Photoinduced decomposition of trichloroethylene on colloidal ferrihydrite and detection of cyanide concentration using silver and gold colloids

Colloids play an important role in the environment. This dissertation discusses two roles that colloids have been used for in our research. We have used colloidal ferrihydrite as the possible site for the destruction of trichloroethylene, and we have used colloidal silver and gold as substrates to detect low levels of cyanide in water samples.; A synthetic ferrihydrite was prepared and identified by powder x-ray diffraction (XRD). It was then used to study whether it could decompose trichloroethylene (TCE) through photostimulation of the colloid. By photoreacting the sample for periods of time on the order of days we were able to photoinduce a reaction with the trichloroethylene. The products of this reaction were monitored using a gas chromatograph with an electron capture detector (GC-ECD). Identification of the photoproducts was performed using a gas chromatograph with a mass selective detector (GC-MS). Only one product has been seen and identified so far, tetrachloroethylene (PCE).; Mining companies use large amounts of cyanide a year, 20 million pounds for example, and because of this they need to manage the use, recovery, and loss of the cyanide. Being able to monitor the concentrations of cyanide in water is a necessary tool for this management. In an effort to provide a better, faster, and more sensitive technique we researched several methods to determine ppb levels of cyanide in water samples.; Our research into a method for the determination of cyanide concentration in water samples utilized two different kinds of colloids. We prepared both silver and gold colloids for this project. This method relies on surface enhanced Raman scattering (SERS) spectroscopy to measure the concentration of the cyanide adsorbed to the surface of the colloid. By employing partial least squares analysis (PLS) we were able to determine a 4 ppb detection limit for the gold colloid using a 633 nm fiber-optic Raman laser system and a 50 ppb detection limit for the silver colloid using a 532 nm fiber-optic Raman laser system.; We describe the preparations of the colloids used as well as present methods of preparing and storing standard cyanide samples.