3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Evaluation of metal nanocomposite polymer inclusion membranes (PIMs) for trace heavy metal extraction in natural waters(2020) Maiphetlho, KgomotsoThe shortcomings of the conventional membranes in water applications such as low stability and the hydrophobic nature reduces the membrane productivity and lifespan. These result in expensive procedures that hinder membrane science technology. Hence, recent investigations have resulted in the synthesis of nanocomposite membranes as an alternative. In this work, silver nanocomposite polymer inclusion membranes (PIMs) were synthesized to evaluate the extraction of trace metal ions in natural waters. To characterise the PIMs, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), contact angle measurements and water uptake measurements were used. The contact angle and the water uptake measurements highlighted that the introduction of the silver nanoparticles (Ag NPs) into the membrane, modified the membrane hydrophobic/hydrophilic character. The evaluation of the synthesized PIMs demonstrated that the PIMs containing Ag NPs exhibit better extraction capacity as opposed to the bare PIMs and the PIM with (40 w.t% D2EHPA, 10 w.t% Ag NPs and 50 w.t% PVC) has the optimum composition. It was then used to optimise the parameters that are important for the extraction of trace metal ions and those were sample pH 5, 1 M HNO3 of the receiving solution and 120 hrs for the extraction time. The selectivity of the nanocomposite PIM was investigated and it was found that its affinity towards a range of divalent cations (Co2+, Ni2+, Cu2+, and Cd2+) in synthetic water solutions, based on the percentage recovery factor of the extracted metal ions, follow the order; Cd 2+ (94) > Cu2+ (87) > Ni2+ (78) > Co2+ (67), where the numerical data in the brackets correspond to the percentage recovery factor of metal ion extracted from the source solution, respectively. This order can be explained by the Hard and Soft Acids and Bases Theory and the hydration energy of the metal cations. However, the stability of the PIM was still compromised during repeated cycle operations despite an improvement of hydrophilicity with introduction of Ag NPs, this was indicated by an appreciable leaching of the carrier (D2EHPA) and Ag NPs in a 4:1 ratio (identical to the ratio of these components in the original membrane). This silver nanocomposite PIM was tested in dam water. No matrix effect was observed on metal ion transport efficiency in such waters. The obtained transport efficiencies for the metal ions were Cd2+ (88), Cu2+ (80) , Ni2+ (62) , Co2+ (70) and Fe2+ (37) respectively. The newly synthesized PIM could be used for future extraction of the target metals in water systems. The designed PIM system has also the potential to be used as passive sampler for in situ extraction of the target metals in water systems. However, further studies are needed to improve the stability of both the carrier and nanoparticles in the membraneItem Characterisation of the structural properties of ECNF embedded pan nanomat reinforced glass fiber hybrid composites(2016-10-11) Bradley, PhilipIn this study, hybrid multiscale epoxy composites were developed from woven glass fabrics and PAN nanofibers embedded with short ECNFs (diameters of ~200nm) produced via electrospinning. Unlike VGCNFs or CNTs which are prepared through bottom-up methods, ECNFs were produced through a top-down approach; hence, ECNFs are much more cost-effective than VGCNFs or CNTs. Impact absorption energy, tensile strength, and flexural strength of the hybrid multiscale reinforced GFRP composites were investigated. The control sample was the conventional GFRP composite prepared from the neat epoxy resin. With the increase of ECNFs fiber volume fraction up to 1.0%, the impact absorption energy, tensile strength, and flexural strength increased. The incorporation of ECNFs embedded in the PAN nanofibers resulted in improvements on impact absorption energy, tensile strength, and flexural properties (strength and modulus) of the GFPC. Compared to the PAN reinforced GRPC, the incorporation of 1.0% ECNFs resulted in the improvements of impact absorption energy by roughly 9%, tensile strength by 37% and flexural strength by 29%, respectively. Interfacial debonding of matrix from the fiber was shown to be the dominant mechanism for shear failure of composites without ECNFs. PAN/ECNFs networks acted as microcrack arresters enhancing the composites toughness through the bridging mechanism in matrix rich zones. More energy absorption of the laminate specimens subjected to shear failure was attributed to the fracture and fiber pull out of more ECNFs from the epoxy matrix. This study suggests that, the developed hybrid multiscale ECNF/PAN epoxy composite could replace conventional GRPC as low-cost and high-performance structural composites with improved out of plane as well as in plane mechanical properties. The strengthening/ toughening strategy formulated in this study indicates the feasibility of using the nano-scale reinforcements to further improve the mechanical properties of currently structured high-performance composites in the coming years. In addition, the present study will significantly stimulate the long-term development of high-strength high-toughness bulk structural nanocomposites for broad applications.