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Title: Spectroelectrochemical Sensor for Pertechnetate Applicable to Hanford and Other DOE Sites

Abstract

New film materials for pertechnetate: A new film material comprised of quaternized poly(4-vinylpyridine) cross-linked with 1,10-diiododecane has been developed for use in the spectroelectrochemical sensor. Films were prepared in a one-pot synthesis by stirring poly(4-vinylpyridine), cross-linker and methyl iodide in 1-butanol for 1 h, after which the solution was spin-coating onto ITO-glass. Film thickness was varied either by changing the spin rate or by dilution of the original precursor solution. The thinnest film prepared was 30 nm; the thickest 930 nm. Spectroscopic ellipsometry was used to study the dynamics of film changes on soaking in aqueous salt solution and on preconcentrating model analyte ferrocyanide. The results document that, on hydration, films expanded by almost 90% in 0.1 M KNO3, then contracted slightly when ferrocyanide solution was introduced probably due to electrostatic cross-linking. IR spectroscopy was used to determine the extent of quaternization of the film. For a polymer solution stirred for 1 h, films were about 20% quaternized. This can be increased to {approx}30% by adding more solvent to the precursor solution and stirring for an additional hour. Solubility of the partially cross-linked material was a factor that limited the quaternization process. Use of a more appropriate solvent may enablemore » greater quaternization. A more quaternized film should preconcentrate more pertechnetate by virtue of having a higher density of charged binding sites. Film ruggedness is critical. To investigate this, films on ITO-glass were soaked in methanol and butanol overnight, in 0.1M KNO3, and in 0.1M KNO3 adjusted to pH 12 and pH 2 for 30 days. Each film was then tested as a spectroelectrochemical sensor for model analyte ferrocyanide. The results showed only the pH 2 conditioned sensor behaved abnormally. The film soaked in pH 2 electrolyte delaminated but did not dissolve. Delamination was most likely due to the acid digestion of the ITO layer of the sensor and not to any film-based process. We have also shown that it is possible to regenerate the film by flushing with 1M KNO3 solution. Response curves were prepared from a single sensor by injecting different concentrations of ferrocyanide, monitoring the uptake, then regenerating the film and injecting the next concentration. To check reproducibility, a film was regenerated 10 times with almost no change in response. Film selectivity was demonstrated by adding a model cationic species, Ru(bipy)32+ to the ferrocyanide sample. Even at 10 times the ferrocyanide concentration, only a very small electrochemical signal and no optical signal due to the cation were observed. Additionally a competitive anion Ru(CN)64- could be distinguished from Fe(CN)64- based on the redox potential and absorbance spectrum differences between the two anions. Both species were preconcentrated into the film, and both could be electrochemically modulated simultaneously or individually. The films exhibited a linear absorbance response to ferrocyanide over the range 0.008-0.2mM. From 0.1mM ferrocyanide solution, the analyte was concentrated in a 320 nm thick film by a factor of {approx}6,000. The films have recently been used at PNNL to repeat cyclic voltammetry experiments with pertechnetate (TcO4) as previously performed with other candidate films. The results showed that the new films performed very well and better than films previously used, and showed reversible waves in the voltammogram with the film present where none appeared when a bare ITO-glass substrate was used. Our results clearly show that cross-linked quaternized poly(4-vinylpyridine) films made this way are superior materials for preconcentrating pertechnetate.« less

Authors:
Publication Date:
Research Org.:
University of Cincinnati, Cincinnati, OH
Sponsoring Org.:
USDOE
OSTI Identifier:
850386
Report Number(s):
EMSP-90076-2004
R&D Project: EMSP 90076; TRN: US200517%%541
DOE Contract Number:
FG02-03ER63655
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
10 SYNTHETIC FUELS; 54 ENVIRONMENTAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANIONS; BUTANOLS; ELECTROLYTES; ELECTROSTATICS; ELLIPSOMETRY; FERROCYANIDES; METHANOL; METHYL IODIDE; PERTECHNETATES; POLYMERS; REDOX POTENTIAL; SPECTROSCOPY; SUBSTRATES; SYNTHESIS

Citation Formats

Heineman, William R. Spectroelectrochemical Sensor for Pertechnetate Applicable to Hanford and Other DOE Sites. United States: N. p., 2004. Web. doi:10.2172/850386.
Heineman, William R. Spectroelectrochemical Sensor for Pertechnetate Applicable to Hanford and Other DOE Sites. United States. doi:10.2172/850386.
Heineman, William R. Wed . "Spectroelectrochemical Sensor for Pertechnetate Applicable to Hanford and Other DOE Sites". United States. doi:10.2172/850386. https://www.osti.gov/servlets/purl/850386.
@article{osti_850386,
title = {Spectroelectrochemical Sensor for Pertechnetate Applicable to Hanford and Other DOE Sites},
author = {Heineman, William R.},
abstractNote = {New film materials for pertechnetate: A new film material comprised of quaternized poly(4-vinylpyridine) cross-linked with 1,10-diiododecane has been developed for use in the spectroelectrochemical sensor. Films were prepared in a one-pot synthesis by stirring poly(4-vinylpyridine), cross-linker and methyl iodide in 1-butanol for 1 h, after which the solution was spin-coating onto ITO-glass. Film thickness was varied either by changing the spin rate or by dilution of the original precursor solution. The thinnest film prepared was 30 nm; the thickest 930 nm. Spectroscopic ellipsometry was used to study the dynamics of film changes on soaking in aqueous salt solution and on preconcentrating model analyte ferrocyanide. The results document that, on hydration, films expanded by almost 90% in 0.1 M KNO3, then contracted slightly when ferrocyanide solution was introduced probably due to electrostatic cross-linking. IR spectroscopy was used to determine the extent of quaternization of the film. For a polymer solution stirred for 1 h, films were about 20% quaternized. This can be increased to {approx}30% by adding more solvent to the precursor solution and stirring for an additional hour. Solubility of the partially cross-linked material was a factor that limited the quaternization process. Use of a more appropriate solvent may enable greater quaternization. A more quaternized film should preconcentrate more pertechnetate by virtue of having a higher density of charged binding sites. Film ruggedness is critical. To investigate this, films on ITO-glass were soaked in methanol and butanol overnight, in 0.1M KNO3, and in 0.1M KNO3 adjusted to pH 12 and pH 2 for 30 days. Each film was then tested as a spectroelectrochemical sensor for model analyte ferrocyanide. The results showed only the pH 2 conditioned sensor behaved abnormally. The film soaked in pH 2 electrolyte delaminated but did not dissolve. Delamination was most likely due to the acid digestion of the ITO layer of the sensor and not to any film-based process. We have also shown that it is possible to regenerate the film by flushing with 1M KNO3 solution. Response curves were prepared from a single sensor by injecting different concentrations of ferrocyanide, monitoring the uptake, then regenerating the film and injecting the next concentration. To check reproducibility, a film was regenerated 10 times with almost no change in response. Film selectivity was demonstrated by adding a model cationic species, Ru(bipy)32+ to the ferrocyanide sample. Even at 10 times the ferrocyanide concentration, only a very small electrochemical signal and no optical signal due to the cation were observed. Additionally a competitive anion Ru(CN)64- could be distinguished from Fe(CN)64- based on the redox potential and absorbance spectrum differences between the two anions. Both species were preconcentrated into the film, and both could be electrochemically modulated simultaneously or individually. The films exhibited a linear absorbance response to ferrocyanide over the range 0.008-0.2mM. From 0.1mM ferrocyanide solution, the analyte was concentrated in a 320 nm thick film by a factor of {approx}6,000. The films have recently been used at PNNL to repeat cyclic voltammetry experiments with pertechnetate (TcO4) as previously performed with other candidate films. The results showed that the new films performed very well and better than films previously used, and showed reversible waves in the voltammogram with the film present where none appeared when a bare ITO-glass substrate was used. Our results clearly show that cross-linked quaternized poly(4-vinylpyridine) films made this way are superior materials for preconcentrating pertechnetate.},
doi = {10.2172/850386},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Dec 01 00:00:00 EST 2004},
month = {Wed Dec 01 00:00:00 EST 2004}
}

Technical Report:

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  • The general aim of our work funded by DOE is the design and implementation of a new sensor technology that offers the unprecedented levels of specificity needed for analysis of the complex chemical mixtures found at DOE sites nationwide. The sensor is based on a unique combination of electrochemistry, spectroscopy and selective partitioning into a film that collectively provide an extraordinary level of selectivity for the target analyte. Our goal is a reversible sensor in which the fluorescent Tc-complex formed in the film is re-oxidized to TcO4 ? and free ligand. TcO4 ? in the film would then re-equilibrate withmore » the sample. The sensor would therefore satisfy requirements for both applications described above. Making significant progress towards this goal has required us to discover new chemistry and spectroscopy for technetium itself. Indeed, we needed to find the first technetium complexes which fluoresced in solution at room temperature ? we have made that breakthrough discovery this last year. We are now in the unique position of being able to reach our goal of a reversible sensor for Tc.« less
  • During the period of this grant several significant milestones have been passed pursuant to designing a fluorescence sensor for pertechnetate (TcO4-). They are as follows: Fluorescence spectroelectrochemistry and less than picomolar limit of detection for a model non-radioactive analyte have been demonstrated. The spectroelectrochemical sensor and associated instrumentation for fluorescence mode of operation have been made, are portable, and easily transported to and used at DOE sites. The sensor has sufficient selectivity for its application to complex samples, even including tank waste, that exist at DOE sites such as the Hanford Site. Pertechnetate has been preconcentrated in sensor films andmore » electrochemically reduced. This is the first critical step in operation of a spectroelectrochemical sensor for TcO4-. New Tc complexes have been made that fluoresce and these complexes have been preconcentrated and electrochemically modulated in a sensor film leading to fluorescence modulation, which is the second critical step in operation of the spectroelectrochemical sensor for TcO4-. We have determined that fluorescence offers a means of dramatically improving the limit of detection. Based on measurements on our new fluorescent complexes of Tc, we estimate the limit of detection for the sensor to be 5 x 10-12M. In related work, we have shown that the sensitivity of the spectroelectrochemical sensor for some metal cations can be improved by forming a metal complex with better optical and electrochemical properties. In addition, some heavy metals can be detected with the spectroelectrochemical sensor by depositing them directly as metals on the sensor surface.« less
  • 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, andmore » 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.« less
  • The general objective is the design and implementation of a new sensor technology that offers the unprecedented levels of specificity needed for analysis of the complex chemical mixtures found at DOE sites nationwide. The specific objectives are threefold: demonstration of the general sensor concept on a variety of model systems; development of a sensor for ferrocyanide with testing on waste tank simulant; and development of a sensor for pertechnetate applicable to the Vadose Zone.
  • No abstract prepared.