Porous Zr2SC-carbon composite microspheres: Possible radiation tolerant sorbents and transmutation hosts for technetium-99

The preparation, characteristics and adsorption properties of novel porous carbon-ceramic composite microspheres are presented. The composites were synthesised by a simple ion exchange process involving the cationic Zr tetramer and commonly-available macroporous sulphonated polystyrene-divinylbenzene cation exchange resins, with subsequent carbothermal reduction at 1350 °C. The materials were extensively characterised with respect to composition, chemical structure and porosity. Carbothermal reduction of the Zr-loaded templates resulted in formation of crystallites of the MAX phase zirconium sulphide carbide (Zr 2 SC) embedded within a highly microporous carbon framework with a macroporous secondary structure inherited from the resin template. Despite the high BET surface areas of the Zr 2 SC-carbon composite microspheres (in some cases, greater than 600 m 2 g −1 ), they are extremely mechanically robust. The microspheres displayed high adsorption selectivity for oxoanions relative to cationic solution species, including perrhenate (ReO 4 − ), a pertechnetate (TcO 4 − ) surrogate. Accumulation of ReO 4 − on the Zr 2 SC particles was unequivocally demonstrated by elemental mapping. Such materials are potential candidates as combined 99 Tc sorbents and reusable transmutation hosts.