title: A study on rhodium and palladium mixed-media sols

authors: Jaine, Jacob Evan

subjects: colloid

abstract: Historically the majority of precious metal sols have been prepared in an aqueous medium, while a much smaller proportion have been prepared in various non‐aqueous solvents. Few however have been prepared in mixtures of the two, this paucity being the raison d’être of this study. The goal therefore was to perform a systematic investigation of the changes in the properties of rhodium and palladium sols generated in mixtures of water and another organic cosolvent across a range of volumetric compositions. Six cosolvents were investigated: methanol, dimethylsulfoxide, acetonitrile, N,N‐dimethylformamide, acetone, and tetrahydrofuran. To stabilise the resulting sols against aggregation four protecting agents were used: poly(vinyl pyrrolidone), poly(vinyl alcohol), poly(acrylic acid), and arabinogalactan, which was a newly‐available polysaccharide extracted from the Western Larch tree. To reduce the metals from their precursor salts, sodium borohydride and hydrazine hydrate were used. The resulting colloids were analysed by Transmission Electron Microscopy (TEM), Photon Correlation Spectroscopy (PCS) and Ultraviolet/Visible Spectrophotometry. The size of the primary particles in the resulting sols was shown by TEM to be inversely proportional to the proportion of cosolvent in which they were generated. A theory was postulated to account for these changes based on temporary stabilisation of the metal nuclei by adsorption of cosolvent molecules. The characteristics of the aggregates observed in the TEM micrographs were shown to be independent of the cosolvent proportion, changing progressively but unpredictably across the composition ranges studied for most systems. This behaviour was believed to be caused by changes in the conformations of the protecting agents, which depended nonlinearly on the composition of the dispersion medium in which they were used. The measurements collected in‐situ by both PCS and UV/Vis were considered to be good indicators of the levels of aggregation observed in the sols ex‐situ by TEM, with any disparities between the two sets of measurements rationalised with relative ease. PCS measurements gave average hydrodynamic diameters of approximately 20 nm – 80 nm for sols generated in purely aqueous dispersion media, depending on the metal and protecting agent used. Infrared spectra were collected of carbon monoxide adsorbed to the surface of the particles of the sols in mixed‐media to determine the effect of the cosolvent proportion on ν(CO)ads. Sols generated for the aforementioned work were found to be of insufficient density for this purpose, so a series of high‐density sols were synthesised especially. Adsorbed CO was successfully detected on rhodium sols in mixtures of water and either MeOH, DMF, DMSO or MeCN. In these cases υ(CO)ads and its intensity decreased as the cosolvent proportion was increased. This behaviour was rationalised by competitive adsorption of the cosolvent molecules onto the surface of the colloidal particles, precluding the adsorption of CO molecules. The consequent decrease in surface coverage was presumed to have lead to a loss of dipolar coupling, affecting the stretching frequency. These data were used to support the theory postulated for the decrease in the average particle size of the sols generated in mixed‐media.

text: A study on rhodium and palladium mixed-media sols Historically the majority of precious metal sols have been prepared in an aqueous medium, while a much smaller proportion have been prepared in various non‐aqueous solvents. Few however have been prepared in mixtures of the two, this paucity being the raison d’être of this study. The goal therefore was to perform a systematic investigation of the changes in the properties of rhodium and palladium sols generated in mixtures of water and another organic cosolvent across a range of volumetric compositions. Six cosolvents were investigated: methanol, dimethylsulfoxide, acetonitrile, N,N‐dimethylformamide, acetone, and tetrahydrofuran. To stabilise the resulting sols against aggregation four protecting agents were used: poly(vinyl pyrrolidone), poly(vinyl alcohol), poly(acrylic acid), and arabinogalactan, which was a newly‐available polysaccharide extracted from the Western Larch tree. To reduce the metals from their precursor salts, sodium borohydride and hydrazine hydrate were used. The resulting colloids were analysed by Transmission Electron Microscopy (TEM), Photon Correlation Spectroscopy (PCS) and Ultraviolet/Visible Spectrophotometry. The size of the primary particles in the resulting sols was shown by TEM to be inversely proportional to the proportion of cosolvent in which they were generated. A theory was postulated to account for these changes based on temporary stabilisation of the metal nuclei by adsorption of cosolvent molecules. The characteristics of the aggregates observed in the TEM micrographs were shown to be independent of the cosolvent proportion, changing progressively but unpredictably across the composition ranges studied for most systems. This behaviour was believed to be caused by changes in the conformations of the protecting agents, which depended nonlinearly on the composition of the dispersion medium in which they were used. The measurements collected in‐situ by both PCS and UV/Vis were considered to be good indicators of the levels of aggregation observed in the sols ex‐situ by TEM, with any disparities between the two sets of measurements rationalised with relative ease. PCS measurements gave average hydrodynamic diameters of approximately 20 nm – 80 nm for sols generated in purely aqueous dispersion media, depending on the metal and protecting agent used. Infrared spectra were collected of carbon monoxide adsorbed to the surface of the particles of the sols in mixed‐media to determine the effect of the cosolvent proportion on ν(CO)ads. Sols generated for the aforementioned work were found to be of insufficient density for this purpose, so a series of high‐density sols were synthesised especially. Adsorbed CO was successfully detected on rhodium sols in mixtures of water and either MeOH, DMF, DMSO or MeCN. In these cases υ(CO)ads and its intensity decreased as the cosolvent proportion was increased. This behaviour was rationalised by competitive adsorption of the cosolvent molecules onto the surface of the colloidal particles, precluding the adsorption of CO molecules. The consequent decrease in surface coverage was presumed to have lead to a loss of dipolar coupling, affecting the stretching frequency. These data were used to support the theory postulated for the decrease in the average particle size of the sols generated in mixed‐media.

year: 2011

title: Long-term variations in fish assemblage, macrophyte community, and water quality in Lake Rotoroa (Hamilton Lake)

authors: Law, Duncan Robert Mckenzie

abstract: Lake Rotoroa (37º48’S, 175º16’E) is a small, shallow, polymictic lake located on the western side of Hamilton City. The lake covers an area of 0.54 km2 with a mean depth of 2.4 m, catchment and riparian margins have been significantly modified into a suburban park-like setting. Due to its urban location and recreational value, exotic flora and fauna have been intentionally and unintentionally introduced. This has resulted in fluctuations in water quality and changes in phytoplankton, fish, and macrophyte assemblages over the past 60 years. The overall aim of this thesis is to summarise the fluctuations in water quality and macrophyte community of Lake Rotoroa associated with introduction of exotic species, and to develop a general understanding of the ecosystem response. This study involved collating and analysing available information on fish assemblages, macrophyte community, and water quality in Lake Rotoroa. Data from nine fish surveys undertaken between 1976 and 2012 has been combined. Water quality and macrophyte data was supplied by NIWA, who have undertaken monitoring for Hamilton City Council as part of the national lakes monitoring programme.

Fishing methods have varied from gill, trap, and fyke netting between 1976 and 2001, with boat electrofishing surveys between 2003 and 2012. Lake Rotoroa has a relatively diverse freshwater fish fauna, comprising two native and six exotic fish species. The fish assemblage is now dominated by the native shortfin eel (Anguilla australis), European perch (Perca fluviatilis), brown bullhead catfish (Ameiurus nebulosus), and tench (Tinca tinca), with low densities of rudd (Scardinius erythrophthalmus) and goldfish (Carassius auratus). Fish density and biomass have varied throughout the survey period, to some extent related to the environmental conditions and macrophyte cover. 

Macrophyte coverage and water quality have undergone considerable changes in the last 30 years, with the collapses of macrophytes stimulating decreases in water quality and increased perch abundance. In 1990, the macrophyte community collapsed with an associated release of nutrients into the water column, causing the lake to become supertrophic. Between 1992 and 2010, water quality improved, with a decrease phosphorus concentrations that apparently limited phytoplankton biomass and improved water clarity. This allowed macrophytes to recolonise the lake to 30% lake bed coverage in 2005 and a consequent improvement from supertrophic to a eutrophic state. Since 2009, the macrophyte community has undergone another collapse, with only a few clumps of native charophytes and Egeria densa present in 2011. The reduction of macrophytes has been accompanied by a decrease in water clarity. The collapse has been attributed to disturbance by grazing from the herbivorous rudd and foraging benthic feeding fish, although other stresses such as decreased water clarity and microcystins may also have had an influence. 

Further research is needed on the selectivity between passive and active fish capture methods used to allow accurate comparisons between the two methods. This will allow for density and biomass estimates to be made for the passive fishing methods previously used and allow greater insight into changes in abundance of fish populations in Lake Rotoroa.

text: Long-term variations in fish assemblage, macrophyte community, and water quality in Lake Rotoroa (Hamilton Lake) Lake Rotoroa (37º48’S, 175º16’E) is a small, shallow, polymictic lake located on the western side of Hamilton City. The lake covers an area of 0.54 km2 with a mean depth of 2.4 m, catchment and riparian margins have been significantly modified into a suburban park-like setting. Due to its urban location and recreational value, exotic flora and fauna have been intentionally and unintentionally introduced. This has resulted in fluctuations in water quality and changes in phytoplankton, fish, and macrophyte assemblages over the past 60 years. The overall aim of this thesis is to summarise the fluctuations in water quality and macrophyte community of Lake Rotoroa associated with introduction of exotic species, and to develop a general understanding of the ecosystem response. This study involved collating and analysing available information on fish assemblages, macrophyte community, and water quality in Lake Rotoroa. Data from nine fish surveys undertaken between 1976 and 2012 has been combined. Water quality and macrophyte data was supplied by NIWA, who have undertaken monitoring for Hamilton City Council as part of the national lakes monitoring programme.

Fishing methods have varied from gill, trap, and fyke netting between 1976 and 2001, with boat electrofishing surveys between 2003 and 2012. Lake Rotoroa has a relatively diverse freshwater fish fauna, comprising two native and six exotic fish species. The fish assemblage is now dominated by the native shortfin eel (Anguilla australis), European perch (Perca fluviatilis), brown bullhead catfish (Ameiurus nebulosus), and tench (Tinca tinca), with low densities of rudd (Scardinius erythrophthalmus) and goldfish (Carassius auratus). Fish density and biomass have varied throughout the survey period, to some extent related to the environmental conditions and macrophyte cover. 

Macrophyte coverage and water quality have undergone considerable changes in the last 30 years, with the collapses of macrophytes stimulating decreases in water quality and increased perch abundance. In 1990, the macrophyte community collapsed with an associated release of nutrients into the water column, causing the lake to become supertrophic. Between 1992 and 2010, water quality improved, with a decrease phosphorus concentrations that apparently limited phytoplankton biomass and improved water clarity. This allowed macrophytes to recolonise the lake to 30% lake bed coverage in 2005 and a consequent improvement from supertrophic to a eutrophic state. Since 2009, the macrophyte community has undergone another collapse, with only a few clumps of native charophytes and Egeria densa present in 2011. The reduction of macrophytes has been accompanied by a decrease in water clarity. The collapse has been attributed to disturbance by grazing from the herbivorous rudd and foraging benthic feeding fish, although other stresses such as decreased water clarity and microcystins may also have had an influence. 

Further research is needed on the selectivity between passive and active fish capture methods used to allow accurate comparisons between the two methods. This will allow for density and biomass estimates to be made for the passive fishing methods previously used and allow greater insight into changes in abundance of fish populations in Lake Rotoroa.

year: 2012

title: Creating a curriculum for indigenous and community languages: Te reo Māori as an example

authors: Bruce, Ian

subjects: linguistics

abstract: Part 1 of this paper introduces the draft Common European Framework of Reference (CEFR) for languages and describes how it was used in the construction of draft New Zealand curriculum guidelines for French and German. Part 2 discusses how the CEFR has been employed in curriculum development in Te Reo Māori at the University of Waikato and suggests that it could also prove useful in relation to curriculum development projects involving indigenous and community languages more generally.

text: Creating a curriculum for indigenous and community languages: Te reo Māori as an example Part 1 of this paper introduces the draft Common European Framework of Reference (CEFR) for languages and describes how it was used in the construction of draft New Zealand curriculum guidelines for French and German. Part 2 discusses how the CEFR has been employed in curriculum development in Te Reo Māori at the University of Waikato and suggests that it could also prove useful in relation to curriculum development projects involving indigenous and community languages more generally.

year: 2002