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Nanomaterials possess unusual chemical and physical properties than their bulk counterparts because of their large surface to volume ratio. This benefit has found applications in the fields of optics, electronics catalysis and biomedicine. Over the past two decades cerium oxide based materials have been extensively studied and used in applications such as glass and ceramics, phosphor/luminescence and in various catalysis and chemical applications. Nanocrystalline cerium oxide materials can benefit not only these applications, but they also possess some unique properties such as blue shift in ultraviolet absorption spectra, shifting and broadening of Raman allowed modes and lattice expansion. Unfortunately, the high specific surface area of the nanocrystalline particles also results in a stronger tendency of the particles to agglomerate. The problem of agglomeration is of prime concern for the particles smaller than 5nm and the beneficial effects of the nanosized particles are usually lost due to the agglomeration problem. Therefore synthesis of non-agglomerated nanocrystalline cerium oxide particles is highly important in improvement of properties for various applications. The present study investigates the use of microemulsion for synthesis of monodispersed, non-agglomerated nanocrystalline cerium oxide particles. Sodium bis(2-ethylhexyl sulphosuccinate (AOT) was used as a surfactant in the microemulsion system used in this study. It was found that the use of hydrogen peroxide as a precipitating agent gives a very stable sol of cerium oxide containing nanocrystalline particles of 3nm in size. The particle morphology and chemical state study was done for these particles and it was found that cerium oxide nanoparticles consist of both Ce(+3) and Ce(+4) valence states while the micron sized cerium oxide particles consist of only Ce(+4) valence state. Different applications of the synthesized cerium oxide nanoparticles were also studied. The beneficial effects of the synthesized nanocrystalline ceria to improve the high temperature oxidation resistance of stainless steel were investigated using oxidation kinetics measurements. For comparing the size effect on the improvement, comparative coatings of 10 μm and 20nm-sized cerium oxide were also studied. It was found that the 3nm-sized ceria gave the best results in improving high temperature oxidation resistance of stainless steel even in cyclic heating conditions. It results in a fine grained scale morphology with improved scale adhesion to the substrate and changed the scale growth mechanism from cation outward to oxygen inward. The role of Ce(+3) valence state in nanocrystalline cerium oxide particles to improve the oxidation resistance is proposed and discussed. Another application of the synthesized nanocrystalline ceria was found in improving lifespan of in vitro cell cultures in collaboration with Molecular Biology and Microbiology Department. Although this is the not main part of this thesis, however, it is worth mentioning that cerium oxide nanoparticles prolonged brain cell longevity by 2-3 fold. Further, these nanoparticles reduced hydrogen peroxide and UV light induced cell injury by over 60%. It is hypothesized that the cerium oxide nanoparticles act as free radical scavengers due to their unique structure, with respect to valence and oxygen defects, to promote cell longevity. Thus nanotechnology plays a vital role at the interface of materials science and molecular and microbiology.

Yes / We present here a quantification of the sorption process and molecular conformation involved in the attachment of bacterial cell wall lipopolysaccharides (LPSs), extracted from Escherichia coli, to silica (SiO2) and alumina (Al2O3) particles. We propose that interfacial forces govern the physicochemical interactions of the bacterial cell wall with minerals in the natural environment, and the molecular conformation of LPS cell wall components depends on both the local charge at the point of binding and hydrogen bonding potential. This has an effect on bacterial adaptation to the host environment through adhesion, growth, function, and ability to form biofilms. Photophysical techniques were used to investigate adsorption of fluorescently labeled LPS onto mineral surfaces as model systems for bacterial attachment. Adsorption of macromolecules in dilute solutions was studied as a function of pH and ionic strength in the presence of alumina and silica via fluorescence, potentiometric, and mass spectrometry techniques. The effect of silica and alumina particles on bacterial growth as a function of pH was also investigated using spectrophotometry. The alumina and silica particles were used to mimic active sites on the surface of clay and soil particles, which serve as a point of attachment of bacteria in natural systems. It was found that LPS had a high adsorption affinity for Al2O3 while adsorbing weakly to SiO2 surfaces. Strong adsorption was observed at low pH for both minerals and varied with both pH and mineral concentration, likely in part due to conformational rearrangement of the LPS macromolecules. Bacterial growth was also enhanced in the presence of the particles at low pH values. This demonstrates that at a molecular level, bacterial cell wall components are able to adapt their conformation, depending on the solution pH, in order to maximize attachment to substrates and guarantee community survival. / The authors thank the Libyan Ministry of Education for financial support during the experimental study. We thank the EPSRC funded consortium “Hard-soft matter interfaces: from understanding to engineering” (EP/I001514/1) for financial support. Emily Caseley, who assisted in the preparation and characterization of AmNS-LPS particles as an MRC Confidence in Concept funded postdoctoral researcher at the University of Bradford, (MC_PC_16038).

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Thesis (Ph. D.)--Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.