Is the sacrificial agent really just a sacrificial agent? A case study on the photocatalytic reduction of U(VI) by alcohols

Photochemical reduction of U(VI) with methanol. [Display omitted] •Alcohols can directly reduce U(VI) with a high efficiency of 98% without a catalyst.•UO2, formaldehyde, and H+ are the final products of the photocatalytic reaction.•Water produces •OH, which attacks the intermediates of alcohols and U(VI).•This work reveals that a sacrificial agent may not be just a sacrificial agent during photocatalysis. Although organic sacrificial agents are often used to improve the efficiency of photocatalytic reactions, the impact of their existence on the performance evaluation of photocatalysts has not been analyzed yet. In this study, to clearly understand the role of organic sacrificial agents in the photocatalytic process, the photocatalytic reduction of hexavalent uranium (U(VI)) by alcohols is systematically analyzed. The results reveal that under the conditions of pH 5, nitrogen atmosphere, visible light irradiation, and no photocatalyst, the alcohol sacrificial agents can directly reduce U(VI) with efficiencies as high as 98%. Uranium dioxide, formaldehyde, and hydrogen ion are identified as the final products of the photocatalytic reaction, and the reaction mechanism is proposed based on the results of electron paramagnetic resonance (EPR) spectroscopy. Accordingly, it is inferred that alcohol as an organic sacrificial agent markedly interferes with the performance evaluation of photocatalysts during the photocatalytic reduction of U(VI). Overall, this study provides valuable insights into the actual role of sacrificial agents in the photocatalytic reduction process.