Photocatalytic Reduction of Perrhenate and Pertechnetate in a Strongly Acidic Aqueous Solution

Pertechnetate (⁹⁹TcO₄^-), a physiologically toxic radioactive anion, is of great concern due to its high mobility in environmental contamination remediation. Although the soluble oxyanion can be photoreduced to sparingly soluble TcO₂·nH₂O, its effective removal from a strongly acidic aqueous solution remains a challenge. Here, we found that low-crystalline nitrogen-doped titanium oxide (N-TiO₂, 0.6 g L^-1) could effectively uptake perrhenate (ReO₄^-, 10 mg L^-1, a nonradioactive surrogate for TcO₄^-) with 50.8% during 360 min under simulated sunlight irradiation at pH 1.0, but P25 and anatase could not. The nitrogen active center formed by trace nitrogen doping in N-TiO₂ can promote the separation and transfer of photogenerated carriers. The positive valence band value of N-TiO₂ is slightly higher than those of P25 and anatase, which means that the photogenerated holes have a stronger oxidizability. These holes are involved in the formation of strong reducing ^•CO₂^- radicals from formic acid oxidation. The active radicals convert ReO₄^- to Re(VI), which is subsequently disproportionated to Re(IV) and Re(VII). Effective photocatalytic reduction/removal of Re(VII)/Tc(VII) is performed on the material, which may be considered a potential and convenient strategy for technetium decontamination and extraction in a strongly acidic aqueous solution.