gr/Lac modified bioelectrode exhibited a kinetic controlled impedance of 4138 Ω. Chronoamperometric experiments showed that the fabricated bioelectrodes exhibited swift electrobiocatalytic activity towards glucose and hydroquinone sensing respectively for graphene and heteroatom graphene. The graphene modified bioelectrode exhibited a linear response of 0.2 to 9.8 mM glucose concentration and a sensitivity of 87.0 μA/mM/cm2, while the heteroatom modified bioelectrode also exhibited a swift response to step by step addition of hydroquinone with a limit of detection of 2.07 μM and dynamic range of 2.07μM to 2.97 mM, thus indicating the tremendous potential of the materials in a wide range of electrobiocatalytic and bioelectronics applications.
Synthesis and characterization of graphene and carbon nanotubes for removal of heavy metals from water
(Vaal University of Technology, 2012-06) Thema, Force Tefo; Moloto, M. J., Prof.; Dikio, E. D., Prof.
The commercial flake graphite was prepared into functionalized graphite oxide (GO) by adopted chemical treatment. After the exfoliation and intercalation of graphite into functionalized graphene oxide that formed stable colloidal dispersion in polar aprotic solvent, the reduction process was undertaken by continuous stirring with hydrazine hydrate in a microwave at 35 oC for two hours. The reduced material was characterized by X-ray diffraction (XRD), attenuated total reflectance (ATR) FT-IR, Ultra-violet visible (UV-vis), atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman microscopy and magnified optical microscopy that confirm the oxidation of graphite and reduction of graphene oxide into graphene sheets. Carbon nanomaterials were synthesized from Co-Sn, Co-Sr and Co-Zn as catalysts supported on Al2O3, CaCO3 and MgO. The as-prepared nanomaterials were characterized by thermogravimetric and derivative thermogravimetric analysis (TGA & DTA), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and the transmission electron microscopy. The intensity ratios (ID/IG) of the D- and G- bands were found to be the same that is averagely at 0.83. The TGA & DTA curves have shown Co-Sn/Al had significant weight loss, Co-Sr/Mg weight loss and decomposition, Co-Sr/Al decomposition and Co-Zn/Mg weight loss. However these weight losses were not significant. The EDS analysis showed all elements which took part in the reaction confirming the success of each synthesis. The SEM images show carbon nanotubes only on samples that have been synthesized on MgO as confirmed by TEM images. Finally the XRD showed some characteristic peaks at desired peaks except that they were other peaks attributed to impurities and armophous carbon. It was also observed that Co-Sn/Ca and Co-Sn/Mg XRD curves showed broad peaks at theta = 24.3o & 42.6o and theta = 23.9o & 43.1o respectively which are lattice structure characteristic peaks.
Synthesis, fabrication and characterization of poly nanofibers and investigation of their adsorption properties
(Vaal University of Technology, 2017-06) Shooto, Ntaote David; Skhwivhilu, L., Dr.; Wankasi, D., Prof.; Dikio, E. D., Prof.
A major challenge for this generation is cleaning up heavy metal pollution disposed during industrial, domestic and agricultural activities. So, to obtain clean water resources, new treatment technologies are needed that can be applied to a broad range of highly toxic heavy metals in water. In this study, metal organic frameworks (MOFs) were synthesized from 1,2,4,5-tertabenzene carboxylic acid with metal salts of; cobalt, copper, iron, antimony, strontium and lanthanum through solvothermal method. The synthesized MOFs were reacted with polyvinyl alcohol (PVA) by electrospinning. To the best of our knowledge it is for the first time that such hybrid materials are synthesized and reported. PVA/MOF materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry analyzer (TGA). The SEM micrographs of PVA/MOFs materials showed relatively uniform nanofibers that were non-beaded and entangled. Some formed patches, while others were partially cross linked. TGA analysis revealed that PVA/MOF nanofibers exhibited higher decomposition temperature than PVA nanofibres. Thus, it confirmed the interactive force between MOF and PVA nanofibres. FTIR plots also exhibited shifts in critical functional group positions, thus it confirmed that there was a given amount of MOFs embedded in the electrospun fibrous mat. PVA/MOFs materials were used in the adsorption of lead ions in solution to study the effects of temperature, time dependant studies and concentrations. The batch adsorption experiments were performed at five different Pb(II) ion concentrations (20, 40, 60, 80 and 100 mg/L), four different temperatures (25, 40, 60 and 80 oC), time dependent studies ranged from (5, 10, 30 and 60 min) and pH of all Pb(II) solutions were recorded to be 5.05. The results indicated that the uptake performance of PVA and PVA/MOFs nanofibers significantly changed with concentration, temperature and time. The PVA/MOFs nanofiber hybrids demonstrated greater adsorption percentage and adsorption capacity for Pb(II) ions than PVA nanofibers. PVA nanofibers showed moderate adsorption percentage and capacity performance of 25.5 % and 44.13 mg/g (meaning 44.13 mg of Pb(II) per gram of PVA nanofibers) while PVA/MOFs nanofibers showed improved percentage and capacity perfomance (PVA/Cu-MOFs 76.36 % and 152.72 mg/g), (PVA/Co-MOFs 59.41 % and 99.28 mg/g), (PVA/La-MOFs 92.27 % and 184.03 mg/g), (PVA/Cd-MOFs 83.19 % and 165.94 mg/g), (PVA/Sb-MOFs 50.66 % - 91.57 mg/g), (PVA/Sr-MOFs 58.85 % - 124.82 mg/g) and (PVA/Fe-MOFs 56.76 % - 108.82 mg/g). The adsorption data of Pb(II) ions on PVA and all PVA/MOFs nanofibers showed that a pseudo-second order kinetic model was more suitable than a pseudo first order kinetic model. The adsorption rate was much faster on PVA/MOFs nanofibers. This is marked by lower activation energy compared to PVA nanofibers activation energy. The Temkin model did not correlate well with all the adsorption data. On the contrary, Freundlich and Langmuir isotherm models described the adsorption data adequately. All PVA/MOFs nanofibers followed Langmuir isotherm model, only PVA nanofibers followed Freundlich isotherm model. The PVA and PVA/MOFs nanofibers gave negative values of enthalpy change (ΔHo) and negative values of Gibbs free energy change (ΔGo) showing the adsorption processes were exothermic and spontaneous. Moreover, obtained positive entropy changes (ΔSo) on PVA, PVA/Fe-MOF, PVA/Cu-MOF, PVA/Co-MOF and PVA/Sb-MOF nanofibers showed that the sorped Pb(II) ions were not restricted on the electrospun nanofibres and physisorption mechanism was dominant, while negative entropy changes (ΔSo) on PVA/Sr-MOF and PVA/La-MOF nanofibers indicated that chemisorption was more dominant. The influence of ubiquitous cations such as Ca(II) and Mg(II) on the adsorption of Pb(II) ions onto PVA and PVA/MOF nanofibers was also assessed. The results showed that the ubiquitous ions had no significant influence on the sorption of Pb(II) ions. Current investigation provides a method to develop novel PVA/MOFs nanofibers hybrid adsorbents for water purification system. The adsorption capacities and removal achieved with the PVA/MOFs nanofibers sorbent were higher than those for PVA sorbent. The electro spun nanofiber sorbents presents an efficient alternative for pre-treating lead ions in aqueous solutions. Results from this research demonstrated that higher performance novel nanofibers, which possessed higher adsorption percentages and capacity capabilities were obtsained far exceeding some of the commonly used adsorbents, were obtained.
X-ray spectroscopic method development for quantitative analysis of manganese ore in the Kalahari basin
(Vaal University of Technology, 2016-11) Bodiba, Abram Lesibana; Horsfall, M., Prof.; Dikio, E. D., Prof.
Manganese is a crucial element in the manufacturing of steel, which in turn is an essential material in many industries including construction and transportation. Its use in the steel making process results in increased strength and resistance. Manganese samples are analyzed quantitatively by volumetric titration techniques. These wet chemistry methods are simple, accurate, and are sufficiently detailed for ordinary personnel to follow with ease. The research method used included the investigation of using secondary standard created from the current mining activities to match the matrix and mineralogy. The matrix matching standard has shown that the mineralogical effect and matrix effect can be controlled by creating the ore specific program. The matrix and mineralogical effect are the main sources of errors in wavelength dispersive X-ray fluorescence analysis with pressed powder pellets. No fundamental parameters corrections and empirical coefficient correction were made on the press pellets calibration lines. The fusion method was investigated as a universal method that can produce fused beads retaining all the elements of interest. The calibration lines were developed from certified reference material and the results were accurate, substantiating that the fusion method elimination the mineralogical effect, matrix effect and particle size effects. Fusion and press pellet methods were compared with the traditional wet chemical method and the results shows no significant difference between the methods. The new methods were tested against three proficiency schemes for manganese and the results were satisfactory, the z-score was below ±3 for all the elements. The participants used different methods including traditional wet chemical analysis and Inductive coupled plasma (ICP). The press pellets method has shown a good correlation with a fusion method were certified reference material was used for calibrations. The new methods were validated using different statistical methods. All the validation criteria were satisfactory. The calibration range for all the lines were satisfactory. The Limit of quantification (LOQ) values for Mn, Fe, CaO, SiO2, MgO, Al2O3, and P were very low. The new methods for the analysis are therefore sensitive enough to give good results for the expected concentration ranges of each element. The statistical analysis performed between fusion and press pellets methods has proven that there was no significant difference between the methods. The conclusion made after the validation procedures was that the methods developed for the analysis of manganese ore was fit for purpose of the analysis of the elements of interest for the Kalahari manganese ore. The study confirmed that the newly developed press pellets methods can be used to analyse routine production samples based on the ore type or the area. Borates fusion method can be used for geological explorations, consignment and trade samples. The proposed XRF methods can replace the traditional wet chemical analysis which is time-consuming, toxic and labour-intensive.

Browse

Browsing Theses and Dissertations (Chemistry) by Author "Dikio, E. D., Prof."

Results Per Page

Sort Options