Unveiling the Critical Role of Surface Hydroxyl Groups for Electro-Assisted Uranium Extraction from Wastewater.

The electro-driven extraction of uranium from fluorine-containing uranium wastewater is anticipated to address the challenge of separating fluoro-uranium complexes in conventional technologies. Herein, we developed hydroxy-rich cobalt-based oxides (CoO x ) for electro-assisted uranium extraction from fluorine-containing wastewater. Relying on theoretical calculations and other spectral measurements, the hydroxy-rich CoO x nanosheets can enhance the affinity for uranium due to the existence of a substantial quantity of hydroxyl groups. Accordingly, the CoO x nanosheets exhibit outstanding U(VI) removal efficiency in the presence of fluorine ions. Through the utilization of X-ray absorption fine structure (XAFS), we confirm that hydroxy-rich CoO x nanosheets capture free uranyl ions to form a sturdy 2O ax -1U-3O eq configuration, which can be achieved through electro-driven fluorine-uranium separation. Notably, for the first time, the whole reaction process of uranium species on the CoO x surface from the initial uranium single atom growth to uranium oxide nanosheets is monitored by aberration-corrected transmission electron microscopes (AC-TEM). This work provides a paradigm for the advancement of novel functional materials as electrocatalysts for uranium extraction, as well as a new approach for studying the evolution mechanism of uranium species.