The application of boron-doped diamond thin-film electrodes for water treatment and water quality monitoring

In this Dissertation, the application of boron-doped diamond electrodes for water treatment (degradation of an organic compound (atrazine)) and water quality monitoring (detection of inorganic ions (arsenic)) is described.; In one project, boron-doped diamond thin-film coated on Ti (diamond/Ti) was used for the anodic degradation of atrazine. The specific aim was to learn how efficiently atrazine can be electro-oxidized at diamond to produce CO 2. The diamond/Ti anode was first evaluated during anodic polarization in 0.1 M H2SO4 and was found to exhibit a stable electrochemical response over time, good activity for the two redox systems, Ru(NH3) 63+/2+ and Fe(CN)63-/4-, and excellent morphological and microstructural stability. The electrooxidative degradation of atrazine was investigated by bulk electrolysis at constant current density (11 or 22 mA/cm2). The intermediate degradation products were detected by HPLC-UV/Vis. The three common degradation products for atrazine, hydroxyatrazine deethylatrazine and deisopropylatrazine, were not detected during the electrolysis. However, radioisotope labeling studies proved that 81% of the 14C-labeled atrazine was oxidized to 14CO2 during a 2-h electrolysis period confirming that diamond is a suitable anode for complete mineralization.; In a second project, a Au-coated boron-doped diamond thin-film electrode was used to detect total inorganic arsenic in water supplies using differential pulse anodic stripping voltammetry (DPASV). The specific aim of the work was to learn how the diamond support influences (i) the formation of Au metal phases and, in term, the formation of the Au-As complex during the deposition step and (ii) the resistance of the nearby Au particles toward adsorption of contaminants in solution (i.e., fouling). In the method, As is codeposited (preconcentrated) with Au on the diamond surface and detected oxidatively by DPASV. Au deposition was found to be uniform over the surface with a nominal particle size of 23 +/- 5 nm under the potentiostatic conditions employed. The electrode provided a sensitive, reproducible and stable response for total inorganic arsenic detection and exhibited better performance than did Au-coated glassy carbon or Au foil electrodes. Sharp and symmetric stripping peaks were generally observed for the Au-coated diamond electrode. As(V) was chemically reduced to As(III) by Na2SO3 before analysis. Limits of detection (LOD) were 0.005 ppb (S/N = 3) for As(III) and 0.08 ppb (SIN = 3) for As(V) in standard solutions. An As(III) concentration of 0.6 ppb was found in local river water with a stable electrode response. Interferences, such as metal ions (e.g., Cu(II)) and organic matter (e.g., humic acid), that commonly cause decreased electrode response sensitivity for arsenic detection in real samples, were minimized through the use of solid phase extraction in the sample preparation. The method provided accurate and reproducible results for total inorganic arsenic detection in two contaminated water samples. The detected total inorganic arsenic concentration differed from the specified concentrations by less than 4%.