Monitoring of Technetium in Groundwater:Development of a Novel QCM Based Sensor

Papageorgiou, Athanasios and Andrieux, Fabrice (2021) Monitoring of Technetium in Groundwater:Development of a Novel QCM Based Sensor. ECS Meeting Abstracts, MA2021 (55). p. 1595. ISSN 2151-2043

Abstract

99Tc, a pure β-emitter with Emax =294 keV, is one of the most significant (t1/2 =2.1×105 y) nuclear waste isotopes, produced by the fission of U with a yield of 6%. Under normal environmental conditions, it is mostly encountered as the pertechnetate ion, TcO4-, which is highly soluble and consequently mobile in water. For this reason, and because it often is the first contaminant to be present in detectable levels, its monitoring into groundwater is a statutory requirement for every nuclear license site. Because of its relatively low concentration in environmental samples, current determination methods of 99Tc involve several steps, such as chemical separation from the matrix, purification and source preparation, prior to radiometric (e.g. liquid scintillation counting) or mass spectroscopic (e.g. inductively coupled plasma mass spectroscopy) determination. The detection of 99Tc may take up to several days, thus making these techniques inappropriate for an emergency situation. Hence, We report on the development of a sensor for the real time monitoring of 99Tc in groundwater based on the Quartz Crystal Microbalance (QCM). The QCM is a piezoelectric resonator, which oscillates in a resonant frequency fs when an electric potential is applied across its body. It is capable of measuring very small changes in mass at its surface, through the change of the resonant frequency. We modify it to respond exclusively to the presence of TcO4-, by application of a novel Ag-4,4bipyridine metal-organic framework thin film built layer-by-layer on a self-assembled monolayer of 4-mercaptopyridine on the gold surface. The film's structure is characterised by several techniques such as XPS, AFM and XRD and we evaluate its response and selectivity by monitoring the changes in the resonant frequency as a function of the concentration of ReO4-, which is a non-radioactive chemical surrogate for TcO4-. Finally, we model the adsorption of ReO4- and other interferences with adsorption isotherms such as Langmuir, Freundlich and Sips.