A thesis submitted to the Faculty of Science, University of the Witwatersrand in fulfilment of the requirements for the degree of Doctor of Philosophy.
WITS University, Johannesburg, 2016. / In this work, natural and synthetic sorbents were investigated for the extraction and removal of different organic compounds (nitroaromatic compounds and polycyclic aromatic hydrocarbons) from aqueous samples.
Natural sorbents like the raw Moringa oleifera seed powder and the physically modified biochared powder were investigated for their potential in the extraction of nitrobenzene (NB) (paper I). For the raw and biochared Moringa oleifera seed powder, the carbon content as determined by energy dispersive X-ray spectroscopy (EDS) was 80% and 70%, respectively. Though the surface area of the biochared was double that of the raw (12.6 m2 g-1 and 6.3 m2 g-1, respectively), the uptake of nitrobenzene by the later was higher in all optimizations and applications investigated. This implied that the interaction type between the Moringa oleifera seed powder and nitrobenzene was more chemisorption than physiosorption. The presence and absence of the proteneous compounds (bearers of the functional groups) infuenced the performance of the Moringa oleifera seed powder as a sorbent. For the raw and biochared Moringa oleifera seed powder sorbent, the kinetic data was best modelled by the pseudo-second-order and the adsorption capacities were found to be 0.084 and 0.071 mg g-1, respectively. As determination by HPLC-UV method, the LOD and LOQ for NB were found to be 11.5 and 38.5 μg L-1, respectively.
In paper II, 2,4-dinitrotoluene was used as an imprint in the synthesis of magnetic molecularly imprinted polymers (MMIPs). These synthetic sorbents were used for the extraction of nitroaromatic compounds (2,4-dinitrotoluene, 2-nitotoluene and nitrobenzene). In all the optimization parameters investigated, the MMIP had a great extraction of 2,4-dinitrotoluene showing the effect of imprinting. For 2,4-dinitrotoluene, nitrobenzene and 2-nitrotoluene HPLC-UV analysis, detection limits of 13.6, 7.7 and 27.2 μg L-1, respectively and good correlations of determination (R2 > 0.993) of all the analytes were obtained. Recoveries of 82.7%, 88.1% and 82.0% were obtained for 2,4-dinitrotoluene,
nitrobenzene and 2-nitrotoluene from spiked real water samples, respectively, with %RSD values ranging from 1.4%-11.9%.
In paper III, another synthetic sorbent, β-cyclodextrin covalently functionalized to carbon nanofibers (β-CD@CNFs) was prepared and fully characterized. This material was loaded in solid phase extraction catridges, which were then applied for the extraction and pre-concentration of six nitroaromatic compounds. High correlations of determination (R2 > 0.997) for 3-nitrotoluene (3-NT), 1,3-dinitrobenzene (1,3-DNB), 2,6-dinitrotoluene (2,6-DNT), 4-nitrotoluene (4-NT), nitrobenzene (NB) and 2-nitrotoluene (2-NT) were obtained. Low limits of detection of 3.3, 7.1, 8.6, 9.7, 23.1 and 13.0 μg L-1 were found for the respective compounds. The applicability of the developed method using β-CD@CNF as a sorbent was investigated using spiked real water samples collected within the vicinity of an operational gold mine and recoveries of 36.6%-102.2% were obtained.
Paper IV dealt with a novel combination of molecularly imprinted polymers (MIPs) dispersed in an organic solvent in membrane assisted solvent extraction (MASE) bags for the extraction of polycyclic aromatic hydrocarbons (PAHs) from sewage wastewater samples from Goudkoppies wastewater treatment plant in Johannesburg, South Africa. Before application to real wastewater, optimization was carried out and toloune was found to be the best acceptor phase, and 80 mg of the MIPs gave optimum extraction of PAHs. 25% N,N-dimethylformamide in aqueous solution as an organic modifier was found to be the best donor composition. An extraction time of 90 min at a stirring rate of 1000 rpm gave the optimum pre-concentration of the PAHs. The optimized parameters where then applied to the sewage wastewater were the effluent was found to be cleaner than the influent.
In paper V, nano-sized fibers were synthesized by electrospinning polyacrylonitrile (PAN). Due to the combination of functional groups along the fiber and the increased surface area due to nano-sizing, there was a great extraction of four nitrotoluenes. The approach was loading a small amount of the
electrospun polyacrylonitrile nano-fibres in pipette tips in a miniaturized pipette tip solid phase extraction (SPE). The linear dynamic range was 150 - 1000 μg L-1 with coefficients of determination of R2 > 0.99 for all the nitroaromatic compounds. Optimum recoveries were recorded at pH 6, 15 mg of the PAN sorbent. Twenty aspirating/dispensing cycles (at the loadind stage) and 1 mL acetonitrile gave maximum recoveries. Application of the PAN-PT-SPE to real wastewater samples gave recoveries ranging from 70% to 115%. The low values of the relative standard deviations (RSD < 12%) meant the method was suitable for application to real wastewater samples. / LG2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21693 |
| Date | January 2016 |
| Creators | Tavengwa, Nikita Tawanda |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (195 leaves), application/pdf |
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