and natural seawater. [5] Recently, porous framework materials (e.g., metal-organic framework (MOF), [6] covalent organic framework (COF), [7] hydrogen-bonded organic framework (HOF) [8] ) have been developed for uranium uptake by combination of ligand complexation and photocatalytic reduction. Most photocatalysts still suffer from inefficient ligand-tometal charge transfer (LMCT), [9] which severely restrict the photocatalytic activity. Recently, single-atom (SA) catalysts have attracted considerable research interest in heterogeneous catalysis over the recent years. [10] Some studies have reported a continuous decrease in catalytic activity with increasing particle size. [11] Hence, it is of great significance to rationally design and control the synthesis of monodispersed metal at the atomic level. Inspired by the iced-photochemical synthesis, [12] we developed ligand-assistant frozen photoreduction approach to anchor atomically dispersed Cu on aminofunctionalized Zr-MOF (Cu SA@UiO-66-NH 2 ). High angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy measurements confirm the atomically dispersed Cu in the form of N-Cu-N. By contrast, there are Cu nanoclusters decorated on UiO-66-NH 2 support (Cu Clu@UiO-66-NH 2 ) by the routine photochemical solution-phase reaction. Compared to the agglomerated active sites, isolated dispersed Cu sites contribute to higher photocatalytic activity, which endow Cu SA@UiO-66-NH 2 adsorbent with enhanced photoreduction-assistant uranium extraction performance from natural seawater together with superior antibacterial ability.
Results and Discussion
Synthesis and Structure CharacterizationUiO-66-NH 2 crystals were synthesized by the traditional solvothermal method [13] and then employed as the catalyst support. The Cu SA@UiO-66-NH 2 sample was prepared through ligandassistant iced photocatalytic reduction route, as illustrated in Uranium extraction from natural seawater is one of the most promising routes to address the shortage of uranium resources. By combination of ligand complexation and photocatalytic reduction, porous framework-based photocatalysts have been widely applied to uranium enrichment. However, their practical applicability is limited by poor photocatalytic activity and low adsorption capacity. Herein, atomically dispersed Cu implanted UiO-66-NH 2 (Cu SA@UiO-66-NH 2 ) photocatalysts are prepared via ligand-assistant iced photocatalytic reduction route. N-Cu-N moiety acts as an effective electron acceptor to potentially facilitate charge transfer kinetics. By contrast, there exist Cu sub-nanometer clusters by the typical liquid phase photoreduction, resulting in a relatively low photocatalytic activity. Cu SA@UiO-66-NH 2 adsorbents exhibit superior antibacterial ability and improved photoreduction conversion of the adsorbed U(VI) to insoluble U(IV), leading to a high uranium sorption capacity of 9.16 mg-U/g-Ads from natural seawater. This study provides new insight for enhancing uranium...