Spectroelectrochemical Sensor for Pertechnetate Applicable to Hanford and Other DOE Sites
The general aim of our work funded by DOE is the design and implementation of a new sensor technology that offers unprecedented levels of specificity needed for analysis of the complex chemical mixtures found at DOE sites nationwide. The specific goal of this project was the development of a sensor for technetium (Tc) that is applicable to characterizing and monitoring the vadose zone and associated subsurface water at the Hanford Site and other DOE sites. The concept for the spectroelectrochemical sensor is innovative and represents a breakthrough in sensor technology. The sensor combines three modes of selectivity (electrochemistry, spectroscopy, and selective partitioning) into a single sensor to substantially improve selectivity. The sensor consists of a basic spectroelectrochemical configuration that we have developed under our previous DOE grants: a waveguide with an optically transparent electrode (OTE) that is coated with a thin chemically-selective film that preconcnetrates the analyte. The key to adapting this generic sensor to detect TcO4- and Tc complexes lies in the development of chemically-selective films that preconcentrate the analyte and, when necessary, chemically convert it into a complex with electrochemical and spectroscopic properties appropriate for sensing. Significant accomplishments were made in the general areas of synthesis and characterization of polymer films that efficiently preconcentrate the analyte, development and characterization of sensors and associated instrumentation, and synthesis and characterization of relevant Re and Tc complexes. Two new polymer films for the preconcentration step in the sensor were developed: partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SSEBS) and phosphine containing polymer films. The latter was a directed polymer film synthesis that combined the proper electrostatic properties to attract TcO4- and also incorporated a suitable ligand for covalently trapping a lower oxidation state Tc complex within the film for spectroelectrochemical detection. Spectroelectrochemical sensors were developed and demonstrated, first using [Re(dmpe)3]+ (dmpe = 1,2-bis(dimethylphosphino)ethane) as a model compound with the non-radioactive Re surrogate for radioactive Tc. A fluorescence based spectroelectrochemical sensor for [Tc(dmpe)3]+/2+was then developed using SSEBS as the preconcentrating film. Portable instrumentation for the fluorescence spectroelectrochemical sensor was fabricated and tested. The effects of components in Hanford subsurface water on sensor performance with a detailed evaluation of the effect of total ionic strength on sensitivity demonstrated the ability to use the spectroelectrochemical sensor on representative water samples. A variety Re and Tc complexes were synthesized and characterized to explore the best ligands to use for detection of Tc. A lower oxidation-state Tc-complex [Tc(dmpe)3]+ (dmpe = 1,2-bis(dimethylphosphino)ethane) was synthesized to use as a model compound for developing Tc sensors. [Tc(dmpe)3]+/2+ exhibited the important properties of solution fluorescence at ambient temperatures and reversible electrochemistry. A range of low oxidation state dioxo Re- and Tc-complexes of formulae [ReO2(py)4]+, [ReO2(CN)4]-, [ReO2(P-P)2]+ and [ReO2(S-S)2]+ (py = pyridine) were synthesized. An exhaustive study of the spectroscopy and electrochemistry of Re(diimine)(CO)3(halide) complexes was performed. These complexes served as models for the Tc(diimine)(CO)3(halide) complexes that were readily formed from Tc(CO)x(halides)6-x complexes which are themselves constituents of tank waste samples from Hanford. Of particular interest were new Tc complexes with the +5 and +6 oxidation states. Tetrabutylammonium salt of tetrachlorooxotechnetate(V), (nBu4N)[TcOCl4] (I) was synthesized and the structure determined. [TcO2(CN)4]3- , [TcO2(en)2]2+ , [TcO2(im)4]+, and [TcO2(py)4]+ (en = ethylenediamine; im = imidazole; py = pyridine) complexes were synthesized and solution and solid state 99Tc NMR spectra were acquired giving the opportunity of determining electric field gradient (EFG) and shielding tensors for a transition metal center with a partially filled d shell.
- Research Organization:
- University of Cincinnati, Cincinnati, OH; Pacific Northwest National Laboratory, Richland, WA
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- FG02-07ER64353
- OSTI ID:
- 1050972
- Report Number(s):
- DOE/ER/64353-Final; DE-FG02-07ER51629
- Country of Publication:
- United States
- Language:
- English
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