Efficient Photocatalytic Reduction of Aqueous Perrhenate and Pertechnetate

The pertechnetate anion ((TcO4-)-Tc-99) is a long-lived radioactive species that is soluble in aqueous solution, in contrast to sparingly soluble (TcO2)-Tc-99. Results are reported for photocatalytic reduction and removal of perrhenate (ReO4-), a nonradioactive surrogate for (TcO4-)-Tc-99, using a TiO2 (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 (CO2-) from oxidation of formic acid, not direct reduction by photogenerated electrons of TiO2. Recycling results indicate that photo catalytic reduction of ReO4- exhibits excellent regeneration and high activity with >95% removal even after five cycles. Tc-99(VII) is more easily reduced than Re(VII) in the presence of NO3- with very slow redissolution of reduced Tc-99. This study presents a novel method for the removal of ReO4-/(TcO4-)-Tc-99 from aqueous solution, with potential application for deep geological disposal.