Plasmonic gold nanostructures: optical properties and application in mercury detection

This thesis investigates the application of plasmonic gold nanostructures for mercury detection. Various gold and silver single nanostructures and gold nanostructure assemblies were characterised in detail by correlated single nanostructure spectroscopy and electron microscopy. Several routes for mercury detection were explored: plasmon resonance energy transfer (PRET) upon Hg2+ binding to immobilised gold nanoparticle-organic ligand hybrid structures and amalgamation of single immobilised gold nanorods upon chemical and upon electrochemical reduction of Hg2+ ions. The amalgamation approach showed large potential with extraordinary shifts of the nanorods’ scattering spectra upon exposure to reduced mercury; a result of compositional and morphological change induced in the nanorod by amalgamation with mercury. A shift of 5 nm could be recorded for a concentration as low 10 nM Hg2+. Through detailed time-dependent experiments insights into the amalgamation mechanism were gained and a model comprising 5 steps was developed. Finally, spectroelectrochemistry proved to be an excellent way to study in real time in-situ the amalgamation of mercury with gold nanorods paving the way for future work in this field.

Gold mining in the Peruvian Amazon: global prices, deforestation, and mercury imports.

Many factors such as poverty, ineffective institutions and environmental regulations may prevent developing countries from managing how natural resources are extracted to meet a strong market demand. Extraction for some resources has reached such proportions that evidence is measurable from space. We present recent evidence of the global demand for a single commodity and the ecosystem destruction resulting from commodity extraction, recorded by satellites for one of the most biodiverse areas of the world. We find that since 2003, recent mining deforestation in Madre de Dios, Peru is increasing nonlinearly alongside a constant annual rate of increase in international gold price (∼18%/yr). We detect that the new pattern of mining deforestation (1915 ha/year, 2006-2009) is outpacing that of nearby settlement deforestation. We show that gold price is linked with exponential increases in Peruvian national mercury imports over time (R(2) = 0.93, p = 0.04, 2003-2009). Given the past rates of increase we predict that mercury imports may more than double for 2011 (∼500 t/year). Virtually all of Peru's mercury imports are used in artisanal gold mining. Much of the mining increase is unregulated/artisanal in nature, lacking environmental impact analysis or miner education. As a result, large quantities of mercury are being released into the atmosphere, sediments and waterways. Other developing countries endowed with gold deposits are likely experiencing similar environmental destruction in response to recent record high gold prices. The increasing availability of satellite imagery ought to evoke further studies linking economic variables with land use and cover changes on the ground.

Hormesis - Stimulation Of Colony Growth In Campanularia-Flexuosa (Hydrozoa) By Copper Cadmium And Other Toxicants

It is shown experimentally that subinhibitory concentrations of a number of toxic, or other agents that are typically inhibitory (copper, cadmium, tributyl tin fluoride, reduced salinity), may stimulate the growth of colonies of the hydroid Campanularia flexuosa, exhibiting a phenomenon known as hormesis. It is suggested that the stimulation of growth is not due to the specific properties of the different toxicants, but to an adaptive response of the hydroid to the inhibitory effect that they have in common. Growth is regulated by a control mechanism and it is proposed that the increased growth is a consequence of overcorrections to low levels of an inhibitory challenge. Examination of the toxicological literature shows that hormesis is a more common occurrence that is generally supposed, and it is suggested that the explanation given here might apply in other cases of hormesis.

Simulating The Impact Of Technological-Change On Dissolved Cadmium Distribution In The Severn Estuary

An estuarine model is described which computes the dispersive and advective properties of the Severn Estuary. It was calibrated and validated using 50 measured salinity distributions and then used to predict the magnitude and sitings of the major inputs of dissolved cadmium levels throughout the estuary. The results provided an impetus for implementing tighter controls on effluents and for improving estimates of cadmium discharges from industrial sources. The model has also been used to investigate the sensitivity of the estuarine system to changes in dispersion; by considering large reductions in the dispersion coefficients it is hoped that the results might be indicative of the environmental consequences following the construction of a tidal power generating scheme.