The inorganic chemistry and geochemical evolution of pans in the Mpumalanga Lakes District, South Africa
- Authors: Russell, Jennifer Lee
- Date: 2009-11-06
- Subjects: Pans (Geomorphology) , Water chemistry , Chemistry, Inorganic , Mpumalanga (South Africa)
- Type: Thesis
- Identifier: uj:8636 , http://hdl.handle.net/10210/2994
- Description: Master of Science , Despite Chrissie Lake being South Africa’s largest freshwater lake, the chemistry of this lake and the surrounding lakes and pans in the Mpumalanga Lake District has never been studied in detail. These closed systems show varying chemistry while being in very close proximity to one another, adding to the uniqueness of this area where pans, usually typical of arid regions, are found in a humid area. The factors affecting the water chemistry of these lakes needed to be identified and explained. In order to evaluate the water chemistry in this unique environment, water samples were taken at the end of the wet and dry seasons, in April and September 2007 respectively. The major pans were sampled, as were adjacent fountains or springs, indicative of the perched groundwater aquifers found in this area, as well as borehole water from the surrounding farms. Alkalinity was determined by manual titration upon returning from the field while pH and conductivity measurements were performed on site. Major cations and anions were analysed for using ICP-OES and Ion Chromatography respectively. Sediment samples were collected from the floor of each pan in the summer sampling and the mineralogy determined by X-ray diffraction (XRD). During September 2007 sampling, precipitates found on the floors and banks of the pans were also collected and analysed using XRD, to identify mineral species precipitating from solution. Results from the above analyses show that each pan in the MLD has a unique chemistry, which cannot be inferred from neighbouring pans. The inorganic chemistry differs from pan to pan as a result of these separate, closed systems being at different stages of the evaporation process. Throughout the path from groundwater to the pan, waters are subject to mineral dissolution and precipitation, adsorption and biological mechanisms, which continually add or remove solutes from solution. Although seemingly simple, there are certainly other factors that play a role in the evolution of the water chemistry. Key to the current inorganic chemistry is the balance between import and export of solutes. The groundwater, predominantly the perched aquifer water, brings solutes into the pans and blowouts of precipitates on the pan floor at the end of the dry season, when the wind is strongest, results in the export of solutes. This process is significant in maintaining the overall freshness of the pans in the MLD, contrasting to their western counter parts that evolve to highly saline saltpans. Other factors such as the periodicity of pans drying completely, the surface area to catchment area ratio (CA/SA), the formation and dissolution of efflorescent crusts and the presence or absence of reeds all have varying effects on the water chemistry of the lakes and pans. Significantly, the amount of evaporative concentration that a pan evolves through has been shown to be dependant on the CA/SA ratio with pans having larger ratios being lower in salinity compared to those with low ratios being the most saline pans. The reservoir available to the pans with the large catchment areas sustains these pans through the dry months and slows the progression of evaporation. It is clear that the factors affecting the hydrochemistry of the pan waters can not be simplified to a single process affecting a single dilute inflow of water to produce our final solution of evaporated pan water. Instead, water in the pans reflects a long-term evolution of solute species, with some memory effect remaining after each season of evaporation. The result is an accumulation of solutes as they are added continuously via dilute inflow and then removed from the waters at various times, particularly during dry periods when evaporite minerals are formed and transported out of the system.
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Template synthesis of palladium and platinum nanoparticles by dendrimer and reverse microemulsions for the catalytic evaluation on various reactions
- Authors: Noh, Ji-Hyang
- Date: 2015-11-09
- Subjects: Palladium catalysts , Chemical reactors , Chemistry, Inorganic , Nanostructured materials , Platinum , Catalysis
- Type: Thesis
- Identifier: uj:14524 , http://hdl.handle.net/10210/15047
- Description: PhD. (Chemistry) , Well-defined palladium and platinum nanoparticles were synthesized by two template methods, namely dendrimer template and reverse microemulsions. For dendrimer template, three dendrimers, generation 4, 5, and 6 hydroxyl terminated poly(amidoamine) dendrimers (PAMAM), G4-OH, G5-OH, and G6-OH, were used as stabilizing agent, with PdCl4 2- or PtCl4 2- metal ions to dendrimer ratio of 40, 80, and 160, respectively. For reverse microemulsions, we employed water/AOT surfactant/isooctane system with water to surfactant ratios (ω0) of 5, 10, and 13, capped with thiol, to produce Pd and Pt nanoparticles. A total of twelve catalysts were characterized by techniques such as UV-Vis spectroscopy, TEM, EDX, and p-XRD. In the dendrimer template method, the synthesis of Pd and Pt nanoparticles in lower concentrations produced smaller sizes with narrower size distributions (2.02 ± 0.45 ~ 2.35 ± 0.58 nm Pd nanoparticles, 1.90 ± 0.44 nm ~ 2.48 ± 0.60 nm Pt nanoparticles) compared to those in higher concentrations (2.74 ± 0.44 ~ 3.32 ± 0.86 nm Pd nanoparticles, 2.81 ± 0.70 nm ~ 3.03 ± 0.47 nm Pt nanoparticles). In the case of thiol-capped Pd and Pt nanoparticles by reverse microemulsions, the range of average particle sizes were 3.47 - 7.51 nm and 3.51 - 4.23 nm for Pd and Pt nanoparticles, respectively. This indicated that a wider size regime was obtained by the reverse microemulsion method as compared to the dendrimer template method. Overall, smaller sizes with narrower size distributions were achieved by using the dendrimer-templated synthetic method rather than reverse microemulsions for both Pd and Pt nanoparticles.
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