Ligand‐Assistant Iced Photocatalytic Reduction to Synthesize Atomically Dispersed Cu Implanted Metal‐Organic Frameworks for Photo‐Enhanced Uranium Extraction from Seawater

Abstract

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...

Advanced Photocatalytic Uranium Extraction Strategies: Progress, Challenges, and Prospects

“…The experiments of extracting U(VI) from real seawater showed that uranium in seawater can be completely removed within 60 min, and the photocatalytic uranium reduction activity of ECUT-SO did not decrease significantly after three cycles, indicating the excellent practical value ( Figure 10 (Bd–Bf)). Although significant contributions were made in recent years to the development of photocatalytic materials for uranium extraction from seawater, it remains a challenge to develop a comprehensive photocatalytic system that meets the requirements for uranium extraction from seawater [ 119 , 120 ]. To develop more efficient photocatalytic materials for uranium extraction from seawater, the selective adsorption ability of catalysts for uranium in seawater should be regarded as an important factor.…”

Highly Selective Extraction of U(VI) from Solutions by Metal Organic Framework-Based Nanomaterials through Sorption, Photochemistry, and Electrochemistry Strategies

“…Figure 3c shows the photoreduction process of U(VI) by the Cu SAs and Zr-oxo clusters. Chen et al 65 Through tuning the electronic structure and charge transfer pathway 64 and adjusting the local charge distribution by optimizing the donor−acceptor structures, 66 the e − −h + pairs could be efficiently separated, and the charge could be quickly transported to the surface-sorbed U(VI), generating enough free active radicals to reduce U(VI) to form insoluble U(IV)O 2 . Yu et al 67 synthesized MnO x /UiO-66/Ti 3 C 2 T x photocatalyst with dual catalytic sites (i.e., MnO x and Ti 3 C 2 T x ).…”

“…Moreover, this material could produce a lot of reactive oxygen species (ROS) in the photocatalysis reaction which could kill marine bacteria effectively. Liu et al synthesized Cu-implanted UiO-66-NH 2 photocatalysts (Cu SA@UiO-66-NH 2 ). Low-temperature X-band electron paramagnetic resonance (EPR) (Figure b) showed that Cu­(II) and Zr­(IV) could be reduced to Cu­(I) and Zr­(III) by the light-generated electrons.…”

“…(a) Illustration of U­(VI) photoreduction by Zr/Ti-MOFs; (b) low-temperature X-band EPR spectra of Cu SA@UiO-66-NH 2 in various states; (c) schematic illustration of the proposed charge transfer path; (d) the U­(VI) photoreduction by MnO x /UiO-66/Ti 3 C 2 T x with different scavengers; (e) LSV curves of U­(VI) reduction; (f) EPR spectra of ·O 2 – radicals, (g) LSV curves of water oxidation; (h) EPR spectra of ·OH radicals; (i) schematic illumination of U­(VI) photoreduction by MnO x /UiO-66/Ti 3 C 2 T x under light irradiation. Part (a) is reprinted with permission from ref , Copyright 2022 Elsevier; (b) and (c) are reprinted with permission from ref , Copyright 2023 John Wiley and Sons; (d–i) are reprinted with permission from ref , Copyright 2022 John Wiley and Sons.…”

Photo‐enhanced uranium recovery from spent fuel reprocessing wastewater via S‐scheme 2D/0D C3N5/Fe2O3 heterojunctions

“…[8][9][10] Recently, a variety of semiconductor-based photocatalysts have been designed to re-extract U(VI) from the liquids through photoreduction processes. [11][12][13] Among them, constructing C 3 N 4 polymers based on 2D materials to control their optical, electronic, and chemical characteristics has gained significant attention for energy or environmental applications. [14][15][16][17][18] Based on the previous work, 19 introducing additional nitrogen-rich moieties into C 3 N 4 can further enhance the visible light absorption efficiency due to the synergistic effect between the azo structure (-N = N-) and the π-conjugated systems.…”