Spectroelectrochemical Sensor for Pertechnetate Applicable to Hanford and Other DOE Sites
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.
- Research Organization:
- University of Cincinnati, Cincinnati, OH
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG02-03ER63655
- OSTI ID:
- 850386
- Report Number(s):
- EMSP-90076-2004; R&D Project: EMSP 90076; TRN: US200517%%541
- Country of Publication:
- United States
- Language:
- English
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