Nanoparticles (NP) offer great merits over controlling thermal, chemical and physical properties when compared to their micro-sized counterparts. The effectiveness of the dispersion of the NP is the key aspect of the applications in nanotechnology. The project studies the characterization and modification of functional NPs aided by the means of large scale molecular thermal dynamic computerized dispersing simulations, in the level of Nanoclusters (NC). Carrying out NP functionality characterisation in fluids can be enhanced, and analysed through computational simulation based on their interactions with fluidic media; in terms of thermo-mechanical, dynamic, physical, chemical and rheological properties. From the engineering perspective, effective characterizations of the nanofluids have also been carried out based on the particles sizes and particle-fluids Brownian motion (BM) theory. The study covered firstly, investigation of the pure CuO NP diffusion in water and hydrocarbon fluids, secondly, examination of the modified CuO NP diffusion in water. In both cases the studies were put under experiments and simulations for data collection and comparison. For simulation the COMPASS forcefield, smoothed particle hydrodynamic potential (SPH) and discrete particle dynamics potential (DPD) were implemented through the system. Excellent prediction of BM, Van der Waals interaction, electrostatic interaction and a number of force-fields in the system were exploited. The experimental results trend demonstrated high coherence with the simulation results. At first the diffusion coefficient was found to be 1.7e-8m2/s in the study of CuO NC in water based fluidic system. Secondly highly concurrent simulation results (i.e. data for viscosity and thermal conductivity) have been computed to experimental coherence. The viscosity trend of MD simulation and experimental results show a high level of convergence for temperatures between 303-323K. The simulated thermal conductivity of the water-CuO nanofluid was between 0.6—0.75W•m−1•K−1, showing a slight increase following a rise in temperature from 303 to 323 K. Moreover, the alkane-CuO nanofluid experimental and simulated work was also carried out, for analysing the thermo-physical quantities. The alkane-CuO nanofluid viscosity was found 0.9—2.7mpas and thermal conductivity is between 0.1—0.4W•m−1•K−1. Finally, the successful modification of the NPs on experimental and simulation platform has been analysed using different characterization variables. Experimental modification data has been quantified by using Fourier Transformation Infrared (FTIR) peak response, from particular ranges of interest i.e. 1667-1609cm-1 and 1668-1557cm-1. These FTIR peaks deduced Carboxylate attachment on the surface of NPs. Later, MD simulation was approached to mimic experimental setup of modification chemistry and similar agglomerations were observed as during experimental conditions. However, this approach has not been presented before; therefore this study has a significant impact on describing the agglomeration of modified NPs on simulation and experimental basis. Henceforth, the methodology established for metal oxide nanoparticle dispersion simulation is a novelty of this work.

This work describes metal (M) and metal oxides (MO) films (where M = Ni, Co and Fe) obtained by electrosynthesis and chemical synthesis, and modified with carbon nanotubes (CNTs) on edged plane pyrolytic graphite electrode (EPPGE). The MO nanoparticles investigated are nickel oxide (NiO), cobalt oxide Co3O4) and iron oxide (Fe2O3). Successful modification of the electrodes with the M or MO/CNT nanocomposite was confirmed by field emission scanning electron microscopy (FESEM), high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), x-ray diffraction spectroscopy (XRD), x-ray photoelectron spectroscopy (XPS), electron dispersive x-ray spectroscopy (EDX), fourier transformed infra-red spectroscopy (FTIR) and ultraviolet-visible (UV-vis) spectroscopy. Electron transport (ET) properties of the modified electrodes was explored using cyclic voltammetry (CV) and electrochemical impedance spectroscopic techniques (EIS) with ferricyanide/ferrocyanide ([Fe(CN) 6]3-/4-) as the redox probe. The electron transfer constant (k0) differs in terms of materials, method of synthesis and electrical equivalent circuits used in the fitting or modelling process. Generally, the k0 values are in the 10-3 – 10-2 cms-1 with Ni nanoparticles having the highest k0 or fastest electron transport. The presence of CNTs also enhances the ET compared with electrodes without CNTs. The electrocatalytic properties of the modified electrodes were explored using the following analytical probes: diethylaminoethanethiol (DEAET), hydrazine, nitrite and dopamine. The study showed that the electrocatalytic oxidation of DEAET and hydrazine was favoured on electrode modified with Ni nanoparticles; nitrite and dopamine were best catalysed by the Co and Fe2O3 nanoparticles, respectively. Electroanalysis results (using chronoamperometry, square wave voltammetry and linear sweep voltammetry) indicated some level of adsorption of DEAET, hydrazine and nitrite on the modified electrode, while dopamine electrocatalytic oxidation and detection followed a simple diffusion controlled process. The adsorption process was found to be physically induced and could be eliminated by repetitive cycling of the electrode in the aqueous electrolyte solution. Electrodes modified with chemically-synthesised material (particularly nickel) were less adsorptive towards DEAET and hydrazine detection, and gave sensitivity and limit of detection values that compared with data obtained using electrochemical deposition / synthesis. The chemical stability and reproducibility of the modified electrodes were determined and discussed. Finally, electrochemical properties were studied to help screen these electrode materials in supercapacitors. CNT-NiO nanocomposites exhibit remarkable super capacitive behaviour in neutral and acidic media compared to the other CNT-MO nanocomposites investigated. Interestingly, the capacitive behaviour of the CNT-NiO was more enhanced in H2SO4 solution than in Na2SO4, possibly due to the high conductivity of the former. The CNT-NiO electrode maintained good stability with only about 5% loss of its specific capacitance after 1000 cycle life. / Thesis (PhD)--University of Pretoria, 2011. / Chemistry / unrestricted

Investigate the interaction of nanomaterials with biological systems, known as nano-bio interaction is of great interest for the assessment of the concern arising from nanomaterials progressive use. Such interaction determines nanomaterials potential effect on human and environment becomes more and more important to understand how they interact with living organisms and the environment. The novel physicochemical characteristics of nanomaterials, such as their small size, large surface area to volume ratio and surface energy, may initiate new toxicological effects due to nanomaterials ability to enter into the biological systems through adsorption and dissolution and modify the structure of various macromolecules An example of these interactions is the adsorption of proteins on nanoparticles surface forming what is known as the 'protein corona'. Therefore, being able to understand how these molecules and other biologically important species are adsorbed and interact, should help us to reduce any adverse impacts of nanoparticles on human health and the environment. Due to the importance of surface composition and surface functionality in nanotoxicology, analytical tools that can probe the change in the structure and composition of the nanoparticles in aqueous media are crucial but remain limited. Therefore in this work, in situ characterization of the liquid–solid interface to probe surface adsorption of environmentally and biologically relevant media on nanoparticle surfaces has been conducted. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy provides the molecular information that allows for the determination of the adsorption mode such as conformational and structural changes of the coordinating ligand. Surface adsorption of titanium dioxide (TiO2) nanoparticles have been investigated in different biological media typically used for toxicity studies and show that the surface composition of TiO2 nanoparticles depends to a large extent on the composition of the medium due to surface adsorption. Moreover, hydrodynamic diameter and surface charge of TiO2 NPs were evaluated using dynamic light scattering DLS. The results indicated that TiO2 NPs undergo different trends in aggregation upon the adsorption of biological media on its surface and zeta potential measurements showed surface charge alterations which are consistent with the aggregation study. In order to understand the dynamic transformations of nanomaterials in biological environments, the effect of dissolution has been predicted. Copper oxide CuO and zinc oxide ZnO nanoparticles were used to study dissolution due to their instability in biological media. Once these particles exposed to solutions they release their ions and tend to aggregate. Therefore, the dissolution of these materials was conducted at size ca. 24 nm and nanoparticles coated with proteins and humic acid employing simulated lung fluids as models to develop a better understanding of how these properties effect the solubility and stability in biological systems. From this study, it was found that both copper oxide and zinc oxide NPs showed different trends in dissolution. Cu and Zn ions once coated with proteins and HA highly dissolved in ALF at low pH 4.5 compared with other fluids (Gamble’s solution and water) at extracellular pH which shows only slightly enhanced in the basal condition. The acidity of ALF may explain the higher solubility of metals that are phagocytized versus those that remain extracellular. Some general conclusions can be drawn from these investigations. It seems that analytical tools to characterize the interfacial region between nanopaerticles and these complex systems provide a reasonably good qualitative and quantitative description of the interactions.

In this work, the crystallographic structure and its changes under thermal treatment of different systems consisting of metal oxide nanoparticles is studied. The principal method used throughout the thesis is x-ray powder diffraction enriched with grazing incidence small angle x-ray scattering when the nanoparticles form an ordered structure or with x-ray absorption spectroscopy when additional information on local crystallographic structure is required. For all the systems the preparation conditions were optimized according to the crystallographic data for further applications.

No description available.

No description available.

Metallic and metal oxide nanoparticles (Nps) have a wide range of applications in various settings including household, cosmetics and chemical industries, as well as for coatings. Nevertheless, an in-depth study of the potential toxic effects of these Nps is still needed, in order to fulfill the mandatory requirement of ensuring the safety of workers, patients and the general public. In this study, Quick Cell colorimetric assays were used to evaluate the in vitro toxicity of different metal oxide Nps [Fe(II,III)Ox, TiOx, ZnO and CeO2] in several cell lines. The ZnO Nps were found to be highly toxic, with a lethal dose ≥100 μg/ml for all the cell lines studied. Western blot was also used to test the ability of the different Nps to activate the complement pathway. However, no activation of this cascade was observed when the Nps were added. In addition, the aggregation state and charge of the Nps in culture media was studied by dynamic light scattering (DLS) and measurement of zeta potential. Transmission Electron Microscopy was used to analyze Np uptake and localization at the cellular level.

Superkondensatorer är energilagringsenheter som har uppmärksammats mer under det senaste decenniet. Några av de fördelar som dessa enheter har varit är lagring av hög effekttäthet, förlängda livscykler och snabba laddnings- och urladdningstider. Dock är superkondensatorer fortfarande begränsade i energitäthet i jämförelse med batterier. För att få högre effekt och energitäthet är en asymmetrisk hybrid superkondensator ett bra alternativ. Denna enhet består av en kolbaserad elektrod för icke-faradaiska reaktioner och en kolelektrod kombinerad med metalloxider för redoxreaktioner. Materialvalet spelar en avgörande roll för förmågan en hybrid asymmetrisk superkondensator ska ha. I denna studie undersöks fyra olika kommersiella kol. Den specifika ytan, porstorlekarna och morfologin jämförs. Dessutom syntetiseras metalloxidernanopartiklar MnO2 och kristallstrukturen undersöks. Därtill beläggs MnO2-partiklarna på de fyra kolen och tillväxten av dessa undersöks. Slutligen analyseras interaktionen mellan jonvätskan 1-butyl-3-metylimidazoliumtetrafluorborat (BMIM[BF4]) som en elektrolyt och de olika kolen. / Supercapacitors are energy storage devices that have drawn attention for the past decade. Some of the advantages of these devices are higher power density storage, extended life cycles, and fast charge and discharge times. However, supercapacitors are still limited in energy density compared to batteries. To obtain higher power and energy densities, a hybrid asymmetric supercapacitor is a good alternative. This device consists of one carbon-based electrode for non-faradaic reactions, and one carbon electrode combined with metal oxides for redox reactions. The material choice is important for the capability of a hybrid asymmetric supercapacitor. In this study, four different commercial carbons are investigated. The specific surface area, pore sizes, and morphology are compared. In addition, metal oxide nanoparticles MnO2 are synthesised, and crystal structure is investigated. Furthermore, the MnO2 particles are deposited on the four carbons and the growth of those is studied. Finally, the interaction between ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM[BF4]) as an electrolyte and the different carbons is studied.

Nanotechnology is blossoming into one of the premiere technologies of this century, but the key to its progress lies in developing more efficient nanosynthesis methods. Variations in synthetic technique, however, can cause variations in size, structure, and surface characteristics, thereby altering the physical properties and functionality of the particles. Careful structural characterizations are thus essential for understanding the properties and appropriate applications for particles produced by new synthetic techniques.In this work, a new ‘solvent-deficient’ method is presented for the synthesis of an unprecedentedly wide range of metal oxide nanomaterials including at least one metal oxide from each group in Groups 3-4, 6-15, and the Lanthanides. XRD, BET, and TEM structural characterizations as well as chemical purity analyses of the products are given. The intermediates associated with the method are also investigated, allowing the reaction parameters to be rationalized and culminating in a proposed mechanism for the reaction. Several of the reaction intermediates are themselves useful products, expanding the range of this already versatile method. Optimized synthesis parameters as well as structural characterizations are presented for one such intermediate product, the iron oxyhydroxide called ferrihydrite.The Al2O3 nanoparticles produced by the new method show promise in catalyst support applications, and the synthesis and structural analysis (XRD, X-ray PDF, 27Al NMR, TG/DTA-MS) of these nanoparticles is provided. The XRD, PDF, and NMR analyses reveal that the initial boehmite-like phase transforms to the catalytically useful gamma-Al2O3 phase at unusually low temperatures (300-400°C), but boehmite-like local structure defects remain which heal slowly with increasing temperature up to 800°C. The ‘pure’ gamma-Al2O3 may still contain randomized, non-cubic, local structure distortions, and it transforms directly to alpha-Al2O3 at ~1050°C. To rationalize the local structure and the absence of the delta- and theta-Al2O3 phases during the alpha-phase transition, relationships between the many Al2O3 phases are presented via innovative symmetry-mode analyses, revealing a potential quazi-topotactic mechanism for the gamma-to-alpha transition.To stabilize the gamma-Al2O3 phase to higher temperatures for catalyst applications, 3 wt% of a lanthanum dopant was added via a new, 1-pot process based on the new solvent-deficient method. This process is described and X-ray PDF, TEM, 27Al NMR, and EXAFS analyses of the La-doped gamma-Al2O3 nanoparticles reveal that the dopant resides as isolated, adsorbed atoms on the gamma-Al2O3 surface. The first coordination shell of the isolated La is increasingly La2O3-like as calcination temperature increases but changes drastically to be more LaAlO3-like after the alpha-phase transition, which is delayed ~100°C by the La dopant. Combining the EXAFS, PDF, NMR, and symmetry-mode analyses, we provide new insight into the mechanism of stabilization provided by the La dopant.

Polyethylene composites which contain low concentrations of metal-oxide nanoparticles e.g. ZnO and MgO are emerging materials for the use in insulations of extruded high-voltage direct-current (HVDC) cables. The challenge in the development of the composites with ultra-low electrical conductivity is to synthesize uniform and high-purity metal-oxide nanoparticles, which are functionalized with hydrophobic groups in order to make them compatible with polyethylene. The thesis reports different approaches to prepare this new generation of insulation materials. Different reaction parameters/conditions – zinc salt precursor, precursor concentrations and reaction temperature – were varied in order to tailor the size and morphology of the ZnO nanoparticles. It was shown that different particle sizes and particle morphologies could be obtained by using different zinc salt precursors (acetate, nitrate, chloride or sulphate). It was shown that 60 °C was a suitable reaction temperature in order to yield particles with different morphologies ranging from nano-prisms to flower-shaped superstructures. For removal of reaction residuals from the particles surfaces, a novel cleaning method based on ultrasonication was developed, which was more efficient than traditional water-replacement cleaning. After cleaning, the presence of one atomic layer of zinc-hydroxy-salt complex (ZHS) on the nanoparticle surfaces was suggested by thermogravimetry and infrared spectroscopy. A method involving three steps – silane coating, heat treatment and silica layer etching – was used to remove the last trace of the ZHS species from the nanoparticle surface while preserving its clean and active hydroxylated surface. The surface chemistry of these nanoparticles was further tailored from hydroxyl groups to hydrophobic alkyl groups with different lengths by reactions involving methyltrimethoxysilane (C1), octyltriethoxysilane (C8) and octadecyltrimethoxysilane (C18). MgO nanoparticles were prepared by aqueous precipitation of Mg(OH)2 followed by a partial transformation to MgO nanoparticles via heat treatment at 400 °C. The surface regions of the MgO nanoparticles convert into a hydroxide phase in humid media. A novel method to obtain large surface area MgO nanoparticles with a remarkable inertness to humidity was also presented. The method involved three steps:  (a) thermal decomposition of Mg(OH)2 at 400 °C; (b) silicone oxide coating of the nanoparticles to prevent inter-particle sintering and (c) a high temperature heat treatment at 1000 °C. These MgO nanoparticles showed essentially no sign of formed hydroxide phase even after extended exposure to humid air. The functionalized metal-oxide nanoparticles showed only a minor adsorption of phenolic antioxidant, which is important in order to obtain nanocomposites with an adequate long-term stability. Tensile testing and scanning electron microscopy revealed that the surface-modified metal-oxide nanoparticles showed improved dispersion and interfacial adhesion in the polyethylene matrix with reference to that of unmodified metal-oxide nanoparticles. The highly “efficient” interfacial surface area induced by these modified nanoparticles created the traps for charge carriers at the polymer/particle interface thus reducing the DC conductivity by more than 1 order of magnitude than that of the pristine polyethylene. / Polyetenkompositer med mycket låga halter av ZnO och MgO metalloxid nanopartiklar är en växande kategori material för användning som isolering av extruderade kablar avsedda för likriktad högspänning. En utmaning i utvecklingen av dessa material kan relateras till den praktiska kompositframställningen, vilken innefattar framställning av högrena metalloxid nanopartiklar som ytmodifieras med hydrofoba molekylstrukturer för att möjliggöra blandning med den hydrofoba polyetenplasten. Denna avhandling behandlar olika metoder för att framställa denna generation av isoleringsmaterial. Vid syntesen av de rena nanopartiklarna krävdes optimering av ett antal olika reaktionsparametrar för att uppnå tillfredställande slutresultat i form av partikelstorlekar och partikelmorfologier. Dessa inkluderade val av zinksalt, zinksaltkoncentration vid utfällning, samt reaktionstemperatur vid framställningen. Experimenten avslöjade att olika partikelstorlekar och partikelmorfologier kunde framställas som endast korrelerat mot källan av zinkjonerna, och berodde av vilka motjoner som zinkatomerna haft i zinksaltet (acetat, nitrat, klorid eller sulfat). Optimering av reaktionstemperaturen visade att ca 60 °C utgjorde en lämplig start för utvärdering av synteserna, som resulterade i olika partikelmorfologier i form av pyramidformade nanopartiklar till blomformationer. Utöver de specifika reaktionsparametrarna utvecklades även en ny ultrasonikeringsmetod för att rena ytorna hos partiklarna från motjoner relaterade till de valda specifika salterna. Metodiken som visade sig avsevärt mer effektiv än sedvanlig rening att utfällda nanopartiklar via repetitivt vattenutbyte, och skapade förutsättningar etablering av kolloidal stabilitet och fragmentering av aggregat i vattensuspensionerna. Efter ultrasonikeringsreningen beräknades de kvarvarande zinkhydroxidsalterna (ZHS) utgöra endast ett atomlager ZHS utifrån termogravimetriska data kompletterade med infraröd spektroskopi. En metod att eliminera de kvarvarande ZHS-komplexen från ytan av partiklarna tillämpades/utvecklades, inkluderade ytbeläggning av partiklarna med silan, följt av värmebehandling samt etsning av den resulterande kiseloxidytan, för att uppnå en ren hydroxylyta på partiklarna. Ytkemin hos dessa partiklar modifierades från att bestå av hydroxylgrupper till att utgöras av hydrofoba alkylgrupper med olika längder relaterade metyltrimetoxysilan (C1), oktyltrietoxysilan (C8), eller oktadekyltrimetoxysilan (C18). Även MgO nanopartiklar framställdes via vattenutfällning av Mg(OH)2 partiklar, vilka omvandlades till MgO nanopartiklar via en lågtemperatur värmebehandling vid 400°C. Ytan av dessa partiklar omvandlades dock till hydroxid i fuktig miljö. En ny metod att bibehålla den stora ytarean av MgO nanopartiklarna med anmärkningsvärd motståndskraft mot att omvandlas till hydroxid utvecklades således. Metoden består av (a) en låg temperatur omvandling av Mg(OH)2, (b) en kiseloxidytbehandling av nanopartiklarna för att undvika partikelsintring vid högre temperaturer och (c) en hög temperaturbehandling vid 1000 °C. De framställda partiklarna uppvisade ingen anmärkningsvärd känslighet mot luftfuktighet och bibehöll MgO sammansättningen efter exponering mot fukt. De modifierade metalloxid nanopartiklarna visade mycket liten adsorption av fenoliska antioxidanter, vilket medförde en långtidsstabilitet hos polyeten nanokompositerna. De ytmodifierade metalloxidpartiklarna visade även förbättrade möjligheter för dispergering och yt-kompatibilitet med/i polyetenmatrisen i jämförelse med omodifierade metalloxidpartiklar, utifrån mätningar baserade på dragprovning och svepelektronmikroskopi. Slutligen, de utvecklade ytorna på de modifierade nanopartiklarna skapade ett polymer/nanopartikel gränssnitt som kunder fungera som laddningsansamlingsområden i nanokompositerna, vilket resulterade i en storleksordning minskad ledningsförmåga hos kompositerna jämfört med den rena polyetenen. / <p>QC 20160829</p>