Efficient Photocatalytic Reduction of Aqueous Perrhenate and Pertechnetate

The pertechnetate anion ( 99 TcO 4 – ) is a long-lived radioactive species that is soluble in aqueous solution, in contrast to sparingly soluble 99 TcO 2 . Results are reported for photocatalytic reduction and removal of perrhenate (ReO 4 – ), a nonradioactive surrogate for 99 TcO 4 –, using a TiO 2 (P25) nanoparticle suspension in formic acid under UV–visible irradiation. Re(VII) removal up to 98% was achieved at pH = 3 under air or N 2 . The proposed mechanism is Re(VII)/Re(IV) reduction mediated by reducing radicals ( · CO 2 – ) from oxidation of formic acid, not direct reduction by photogenerated electrons of TiO 2 . Recycling results indicate that photocatalytic reduction of ReO 4 – exhibits excellent regeneration and high activity with >95% removal even after five cycles. 99 Tc(VII) is more easily reduced than Re(VII) in the presence of NO 3 – with very slow redissolution of reduced 99 Tc. This study presents a novel method for the removal of ReO 4 – / 99 TcO 4 – from aqueous solution, with potential application for deep geological disposal.