Nasir, Jamal
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Publication Access status: Open Access , Defects in high lattice energy metal oxides by magnetic resonance and X-ray diffraction(2025-06-02)The properties of all crystalline solids are affected by structural defects and disorder. Some crystal structures tolerate or even favor various forms of defects while others restrict imperfections. How does the structure of high-valence metal oxides accommodate and keep impurities? This PhD was undertaken to experimentally examine some relationships between defects in high-valence metal oxides and their properties. As an ideal model system and technologically important material, a large part of the work is focused on alumina in two forms: anodic alumina (AAO) and fumed alumina. Some other high-valence oxides such as TiO2 and CeO2 were studied to a lesser extent. AAO films anodized in H2C2O4 were subjected to heat treatments up to 1 050 ◦C mostly in air and investigated by MAS NMR, MQMAS, XRD, ESR, FESEM and nanoindentation. A series of fumed aluminas with BET surface areas from 220 to 30m2 g−1 were also investigated by similar techniques. Deemed an essential technique to the research, the MQMAS experiment was practised on the 23Na isotope in a heavily disordered metal amide material. Additionally, it was necessary to carry out a systematic study of Guinier X-ray diffraction cameras in order to identify sources of instrumental and procedural errors in the XRD data. With the implementation of a rotatable, circular sample holder, the IPreader digitization software, and a data averaging script, the quality of the data was suitable for a reliable Rietveld refinement as quantitatively tested. With the heat treatments of AAO films and ESR, correlation between color and concentration of paramagnetic impurities was observed. The microstructural transformations in AAO, including those involving disorder, were monitored up to the highest temperature, and correlated with the mechanical properties. Similarly, a clear and consistent correlation between the microstructure of fumed alumina and its surface area, or equivalently, flame residence time, was observed. Several H species in the form of isolated OH groups were detected. Overall, the degree of defects and disorder in these oxides depended on the temperature and duration of heat treatment. The higher the temperature, the lower the level of impurities and disorder after cooling. In the case of AAO, a thermal hardening occurred above 1 000 ◦C. A similar trend is expected in other high-valence metal oxides if the atmosphere and cooling rate are chosen right.Source Type:Doctoral Thesis1 15 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Structure and phase changes of alumina produced by flame hydrolysisFumed alumina from the combustion of AlCl 3 produced nano pArticles with specific areas from 30 to 220 m 2 g −1 (BET) which were characterized by powder X-ray diffraction, 27 Al solid-state NMR and transmission electron microscopy.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Synthesis and Characterization of Iron-Doped TiO2 Nanotubes (Fe/TiNTs) with Photocatalytic ActivityOne of the most significant global challenges for humans is environmental pollution. The technology to control this problem is the utilization of semiconductors as photocatalysts. In the current study, iron-doped titania nanotubes (Fe/TiNTs) with increased photocatalytic effect were synthesized via a modified hydrothermal method. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy (TEM), gas adsorption, electron spin resonance (ESR) and UV–Vis diffuse reflectance spectroscopy (DRS). TEM results indicated that Fe/TiNTs have a tubular and uniform structure with an average outer diameter of 23–48 nm and length of 10–15 µm. ESR and DRS revealed that Fe3+ ions were successfully introduced into the TiNT structure by replacing Ti4+ ions. An enhanced light absorption in the range of 400–600 nm additionally indicated successful doping. The band gap was narrowed as iron wt% was increased. The photocatalytic activity was evaluated by the degradation of methyl orange (MO) in the presence of Fe/TiNTs and TiTNs by monitoring the degradation of MO under UV light irradiation. An acceleration on the hydration of Portland cement was observed in the presence of 2.0 wt% Fe/TiNTs. Fe/TiNTs can be used as a nanomaterial in cement-based building materials to provide self-cleaning properties to the surface of concrete even in indoor environments.Source Type:Article7