In order to improve the performance and fundamental understanding of conducting polymers, development of new nanotechnologies for engineering aggregated states and morphologies is one of the central focuses for conducting polymers. In this work, we demonstrated an interfacial engineering method for the rational synthesis of a two-dimensional (2D) polyaniline (PANI) nano-array and its corresponding nitrogen-doped porous carbon nanosheets. Not only was it easy to produce a sandwich-like 2D morphology, but also the thickness, anchored ions and produced various metal phosphides were easily and rationally engineered by controlling the composition of the aqueous layer. The novel structural features of these hybrids enabled outstanding electrochemical capacitor performance. The specific capacitance of the as-produced diiron phosphide embedded nitrogen-doped porous carbon nanosheets was calculated to be as high as 1098 F g−1 at 1 A g−1 and an extremely high specific capacitance of 611 F g−1 at 10 A g−1, outperforming state-of-the-art performance among porous carbon and metal-phosphide-based supercapacitors. We believe that this interfacial approach can be extended to the controllable synthesis of various 2D material coupled sandwich-like hybrid materials with potential applications in a wide range of areas.

Thesis (M.Sc.(Chemistry)) -- University of Limpopo, 2022 / Water contamination caused by toxic elements has serious human health and ecological implications. The increasing quantity of toxic elements in surface and groundwater is currently an area of greater concern, especially since many industries are discharging their metal containing effluents into freshwater without any adequate treatment. The mineral dissolution in mining regions is highly enhanced by mining and smelting activities. The mine waste and drainage in areas surrounding mines have high levels of toxic element contamination above the permissible limits. Contamination of groundwater by toxic elements such as As, Fe, Mn, Al, Cr, Zn and Co due to operational activities of surrounding mines in the Sekhukhune district was reported by several researchers. Removal of toxic elements from contaminated water is a big challenge. The affected communities need to attain a safe water supply source for daily usage, hence there is an urgent need of technologies for the treatment of water supplies contaminated with these toxic elements to ensure the safety of potable water. The study was undertaken by modifying nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) and investigating the removal of chromium, nickel and lead from anthropogenic contaminated groundwater in the Sekhukhune area, in Limpopo. The as-prepared N-MWCNTs functionalised with metal oxide, thiol and amino functional groups are expected to increase the surface area of the nanocomposite, which can facilitate high adsorption of contaminants from water samples. The adsorption capabilities for the removal of these toxic elements by modified N MWCNTs nanocomposites were investigated in batch studies as a function of different parameters. The parameters studied included pH, contact time, adsorbent dosage, initial concentration, temperature, competing ions and reusability. The optimum condition was then acquired for removal of selected toxic elements from real water studies. The removal efficiencies of the as-prepared nanocomposites were pH dependent and the optimal pH values for adsorption was 5.5, 1.5, 11 and 6 at optimum contact time of 10, 80, 60 and 120 min and dosage of 0.30, 0.35, 0.05 and 0.6 g/L for Cr(III), Cr(VI), Ni(II) and Pb(II), respectively. The prepared nanocomposites were characterised using various techniques such as Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmet-Teller (BET) and thermogravimetric analysis (TGA). The FTIR analysis confirmed the presence of Fe3O4, -SH and -NH2 groups on the functionalised MWCNTs. The PXRD analysis further supported that the synthesized nanocomposites consisted of hexagonal graphite structure of MWCNTs. Furthermore, SEM and TEM results showed that the introduced functional groups were uniformly attached on the surface of the MWCNTs. The BET analysis indicated that the surface area of the modified MWCNTs nanocomposites increased significantly as compared to the acid treated MWCNTs. In addition, TGA showed that the M-MWCNTs (M = modified) nanocomposites possess high thermal stability. Raw N-MWCNTs showed higher stability as compared to oxidised N-MWCNTs, which decomposes at lower temperatures of 200 °C. No weight loss was observed below 800 °C for the hydrazine functionalised nanocomposites as compared to the triethylenetetramine (TETA)- substituted nanocomposites, which showed weight loss at 300 °C. Toxic elements in solutions before and after treatment were quantified using flame atomic absorption spectrometry (F-AAS). The adsorption isotherms of the as-prepared nanocomposites for chromium, nickel and lead removal fitted both the Langmuir and Freundlich model depending on the adsorbent used, which suggest that the adsorption process met both monolayer and heterogeneous adsorption. Thermodynamic analysis showed that the adsorption of Cr(III), Cr(VI), Ni(II) and Pb(II) ions are spontaneous and endothermic. The as-prepared nanocomposites showed an outstanding regeneration performance retaining over 50% toxic elements removal. Thus, the as prepared nanocomposites are promising for practical application in toxic element treatment. Analysis of the collected river and borehole water in Sekhukhune indicated that the concentration of total chromium, nickel and lead before treatment varied from (0.207 to 0.286 mg/L), (0.226 to 0.380 mg/L) and (3.301 to 8.017 mg/L), respectively which were above acceptable levels recommended by the South African National Standards (SANS), United States Environmental Protection Agency (USEPA) and World Health Organisation (WHO), i.e., 0.05 mg/L, 0.07 mg/L and 0.01 mg/L. After treatment, the nanocomposites were able to remove 100% of the metal ions from the water. TETA-functionalised nanocomposites showed greater removal efficiencies in comparison to the hydrazine-functionalised nanocomposites for all the studies done. / Water Research Commission (WRC)

Die kürzliche globale COVID-19-Pandemie hat deutlich gezeigt, dass hohe medizinische Kosten eine große Herausforderung für unser Gesundheitssystem darstellen. Daher besteht eine wachsende Nachfrage nach personalisierten tragbaren Geräten zur kontinuierlichen Überwachung des Gesundheitszustands von Menschen durch nicht-invasive Erfassung physiologischer Signale. Diese Dissertation fasst die Forschung zur Laserkarbonisierung als Werkzeug für die Synthese flexibler Gassensoren zusammen und präsentiert die Arbeit in vier Teilen. Der erste Teil stellt ein integriertes zweistufiges Verfahren zur Herstellung von laserstrukturiertem (Stickstoff-dotiertem) Kohlenstoff (LP-NC) ausgehend von molekularen Vorstufen vor. Der zweite Teil demonstriert die Herstellung eines flexiblen Sensors für die Kohlendioxid Erfassung basierend auf der Laserumwandlung einer Adenin-basierten Primärtinte. Die unidirektionale Energieeinwirkung kombiniert mit der tiefenabhängigen Abschwächung des Laserstrahls ergibt eine neuartige geschichtete Sensorheterostruktur mit porösen Transducer- und aktiven Sensorschichten. Dieser auf molekularen Vorläufern basierende Laserkarbonisierungsprozess ermöglicht eine selektive Modifikation der Eigenschaften von gedruckten Kohlenstoffmaterialien. Im dritten Teil wird gezeigt, dass die Imprägnierung von LP-NC mit Molybdäncarbid Nanopartikeln die Ladungsträgerdichte verändert, was wiederum die Empfindlichkeit von LP-NC gegenüber gasförmigen Analyten erhöht. Der letzte Teil erläutert, dass die Leitfähigkeit und die Oberflächeneigenschaften von LP-NC verändert werden können, indem der Originaltinte unterschiedliche Konzentrationen von Zinknitrat zugesetzt werden, um die selektiven Elemente des Sensormaterials zu verändern. Basierend auf diesen Faktoren zeigte die hergestellte LP-NC-basierte Sensorplattform in dieser Studie eine hohe Empfindlichkeit und Selektivität für verschiedene flüchtige organische Verbindungen. / The recent global COVID-19 pandemic clearly displayed that the high costs of medical care on top of an aging population bring great challenges to our health systems. As a result, the demand for personalized wearable devices to continuously monitor the health status of individuals by non-invasive detection of physiological signals, thereby providing sufficient information for health monitoring and even preliminary medical diagnosis, is growing. This dissertation summarizes my research on laser-carbonization as a tool for the synthesis of functional materials for flexible gas sensors. The whole work is divided into four parts. The first part presents an integrated two-step approach starting from molecular precursor to prepare laser-patterned (nitrogen-doped) carbon (LP-NC). The second part shows the fabrication of a flexible LP-NC sensor architecture for room-temperature sensing of carbon dioxide via laser conversion of an adenine-based primary ink. By the unidirectional energy impact in conjunction with depth-dependent attenuation of the laser beam, a novel layered sensor heterostructure with a porous transducer and an active sensor layer is formed. This molecular precursor-based laser carbonization method enables the modification of printed carbon materials. In the third part, it is shown that impregnation of LP-NC with molybdenum carbide nanoparticle alters the charge carrier density, which, in turn, increases the sensitivity of LP-NC towards gaseous analytes. The last part explains that the electrical conductivity and surface properties of LP-NC can be modified by adding different concentrations of zinc nitrate into the primary ink to add selectivity elements to the sensor materials. Based on these factors, the LP-NC-based sensor platforms prepared in this study exhibited high sensitivity and selectivity for different volatile organic compounds.

Hierarchically porous nitrogen-doped graphene frameworks (N-GFs) are fabricated through the ice-templating of GO with polyethylenimine and the thermal treatment of the resultant hybrids. As cathode materials in lithium ion batteries (LIBs), the obtained N-GFs exhibit an outstanding specific capacity of 379 mA h g−1 at 0.5 A g−1 for 2500 cycles. Even at an ultrahigh current density of 5 A g−1, the N-GFs maintain a capacity of 94 mA h g−1, superior to that of most reported LIB cathode materials. The experimental results and quantum mechanics calculations suggest that pyridinic-like N and pyridinic N-oxide in graphene are responsible for the excellent cathodic performance of the bipolar N-GFs by providing fast surface faradaic reactions with both p- and n-doped states.

Hierarchically porous nitrogen-doped graphene frameworks (N-GFs) are fabricated through the ice-templating of GO with polyethylenimine and the thermal treatment of the resultant hybrids. As cathode materials in lithium ion batteries (LIBs), the obtained N-GFs exhibit an outstanding specific capacity of 379 mA h g−1 at 0.5 A g−1 for 2500 cycles. Even at an ultrahigh current density of 5 A g−1, the N-GFs maintain a capacity of 94 mA h g−1, superior to that of most reported LIB cathode materials. The experimental results and quantum mechanics calculations suggest that pyridinic-like N and pyridinic N-oxide in graphene are responsible for the excellent cathodic performance of the bipolar N-GFs by providing fast surface faradaic reactions with both p- and n-doped states.