Enhanced uranium separation by charge enabling γ-MnO₂ with oxygen vacancies

Numerous efforts have been devoted to understanding the electron transfer process of uranium (UO₂²⁺) on adsorbent materials, whereas the potential oxygen vacancies (OVs) in metal oxides have long been overlooked. Once these interactions are taken into account, the emerging molecular orbital effects undoubtedly affect the adsorption process. Here, we synthesized CC/γ-MnO₂ by growing MnO₂ on carbon cloth (CC), followed by the creation of oxygen vacancies (OVs) through electrochemical methods to form CC/γ-MnO₂-OVs. The CC/γ-MnO₂-OVs shows significantly enhanced selectivity and durability for UO₂²⁺, with the maximum adsorption capacity increasing from 456.8 to 1648.1 mg/g (by a factor of 3.6). Theoretical calculations suggest that the generation of OVs leads to an increase in charge transfer and a decrease in adsorption energy between UO₂²⁺ and CC/γ-MnO₂, due to the interaction between Mn 3d orbital in CC/γ-MnO₂ and O 2p orbital in UO₂²⁺. The OVs in CC/γ-MnO₂ provide a spatial structure for anchoring the OU=O moiety of UO₂²⁺, while the surface van der Waals forces and the formation of chemical bonds between Mn-U contribute to charge interactions. This synergistic effect allows CC/γ-MnO₂-OVs to exhibit favorable selectivity, a large adsorption capacity, and rapid adsorption kinetics towards uranyl ions. This work achieves enhanced UO₂²⁺ separation by introducing OVs in CC/γ-MnO₂ through a facile electrochemical strategy, highlighting the great potential for nuclear waste processing.