NiSi is an attractive material in the production of CMOS devices. The problem with the utilization of NiSi, is that there is no proper method of cleaning the oxide on the surface. Sputtering is the most common method used for the cleaning, but it has its own complications. Dry cleaning methods include the reactions with radicals and these processes are not well understood and are the focus of the project. Dissociated NF3 and NH3 were used as an alternative and XPS is the technique to analyze the reactions of atomic fluorine and nitrogen with the oxide on the surface. A thermal cracker was used to dissociate the NF3 and NH3 into NFx+F and NHx+H. There was a formation of a NiF2 layer on top of the oxide and there was no evidence of nitrogen on the surface indicating that the fluorine and hydrogen are the reacting species. XPS spectra, however, indicate that the substrate SiO2 layer is not removed by the dissociated NF3 and NiF2 growth process. The NiF2 over layer can be reduced to metallic Ni by reacting with dissociated NH3 at room temperature. The atomic hydrogen from dissociated ammonia reduces the NiF2 but it was determined that the atomic hydrogen from the ammonia does not react with SiO2.

Inorganic colloidal synthesis, without a doubt, lies at the foundation of many contemporary areas of nanoscience and nanotechnology. At the advent of the 21st century, much progress has been made in the size, shape / morphological control and surface engineering of metal oxides resulting in a diverse library of macroscopic crystal architectures with well-defined surface properties. In this thesis, we start by introducing the self-assembly of the iron(oxy-, hydro-)xide while briefly reviewing some fundamental concepts of solid-state chemistry. Specific information on the family of iron oxide and iron(oxy-, hydro-)xide, as relevant to crystalline phase control, has been highlighted to direct our discussion of the synthesis of diverse crystal morphologies. Furthermore, we briefly underline and discuss the kinetic and thermodynamic control of colloidal crystal morphologies through reasonably established knowledge of anisotropic growth rates in the perspective of iron oxides' facets or crystalline planes. Lastly, we review the state-of-the-art wet chemical synthetic approaches, while using different iron(oxy-, hydro-)xide crystals as examples, for the purpose of explaining our synthetic work of choice. The main work of this thesis is entirely focused on the "facile synthesis and fine morphological tuning of branched hematite (??-Fe2O3) crystals for photodegradation of azo-type dyes".. We would discuss the crucial parameters for fine morphological tuning in the context of controlling the anisotropic growth rates of branched ??-Fe2O3 crystals instead of phase transformation. In our work, we have significantly improved the synthesis of dendritic "feather-like" and "starfish-like" for their size reduced variants for use in photocatalysis.

Sulfur adsorbed on metallic and oxide surfaces, whether originating from gaseous environments or segregating as an impurity to metallic interfaces, is linked to the deterioration of alloy performance. This research dealt with investigations on the interactions between sulfur and iron or iron alloy metallic and oxide surfaces under ultrahigh vacuum conditions. Sulfur was either intentionally dosed from a H2S source on an atomically clean metal surface, or segregated out as an impurity from the bulk to the metal surface by annealing at elevated temperatures.

Orientador: Mauricio Boscolo / Banca: Diogo Paschoalini Volanti / Banca: João Batista Oliveira dos Santos / Banca: Altair Benedito Moreira / Banca: Fernanda Perpétua Casciatori / Resumo: A valorização do etanol e da biomassa de cana de açúcar utilizando reações catalisadas por óxidos é apresentada neste trabalho. Os óxidos utilizados são derivados de hidrotalcitas com a fórmula geral: Mg6Al2(CO3)(OH)16·4(H2O) e modificadas por íons Ag2+, Cu2+, Fe3+, La2+, Nb5+, Ni2+, In3+ e Pd2+. O material após a caracterização foi utilizado em reações empregando reatores de aço inox, buscando a conversão do etanol em produtos de maior peso molecular e valor agregado, principalmente através da reação de Guerbet. Os produtos obtidos foram analisados por cromatografia a gás (GC-FID e GC-MS) e os resultados foram comparados e discutidos com os dados da caracterização do material e com auxílio da literatura científica. A modificação do óxido por cada íon apresentou um perfil diferente de reação e produtos. Com o lantânio obtive-se maior conversão de etanol em produtos utilizando álcool hidratado, e uma quantidade significativa de compostos C6 e uma seletividade de 42% para hexanol, foram obtidos. Por outro lado, o melhor rendimento (~30%) na síntese de butanol foi obtido com óxido modificado pelo íon nióbio, enquanto a adição de prata promoveu a redução da atividade catalítica do óxido. Além da conversão de etanol, os resultados obtidos pelas reações com a adição de biomassa demonstraram que é possível desestruturar o material lignocelulósico e obter compostos fenólicos e furânicos provenientes da lignina e dos carboidratos, respectivamente. A presença de hidrogênio no meio... / Abstract: Increasing the value of ethanol and sugarcane biomass by reactions catalyzed by oxides is presented in this work. The oxides used are derived from hydrotalcites, whose general formula is: Mg6Al2 (CO3)(OH)16·4(H2O), modified by Ag, Cu, Fe, La, Nb, Ni, In or Pd. The catalysts synthesized were characterized by their surface area the number of acid and basic catalytic sites, X-ray diffraction and infrared spectroscopy. The conversion of ethanol into products of higher molecular weight and with added value, mainly through the Guerbet reaction, was performed in reactions in supercritical state using stainless steel reactors and oxides as catalysts. The products were analyzed by gas chromatography (GC-FID and GC-MS) and the results were compared with the available characterization data of the material and previous studies in the scientific literature. Oxide modification by each different ion showed a different reaction profile and different products. Lanthanum addition showed better results using anhydrous alcohol and a significant amount of C6 compounds, such as hexanol (42% selectivity), were obtained. On the other hand, the best yields (~30%) for butanol were obtained with the oxide modified by niobium, while the addition of silver led to the reduction of the catalytic activity of the oxide. The addition of biomass into a supercritical ethanol reaction showed that the lignocellulosic material can be deconstructed, phenolic, and furanic compounds from lignin and carbohydrates, ... / Doutor

Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2022 / Heart and Stroke Foundation South Africa (HSFSA) reports that about 17.3% of deaths in the country are associated with heart-related diseases and this rate is expected to increase to 41% by the year 2030. This severe increase in death cases is related to diseases caused by consumption of meat (i.e., pork, fish, red meat, and poultry) with high levels of hypoxanthine. Therefore, this raises the need to investigate and detect hypoxanthine levels in the meat. This study aimed at developing a highly stable and sensitive biosensor for the detection of hypoxanthine in fish meat using the glassy carbon electrode (GCE) modified with carbon nanocomposites materials (consisting of metal oxides doped multi-walled carbon nanotubes (MO-MWCNTs) that are treated with amine groups) and an enzyme, xanthine oxidase (XOD) as a catalyst. The sol gel method was used to prepare the metal oxides including zinc oxide (ZnO), zirconium dioxide (ZrO2), manganese (MnO2), cobalt oxide (Co3O4), and titanium dioxide (TiO2). The in-situ method of functionalisation of MWCNTs was employed to increase their current outputs/sensitivity using selected amines, namely, methylenediamine, hydrazine, ethylenediamine (EDA), and triethylenetetramine (TETA). The electrochemical properties of the metal oxides and amine functionalised MWCNTs were studied using both cyclic and differential pulse voltammetry. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of carboxyl (COOH), hydroxyl (OH), and amino (NH2) groups on the surface of the modified MWCNTs; as well as formation of stretching vibrations which appear at lower wavelengths due to the metallic species within the nanocomposite. Thermal gravimetric analyser (TGA) was employed to determine the thermal stability of the nanocomposite. Scanning electron microscopy (SEM) was used to confirm the composite structure and correct deposition of the metal oxides on the walls of MWCNTs. XRD was used to confirm correct structure formation, the crystallinity, and the purity of the nanocomposite. Optimum conditions of the developed biosensor were determined, and the application of the developed biosensor was undertaken on fish meat bought at the local supermarket using the Cyclic and Differential pulse voltammetric techniques. Two highly electrochemical metal oxides among others were TiO2 and Co3O4. The modified MWCNTs containing TETA possess good electrochemical properties with improved sensitivity and selectivity towards hypoxanthine. The presence of metal oxides on MWCNTs and their treatments with amines as confirmed by techniques such as TGA, SEM, XRD, and FTIR have provided a suitable matrix for the immobilisation of the enzyme, namely, xanthine oxidase at 0.5 unit (U). TGA results showed that the unmodified MWCNTs decompose at around 600 0C, but when they are modified with acids and amine decomposition starts at 230 0C, proving that functionalisation of MWCNTs tempers with their thermal stability. Based on the SEM morphological results, attachment of the amines and metal oxides on MWCNTs was seen at x60 000 magnification. Morphology of acid treated MWCNTs appeared thinner, revealing that acids tends to deteriorate the MWCNTs, while the amino treated MWCNTs appeared well modified with less damage on the MWCNTs. XRD confirmed the successful purification of MWCNTs with the intense diffraction peak at 260 that can be assigned to the (002) reflection of graphite. The strong diffraction peak at 250o and a broad peak at 450 indicate that the titania nanoparticles are pure and in the anatase phase. They also show successful deposition of the titanium dioxide onto the surface of the MWCNTs. However, on the formation of cobalt oxide two phases were observed which were CoO, and Co3O4, and on bimetallic nanocomposite (cobalt titanium oxide) also two phases were observed which were CoTiO3, and Co2TiO4. It was found that the sensor performs better at 25 oC at a pH of 7.5 in a phosphate buffer at concentration of 5 mM. The limit of detection of the biosensor was found to be 0.16 nM. The highly electroconductive electrode was XOD/3%Co2TiO4-MWCNTs-TETA/GCE, which was selected for analysis of fish meat. The biosensor has shown low interfering values with high stability, good reusability retaining 73.4% of its initial performance after 50 days of continuous study. The excellent results were obtained on fish meat analysis using cyclic and differential pulse voltammetry revealed that even meat which is deep frozen can also deteriorate as time passes by. Altogether, the findings from this study suggest that the developed biosensor is a reliable analytical tool for the determination of freshness of fish meat using hypoxanthine levels as a marker / National Research Foundation (NRF) and Sasol Inzalo Foundation

No description available.

Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2022 / Heart and Stroke Foundation South Africa (HSFSA) reports that about 17.3% of deaths in the country are associated with heart-related diseases and this rate is expected to increase to 41% by the year 2030. This severe increase in death cases is related to diseases caused by consumption of meat (i.e., pork, fish, red meat, and poultry) with high levels of hypoxanthine. Therefore, this raises the need to investigate and detect hypoxanthine levels in the meat. This study aimed at developing a highly stable and sensitive biosensor for the detection of hypoxanthine in fish meat using the glassy carbon electrode (GCE) modified with carbon nanocomposites materials (consisting of metal oxides doped multi-walled carbon nanotubes (MO-MWCNTs) that are treated with amine groups) and an enzyme, xanthine oxidase (XOD) as a catalyst. The sol gel method was used to prepare the metal oxides including zinc oxide (ZnO), zirconium dioxide (ZrO2), manganese (MnO2), cobalt oxide (Co3O4), and titanium dioxide (TiO2). The in-situ method of functionalisation of MWCNTs was employed to increase their current outputs/sensitivity using selected amines, namely, methylenediamine, hydrazine, ethylenediamine (EDA), and triethylenetetramine (TETA). The electrochemical properties of the metal oxides and amine functionalised MWCNTs were studied using both cyclic and differential pulse voltammetry. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of carboxyl (COOH), hydroxyl (OH), and amino (NH2) groups on the surface of the modified MWCNTs; as well as formation of stretching vibrations which appear at lower wavelengths due to the metallic species within the nanocomposite. Thermal gravimetric analyser (TGA) was employed to determine the thermal stability of the nanocomposite. Scanning electron microscopy (SEM) was used to confirm the composite structure and correct deposition of the metal oxides on the walls of MWCNTs. XRD was used to confirm correct structure formation, the crystallinity, and the purity of the nanocomposite. Optimum conditions of the developed biosensor were determined, and the application of the developed biosensor was undertaken on fish meat bought at the local supermarket using the Cyclic and Differential pulse voltammetric techniques. vi Two highly electrochemical metal oxides among others were TiO2 and Co3O4. The modified MWCNTs containing TETA possess good electrochemical properties with improved sensitivity and selectivity towards hypoxanthine. The presence of metal oxides on MWCNTs and their treatments with amines as confirmed by techniques such as TGA, SEM, XRD, and FTIR have provided a suitable matrix for the immobilisation of the enzyme, namely, xanthine oxidase at 0.5 unit (U). TGA results showed that the unmodified MWCNTs decompose at around 600 0C, but when they are modified with acids and amine decomposition starts at 230 0C, proving that functionalisation of MWCNTs tempers with their thermal stability. Based on the SEM morphological results, attachment of the amines and metal oxides on MWCNTs was seen at x60 000 magnification. Morphology of acid treated MWCNTs appeared thinner, revealing that acids tends to deteriorate the MWCNTs, while the amino treated MWCNTs appeared well modified with less damage on the MWCNTs. XRD confirmed the successful purification of MWCNTs with the intense diffraction peak at 260 that can be assigned to the (002) reflection of graphite. The strong diffraction peak at 250o and a broad peak at 450 indicate that the titania nanoparticles are pure and in the anatase phase. They also show successful deposition of the titanium dioxide onto the surface of the MWCNTs. However, on the formation of cobalt oxide two phases were observed which were CoO, and Co3O4, and on bimetallic nanocomposite (cobalt titanium oxide) also two phases were observed which were CoTiO3, and Co2TiO4. It was found that the sensor performs better at 25 oC at a pH of 7.5 in a phosphate buffer at concentration of 5 mM. The limit of detection of the biosensor was found to be 0.16 nM. The highly electroconductive electrode was XOD/3%Co2TiO4-MWCNTs-TETA/GCE, which was selected for analysis of fish meat. The biosensor has shown low interfering values with high stability, good reusability retaining 73.4% of its initial performance after 50 days of continuous study. The excellent results were obtained on fish meat analysis using cyclic and differential pulse voltammetry revealed that even meat which is deep frozen can also deteriorate as time passes by. Altogether, the findings from this study suggest that the developed biosensor is a reliable analytical tool for the determination of freshness of fish meat using hypoxanthine levels as a marker. / NRF Sasol Inzalo Foundation

In this project, the TMP method was employed to produce “active sites.” These active sites are for influencing and controlling the Co₃O₄ growth. One of the aims was to investigate what effect the grafting of the molecular precursor has on the nature and distribution of active sites on the various support materials. The second aim was to investigate the effect an increase in molecular precursor loading, in various impregnation steps, has on the nature and distribution of the active sites. The third aim was to investigate the effect of the steric constraints of ligand groups, by changing the molecular precursor, on the nature and distribution of active sites. The fourth aim was to use the different aspects discussed above and apply them to investigate what effect the above-mentioned modifications have on Co₃O₄ morphology. While another aim was to investigated what effect varying the quantity of Co(NO₃)₂•6H₂O has on Co₃O₄ morphology. Lastly, we investigated what effect varying the impregnation procedure and calcination temperature have on the Co₃O₄ morphology. The effect the support has on the phase of titanium molecular precursor was investigated using molecular precursor, ⁱPrOTi[OSi(O[superscript(t)]Bu₃)]₃. The supports used were Silica 922, NanoDur, Aerosil 200, Stöber spherical silica, SBA-15, mod MCM-41 and sMCM-41. The molecular precursor ⁱPrOTi[OSi(O[superscript(t)]Bu₃)]₃ was revealed to be in the orthorhombic TiO₂ with space group P(cab), normal brookite lattice, on Silica 922 after calcination but only an isolated area displaying this morphology. Generally we do not observe any TiO₂ on the support, which indicates that we have produce site-isolated sites, suggesting the TMP method has been successful on all of the various supports. The emphasis is placed on the effect of this molecular precursor and the respective support has on the Co₃O₄ morphology in Chapter 3. In this Chapter, a unique morphology was observed on Silica 922 which showed Co₃O₄ nanorods of cubic Co₃O₄ in the space group Fd-3m. Silica 922 was used for the remainder of the thesis to investigate the effect the quantity of molecular precursor has on the nature of active sites and Co₃O₄ morphology in Chapter 4. This support was also used to investigate the effect the amount of Co(NO₃)₂•6H₂O has on Co₃O₄ morphology in Chapter 5. This support was lastly used to investigate the steric constraints of the ligand groups, Ti[OSi(O[superscript(t)]Bu)₃]₄ (TiSi4), ⁱPrOTi[OSi(O[superscript(t)]Bu)₃]₃ (TiSi3), (OtBu)₃TiOSi(O[superscript(t)]Bu)₃ (TiSi) and the least sterically constrained Ti(OⁱPr)₄ has on the loading of precursor and Co₃O₄ morphology in Chapter 6.

The spallation of aluminum, chromium, and iron oxide scales is a chronic problem that critically impacts technological applications like aerospace, power plant operation, catalysis, petrochemical industry, and the fabrication of composite materials. The presence of interfacial impurities, mainly sulfur, has been reported to accelerate spallation, thereby promoting the high-temperature corrosion of metals and alloys. The precise mechanism for sulfur-induced destruction of oxides, however, is ambiguous. The objective of the present research is to elucidate the microscopic mechanism for the high-temperature corrosion of aluminum alloys in the presence of sulfur. Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM) studies were conducted under ultrahigh vacuum (UHV) conditions on oxidized sulfur-free and sulfur-modified Al/Fe and Ni3Al(111). Evaporative deposition of aluminum onto a sulfur-covered iron surface results in the insertion of aluminum between the sulfur adlayer and the substrate, producing an Fe-Al-S interface. Aluminum oxidation at 300 K is retarded in the presence of sulfur. Oxide destabilization, and the formation of metallic aluminum are observed at temperatures > 600 K when sulfur is located at the Al2O3-Fe interface, while the sulfur-free interface is stable up to 900 K. In contrast, the thermal stability (up to at least 1100 K) of the Al2O3 formed on an Ni3Al(111) surface is unaffected by sulfur. Sulfur remains at the oxide-Ni3Al(111) interface after oxidation at 300 K. During annealing, aluminum segregation to the g ¢ -Al2O3-Ni3Al(111) interface occurs, coincident with the removal of sulfur from the interfacial region. A comparison of the results observed for the Al2O3/Fe and Al2O3/Ni3Al systems indicates that the high-temperature stability of Al2O3 films on aluminum alloys is connected with the concentration of aluminum in the alloy.

Metal and oxide interactions are of broad scientific and technological interest in areas such as heterogeneous catalysis, microelectronics, composite materials, and corrosion. In the real world, such interactions are often complicated by the presence of interfacial impurities and/or high electric fields that may change the thermodynamic and kinetic behaviors of the metal/oxide interfaces. This research includes: (1) the surface hydroxylation effects on the aluminum oxide interactions with copper adlayers, and (2) effects of high electric fields on the interface of thin aluminum oxide films and Ni3Al substrate. X-ray photoelectron spectroscopy (XPS) studies and first principles calculations have been carried out to compare copper adsorption on heavily hydroxylated a- Al2O3(0001) with dehydroxylated surfaces produced by Argon ion sputtering followed by annealing in oxygen. For a heavily hydroxylated surface with OH coverage of 0.47 monolayer (ML), sputter deposition of copper at 300 K results in a maximum Cu(I) coverage of ~0.35 ML, in agreement with theoretical predictions. Maximum Cu(I) coverage at 300 K decreases with decreasing surface hydroxylation. Exposure of a partially dehydroxylated a-Al2O3(0001) surface to either air or 2 Torr water vapor results in recovery of surface hydroxylation, which in turn increases the maximum Cu(I) coverage. The ability of surface hydroxyl groups to enhance copper binding suggests a reason for contradictory experimental results reported in the literature for copper wetting of aluminum oxide. Scanning tunneling microscopy (STM) was used to study the high electric field effects on thermally grown ultrathin Al2O3 and the interface of Al2O3 and Ni3Al substrate. Under STM induced high electric fields, dielectric breakdown of thin Al2O3 occurs at 12.3 } 1.0 MV/cm. At lower electric fields, small voids that are 2-8 A deep are initiated at the oxide/metal interface and grow wider and deeper into the metal substrate, which eventually leads to either physical collapse or dielectric breakdown of the oxide film on top.