Theses and Dissertations (Chemistry)

Permanent URI for this collection

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

Browse

Now showing 1 - 20 of 87

Determination and removal of organochlorine pesticides by activated macadamia nutshell in water and sediment alongside Vaal River using GC-MS
(Vaal University of Technology, 2017-10) Phele, Mokete John; Rimayi, C.; Mthunzi, F., Dr.
A rapid and reliable method was developed and applied for the simultaneous determination of 15 organochlorine pesticides (OCPs) in water and sediment. OCPs are continually detected in the environment due to their increasing applications in agriculture and industry, their presence in the environment are not desirable since they are well known to have negative impact in humans and animals. Thus, there has been a continual demand to monitor the presence of OCPs within the environment. The analytical technique employed was gas chromatography equipped mass spectrometer (GC–MS). The correlation coefficients from linear regression for the analysed concentrations were >0.9998. The limits of detection (LODs) varied between 0.068 ppm for 4, 4-DDT and 0.021 ppm for endrin, and the limits of quantitation (LOQs) ranged from 0.06 to 0.23 ppm. The average recoveries varied between 92.08 and 99.71 %. Relative standard deviations (RSD %) ranged from 2.01 to 6.42 %. Sediment samples were extracted using accelerated solvent extraction (ASE), it was found that the limits of quantification ranged from 0.002 to 0.004 ppm, and the average recoveries were in the range 63.2 % - 96 % with standard deviations in the range 3 %-12 %. Macadamia nutshell was characterised using FTIR, spectroscopy and scanning electron microscope (SEM). The functional groups present were found to be O-H stretching vibration of hydrogen bonded hydroxyl groups, aliphatic C-H stretching vibration and C-OH stretching of phenolic groups. SEM image revealed that the material consisted of flaky long fold-like structure which are typical of plant materials.
Adsorption and Photodegradation of Molasses Wastewater using TiO2-ZnO Hybrid Nanocatalysts Supported on Activated Carbon and Silica
(Vaal University of Technology, 2017-03) Otieno, Benton Onyango; Naidoo, E. B., Prof.; Aoyi, Ochieng, Prof.
There is an increasing use of composite materials in photo-catalysed remediation of wastes such as molasses wastewater (MWW), which is characterised by high organic load and a dark brown colour caused by biorecalcitrant melanoidin compounds. This study was carried out to determine the photocatalytic efficiency of a TiO2-ZnO hybrid supported onto activated carbon (AC) and silica for the remediation of MWW. Immobilisation of ZnO onto synthesised TiO2 formed TiO2-ZnO, which was then supported onto AC and silica, to give TiO2-ZnO/AC and TiO2-ZnO/Silica composites, respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX) and Fourier Transform Infrared (FTIR) spectroscopies, and transmission electron microscopy (TEM), revealed the successful hybridisation of TiO2 and ZnO, and the subsequent support of the hybrid onto AC and silica. Thermal stability of the synthesised composite catalysts was studied by differential thermal analysis (DTA) and thermal gravimetric analysis (TGA). Photoluminescence (PL) spectroscopy further revealed a restrained electron-hole pair recombination resulting from both the successful formation of a heterojunction in the hybrid, and the introduction of electron accepting AC support. Introduction of a silica support on the other hand increased the rate of recombination resulting in reduced quantum efficiency of the TiO2-ZnO/Silica composite, hence AC was adopted as the ideal support material for this study. Photodegradation was monitored in terms of colour and total organic carbon (TOC) reductions, and nitrate formation. It was observed that the TiO2-ZnO hybrid, due to its desirable optical properties, had better activity than the respective oxides (TiO2 and ZnO). On supporting the hybrid onto AC, both adsorption and photocatalytic activities were further enhanced with improved overall colour removal of 86% from 68%. Photodegradation followed pseudo-first order rection model, with the rate constant (𝑘𝑎𝑝𝑝) decreasing from 0.0701 to 0.0436 min-1 with increased MWW initial concentration from 3000 to 6000 ppm. Formation of nitrates confirmed a reductive pathway for the degradation of melanoidins. The UV-photodegradation process was found to be 33-fold less energy intensive for colour reduction as compared to TOC reduction, with energy demands of 35 and 1183 kWh/m3, respectively. Sorption of MWW onto TiO2-ZnO/AC fitted well with the Freundlich isotherm and were found to be endothermic in nature with physisorption being the rate determining step. An optimum pH of 5 for the degradation process was determined. The robustness of the composite TiO2-ZnO/AC photocatalyst was revealed by its high reusability up to four cycles.
Assessment of carcinogenic PAHs, their oxy-derivatives and heavy metals in soil and sediments from coal mine in Witbank, Mpumalanga Province, South Africa
(Vaal University of Technology, 2022-11-14) Nqaba, Zoleka; Akpotu, S. O., Dr.; Okoli, P. C., Dr.; Pholosi, A., Dr.
Fossil fuels provide more than two-thirds of the world’s energy needs with a significant contribution from coal. Coal is referred to as “dirty energy” and it is still used as an energy source because of its vast availability and relatively low cost of production. In South Africa, Witbank mines in Mpumalanga province have the largest coal deposits, supplying power stations that generates 41% of the country’s electricity. Coal mining results in anthropogenic hazardous emissions such as slag waste and coal dust with high concentrations of organic and inorganic pollutants. Polycyclic Aromatic Hydrocarbons (PAHs) are emitted by incomplete coal combustion resulting into coal ash which can contain large quantities of heavy metals. PAHs and heavy metals are known to be major contributors to the environmental pollution due to their negative effects on human health and the ecosystem. As a result this study aims to investigate heavy metals, PAHs and their oxy-derivatives in areas affected by coal soil pollution in Mpumalanga. In this research, 132 soil and sediments samples were collected from 6 coal-containing areas in Mpumalanga (i.e. Greenside coal mine, Kriel power station, Klipfontein dam, Kriel dam, Middleburg dam, and Witbank dam) and these were investigated for their physiochemical properties (pH, TOC, TOM determined by pH electrochemical method and Walkerly Black Method), presence of heavy metals and organics (PAHs and oxy-PAHs). Soil and sediment samples were collected in both winter and summer seasons in 2019. Soil samples were characterised using FTIR and SEM-EDX spectroscopy for functional groups and determination of metal elements, respectively. Heavy metals present in the samples were investigated and the assessment of possible risks of exposure was studied. Heavy metals investigated included Zn, Cu, Co, Fe, Mn, Cr, and Pb. The coefficients of determination of the calibration standards for heavy metals were greater than 0.995 and the recovery values ranged between 75 - 105 %. For the organic pollutants, an extraction method was developed. Organic Pollutants analysed include naphthalene, acenapthene, fluorene, anthracene, pyrene, benzo(a)pyrene and 1,4-naphthalene. Samples were extracted using soxhlet and ultrasonic bath techniques and extracts were analysed using gas chromatography mass spectrometry (GC-MS). The GC-MS method developed was validated by inter-day and intra-day reproducibility of standards, recovery test, linearity of calibration method and limits of quantification and detection. Coefficient determination of the calibration standards were greater than 0.995 for PAHs and recovery values ranged between 60 - 86 %. All the heavy metals that were analysed were detected in all the samples. Generally, it was observed that Greenside and Kriel samples had higher metal concentration as compared to the dams (Klipfontein, Kriel, Middleburg and Witbank) and these had the following range: Fe > Mn > Cr > Pb > Cu > Co. The results for the organics followed a similar trend as the heavy metals, that is, samples from Greenside and Kriel had higher concentration of PAHs as compared to the samples from the dams (Flt > Pyr > Anthr> 1,4-napth > Nap > Flu> benzo(a)anthr > Acy). Based on the results, the concentrations of heavy metals and organics in soil were slightly higher than the World Health Organization limits for these pollutants. This is concerning because the studied areas include residential and agricultural communities. As a result, a continuous and routine monitoring of these pollutants is required to preserve the environment and the health of humans and animals living around the area.
Surface modification of biochar composite made from tea waste for the removal of selected organic pollutants from aqueous medium
(Vaal University of Technology, 2022-11) Mashoene, Tumelo Nortica; Lawal, A., Dr.; Taka, A. Leudjo, Dr.; Klink, M., Prof.
Domestic, agricultural, and industrial waste has been investigated as a substitute for activated carbon adsorbents. This research converted waste tea-based adsorbent, coupled with reduced graphene oxide, and further modified with deep eutectic solvents. This innovative biochar modification was investigated to overcome the limitations of the tea-waste biochar nanocomposite alone and the removal of organic contaminants from simulated wastewater. Fourier Transformed Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM–EDS), Brunauer, Emmett, and Teller (BET) surface area analysis, and pH at point of zero charge (pH PZC) was used to characterize the synthesized materials (biochar, biochar/reduced graphene oxide (biochar/rGO), biochar/reduced graphene oxide/deep eutectic solvent-cetyltrimethylammonium bromide (biochar/rGO/DES-CTAB), and biochar/reduced graphene oxide/deep eutectic solvent-glycerol (biochar/rGO/DES-glycerol)). The results showed that the principal material biochar was modified by a show of added functional groups and surface structural changes. The materials biochar, biochar/rGO, biochar/rGO/DES-CTAB, and biochar/rGO/DES-glycerol were applied for the removal of ZDV and phenol from the aqueous medium. Batch adsorption studies were conducted to optimize operating parameters such as adsorbent dose, solution pH, contact time, and initial concentration. Pseudo-first-order (PFO), Pseudo-second-order (PSO), and intraparticle diffusion (IPD) kinetic models were determined to investigate the mechanism of the adsorption process. The coefficient of correlation, R2, was used to determine the best fit of the kinetic models. The adsorption results showed that DES-glycerol-modified adsorbent was more efficient in removing the pollutants ZDV and phenol than biochar, biochar/rGO, and biochar/rGO/DES-CTAB adsorbents. In addition, the results showed that an acidic medium of pH 2.00 and a contact time of 1h30min and 30 min is sufficient for removing ZDV and phenol respectively, from an aqueous medium. The experimental data best fit into PSO models and assumed a variety of interactions between the adsorbent surface and adsorbate molecules and IPD wasn’t the only rate-determining step. The Langmuir and Freundlich models further examined the experimental data to assess the adsorbate-adsorbent interactions at equilibrium. Equilibrium experiments revealed that adsorption adhered to the Langmuir isotherm, demonstrating the homogeneity of adsorption sites. This study demonstrates the feasibility of the conversion and modification of common tea waste into a useful adsorbent for the remediation of organic contaminants from wastewater, thus creating an opening for the application of waste tea-based adsorbent in industrial settings.
Removal of Pb(II), Cu(II), Cd(II), Cr(VI), methylene blue dye (MB) and inhibition of bacteria growth using modified fennel seeds from aqueous solutions
(Vaal University of Technology, 2022) Mabungela, Ntandokazi; Naidoo, E. B., Prof.; Mtunzi, F., Prof.; Shooto, N. D., Dr.
Water contamination with pollutants like toxic heavy metals, dyes and pathogens is currently a global problem. Toxic heavy metals and dyes are not degradable and persist in environment, while pathogens are responsible for waterborne disease problem. Therefore, it is crucial to remove these pollutants from wastewater. Hence, this work reports mono, binary and ternary adsorption of copper-Cu(II), cadmium-Cd(II), lead-Pb(II), chromium-Cr(VI), methylene blue dye-MB and antimicrobial studies against Escherichia coli (E. Coli) and Staphylococcus aureus (S. aureus) and the resultant activated carbon (AC) was treated with potassium permanganate (KMNO4) from aqueous solution by pristine and modified fennel seeds. Pristine fennel seeds (PFS) were modified with acidic solution of hydrochloric acid (HCl), nitric acid (HNO3), sulphuric acid (H2SO4), phosphoric acid (H3PO4) and alkaline solutions of sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)2). PFS were also carbonized at different temperature of 500, 600 and 700 ℃ and treated AC obtained with potassium permanganate (KMNO4). Lastly, fennel seeds were incorporated with iron(III) oxide nanoparticles (Fe2O3 NP), iron(III)-1,2,3,4-tetracarboxylic acid (Fe-TCA) and binary nanoparticles of CuO-ZnO in a ratio of 1:2 & 2:1. Fennel based adsorbents were characterized using Scanning Electron Microscope with Energy Dispersive Spectroscopy- (SEM-EDS), Fourier Transform Infrared (FTIR), X-Ray Diffraction (XRD), Ultraviolet-Visible Spectroscopy (UV-Vis), Transmission Electron Microscope (TEM), Thermogravimetric Analyser (TGA) and Brunauer-Emmett-Teller (BET). The SEM results showed that the surface morphology of the fennel based adsorbents became more porous with cavities compared to PFS. The FTIR results revealed that the adsorbents surface had hydroxide (-OH), carbonyl (-C=O) and carboxyl (-COOH) functional groups. XRD results showed a diffraction peaks around 19 ⁰ and 23 ° which are attributed to the presence of cellulose. TEM images of the composites indicated deposits of nanoparticles on the surface of fennel seeds. TGA results showed a weight loss around 205-556 ℃ for PFS and 205-507 ℃ for composites and that was due to breakdown of lignocellulosic material in fennel seeds. The physicochemical characteristics such as cation exchange capacity (CEC) and Brunauer, Emmett and Teller (BET) surface area were enhanced after impregnation when compared with PFS. The adsorption of Cr(VI) and growth inhibition of Escherichia coli and Staphylococcus aureus on binary nanoparticles of CuO-ZnO were investigated. The binary CuO-ZnO nanoparticles were prepared through co-precipitation method. The highest adsorption capacity recorded at pH 2 and 308 K were 75.96 and 84.77 mg/g for FS/CuO-ZnO[1:2] and FS/CuO-ZnO[2:1], respectively. The antibacterial assays indicated that the materials are effective in preventing the growth of microbial growth. Removal and photo-degradation of methylene blue dye from aqueous solution using FS-NP and FS-TCA composites were examined. The maximum adsorption capacity recorded for PFS was 13.21 mg/g while for FS-NP and FS-TCA was 32.84 and 42.89 mg/g, respectively. PFS showed no activity for photocatalytic degradation properties while PF-NP and PF-TCA recorded 58.97 and 48.62 % efficiencies, respectively. The ternary removal of metal ions of copper Cu(II), lead Pb(II), and methylene blue (MB) dye on pure and acid treated fennel seeds biomaterials from aqueous solution by batch adsorption was investigated. Pure fennel seeds were labelled (PFS), nitric and sulphuric treated seeds were labelled (NAFS) and (SAFS) respectively. Adsorption data showed that all biomaterials had a higher affinity for MB dye more than Pb(II) and Cu(II) metal ions. The maximum adsorption capacities onto PFS were 6.834, 4.179 and 2.902 mg/g; NAFS 15.28, 14.44 and 4.475 mg/g; while for SAFS 19.81, 18.79 and 6.707 mg/g respective for MB dye, Pb(II) and Cu(II) ions. Binary adsorption of Copper (Cu(II)) and Chromium (Cr(VI)) from aqueous solution using activated carbon-AC and AC functionalized with KMnO4 derived from fennel seeds was examined. Activated carbon-AC from fennel seeds was obtained at different temperatures of 500, 600 and 700 °C and the results were named FS-500, FS-600 and FS-700. Thereafter, each sample was chemically treated with KMnO4 solution to obtain KMFS-500, KMFS-600 and KMFS-700. The results showed that the KMFS-700 and FS-700 adsorbed more than KMFS- 600, KMFS-500, FS-600 and FS-500 for both Cu(II) and Cr(VI) metals. The maximum adsorption capacity on FS-700 was 19.886 mg/g and 8.510 mg/g for Cu(II) and Cr(VI) whilst on FS-600 were 15, 423mg/g and 1.202 mg/g and on FS-500 were 16. 921mg/g and 1.722mg/g, respectively. The maximum adsorption capacity on KMFS-700 was 19.786 mg/g and 10.572 mg/g for Cu(II) and Cr(VI) whereas on KMFS-600 were 15, 735mg/g and 8.109 mg/g and on KMFS-500 were 17. 648 mg/g and 3.479mg/g, respectively. Binary adsorption of toxic metal ions of Cu(II) and Pb(II) from aqueous solution by pristine and modified fennel seeds was studied. Pristine fennel seeds (PFS) were chemically treated with acidic and alkaline solutions to develop modified adsorbents designated ATFS and BTFS respectively. The maximum uptake of Cu(II) and Pb(II) on PFS was 3.345 and 11.524 mg/g. While for ATFS 3.78 and 13.07 mg/g, and BTFS 8.143 and 14.85 mg/g, respectively Simultaneous removal of copper Cu(II), cadmium Cd(II), and methylene blue dye (MB) from an aqueous solution using PFS and modified fennel seeds was investigated. The pristine fennel seeds (PFS) were chemically treated with phosphoric acid (H3PO4) and calcium hydroxide (Ca(OH)2) solutions to produce H3FS and CaFS, respectively. The maximum adsorption capacity for Cu(II) by PFS, H3FS and CaFS was 7.208, 5.504, and 5.791 mg/g, respectively. For Cd (II) by PFS, H3FS and CaFS, it was 2.274, 5.021 and 12.3 mg/g, respectively. The maximum adsorption capacity of MB by PFS, H3FS and CaFS was 11.114, 4.071 and 18.468 mg/g. This thesis is written in an artile format.
Nickel and Zinc sulfide nanoparticles and thin films prepared from substituted Thiourea based complexes
(Vaal University of Technology, 2022-11) Jawore, Abera; Moloto, M. J., Prof.; Nate, Z., Dr.; Xaba, T., Prof.
Nanomaterials have attracted a great attention in this generation. Nanotechnology is currently one of the most advancing technologies utilized in many fields such as in semiconductors, solar cells medicine, agriculture, photovoltaic cell, sensors, and electroluminescent. Various methods have been employed to synthesize metal sulfide nanomaterials, however, many of the present methods use toxic and expensive starting materials which bring the problems into the society. The advancement of nanotechnology makes life better and brings about new inventions that can solve many problems in our daily lives. Thin films also have many benefits in our days, such as solar cell semiconductors, minimizing environmental pollution by replacing fuel gas. The combination of nanomaterials and thin films are core of civilization, green chemistry, and energy source. This study aimed to investigate the effect of different parameters such as reaction temperature, concentration of precursor, and reaction time on the physical properties of zinc sulfide (ZnS) and nickel sulfide (NiS) nanoparticles. The nanoparticles were synthesized from (Z)-2-(pyrrolidin-2- ylidene) thiourea zinc (II) complex and (Z)-2-(pyrrolidin-2-ylidene) thiourea nickel(II) complex using the hydrothermal method. The synthesized nanoparticles were capped using hexadecylamine (HDA) and trioctylphosphine oxide (TOPO). The synthesized nanoparticles were characterized using various techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis absorption spectroscopy, and photoluminescence spectroscopy. The TEM images of the HDA capped zinc sulfide nanoparticles synthesized from 0.5 mg of the precursor showed quite agglomerated, rod-like structures, small and size particles with an average particle size of 4.46 nm. The HDA capped zinc sulfide nanoparticles synthesized from 1 mg of precursors showed polydispersity small spherical and agglomerated particles. The TEM images of TOPO capped zinc sulfide nanoparticles synthesized from 0.5 mg of the precursor showed small spherical sized particles with an average particle size of 2.16 nm and 2.86 nm. It was noted that the size of the particles increases when the concentration of the increases. The UV-Vis spectra of the HDA capped ZnS nanoparticles revealed two narrow absorption peaks at 304 nm and 307 nm, while the TOPO capped ZnS nanoparticles had an absorption peak of 301 nm. The photoluminescence spectra of both capped ZnS nanoparticles revealed two narrow emission peaks at 405 nm and 445 nm, and 409 nm and 433 nm respectively. The XRD patterns of both capped ZnS nanoparticles revealed mainly peaks at 21.2º, 23.3º, 25.4º, 27.1º, and 29.7º corresponding to the (300), (400), (401), (402) and (403) planes of the hexagonal phase. The TEM images of the HDA capped NiS nanoparticles revealed irregular, agglomerated particles in the size range of 6.31 nm to 7.46 nm, while the TOPO capped NiS nanoparticles showed an average particle size of 6.31 nm. The XRD patterns of the HDA capped NiS nanoparticles exhibited a hexagonal phase, as evidenced by the peaks at 20 º (100), 26.4º (101), 32.6º (102) and 49.2º (104). The TOPO capped NiS nanoparticles showed peaks at 30.22º (111), 32.35º (200), 34.19º (210), 38.96º (211), 44.77º (220), 50.94º (311), and 59.58º (023), which correspond to the nickel sulfide cubic phase. This study provides a better understanding of the synthesis, characterization and properties of ZnS and NiS nanoparticles and thin films.
Preparation of superhydrophobic polyethersulfone/zinc oxide nanocomposites for water treatment
(Vaal University of Technology, 2022) Nombasa, Dumile; Oluwafemi, S. O., Prof.; Nelana, S., Dr.; Klink, M. J., Prof.
Membrane distillation is a water desalination method involving evaporation through a hydrophobic, microporous membrane under a vapour pressure gradient between the porous hydrophobic membrane and separating water vapour from a salty water stream by allowing only water vapour and other volatile molecules to pass through the membrane. Polymer membranes utilized in membrane distillation are reliable, with a low cost and low energy demands, are easy to use, produce ultra-pure water, and achieve complete rejection of ions, cells etc. However, these membranes are prone to fouling, resulting in a short lifespan and high energy demand. This work addresses the membrane fouling of Polyethersulfone (PES) functionalised with Zinc Oxide (ZnO) nanomaterials using Non-solvent Induced Phase Separation (NIPS) ) to form flat sheet PES/ZnO nanocomposite membranes of 102 to 142 μm thickness and 53.33 to 56.44 porosity(%). First, ZnO NPs and ZnO NRs were synthesized using the sol-gel and hydrothermal methods, respectively. The formation of the ZnO nanomaterials was confirmed through characterization techniques such as Ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy, Scanning electron microscope (SEM), Energy dispersive spectroscopy (EDS) and Transmission electron microscope (TEM). The ZnONPs and ZnONRs were then uniformly dispersed into PES polymer blends to fabricate PES/ZnONP and PES/ZnONR nanocomposite membranes. Secondly, the nanocomposite membranes were modified via grafting with low surface energy molecules 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (PFTS) and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDTS). The functionalisation success of the ZnO nanomaterials embedded in the PES/ZnO nanocomposite membranes and their modification membranes were assessed for improved surface properties and confirmed by FTIR, SEM, EDX and OCA. The highest increase in the water contact angle( WCA) was observed from 57° for the pristine membrane to 116° for PES/ZnONP(1%)/PFDS(5%) and 124° for PES/ZnONR(5%)/PDTS(5%) nanocomposite membranes. This work fabricated a novel near superhydrophobic PES/ZnO nanocomposite membrane with enhanced separation properties for high saline water treatment.
Electrospun chlorinated carbon nanotubes/Fe2O3/PVA nanocomposite fibrous material for the removal of oil in aqueous solutions
(Vaal University of Technology, 2023-03-16) Motlokoa, Teboho Ridwell; Viljoen, E. L., Dr.; Maboya, W. K., Dr.
In general water pollution worldwide is alarming, hence wastewater treatment is becoming a very paramount area of scientific research. Oil spills are a major source of contamination for sea and coastal waters and results in the death of marine animals. A variety of solid adsorbents are available for removal of organic and inorganic pollutants from water. However most absorbents are not recoverable and reusable, while some become a source of secondary pollution after use. A variety of solid absorbents are available for removal of organic and inorganic pollutants from water. In this study, four sorption materials were developed to be applied as sorbents for the removal of diesel oil in aqueous solutions. The sorption material consisted of chlorinated carbon nanotubes (Cl-CNTs) loaded with iron oxide nanoparticles that are embedded in a Polyvinyl Alcohol (PVA) polymer matrix. The sorption capacity of the materials was evaluated in the separation of a mixture containing diesel oil and water. The chlorinated carbon nanotubes were synthesized using chemical vapour deposition and thereafter iron oxide nanoparticles were added using co-precipitation methods. Transmission Electron Microscope (TEM) images showed that the Cl-CNTs had a spaghetti-like morphology. Secondary growth of nanofibers on the outer walls of the main CNTs was also observed in some nanoparticles. The outer diameter size of the CNTs were between 21.8 nm and 28.3 nm. The iron oxide nanoparticles that formed in the presence of the CNTs were spherical in shape with a size of 20.0 nm and uniformly distributed on the CNTs surface. X-Ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the iron oxide phase was Fe2O3. Fourier Transform Infra-Red (FTIR) analysis showed that the CNTs were made of sp2-hybridised carbon and their surface contained carbonyl groups. Nanofiber composite mats were prepared by electrospinning Cl-CNTs and Cl-CNTs/Fe2O3 suspended in PVA polymer solutions. The amount of Cl-CNTs and Cl-CNTs/Fe2O3 added to the PVA matrix were varied resulting in morphology changes in the polymer fibres as determined by Scanning Electron Microscopy (SEM). The PVA polymer had a fibre size of 371 nm which increased to 580 nm with the addition of 0.1 wt.% Cl-CNTs. The fibre size decreased to 413 and 211 nm with the addition of 0.2 wt.% and 0.5 wt.% Cl-CNTs, respectively. The addition of the Cl-CNTs prevented the bead formation, which was observed in the pure PVA fibres. The average diameters of the fibres were 366, 275, 219 and 169 nm, for 0.1, 0.5, 0.7 and 1 wt.% Cl-CNTs/Fe2O3, respectively. High amounts of inter-fibre fusing were observed for the 0.1 wt.% Cl-CNTs/Fe2O3/PVA matrix. The amount of inter-fibre fusing decreased with addition of higher concentrations of Cl-CNTs/Fe2O3. The Fe2O3/Cl-CNTs/PVA nanofibers was crosslinked using either glutaraldehyde or heat to improve their stability in water. The crosslinking process also caused changes in the morphology of the fibres; for instance, inter-fibre fusions were observed when glutaraldehyde was used. The Cl-CNTs/PVA nanofibers mat had the highest oil sorption capacity of 9.9 g/g. The Fe2O3/Cl-CNTs/PVA nanofibers mat had the lowest capacity of 7.6 g/g but it increased to 9.2 g/g after crosslinking with heat at 40 °C. Thus far, our findings suggest that the synthesized nanofiber mats can be suitable for use as absorbents for floating oil in aqueous solutions with the use of an easily degradable polymer matrix. Further study can be employed using Brunauer – Emmett – Teller (BET) analyses to understand the porosity and surface area of the material which will help more in understanding the sorption capacity of the material.
Fabrication of polymeric composite nanofiber materials and their antibacterial activity for effective wound healing
(Vaal University of Technology, 2023) More, Dikeledi Selinah; Moloto, N., Prof.; Moloto, M. J., Prof.
The synthesis of Ag and Cu nanoparticles was carried out using the thermal decomposition method in the presence of oleylamine as a capping agent. This method was used because it can produce uniform and monodisperse nanoparticles with controlled size distribution. The nanoparticles synthesized under various conditions were characterized by transmission electron microscopy (TEM), UV/Vis spectroscopy, photoluminescence spectroscopy (PL), and X-ray diffraction (XRD). The effect of precursor concentration on the morphology and size of the nanoparticles was investigated. It was observed that an increase in the precursor concentration resulted in an increase in particle sizes with different morphologies for both Ag and Cu nanoparticles. The increase in particle sizes for Ag nanoparticles was due to Ostwald ripening, while for Cu nanoparticles it was due to agglomeration, as Cu tends to oxidize in the atmosphere, leading to a change in particle size and shape. However, the ability to control and manipulate their physical and chemical properties depends on tuning their size and shape. Therefore, varying the precursor concentration helped in selecting the optimal concentration for this study. The nanoparticles produced were used in another study as fillers or additives for the production of nanofiber composites. The development of nanofibers by electrospinning process has led to potential applications in filtration, tissue engineering scaffolds, drug delivery, wound dressing and etc. The current study is an attempt to fabricate composite nanofibers that can be used as wound dressing material for effective wound healing. The approach involves the blending of two different polymers both being biocompatible and biodegradable were one is a natural polymer and the other is a synthetic polymer. In this study, different weight ratios of CS/PVA blends, Ag/Cu/CS/PVA, Ag/CS/PVA and Cu/CS/PVA composite fibers have been successfully prepared by the electrospinning process. The tip-to-collector distance was kept at 15 cm and the applied voltage was varied from 15 to 25 kV. The effects of the weight ratios applied voltage and the nanoparticles loading on the morphology and diameter of the fibers were investigated. The resultant fibers were characterized using scanning electron microscopy (SEM), XRD, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA) and UV-Vis spectroscopy. The SEM results showed that an increase the amount of chitosan in the CS/PVA blend resulted in a decrease in the fiber diameters while an increase in the voltage from 15 to 25 kV led to a decrease in the fiber diameters. Furthermore, an increase in fiber diameters was observed with irregular morphologies upon addition of Ag/Cu nanoparticles into the blend. The latter changes are perceived to be as a result of an increased conductivity and a higher charge density. The XRD results showed peaks which correspond to Ag in the face centred cubic. Ag peaks are more dominant than Cu peaks in the XRD of the mixed nanoparticles. The FTIR spectra of the Ag/Cu/CS/PVA composite fibers gave almost identical features as the blend. This proves that there was an interaction between CS and PVA polymer due to intermolecular hydrogen bonding. The TGA curves showed no significant effect on the thermal stability of the composite fibers upon addition of different nanoparticles loadings. The absorption spectra of the composite fibers showed an improved optical properties compared to the blend. For Ag and Cu nanoparticles composite fibers it was observed that addition of Ag nanoparticles in the blend resulted in an increase in fiber diameters with uniform morphology whereas for Cu resulted in a decrease in fiber diameters. Both Ag and Cu composite fibers showed an improved optical properties. The effect of CS/PVA, Ag/Cu, Ag, and Cu nanofibers on the selected microorganism (K.pneumoniae, S. aureus, P. aeruginosa, and E.coli) was evaluated using the disk diffusion method. It was observed that Ag/Cu/CS/PVA composite fibers showed greater activity against all microorganisms compared to Ag and Cu composite fibers. The alamar blue and Pierce Lactase dehydrogenase (LDH) assay were used to assess the effect of the blend and the composite fibers on cell viability and cytotoxicity, respectively. The results show that the prepared blend and the composite fibers did not have any toxic effect on human adipose derived stem cells (hADSC). The results also showed that as the concentration of Ag/Cu nanoparticles was increased the viability of the cells also increased after 24 hour incubation. More proliferation was observed in day 1 compared to day 3. The 30/70 blend showed more viable cell compared to the negative control. For Ag and Cu composite fibers the 30/70 CS/PVA blend increased cell proliferation after 3 days with 17% more viable cells compared to the negative control. These results show that the prepared blend with its composite fibers are biocompatible with human (ADSC) and may be suitable for use in biomedical application such as wound dressing.
Polymer intercalation of chemically bath deposited iron sulphide and nickel sulphide thin films
(Vaal University of Technology, 2017) Molete, Puleng Alina; Moloto, M. J., Prof.
In chemical bath deposition (CBD) method, deposition of metal chalcogenide semiconducting thin films occurs due to substrate maintained in contact with a dilute chemical bath containing metal and chalcogenide ions. Semiconducting nickel sulphide (NiS) and iron sulphide (FeS) thin films have been prepared on a glass substrate by varying the deposition parameters such as the concentration of solutions, deposition time, temperature and pH. Multi-layered thin films were deposited on glass substrate and the spin-cast conductive polymer, poly (3.4-ethylenedioxythiopene) polystyrene sulfonate (PEDOT: PSS) was intercalated. The characterization of the films was carried out using UV-Vis spectroscopy, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and X-ray diffraction (XRD). Single layer nickel sulphide was deposited at room temperature, pH 10 and the deposition period of 3 hours, triethanolamine was used as the complexing agent. Iron sulphide was deposited for 6 hours at 70 °C with the pH of 2.5 using EDTA as a complexing agent. Generally the iron and nickel sulphide were prepared from their respective nickel or iron salt and the thiourea or thiosulfate as a source of sulphide ions in solution. SEM and AFM results show that the FeS film is evenly coated and has uniform grain size with the roughness of ~22.4 nm and thickness of ~23.8 nm. The optical absorption analysis of FeS showed the band gap energy of ~2.9 eV which blue shifted from the bulk. The EDX analysis confirms the compositions of iron and sulphur in FeS films. XRD pattern showed amorphous films for both FeS and NiS thin films due to the amorphous nature of the glass substrate. The optical data of NiS film were analysed and exhibited the band gap energy of ~3.5 eV and ~3.3 eV for successive ionic layer adsorption and reaction (SILAR), which is the modified CBD, both blue shifted from the bulk. The films were observed to have thickness value of ~35.7 nm and ~2.3 nm SILAR with the roughness of ~112.5 nm and ~35.4 nm SILAR from AFM results. SEM confirmed the uniformly distributed film presented by AFM analysis. The chemical composition of Ni and S were confirmed by EDX spectra. The PEDOT: PSS was intercalated between the FeS as the first layer and NiS as the top layer which gave the thickness of ~18.7 nm and roughness of ~115.2 nm from AFM analysis. PEDOT: PSS acted as a passive layer that protects and stabilize the FeS layer and NiS as the third active layer which enhanced the optical absorption of the film when using SILAR method for solar application.
Isolation of Pelargonium alchemilliodes L L'Her active compounds and their effects on bacterial growth and keratinocytes in vitro
(Vaal University of Technology, 2019-07) Makanyane, Madikoloho Daniel; Ssemakalu, Cornelius Cano, Dr.; Okoli, Bamidele Joseph, Dr.; Mtunzi, Fanyana, Prof.
Context: Pelargonium alchemilliodes L L' Her is an evergreen shrub, cultivated principally for the medicinal essence and decoction in Southern Africa for the treatment of skin problems, and wounds. Objective: the aim of the study was to optimize the extraction of phenolics and flavonoids from P. graveolens by response surface methodology with particular attention on the proliferative and cytotoxic effects on human keratinocytes, as well as the antioxidant and antibacterial activities and also to isolate active compounds. Materials and Methods: The optimization was achieved by Box-Behnken design. Extract, metabolite yields, and minimal inhibitory concentrations (MIC) were determined by gravimetric, spectrophotometric, and microdilution methods, respectively. The antiradical potentials were evaluated using the phosphomolybdate. 2,2-diphenyl-1-picrylhydrazyl, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and lipid peroxidation assays, the diterpenoids were isolated and purified using open column chromatography, PTLC, and characterized with FTIR, NMR. The kinetics of the lipid protective activity was studied and fitted into models. The proliferative and cytotoxic effects were evaluated using the CellTiter® Blue cell viability and lactate dehydrogenase assay. Results: The regression coefficient r2 ≥ 0.9775 indicated a close correlation between actual and predicted values of the responses. The ideal parameter for the extraction of phenolics and flavonoids by macerations was determined as an extraction time: 9.63-12.01 h, material mass: 2.62-3.00 g, agitation speed: 143.11-197.11 rpm, and solvent volume: 68.06-69.87 mL. The optimal extractable acetone and methanol crude, flavonoids, and phenolic are (28.87±2.15%, 24.11±1.15%), (7.11±1.03 mg QE/g, 5.98±0.87 mg QE/g) and (58.08±0.88 mg GAE/g, 55.91±1.15 mg GAE/g), respectively. The detected different chemical groups of polyphenolic compounds such as alkaloids, saponins , sterols, terpenoids, flavonoids, tannins, phenols and cardiac glycosides from methanol and acetone extracts were in correlation with optimized yields. Two triterpenoids compounds 1-hydroxy-30-norlanosta-6, 8-diene and 1 2,3,4a,8,9,10,10a-octahydro-2-(2-hydroxypent-4-enyl)-4a-vinyl-1H-benzo[c]chromen-6(10bH)-one were isolated form methanol extracts. The main components of essential oils were citronellal (5.99%), citranellol (26.2%), geraniol (8.56%), citronellyl butyrate (20.3%), trans-farnesol (9.53%) and they were characterized by high amounts of oxygenated hydrocarbons (67.6%), followed by sesquterpene hydrocarbons and oxygenated sesquiterpene (9.32%) and the least being mornoterpene hydrocarbons (5.20%). Total antioxidant capacity and reducing power were comparable to standard gallic acid, while the antiradical activity has IC50 value of 0.18±0.03-8.98±0.15 mg/mL. Further, the lipid protective revealed a dose-dependent activity fitting into a pseudo-second-order kinetic model. MIC value of 1.56 mg/mL for extracts was registered against Staphylococcus aureus and salmonella typhi comparable to chloramphenicol. There was a significant (P < 0.05) increase in cell proliferation and viability when the extract was administered at concentrations of ≤50 μg/mL. However, at ≥100 μg/mL concentrations at ≤ 1000 μg/mL for essential oil exhibited a significnt cytotoxicity in comparison to the untreated cell. Conclusion: These biological activities are confirmation of the phytomedicinal application and possible source of pharmaceutical compounds. However, administration of the decoction should take into cognizance the antiproliferative effect at doses ≥100 μg/mL as well as the potential to induce and maintain keratinocyte proliferation at low concentration with an eye on the antiproliferative effect at concentrations ≥100 μg/mL, except the P. Alchemilliodes essential oils at ≤ 1000 μg/mL.
The effect of solar irradiated vibrio cholerae on the immunochemistry of dendritic cells
(Vaal University of Technology, 2015-08-24) Ssemakalu, Cano Cornelius; Ubomba-Jaswa, Eunice, Dr.; Motaung, Keolebogile Shirley, Dr.; Mtunzi, Fanyana, Dr.; Pillay, Michael, Prof.
Cholera is a waterborne disease caused by toxigenic strains of Vibrio cholerae. The spread of cholera in developing countries has largely been imputed to the unavailability of proper water treatment and sanitary infrastructure as well as poor hygiene. In order to prevent the contraction and spread of cholera the use of solar disinfection (SODIS) to treat water in waterborne endemic communities has been recommended by the World Health Organization (WHO). SODIS is a water sterilizing method that relies on natural sunlight to improve the microbiological quality of water. During SODIS the culturability of the water contaminating microorganisms is inactivated by the ultraviolet component of solar radiation. The success of SODIS treatment of water in alleviating the risks associated with the contraction of waterborne diseases such as cholera has been attributed to the effectiveness, with which the water is treated, simple application as well as low cost of materials required. Currently SODIS research has been dominated by studies geared towards understanding how the microbial inactivation occurs, enhancement of the disinfection process and health impact assessments. However, little to no research has been directed towards exploring the role played by the immune system following the consumption of the solar irradiated water pathogens such as V. cholerae. SODIS of microorganisms in water results in immunologically important microbial states and components that could induce an immune reaction or response. In view of the role of dendritic cells in shaping an immune response, the effect that solar irradiated V. cholerae in water has on the immunochemistry of the dendritic cells in vitro was investigated. Prior to the stimulation of the dendritic cells with the solar irradiated cultures of V. cholerae, the first objective required an evaluation on the impact that solar irradiation has on the production and secretion of the cholera toxin by V. cholerae in water. The results from this evaluation showed that solar ultraviolet radiation was incapable of inducing the secretion of the cholera toxin. Furthermore, there was extensive DNA degradation in the solar irradiated cultures of V. cholerae. The second objective was to investigate the ability for solar irradiated cultures of V. cholerae in water to induce the phenotypic maturation of immature dendritic cells in vitro. In order to achieve this objective, solar and non-solar irradiated, chemically/ heat inactivated and phosphate buffered saline (PBS) prepared cultures of V. cholerae as well as lipopolysaccharide (LPS) and cholera toxin-β (CTB) subunit were each used to stimulate immature dendritic cells. After 48 hours of stimulation the dendritic cells were assessed for the expression of CD54, CD80, CD83, CD86, MHC-I and MHC-II on their cell membrane. The results showed an increase in the expression of all the maturation phenotypic markers with CD54, CD86 and MHC-I being the most prominent ones on the surface of the dendritic cells stimulated with solar irradiated cultures of V. cholerae. The third objective was to assess the profile of the cytokines and chemokines secreted by the dendritic cells following their stimulation with solar and non-solar irradiated, chemically/heat inactivated and PBS prepared cultures of V. cholerae as well as LPS and CTB subunit. After 48 hours of dendritic cell stimulation the tissue culture media from each treatment was quantitatively and qualitatively analysed for the presence of interleukin (IL)-1α, IL-1β, IL-6, IL-7, IL-10, IL-12p40, IL-12p70, IL-15, IL-23, IL-27, macrophage inflammatory protein (MIP)-1α, MIP-1β, MIP-2, Regulated on Activation, Normal T cell Expressed and Secreted (RANTES) and tumor necrosis factor (TNF)-α. The analysis revealed that solar irradiated cultures of V. cholerae induced dendritic cells to secrete significant levels of pro-inflammatory cytokines in comparison to the unstimulated dendritic cells. Furthermore the profile of the cytokines and chemokines secreted by the dendritic cells in response to the solar irradiated cultures of V. cholerae in water was similar to that required to induce a T- helper (Th) Th2 immune response. The fourth objective was to assess the expression of the toll like receptor (tlr) genes by the dendritic cells following their stimulation with solar and non-solar irradiated, chemically/heat inactivated and PBS prepared cultures of V. cholerae as well as LPS and CTB subunit. After 48 hours of stimulation total RNA was extracted from the dendritic cells and subjected to real time quantitative polymerase chain reaction (RT qPCR) assay for tlr 1, 2, 3, 4, 5, 6, 9, 11, 12 and 13. The results showed no significant increase or decrease in the expression of most tlr genes in comparison to the unstimulated dendritic cells. This observation is synonyms with dendritic cell maturation. Taken together these findings show that solar irradiated cultures of V. cholerae were able to induce the maturation of immature dendritic cells in vitro. Furthermore dendritic cells stimulated with solar irradiated cultures of V. cholerae produced pro-inflammatory cytokines and chemokines. The results from this study suggests that the consumption of SODIS treated could provide immunological benefits.
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, 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.
Synthesis and characterization of metal oxide thin films, metal sulfide and metal oxide polymer nanocomposites and studies of their application in water treatment
(Vaal University of Technology, 2017-08-10) Xaba, Thokozani; Moloto, N., Prof.; Moloto, M. J., Prof.
The study based on thiourea derivatives has received significant interest from several disciplines due to their variable bonding modes, promising biological implications and their complexation capacity. Thiosemicarbazones are a stimulating type of ligands that reveals a diverse range of biological activities. They are effectual intermediates for the production of pharmaceutical and bioactive materials which makes them very useful in the field of medicinal chemistry. The FTIR spectral variations in the stretching frequencies of C=N, C–N and C=S that appeared at 1663, 1327 and 726 cm-1, respectively confirmed the formation of the ligand. The present study describes the preparation of (Z)-2-(pyrrolidin-2-ylidene)thiourea ligand for the synthesis of ZnS, CdS and Ag2S nanoparticles via homogeneous/chemical precipitation technique. The effect of different capping agents such as starch, PVP, PEG, PVA, and the role of ammonium hydroxide solution during the synthetic processes was investigated and distinguished. The study based on the effect of capping molecule on the formation of nanoparticles proved that the capping agent has a great influence on the formation of nanoparticles. The FTIR spectra of the capped nanoparticles revealed the shift toward the higher frequencies compared with the uncapped metal sulfide nanoparticles. The metal sulfide nanoparticles also showed an increased in energy band gaps which were different from the bulk materials. The 2-hydroxy-1-naphthaldehyde is regarded as a low-cost ligand which has also been widely used in biological synthesis to determine free amino acid groups. The metal complexes of this ligand are easily prepared and can be used to synthesize metal oxide nanomaterials at low cost which are environmentally friendly that can be expended in bio-applications. The preparation of the Zn, Cd and Ag complexes based on the bis(2-hydroxy-1-naphthaldehydate ligand through the reaction desired metal acetate are reported and confirmed by FTIR spectroscopy, elemental analysis and thermogravimetric analysis (TGA). There has been a great research significance for the synthesis of metal oxide since such materials have high specific surface area and a high fraction of surface atoms. The synthesis of ZnO, CdO and Ag2O nanoparticles through thermal decomposition of the Zn(II), Cd(II) and Ag(I) complexes into trioctylphosphene oxide (TOPO) and/or hexadecylamine (HDA) at different decomposition temperatures is reported. The study proved that the combination of oleylamine as a solvent and TOPO as a capping molecule produced controlled shaped and reasonably dispersed particles. The XRD patterns of all the metal oxide nanoparticles synthesized with TOPO were showing face-centred cubic structures. These metal oxide based complexes were also used as single source precursors to prepare metal oxide thin films at different annealing temperatures on the glass substrate using different methods such as annealing, thermal decomposition, aerosol assisted chemical vapour deposition (AACVD) methods. The optical absorption and size distribution of the synthesized nanoparticles and thin films have been explored using XRD, SEM, AFM, FTIR, PL and UV-Vis spectroscopy techniques. The results show that the decomposition temperature has a huge effect on the formation of the nanomaterials. The SEM images of the as synthesized nanoparticles revealed different shapes of the particles as the decomposition temperature is increased. A change in X-ray diffraction pattern was observed when the decomposition temperatures were increased. The capped metal sulphides and metal oxide nanoparticles were then allowed to react with polydadmac or chitosan to form the polymer nanocomposites. The optical absorption, luminescence properties, size distribution and the bonds distribution of the polymer nanocomposites were characterized with UV-Vis, PL and FTIR spectroscopy. The structural and morphological properties have been studied by XRD, TEM and SEM. The absorption analysis of the prepared nanocomposites revealed the properties of both nanoparticles and polymers. Chitosan and polydadmac are biopolymers that have been proven as the best adsorbents to remove the heavy metal ions from wastewater.In this study, polydadmac and chitosan based metal sulphide and metal oxide nanocopmposites were used as adsorbents for the removal of Fe(III) from the wastewater. The batch experiments were conducted to achieve the optimum conditions. The effect of pH, contact time, and initial metal ion concentration were also determined. The pH = 8 was found to be the optimum pH for the removal of Fe(II) ions from the water sample by utilizing pure chitosan and chitosan nanocomposites as adsorbents.
Adsorption of nitrate and fluoride anions from aqueous solutions using doped magnetite-pinecone nanocomposites
(Vaal University of Technology, 2022-03-23) Frans, Nonhlanhla; Ofomaja, A. E., Prof.; Akpotu, S., Dr.; Pholosi, A., Prof.
The increasing rate of pollutants, such as nitrate and fluoride from industrial and agricultural sources in the environment, especially in water bodies, is becoming alarming. Excessive nitrate and fluoride concentration in water cause environmental toxicity and hazard such as eutrophication and toxic, chronic illnesses such as methemoglobinemia. Hence, there is an urgent need to remove these pollutants from water. There have been a few successful strategies for the purification of pollutants contaminated water. Adsorption has been applied to remove pollutants from aqueous media due to its flexibility, ease of use, cost-effectiveness and ability to adsorb contaminants at low concentrations. Various adsorbents have been applied to remove nitrate and fluoride anions, and doped magnetic has shown to be effective in removing these anions. In this study, manganese doped magnetite coated pinecone (Mn-MNP-PCP) and lanthanum doped magnetite coated pinecone (La-MNP-PCP) nanocomposite were prepared using the co-precipitation method. Fourier Transform Infra-Red (FT-IR), Scanning electron microscopy (SEM), Energy-dispersive x-ray spectroscopy (EDS), Thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) were used to determine the surface groups, structure and morphology, chemical composition, thermal stability and phase determination (amorphous or crystalline) structure of the synthesised Mn-MNP-PCP and La-MNP-PCP adsorbents, respectively. In addition, batch adsorption experiments were conducted to evaluate the effects of solution pH, adsorbent dose, initial solution concentrations, contact time, adsorption kinetics, adsorption isotherm and the impact of co-existing anions on the adsorption of nitrate and fluoride ions. The mechanism of adsorption processes was also determined using equilibrium isotherm modelling results and thermodynamic parameters. The maximum adsorption capacity of Mn-MNP-PCP and La-MNP-PCP adsorbents for nitrate adsorption was 22.8 mg/g and 37.7 mg/g at solution pH 4, while the adsorption efficiency was 45.6% and 75.4%. Fluoride removal occurred at pH 2 with the adsorption capacity of 46.2 mg/g and 44.77 mg/g with the removal efficiency of 92.4 % and 89.6% on both Mn-MNP-PCP and La-MNP-PCP adsorbents. The optimum adsorbent dose for both Mn-MNP-PCP and La-MNP-PCP in the adsorption of nitrate and fluoride was 1 g/L. The optimum time for the uptake of nitrate and fluoride onto MNP-PCP and La-MNP-PCP was between 15 – 20 min. The competing phosphate and sulphate ions impacted the nitrate adsorption, while the presence of carbonate and chloride had positive nitrate adsorption onto both Mn-MNP-PCP and La-MNP-PCP nanocomposites. The decrease in nitrate adsorption may be attributed to the lower affinity of Mn-MNP-PCP and La-MNP-PCP for nitrate and a competition between the nitrate ions and co-existing anions for the active sites. The presence of all competitive ions decreased the fluoride adsorption onto Mn-MNP-PCP and La-MNP-PCP nanocomposites. The multi-valent anion with higher charge density have been reported to be more readily adsorbed than monovalent anion. The equilibrium data for nitrate and fluoride ions uptake was best described by Langmuir isotherm, which predicts the formation of ionic or covalent chemical bonds between the adsorbent and adsorbate. In the same vein, pseudo-second-order model is considerably suitable for nitrate and fluoride ions adsorption, which showed that their uptake was fast. Conclusively, La-MNP-PCP adsorbent is an effective adsorbent for nitrate adsorption, while Mn-MNP-PCP effectively trmoved fluoride ions from the aqueous solution.
The fabrication of ClNCNTs/Fe3O4 nanoparticles for the removal of Pb2+ ions in aqueous solution
(Vaal University of Technology, 2021-12-13) Sebake, Morongwa Sowela Mary-Jane; Maubane-Nkadimeng, Manoko S., Dr.; Maboya, Winny K., Dr.
Removal of wastewater pollutants is urgent as they are continuously defiling the limited freshwater resources, affecting the ecosystem, aquatic and terrestrial life. Carbon nanotubes-based adsorbent materials are effective for removal of wastewater pollutants owing to their large specific surface area. Surface modification of carbon nanotubes (CNTs) can mediate specific pollutant adsorption and increase CNTs colloidal stability and chemical reactivity. Heavy metal pollution of wastewater is one of the major threats, as this metals can be toxic to humans when present at certain concentrations in drinking water. This study report the synthesis of chlorine functionalized and nitrogen doped carbon nanotubes (ClNCNTs) loaded with iron oxide nanoparticles and their use as adsorbents for Pb2+ ions in aqueous solutions. Carbon nanomaterials that are functionalized with chlorine and doped with nitrogen were successfully synthesized. This was done through pyrolysis of a mixture of dichlorobenzene and acetonitrile (in a 1:1 volume ratio) over 10% Fe-Co/CaCO3 bi-metallic catalyst via chemical vapour deposition (CVD) method. Addition of chlorine and nitrogen to the CNTs was to enable defect and disorder creation on the surface of the nanotubes which is envisaged to create nucleation sites on the their surface for better adhesion of the iron oxide nanoparticles. Different loadings of magnetite (Fe3O4) nanoparticles on the surface of the ClNCNTs was achieved using a co-precipitation method. The synthesized materials were charaterized by Raman spectroscopy, Transmission electron microscopy (TEM), Powder X-ray diffraction (PXRD) spectroscopy, Thermal gravimetric analysis (TGA), Brunauer Emmett and Teller (BET) and X-ray photoelectron spectroscopy (XPS). Highly defected CNTs, some with hollow and others with bamboo-compartments due to nitrogen inclusion were obtained. The effect of metal salt concentration in wt.% (10, 20, 30 and 53 wt.%) was investigated. The increase in wt.% loading has resulted in an increase in surface area, and a decrease in thermal stability as a result of defected Fe3O4/ClNCNTs. In addition, agglomeration was observed at 30 and 53 wt.% loading, due to large amount of iron present. The identity of the Fe3O4 nanoparticles was confirmed by PXRD and XPS with two iron peaks deconvoluted at 725.6 eV and 721 eV respectively. The percentage loading of the Fe3O4 nanoparticles at the surface of the ClNCNTs was affirmed by TGA analysis, where the residual mass obtained from TGA were closely related to the mass percentages added. Different nitrogen environments namely, the quatenary, pyridinic, pyrollic and nitrogen oxides were also observed, whilst chlorine could not be deconvoluted because it was present in very limited amount probably it was masked by the iron oxide nanoparticle. Thus, a 20 wt.% Fe3O4/ClNCNTs was chosen as an optimum, due to uniform distribution of spherical nanopaticles observed along the radial length of ClNCNTs that had an average size of 10 ± 4.5 nm. The synthesized ClNCNTs and a nanocomposite made from a 20 wt.% Fe3O4/ClNCNTs were applied in the removal of Pb2+ ions from aqueous solution. The results obtained showed that a nanocomposite made from a 20 wt.% Fe3O4/ClNCNTs had a better adsorption capacity of 17.0 mg/g as compared with 14.8 mg/g for ClNCNTs.
Copper oxide-carbon catalysts for the oxidation of methylene blue
(Vaal University of Technology, 2020) Makamu, Anza Reliance; Ofomaja, Prof.; Viljoen, E. L., Dr.
Organic water pollutants such as dyes are difficult to biodegrade. In this study Fenton, photo-Fenton and photocatalysis were used to degrade methylene blue dye in the presence of copper oxide catalysts. The copper oxide catalysts were prepared with a precipitation reduction method. The effect of different preparation parameters on the catalyst properties and catalytic activity were investigated. The reducing agents, ascorbic acid (ASC, C6H8O6), hydrazine (N2H4), sodium boron hydride (NaBH4) and glucose (C₆H₁₂O₆) could be used to obtain the desired Cu2O phase. ASC, N2H4 and NaBH4 were able to reduce copper (II) to copper (I) at room temperature whereas glucose required a higher reduction temperature. Stoichiometric amounts of the reducing agents ASC, N2H4 and glucose and double the stoichiometric amount of NaBH4 were required to obtain Cu2O. A further increase in the amounts of NaBH4 and N2H4 resulted in the formation of copper metal (Cu (0)). High amounts of ASC did not over-reduce the copper. ASC also functioned as capping molecule and anti-oxidant preventing the oxidation of the Cu2O to CuO in air after preparation. Hydrazine was thus not able to protect the Cu2O against oxidation. The SEM results showed that an increase in the amount of the precipitating agent, NaOH, resulted in an increase in the particle sizes. The particle shapes changed from spherical to cubic when a high amount of NaOH was used with hydrazine as reducing agent. Smaller particle sizes were obtained when CuCl2 was used instead of CuSO4 and Cu(NO3)2. Larger crystallites formed when the preparation temperature was increased from room temperature to 100°C with glucose as reducing agent. TEM and XRD analyses showed that the micro-particles seen in SEM analyses are made up of nano-particles. The catalysts were not active for photocatalysis which may be explained by the oxidation of these nano-particles to form the photocatalytic inactive CuO. The catalysts were shown to be active for Fenton and photo-Fenton degradation. The addition of graphene and activated carbon to the Cu2O catalysts were detrimental to the catalytic activity. The percentage degradation of methylene blue by the Fenton reaction increased with an increase in the BET surface area from 1.5 m2/g to 10 m2/g and a further increase in the surface area resulted in a decrease in the percentage degradation. A direct correlation between the Fenton catalytic activity and the pore size were found which indicate that the reaction was mass transfer limited.
Plasmon catalyst dispersed on carbonised pinecone for enhanced degradation of organic contaminants
(Vaal University of Technology, 2020-11) Olalekan, Sanni Saheed; Viljoen, Elvera, Dr.; Ofomaja, Augustine, Prof.
Aromatic organic contaminants are difficult to biodegrade, and thus effective green technologies are required to remove these pollutants from the ecosystem. Tetracycline antibiotic, an organic water pollutant, can be degraded by heterogeneous photocatalysis using an appropriate catalyst, with capability in converting the visible light energy into active species. The thesis focused on silver nanoparticles anchored on silver bromide (Ag/AgBr) as a plasmonic catalyst dispersed on activated carbon (ACK), were used as a photocatalyst (AABR-ACK) in tetracycline removal. The aim is to develop a catalyst that is active in low intensity visible light, whilst the addition of activated carbon will increase the light absorption and separate the charge pairs, after the photocatalyst has been excited by the visible light. The activated carbons were derived from pinecone pyrolyzed in a microwave. The pinecone mass to potassium hydroxide impregnation ratio and microwave pyrolysis time influenced the activated carbon properties. An impregnation ratio of 2.24 and microwave pyrolysis time of 16 minutes at constant microwave power of 400 W yielded the activated carbon with the best-developed porous structure and electrochemical properties. This activated carbon was used during the optimisation of the Ag/AgBr activated carbon (AABR-ACK) catalysts preparation using a thermal polyol precipitation method and response surface methodology. The most active catalyst was the AABR-ACK 11 obtained by a preparation temperature of 140 ºC, time (17.50 minutes), mass of surfactant and activated carbon (0.26 g and 0.03 g) respectively. This catalyst had an ordered nanospheres morphology, reduced electron-hole recombination rate, better electrochemical properties and exhibited enhanced activity on the tetracycline antibiotic removal in comparison to other Ag/AgBr activated carbon catalysts. A percentage degradation of 92% was obtained in 180 minutes were obtained with the AABR-ACK 11 catalyst. The photocatalyst prepared using the best activated carbon derived from pinecone developed in this study was compared to photocatalysts prepared using commercial activated carbon and biochar. The Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon degraded the tetracycline to 92%, which is significantly higher than the percentage degradations (80% and 74%) for the catalyst prepared using commercial activated carbon and biochar catalysts respectively. The higher activity of the Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon was due to the conductive attributes of the catalyst support for accelerated transfer of photo-induced electrons. The Ag/AgBr activated carbon catalysts using pinecone- derived activated carbon also exhibited better performance on tetracycline removal when compared to photocatalysts reported in literature. Two catalyst preparation methods, thermal polyol and deposition precipitation, were compared. The thermal polyol method yielded a more active catalyst for the degradation of the tetracycline in comparison to the deposition precipitation method. The degradation reaction conditions such as pH, light intensity and degradation temperature influenced the rate of the reaction. The highest rate of degradation was obtained at a pH of seven, white light and 40 ºC temperature. The intermediate products formed because of hydroxylation, deamination, demethylation and dehydration during the photocatalytic degradation of tetracycline antibiotics were identified using liquid chromatography mass spectrometer. Quenching experiments with hydroxyl, hole, and superoxide anion species showed that the most important radical responsible for the tetracycline degradation was the superoxide anion radical.
Development of a sensitive electrochemical sensor based on carbon dots and graphitic carbon nitride for the detection of 2-chlorophenol and arsenic (III) in water
(Vaal University of Technology, 2021-02) Moundzounga, Theo Herman Gael; Oseghe, E. O., Dr.; Peleyeju, M. G., Dr.; Ofomaja, A. E., Prof.; Klink, M. J., Dr.
The presence of organic and inorganic pollutants in aqueous environments is one of the major challenges confronting man. It is therefore important to develop sensitive, versatile and cheap techniques for their detection. Arsenic (III), 2-chlorophenol (2-CP) and sulfamethoxazole (SMX) are priority pollutants that pose health threats to humans and animals. This study was thus aimed at exploring two promising carbon nanomaterials as electrode modifiers for the electrochemical sensing of arsenic (III), 2-CP and SMX in water. Glassy carbon electrode (GCE) was modified with a nanocomposite of carbon dots (CDs) and graphitic carbon nitride (g-C3N4) and used as a sensor for the analytes in aqueous media. The CDs was prepared by a facile one-pot hydrothermal method using pine cone as the carbon source; g-C3N4 and g-C3N4/CDs nanocomposite were prepared via the microwave irradiation heating method. CDs, g-C3N4 and g-C3N4/CDs were dropped-dried on the surface of bare GCE. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the prepared materials. GCE, g-C3N4/GCE, CDs/GCE and g-C3N4/CDs/GCE electrodes were electrochemically investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) using a ferrocyanide [Fe (CN) 6]3-/4- redox probe. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical behavior of arsenic (III), 2-CP and SMX on different electrodes (GCE, CDs/GCE, g-C3N4/GCE and g-C3N4/CDs/GCE) were investigated by differential pulse voltammetry (DPV) under optimized conditions in a phosphate buffer solution (pH 7.6, 6 and 5 for 2-CP, As (III) and SMX respectively). The results demonstrated that the g-C3N4/CDs/GCE electrode significantly enhanced the oxidation peak current of all three analytes. The detection sensitivity of the analytes was greatly improved, suggesting that this new modified electrode has great potential in the determination of trace level of arsenic (III), 2-CP and SMX in water. The oxidation peak currents displayed a linear relationship to concentrations for 2-CP (0.5 - 2.5 μM, R2=0.958, n=5), arsenic (III) (2 - 10 μM R2=0.978, n=5) and SMX (0.3 - 1.3 μM R2=0.9906, n=5). The detection limits of 0.62 μM, 1.64 μM and 0.10 μM were obtained for 2-CP, arsenic and SMX, respectively. Phenol and 4-chloro-3-methyl-phenol were found to interfere with the detection of 2-CP, while, Cu2+, Zn2+, Pb2+ and Cd2+ were the only significant ions that interfered with the electrochemical detection of arsenic (III). EDTA was used as a ligand to mask the interference effects of copper, cadmium, lead and zinc on arsenic sensing. The modified electrode (g-C3N4/CDs/GCE) was used to determine arsenic, 2-CP and SMX in spiked tap and effluent water samples by the standard addition method and the results showed percentage recoveries varying from 93-118% for 2-CP, 98-100% for arsenic and 80-105% for SMX. The outcomes of this study established that the nanocomposite material represents an easy and sensitive sensing platform for the monitoring of arsenic (III), 2-CP and SMX in aqueous media.

Browse

Recent Submissions