Small silver nanoclusters are synthesized using polycytosines as matrices. Different size silver nanoclusters ranging from Ag1 to Ag7 exhibit bright emission maxima at blue (480nm), green (525nm), red (650nm), and IR (720nm) wavelengths with varying the excitation wavelengths. With electrophoresis, correlation of emission with mass spectra, the Ag cluster sizes are identified with blue emitters as Ag5, green emitters as Ag4, red emitters as Ag3, and IR emitters as Ag2. Ag4 and Ag5 appear to be partially oxidized while Ag2 and Ag3 are likely fully reduced. Silver cluster stability and their dynamics are observed from silver clusters encapsulated by polycytosine (Cm:Agn). From length study of polycytosine, the longer the polycytosine is, the more stable the larger clusters such as Ag5 are. In time-dependent optical measurements, isosbestic points are observed from Cm:Agn by converting red and IR species into blue and green species, while in the case of temperature-dependent optical properties, with increasing temperature, the blue (oxidized Ag5) and green (oxidized Ag4) emitters convert into the red (Ag3) and IR (Ag2) emitters. NaCl-dependent optical measurements support the assignments of oxidized and fully reduced silver emitters. Circular dichroism (CD) is used to investigate conformational changes in Cm and Cm:Agn with varying conditions (time, temperature and NaCl) and the studies indicate that no conformational changes in Cm:Agn are observed from the time and temperature, while the conformational changes in Cm:Agn are observed from the NaCl studies. From pH-dependent emission study of Cm:Agn, the silver nanocluster dynamics slow down at high pH. Using confocal microscopy technique, single molecules on IR species, C12:Ag2 are investigated and demonstrate that C12:Ag2 is brighter and more photostable than Cy5 which is known to be one of the best IR dyes. With low excitation power, molecules can be monitored for hours, giving bright blinking free, stable fluorescence. The photophysics of this new dye make it a promising candidate for single molecule studies in biological applications.

M. Tech. Chemical Engineering. / Discusses the scope of this research study composes of three interactive steps. The first step involves the design of the specific zeolite system (ZSM-5) and the set-up of an autoclave reactor for the hydrothermal synthesis of this and other zeolites and nano materials, then the oxidation catalyst (TS-1) development, i.e. the substitution of aluminium with titanium in the zeolite framework, and finally the formulation and preparation of the isomorphous Silicalite zeolite by omitting the aluminium in the synthesis. And further, set-up of suitable equipments and apparatus for the catalytic testing of the Titanium Silicalite-1 in the oxidation reaction of phenol as the test reaction. Therefore, the overall objectives of this research are: set up an autoclave reactor for the hydrothermal synthesis, formulation of a synthesis recipe for MFI family of catalysts in the laboratory, synthesis of ZSM-5, Silicalite-1, and TS-1 zeolites catalysts in the laboratory, characterization and optimization of the of catalysts listed above, testing the Ti-Silicalite catalyst in the oxidation reaction of phenol with hydrogen peroxide, as the oxidant, set up analytical system (Gas Chromatography, ASS) for analysis of catalyst performance in the oxidation reaction, Evaluate the conversion of the reaction and the selectivity of the individual catalysts reaction Evaluate the conversion of the reaction and the selectivity of the individual catalysts reaction and verify results obtained and compare with systems described in the literature.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The use of various ‘smart materials’ (briefly meaning materials that respond to a change in their environment) is currently of interest to both academics and industry. The primary aim of the current study was to entrap photochromic (PC) dyes in miniemulsions, as a means to improve their fatigue resistance, thus synthesizing smart nanoparticles. In the coatings industry the use of aqueous systems is becoming a common requirement for health and environmental reasons. Miniemulsion entrapment allows the direct dispersion of PC dyes into aqueous systems while allowing for the opportunity to tailor-make the host matrix in order to obtain a suitable PC response and improved fatigue resistance. The optimal instrument set-up required to establish the PC response of films of the so-called smart nanoparticles (i.e. PC miniemulsions) was determined. A UV-Vis instrument with a chip-type UV LED mounted inside for activation of the samples provided PC response results. A tungsten lamp with filter provided deactivation of the samples. A stable butyl methacrylate (BMA) miniemulsion formulation was established by conducting a design of experiments. A chromene and spironapthoxazine (SNO) PC dye were entrapped in the BMA miniemulsion. A hindered amine light stabiliser (HALS) was also entrapped with the SNO dye in the BMA miniemulsion to further improve the fatigue resistance. The following PC properties of the smart nanoparticles films were evaluated: colourability, thermal decay rate, half-life and fatigue resistance. To compare results with conventional systems, a BMA solution polymer was prepared. The SNO dye and different concentrations of the HALS were mixed with the BMA solution polymer. In comparison to the SNO smart nanoparticles the chromene smart nanoparticles films had lower colourability, but better fatigue resistance. Incorporating HALS at levels of 0.5–2% in the BMA miniemulsion with PC dye did not lead to any significant improvement in fatigue resistance, yet films of the BMA solution polymer showed some improvement. SNO dye incorporated at 1% gave similar colourability in both miniemulsion and in solution polymer, yet the fatigue resistance of the films of the PC miniemulsions was much better. / AFRIKAANSE OPSOMMING: Die gebruik van verskeie “slim materiale’ (kortliks beskryf as materiale wat reageer op `n verandering in hul omgewing) is tans van belang vir beide akademici en die industrie. Die hoofdoel van hierdie studie was om miniemulsietegnologie te gebruik om fotochromiese (FC) kleurstowwe vas te vang, vir die sintese van slim nanopartikels, om sodoende die weerstand teen afgematheid te verbeter. In die verfindustrie word die gebruik van waterbasissisteme meer algemeen weens gesondheids- en omgewingsredes. Die gebruik van miniemulsie sisteme om materiale vas te vang maak dit moontlik om FC kleurstowwe direk in waterbasissisteme te meng. Die sintese van `n unieke gasheer matriks word benodig om die optimum FC verandering te toon en weerstand teen afgematheid te verbeter. Om die FC verandering van die sogenaamde slim nanopartikel films (d.w.s. FC miniemulsies) te ondersoek was `n gepaste instrumentele opstelling nodig. Dit is vasgestel dat `n UV-Vis instrument waarin `n skyfie-tipe UV LED gemonteer is vir aktivering van die monsters, reproduseerbare resultate gegee het. Die monsters is gedeaktiveer deur gebruik te maak van `n tungsten lig met ‘n filter. `n Eksperimentele ontwerp is toegepas om `n stabiele butielmetakrielaat (BMA) miniemulsie formulasie te verkry. `n ‘Chromene’ en ‘spironapthoxazine’ (SNO) FC kleurstof is in die BMA miniemulsie vasgevang tesame met `n verhinderde amien ligstabiliseerder (VALS) om die weerstand teen afgematheid verder te verbeter. Die volgende FC eienskappe van die slim nanopartikels is gemeet: kleurintensiteit, tempo van termiese verwering, half-lewe en weerstand teen afgematheid. `n BMA polimeeroplossing is berei om resultate mee te vergelyk. Die SNO kleurstof en verskillende konsentrasies van die VALS is met die BMA polimeeroplossing gemeng. In vergelyking met die slim SNO nanopartikels het die intelligente chromene nanopartikelfilms `n swakker kleurintensiteit gehad, maar `n hoër weerstand teen afgematheid. Die gebruik van 0.5–2% VALS in die BMA miniemulsie met FC kleurstof het minimale verbetering in weerstand teen afgematheid getoon, maar daar was wel `n beduidende verbetering in die geval van films met FC kleurstof in `n BMA polimeeroplossing. Byvoeging van 1% SNO kleurstof in `n BMA miniemulsie of polimeeroplossing het dieselfde kleurintensiteit gelewer, maar die weerstand teen afgematheid van die FC miniemulsie was baie beter.

Nanoalloys are an exciting new class of materials in the growing field of nanotechnology. Nanoalloys consist of the nanoscale co-aggregation of two or more metals with a potential to form compositionally-ordered phases or superstructures that have properties unlike those of the individual metal clusters or of bulk alloys of the constituent metals. This research seizes the opportunity that the nanoscale domain has to offer, and focuses on the synthesis of iron and cobalt nanoalloys via the simultaneous decomposition of iron cobalt organometallic precursors in a stabilizing environment, accompanied by the thorough characterization of the resulting nanoclusters. Zero-valent FeCo nanoalloys may potentially have interesting uses as magnetic materials. Since these clusters have sizes less than the size of their magnetic domain, the clusters will exhibit single domain magnetism. This magnetism may be observed by the presence of chain structures of FeCo nanoclusters due to the alignment of their single magnetic domains. In order to create a near-atomically homogeneous nanoalloy without preferential aggregation of its metal atom constituents, no clustering and phase separation should take place. In the bulk, alloys of iron and cobalt phase separate over most of the compositional range. Conversely, at the nanoscale, it may be possible to synthesize nanoalloy structures that are not normally favorable at given compositions, by the manipulation of reaction kinetics. In order to produce an atomically mixed nanoalloy, the transformation reactions of the organometallic precursors should display similar kinetic features, i.e. similar reaction rates. Therefore, the reaction kinetics of all the species in the reaction must be similar to avoid competition between them. As a result, kinetic control of the individual transformation reaction rates of each species may be used to modulate the aggregation and phase separation of the different species, and consequently control cluster morphology. This work has provided the framework for the design of synthesis methods that enable the control of the structure of FeCo nanoalloys with careful attention to precursor decomposition kinetics and the correlation between reaction kinetics and nanoalloy morphology.

Diatoms possess characteristics such as abundance, diversity, and high reproductivity, which make their nano-structured frustules (diatom frustules) attractive for a wide range of applications. To overcome the limitation of their silica based frustule composition, diatom frustules have been converted into a variety of materials including silicon, silicon carbide, silver, gold, palladium and carbon in the present study. The compositions and the extent of shape preservation of the replicas are examined and evaluated with different characterization methods such as X-ray diffraction, SEM, TEM and FTIR analyses. These replicas still retained the complex 3D structures and nano-scaled features of the starting diatom frustules. Some properties and possible applications of converted materials are explored and the kinetics and thermodynamics related to the successful replications (conversions) are also studied and discussed.

During the attempts to carry out Suzuki coupling reactions, the σ-bonded Pd−Caryl benzochalcogenadiazolyl complexes trans-[ClPd(PPh3)2(C6H2BrN2E)] (E = S, Se) were isolated. The corresponding bromo derivatives were also synthesized on purpose to investigate their activity in Stille coupling reactions. A head-to-tail dimer trans- [{ClPd(PPh3)(μ-C6H2BrN2Se)}2] was synthesized from the thermolysis of trans- [ClPd(PPh3)2(C6H2BrN2Se)] in the presence of SeO2. The reduction potentials of the mononuclear and dinuclear complexes were measured by cyclic voltammetry (CV) and square wave voltammetry (SWV). 4,7-bis(2/4-pyridyl)benzochalcogenadiazole ligands were synthesized by Stille coupling reactions and the 1,5-bis(4-pyridyl)naphthalene ligand was prepared by a Suzuki coupling reaction. Reactions of the labile complex [BrRe(CO)4(NCMe)] with 4,7-bis(4- pyridyl)benzochalcogenadiazole ligands in a 2:1 ratio afforded self-assembled molecular rods [{ReBr(CO)4}2(μ-4,7-bis(4-pyridyl)benzochalcogenadiazoles)]. Palladium directed molecular squares [(enPd)(μ-4,7-bis(4-pyridyl)benzochalcogenadiazole)]4[PF6]8 were prepared by reactions of enPd(PF6)2 and 4,7-bis(4-pyridyl)benzochalco-genadiazoles in a 1:1 ratio. The optoelectronic properties of the ligands and the molecular rods were investigated by CV and SWV, and by luminescence spectroscopy. The optical properties of the square complexes were also studied by luminescence spectroscopy. / xvii, 152 leaves : ill. (some col.) ; 29 cm

Advancing the field of nanotechnology to incorporate the unique properties observed at the nanoscale into functional devices has become a major scientific thrust of the 21st century. New fabrication tools and assembly techniques are required to design and manufacture devices based on one-dimensional nanostructures. Three techniques for manipulating nanomaterials post-synthesis have been developed. Two of them involve direct contact manipulation through the utilization of a physical probe. The third uses optically generated surface acoustic waves to reproducibly control and assemble one-dimensional nanostructures into desired locations. The nature of the third technique is non-contact and limits contamination and defects from being introduced into a device by manipulation. While the effective manipulation of individual nanostructures into device components is important for building functional nanosystems, commercialization is limited by this one-device-at-a-time process. A new approach to nanostructure synthesis was also developed to site-specifically nucleate and grow nanowires between two electrodes. Integrating synthesis directly with prefabricated device architectures leads to the possible mass production of NEMS, MEMS and CMOS systems based upon one-dimensional nanomaterials. The above processes have been pursued to utilize piezoelectric ZnO nanobelts for applications in high frequency electronic filtering as well as biological and chemical sensing. The high quality, single crystal, faceted nature of these materials make them ideal candidates for studying their properties through the designs of a bulk acoustic resonator. The first ever piezoelectric bulk acoustic resonator based on bottom-up synthesized belts will be demonstrated. Initial results are promising and new designs are implemented to scale the device to sub-micron dimensions. Multiple models will be developed to assist with design and testing. Some of models presented will help verify experimental results while others will demonstrate some of the problems plaguing further investigations.

The demands for advanced power sources with high energy efficiency, minimum environmental impact, and low cost have been the impetus for the development of a new generation of batteries and fuel cells. One of the key challenges in this effort is to develop and fabricate effective electrodes with desirable composition, microstructure and performance. This work focused on the design, fabrication, and characterization of nanostructured electrodes in an effort to minimize electrode polarization losses. Solid-state diffusion often limits the utilization and rate capability of electrode materials in a lithium-ion battery, especially at high charge/discharge rates. When the fluxes of Li+ insertion or extraction exceed the diffusion-limited rate of Li+ transport within the bulk phase of an electrode, concentration polarization occurs. Further, large volume changes associated with Li+ insertion or extraction could induce stresses in bulk electrodes, potentially leading to mechanical failure. Interconnected porous materials with high surface-to-volume ratio were designed to suppress the stress and promote mass transport. In this work, electrodes with these unique architectures for lithium ion batteries have been fabricated to improve the cycleability, rate capability and capacity retention. Cathodic interfacial polarization represents the predominant voltage loss in a low-temperature SOFC. For the first time, regular, homogeneous and bimodal porous MIEC electrodes were successfully fabricated using breath figure templating, which is self-assembly of the water droplets in polymer solution. The homogeneous macropores promoted rapid mass transport by decreasing the tortuosity. And mesoporous microstructure provided more surface areas for gas adsorption and more TPBs for the electrochemical reactions. Moreover, composite electrodes were developed with a modified sol-gel process for honeycomb SOFCs. The sol gel derived cathodes with fine grain size and large specific surface area, showed much lower interfacial polarization resistances than those prepared by other existing processing methods. Nanopetals of cerium hydroxycarbonate have been synthesized via a controlled hydrothermal process in a mixed water-ethanol medium. The formation of the cerium compound depends strongly on the composition of the precursors, and is attributed to the favored ethanol oxidation by Ce(IV) ions over Ce(IV) hydrolysis process. Raman studies showed that microflower CeO2 preferentially stabilizes O2 as a peroxide species on its surface for CO oxidation.

Numerous organisms produce ornately detailed inorganic structures (often known as shells) with features on length scales from 50 nm to several centimeters. One class of such organisms are the diatoms; microscopic algae that form silica frustules. Another group of algae, the coccolithophorids, produce similar calcium carbonate structures. Over 100,000 species comprise these two classes of algae, every one of which is endowed with a unique cytoskeleton structure. Using various types of displacement reactions, the chemistry of the original structure can be modified to produce a new material. Magnesium vapor has been found to displace the silicon in diatom frustules to yield an MgO structure. The conversion has been reported at temperatures from 650°C to 900°C. In the current work, the conversion and processing of silica frustules to MgO was examined in depth. The effect of reaction temperature on grain size and extent of conversion was evaluated. With the goal of obtaining high purity MgO structures, various methods for removing the silicon products of reaction were investigated. Wet chemistry and high temperature vapor etches were evaluated. The MgO reaction served as an intermediate step in the production of magnesium tungstate diatoms, which were imbued with photoluminescent properties. Reactions were identified to allow the conversion of calcium carbonate (calcite) structures to alternative chemistries. Calcite sand-dollars were converted to calcium tungstate or calcium molybdate by aqueous solution chemistry. In this process, sand dollar tests (shells) and coccolithophore frustules were reacted with ammonium para-molybdate or ammonium para-tungstate. The reactions were evaluated for shape preservation, phase purity, and photoluminescence of the structures.