Extractive thin-film composite membranes for the isotopic screening of plutonium in water

Abstract

Isotopic determination of trace-level Pu in water requires time-consuming concentration and sample preparation steps, and the samples routinely must be prepared off-site from the contamination source. An analytical method that combines on-site Pu concentration with spectroscopic screening would be a valuable tool for environmental monitoring and nuclear forensics. This contribution describes the development of extractive polymer thin-film composite (e-TFC) membranes for the rapid concentration and isotopic determination of Pu from water. The e-TFC membranes were prepared by spin coating Pu-extractive copolymers on the surface of an ultrafiltration membrane. The copolymers were synthesized from methyl methacrylate or 4-methylstyrene and a Pu-reactive monomer. Three Pu-reactive monomers were evaluated for their ability to create copolymers that were suitable for casting and capable of extracting Pu from water at trace levels. Copolymers containing 5% (w/w) ethylene glycol methacrylate phosphate (EGMP) had distribution coefficients of 92.7 ± 18.5 L/kg for 242Pu at pH 6.8. e-TFC membranes prepared with an EGMP-based copolymer active layer were effective for concentrating 242Pu from a 4.53 Bq/mL (1.26 × 10−8 M) solution at pH 6.8. The resulting alpha spectra of Pu-loaded e-TFC membranes achieved energy resolutions (full-width at half-maximum, FWHM) of 71.7 ± 8.7 keV, allowing for the isotopic discrimination of 242Pu from 238Pu/241Am also present in the solution.