Reduction Of Uranium Research Articles

Diketopyrrolopyrrole-triggered low exciton binding energy in D-A covalent organic framework for enhanced uranyl photoreduction

Construction of donor–acceptor covalent organic framework (D-A COFs) photocatalysts is regarded as promising path to promote photocatalytic reduction of uranium, but faces greater challenge due to high exciton binding energies (Eb). In this work, we construct a D-A COF (named Py-DPP-COF) with dye diketopyrrolopyrrole (DPP) unit as acceptor to minimize the Eb (56.5 meV). Importantly, experimental and computational studies reveal that DPP unit as adsorption and photocatalytic active sites play a pivotal role for catalyzing photoreduction of UVI to UIV. The Py-DPP-COF not only broadens the visible light absorption and promotes charge transfer, but also enhances interfacial mass transfer, achieving a higher uranium extraction capacity of 903.6 mg g−1. To our knowledge, this is the first application of DPP-based COFs for photocatalytic reduction of uranium, which greatly inspires the exploration of novel COFs photocatalysts for photo-induced radionuclide removal.

Engineering exciton dissociation and intermolecular charge transfer to boost superoxide radical in conjugated microporous polymers for simultaneous elimination of coexisting contaminants

Simultaneous photocatalytic elimination of coexisting contaminants with polymeric semiconductors are highly urgent for environmental purification. Nevertheless, the insufficient exciton dissociation and charge transfer in polymeric photocatalysts results in unsatisfactory photocatalytic performance. Herein, we proposed a sulfur-contained linkages engineering strategy via regulating donor–acceptor interactions to boost exciton dissociation and intermolecular charge transfer for efficient generation of superoxide radical. With the low exciton binding energy (50.11 meV) and short average lifetime (τavg‑TAS) of the photoinduced exciton (478.1 ps), the resultant BDT-Tr deriving from BDT and 2,4,6-tris(4-bromophenyl)-1,3,5-triazine exhibited efficient exciton dissociation and charge transfer, enabling superior photocatalytic degradation of ofloxacin (∼94.0 % in 2 h) than that of TTP-Tr (∼87 %) and DTT-Tr (∼76 %) when coupled with the uranium (VI) reduction (∼96.0 % in 1 h). This is the first work highlights the photocatalytic removal of coexisting aqueous pollutants with CMPs-based photocatalysts, which might facilitate the exploration of polymeric semiconductors for wastewater purification.

Constructing Stable Nitrogen-Rich Core-Shell CdS@MC for Photocatalytic Reduction of U(VI) in Air without Sacrificial Agent.

Photocatalytic reduction of uranium from U(VI) to U(IV) has been recognized as an effective treatment method for uranium wastewater. However, most photocatalysts have to be reduced under inert gas and sacrificial agent. Here, a class of nitrogen-rich core-shell photocatalysts (CdS@MC) with high stability was successfully prepared by modifying CdS with melamine and cyanuric chloride condensation. When the initial concentration of U(VI) was 100 mg/L and the solid-liquid ratio was 0.2 g/L, the removal of U(VI) by CdS@MC without sacrificial agent under air could reached 95%. The removal rate was still above 80% after five cycles with good stability and good removal rate of U(VI) at high salt concentration. CdS@MC not only efficiently generates electrons for photocatalytic reduction of U(VI), but also generates H2O2 from O2, which then reacts with uranyl ions to produce metastudtite. This study provides a new direction for the study of efficient uranium removal photocatalysts without sacrificial agent in air environment.

Tuning local charge polarization of covalent organic frameworks for enhanced photocatalytic uranium (VI) reduction

The introduction of local charge polarization is an effective strategy to improve the electrostatic potential difference of covalent organic frameworks (COFs) photocatalysts. Herein, BPDA-COF with donor–acceptor (D-A) structure was firstly synthesized by using triphenyl-triazine and biphenyl monomers. Subsequently, the hydroxyl and bis(2-methoxyethyl)ether (PEO)-chains with increasing local charge polarization were introduced to synthesize DHBD-COF and PEO-COF, respectively. PEO-COF with electronegative and flexible PEO-chains created a strong local charge polarization to enhance the electrostatic potential differences, thus promoting the spontaneous transfer of electrons and inhibiting the recombination of electrons and holes. Furthermore, the super-hydrophilic PEO-chains provided super-strong uranium mass transfer capacity. Benefiting from these, PEO-COF exhibited excellent photocatalytic uranium reduction capabilities (1427.9 mg g−1). This work provides a novel insight to adjust the local charge polarization at the molecular level and broadens the strategy of photocatalytic reduction of U(VI) with COFs.

Interface-Confined nanocatalysts at hollow porous nanofibers for High-Performance cascaded remediation of radioactive wastewater

The evolution of efficient remediation technologies for radioactive wastewater is crucial for the sustainable development of nuclear energy. The cascade strategy that combines adsorption and photocatalysis has emerged as one of the most ground-breaking approaches. However, the current composite materials are undesirable in practical applications due to the low interface exposures of nanocatalysts with limited light utilization, undesirable mass transfer as well as long free radical diffusion distances from photocatalytic sites to adsorption sites. Herein, we present the fabrication of hollow porous composite nanofibers (HPN) with high interface exposures of nanocatalysts and reduced mass transfer resistances via the interface-confined engineering by integrating coaxial electrospinning with non-solvent-induced phase separation. The hollow porous architecture effectively diminishes mass transfer resistance, leading to rapid adsorption and providing sufficient uranyl ions for the subsequent cascade photoreduction. Meanwhile, the high interface exposure of the nanocatalysts enables efficient uranium reduction, which serves to regenerate the adsorption sites for higher adsorption capacity as well as durable stability. Such an elegant architecture allows the HPN to achieve an over 2-fold improvement in removal rates than that of conventional composite nanofibers and removal ratios as high as 98.86 % within 270 min. The design concept and outstanding performance make it a promising and practical technology for the remediation of radioactive wastewater.

Precise Regulation of Interlayer Stacking Modes in Trinuclear Copper Organic Frameworks for Efficient Photocatalytic Reduction of Uranium(VI).

The interlayer stacking modes of 2D covalent-organic frameworks (COFs) directly influence their structural features, ultimately determining their functional output. However, controllably modulating the interlayer stacking structure in traditional 2D metal-free COFs, based on the same building blocks, remains challenging. Here, two trinuclear copper organic frameworks are synthesized successfully with different interlayer stacking structures: eclipsed AA stacking in Cu3-PA-COF-AA and staggered ABC stacking in Cu3-PA-COF-ABC, using the same monomers. Remarkably, various functionalities, including porosity and electronic and optical properties, can be effectively regulated by interlayer stacking. As a result, Cu3-PA-COF-AA and Cu3-PA-COF-ABC exhibit significantly different activities toward the photoreduction of U(VI), presenting a promising strategy for removing radioactive uranium pollution. Due to its broader visible-light absorption range and superior photogenerated carrier migration and separation efficiency, Cu3-PA-COF-AA achieves a U(VI) removal ratio of 93.6% without additional sacrificial agents in an air atmosphere-≈2.2 times higher than that of Cu3-PA-COF-ABC (42.0%). To the best of the knowledge, this is the first study to elucidate the effect of interlayer stacking in COFs on the photocatalytic activity of U(VI) reduction. This finding may inspire further exploration of the structure-function relationship in COFs as photocatalysts and their potential for photoinduced removal of radionuclides.

Synthesis of Quinone‐Amine‐Linked Covalent Organic Frameworks for Boosting the Photocatalytic Removal of Uranium

AbstractCompared to imine covalent organic frameworks (COFs), the superior stability of amine‐linked COFs renders them more suitable for long‐term harsh real‐world environments. Their numerous amine sites can serve as functional groups or be subjected to post‐modification to further enhance the performance of the material. However, the assortment and abundance of amine‐linked COFs via currently lacking due to restricted monomer varieties and synthetic methods. Herein, this study presents an innovative approach for synthesizing quinone‐amine‐linked COFs by directly combining 2,5‐dihydroxy‐1,4‐benzoquinone (DHBQ) with various amine monomers and introduce a novel photocatalyst, DHBQ‐TAPP‐COF, specifically tailored to efficiently reduce uranium in harsh environments. DHBQ‐TAPP‐COF features a unique donor–acceptor structure, with the DHBQ units serving as acceptors because they contain abundant oxygen atoms that facilitate metal ion coordination, thereby enhancing charge carrier separation, carrier utilization, and uranium reduction efficiency. The quinone‐amine linkages offer improved stability, extended π‐conjugation, heightened local polarity, and conductivity, which enable efficient carrier transfer within the material and thus enhance the overall performance of the uranium photocatalyst. The proposed photocatalyst can efficiently reduce U(VI) without sacrificial agents or decomposition to precipitate UO2 at a recovery rate exceeding 98%. This catalyst provides an efficient and convenient strategy for the stable and high‐performance photocatalytic reduction of uranium.

Catalytic Effect of Titanium Ions on the Cathodic Reduction of Selenium (VI), Copper (II), Uranium (VI) Ions and Other Metals in an Aqueous Solutions

It is known that catalytic processes are widely applied in the field of organic chemistry; however they also play a significant role in inorganic chemistry. Nonetheless, numerous unresolved issues persist in the technology of inorganic substances and the extraction of metals and nonmetals in their elemental states. This publication aims to consolidate the results of our pioneering research utilizing the redox Ti (IV)–Ti (III) system, which demonstrates a catalytic action on the cathodic reduction of selenium (VI), copper (II), platinum (IV), palladium (IV), bismuth, arsenic (V) ions, uranium (VI), as well as manganese dioxide suspension. It has been demonstrated that in the presence of the redox Ti (IV)–Ti (III) system, hard-to-reduce selenate ions can be reduced at room temperature. The catalytic action of the redox Ti (IV)–Ti (III) system has been reliably demonstrated, and the reaction mechanism has been established. In the electrochemical production of metal powders (Cu, Pt, Pd, Bi) at cathode current densities exceeding the limiting value, a portion of the current is irreversibly lost to the discharge of hydrogen ions. Consequently, the current efficiency (CE) for powder production does not exceed 80 %. We have established that in the presence of titanium (IV) ions, due to their catalytic action, the CE increases by more than 15 %. It has also been shown that during the cathodic polarization of hexavalent uranium its reduction to uranium (IV) in the presence of the catalyst increases by more than 50 %. The reduction of hard-to-reduce arsenate ions in the presence of titanium (IV) ions proceeds with high CE to the active trivalent state, and further reduction can proceed electrochemically. The cathodic reduction of a manganese dioxide suspension was investigated. In the presence of a catalyst — titanium (IV) ions, manganese in this dioxide is reduced to the divalent state with a current efficiency exceeding 90 %.

Kinetic Study and Process Optimization of Plutonium Barrier Units for Enhanced Plutonium Stripping in the PUREX Process

In the PUREX (the plutonium uranium reduction extraction) process, a plutonium barrier unit (1BXX) is used to achieve deep plutonium stripping. According to the operating experience of the French reprocessing plant, after the separation of uranium and plutonium in the first cycle (1B + 1BXX), the plutonium barrier unit has excellent stripping effect, such that the removal of plutonium from uranium can already be achieved in the first cycle, and the second cycle only needs to focus on the removal of neptunium from uranium in order to obtain a qualified uranium product. In recent decades, China has also been actively conducting research on the plutonium barrier unit process to reduce the plutonium concentration in the primary uranium product in the first cycle to avoid the need to remove neptunium and plutonium at the same time in the second cycle, and to improve the efficiency and feasibility of reprocessing. Due to the lack of design basis for plutonium barriers to achieve deep plutonium stripping at present, this study conducts a basic study on the plutonium barrier unit, aiming to provide data for the optimization of plutonium barriers in the actual reprocessing process at a later date. In this work, a kinetic study on the reduction and stripping of trace plutonium from dibutyl phosphate-containing organic phases was carried out first, and the kinetic equations for the reduction and stripping of Pu(IV) by U(IV) under flow process conditions were obtained. The effects of U(IV) addition on the extraction loss of U(IV) and the concentration distribution of U(IV) at various stages were investigated by process simulation. Additionally, the oxidation of U(IV) under process conditions was investigated to clarify the process chemistry of U(IV) oxidation and to provide a reference for the oxidation consumption of U(IV). Finally, the process parameters of the plutonium barrier unit were preliminarily designed based on the above research.

A synergistic bioelectrochemical-photocatalytic system for efficient uranium removal and recovery

Bioelectrochemical system (BES) is a promising technology for uranium recovery, which also enables simultaneous electricity generation. However, the bioelectrochemical recovery of uranium is hindered by its slow process due to the low reduction potential provided by microorganisms. Herein, we developed an innovative bioelectrochemical-photocatalytic system (BEPS) that combines the advantages of BES and photocatalysis, achieving enhanced uranium removal and recovery. The photogenerated electrons in BEPS possess a more negative reduction potential and stronger reduction capability than microbial electrons in BES, significantly accelerating uranium reduction and deposition on the electrode surface. Moreover, the electrons from the bioanode combine with photogenerated holes through the external circuit, effectively inhibiting the recombination of charge carriers. The BEPS significantly enhances uranium removal efficiency, kinetic, and electricity generation through a synergistic coupling mechanism between the bioanode and photocathode. Notably, the UO2 deposited on the electrode surface exhibited a recovery efficiency of 98.21 ± 1.37%, and the regenerated electrode sustained its photoelectric response and uranium removal capabilities. Our findings highlight the potential of the BEPS as an effective technology for uranium recovery and electricity generation.

Redox-active sp2-c connected metal covalent organic frameworks for selective detection and reductive separation of uranium

It is economically desirable to develop a material that can simultaneously detect and recover uranium. Herein, a CC-bridged two-dimensional metal-covalent organic framework (Cu-BTAN-AO MCOF) was constructed by condensation of metal single crystals with a rigid structure (Cu3(PyCA)3) and cyano monomers (BTAN) via Knoevenagel reaction for simultaneous detection and adsorption of uranium. The amidoxime group within the pore and the presence of unsaturated Cu(I) in the framework facilitate the adsorption of uranyl ions onto the amidoxime group, leading to fluorescence quenching via the photoinduced electron transfer (PET) mechanism, achieving a detection limit of as low as 167 nM uranyl ions. Furthermore, Cu-BTAN-AO demonstrates exceptional efficiency in capturing uranium from wastewater characterized by rapid kinetics and superior selectivity. It is noteworthy that Cu-BTAN-AO is the first example of simultaneous detection, adsorption and chemical reduction of uranium using metal centers and functional groups in MCOF, indicating that Cu-BTAN-AO has great potential for the detection and recovery of uranium-containing wastewater. This design strategy may also be applicable to advancing sensing and energy materials for other important metal ions.

Regulatory roles of extracellular polymeric substances in uranium reduction via extracellular electron transfer by Desulfovibrio vulgaris UR1

The pathway of reducing U(VI) to insoluble U(IV) using electroactive bacteria has become an effective and promising approach to address uranium-contaminated water caused by human activities. However, knowledge regarding the roles of extracellular polymeric substances (EPS) in the uranium reduction process involving in extracellular electron transfer (EET) mechanisms is limited. Here, this study isolated a novel U(VI)-reducing strain, Desulfovibrio vulgaris UR1, with a high uranium removal capacity of 2.75 mM/(g dry cell). Based on a reliable EPS extraction method (45 °C heating), manipulation of EPS in D. vulgaris UR1 suspensions (removal or addition of EPS) highlighted its critical role in facilitating uranium reduction efficiency. On the second day, U(VI) removal rates varied significantly across systems with different EPS contents: 60.8% in the EPS-added system, 48.5% in the pristine system, and 22.2% in the EPS-removed system. Characterization of biogenic solids confirmed the reduction of U(VI) by D. vulgaris UR1, and the main products were uraninite and UO2 (2.88–4.32 nm in diameter). As EPS formed a permeable barrier, these nanoparticles were primarily immobilized within the EPS in EPS-retained/EPS-added cells, and within the periplasm in EPS-removed cells. Multiple electroactive substances, such as tyrosine/tryptophan aromatic compounds, flavins, and quinone-like substances, were identified in EPS, which might be the reason for enhancement of uranium reduction via providing more electron shuttles. Furthermore, proteomics revealed that a large number of proteins in EPS were enriched in the subcategories of catalytic activity and electron transfer activity. Among these, iron-sulfur proteins, such as hydroxylamine reductase (P31101), pyruvate: ferredoxin oxidoreductase (A0A0H3A501), and sulfite reductase (P45574), played the most critical role in regulating EET in D. vulgaris UR1. This work highlighted the importance of EPS in the uranium reduction by D. vulgaris UR1, indicating that EPS functioned as both a reducing agent and a permeation barrier for access to heavy metal uranium.

Ferrocene-based 2D metal–organic framework nanosheet for highly efficient photocatalytic seawater uranium recovery

Sustainable uranium supply is critical for the long-term development of nuclear energy. The photocatalytic reduction of soluble hexavalent uranium to insoluble tetravalent uranium using photocatalysts has been recognized as a highly promising method for uranium recovery. However, existing photocatalysts face limitations such as restricted visible-light absorption and poor charge transfer capability, which hinder their photocatalytic uranium recovery performance. In this work, 1,1′-ferrocene dicarboxylic acid (FcDA) was introduced to synthesize the photocatalyst Zr-Fc-MOF3. The incorporation of FcDA broadened the visible light absorption range and reduced the band gap of Zr-Fc-MOF3, thereby enhancing electron-hole pair separation and carrier transport efficiencies. Moreover, the two-dimensional (2D) nanosheet structure of Zr-Fc-MOF3 provided a large surface area, allowing full exposure of active sites. Additionally, Fe(II) in FcDA generated photoelectrons upon light excitation to facilitate uranium reduction, and the recyclable redox behavior of Fe(II) conferred high reusability of the photocatalyst. Consequently, Zr-Fc-MOF3 demonstrated a high photocatalytic uranium recovery capacity of 8.29 mg g−1 over 10 days in natural seawater (NSW), with a uranium recovery rate of 0.829 mg g−1 d−1, surpassing most other photocatalysts applied in NSW. These findings suggest that designing 2D nanosheet materials with ligands capable of efficient photoelectron generation is a promising approach for developing high-performance uranium recovery photocatalysts.

Oxygen vacancy-mediated activation of Zn-O bonds at the S-scheme heterostructure interface for efficient uranium collection and resistance to biological contamination

Efficient reduction of U(VI) to U(IV) during seawater uranium extraction remains a challenge. Here, cerium dioxide quantum dots were bonded to the surface of indium zinc sulfide (ZIS) to form ZIS composite cerium dioxide quantum dots (ZIS/QDs-Ce). The oxygen vacancies are able to activate the Zn-O bonds at the ZIS and QDs-Ce interfaces, thus enabling the constructed S-scheme heterojunction to show great potential in facilitating the separation and transfer of photogenerated carriers. ZIS/QDs-Ce exhibited high anti-bio-pollution activity by generating biotoxic free radical reactive oxygen species (ROS). The photo-induced reduction of uranium by ZIS/QDs-Ce in 10 ppm uranium spiked simulated seawater reached 99.6 %. Oxygen vacancies cause distortions in the crystal field, and the Zn-O bond activation process triggers the movement of ZIS/QDs-Ce from the singlet low-spin state to the stable triplet state, resulting in free-carrier trapping centers and optimized electronic energy band structures. ZIS/QD-Ce has superior uranium extraction capabilities and is highly recommended for uranium extraction from seawater.

Effective charge separation in CdS@PANI heterostructure for ultrafast visible light-driven photocatalytic reduction of uranium(VI)

The efficient treatment of uranium-containing wastewater provides guarantee for sustainable development of nuclear energy. In this work, a heterogeneous interface structure for photocatalytic reduction of U(VI) was proposed by in-situ decoration of cadmium sulfide (CdS) nanoparticles on polyaniline (PANI) nanorods. The strong coupling between CdS and PANI precisely modulated the interface electronic structure, which promoted the photogenerated charge separation. Multiple spectroscopic characterizations revealed that the interfacial charge polarization with the electrons gathering at the CdS surface and the holes gathering at the PANI, facilitating the performance of photocatalytic reduction of U(VI) under visible light irradiation. The optimal CdS@PANI-10 shows ultrafast U(VI) reduction with efficiency of over 96 % in 5 min. Moreover, the photocatalytic reduction of U(VI) over CdS@PANI-10 can also be activated by direct natural sunlight irradiation. The improvement of catalytic activity of CdS@PANI nanocomposite is due to faster charge separation and migration at the interface between CdS and PANI, as well as the formation of Type-II heterojunction, which was also beneficial for suppressing the CdS photocorrosion. This work introduces a potential strategy to design advanced photocatalysts with efficient electrons and holes separation toward practical application in uranyl ion conversion.

A self-driven solar coupling system with activated carbon felt cathode for resourcefully purifying uranium and organic contaminated water

With the continuous development of nuclear energy, it becomes increasingly important to recover uranium from the radioactive wastewater, in which various organics may combine with uranyl ions (UO22+) to form refractory complexes. Developing highly active cathode materials for uranium reduction is essential to improve the performance of self-driven solar coupling system (SSCS) in treating complex radioactive wastewater. In this study, an activated carbon felt (ACF) cathode is prepared by anodizing carbon felt (CF) in NaOH solution to adjust the surface morphology and functional groups. The ACF is then used in a SSCS combined with a TiO2 nanorods array (TNA) photoanode for the efficient recovery of uranium and the rapid degradation of organic pollutants with simultaneous electricity generation. Compared to CF, the functionalized ACF with oxygen-containing functional groups, provides sufficient sites for UO22+ adsorption and facilitates the charge separation. The SSCS with the ACF cathode exhibits removal ratios of approximately 99.9 % for tetracycline hydrochloride (TCH) and UO22+, with removal rates of ∼ 0.025 and ∼ 0.154 min−1, respectively. In contrast, the SSCS with the CF cathode achieves removal rates of ∼ 0.006 and ∼ 0.026 min−1. Additionally, a maximum power density of 0.94 mW·cm−2 with a fill factor of 23.36 % is achieved. After 20 cycles, the system maintains removal ratios of 99.1 % for TCH and 98.2 % and UO22+. Intensive investigation also reveals that the system functions robustly in treating complex wastewater with a complicated condition of pH, co-exited ions, and various pollutant concentrations. Furthermore, efficient removal of organics and uranium is also achieved from polluted seawater or under real sunlight illumination. This paper presents a simple method to prepare low-cost, highly active and stable cathodes for uranium reduction in an easy-to-operated, energy-saving and economical solar-driven system.

Co/N-codoped carbon nanoplate array coated carbon fiber cathode for solar driven uranium extraction from complex radioactive wastewater

Organics bring great challenge on uranium reduction due to the formation of stubborn complexes between uranyl ions (UO22+) and organics. Herein, we developed an effective strategy to synchronously degrade organics and extract uranium from complicated radioactive wastewater, accompanied with electricity generation, by a novel self-driven photocatalytic fuel cell (NSPFC) system, in which a three-dimensional (3D) Co/N-doped carbon nanoplate array (Co-N-C/CF) decorated carbon fiber is employed as the cathode for highly efficient UO22+ reduction. Compared to pure CF, the optimized Co-N-C/CF cathode increases the rate constants (k) by 9 and 9.1 times for UO22+ and organic elimination, respectively, and improves electricity output by 2 times (Pmax, 1180 μW/cm2). This improvement should be ascribed to the 3D morphology of Co-N-C/CF that provided plenty of surface area for U(VI) reduction, and the doping of N and Co, which effectively increased the U(VI) adsorption sites and optimized the electron behavior on the cathode, respectively. These features endow the NSPFC system with excellent adaptability in treating complex radioactive wastewater with a wide range of pollutant concentration, pH, co-existed ions, pollutant organics and natural organic matters. Fascinating activity is also achieves in treating polluted seawater or under real sunlight illumination. This work not only provides a outstanding nanostructured cathode for uranium reduction but also suggests a charming system to resourcefully treatment of radioactive wastewater or polluted water bodies.

One-step synthesis of O, P co-doped g-C3N4 under air for photocatalytic reduction of uranium

The photocatalytic reduction of uranium from nuclear wastewater represents a promising method for both uranium extraction and environmental remediation. This approach facilitates the recovery of uranium resources for the nuclear industry while addressing environmental pollution. Despite significant research advancements, there remains a need for cost-effective and environmentally friendly catalytic materials. In this context, we present a two non-metal O, P co-doped g-C3N4 (OPCN) synthesized via a simple one-step thermo-polymerization in air. OPCN demonstrates a high uranium reduction efficiency of 94.9 % under white LED light illumination. Even after five cycles, OPCN maintained a reduction efficiency of 81.7 %, highlighting its stability and reusability. Additionally, OPCN also performs effectively in uranium reduction under natural sunlight and exhibits impressive antimicrobial properties. These features position OPCN as a promising candidate for practical environmental applications.

Covalent triazine framework nanosheets for photo-enhanced uranium extraction

Uranium extraction is the cornerstone of the sustainable development of the nuclear industry. Although a variety of porous framework materials for uranium extraction have been explored over the past few decades, almost all of them have been limited to bulk powder materials. In particular, due to the strong interlayer π-π interaction, the specific recognition sites and photocatalytic active centers of bulk two-dimensional framework materials are severely buried, resulting in the inability to exploit the optimal performance of the materials. In this study, a novel hydroquinone modified covalent triazine frame nanosheets (H-CTF-NSs) is reported for the first time, which is designed for specific extraction and photocatalytic reduction of uranium. The densely distributed hydroquinone and triazine units in the H-CTF-NSs synergistically form high-affinity binding sites, and the ultrathin nanosheets facilitate the exposure of binding sites and catalytically active centers, and accelerate the diffusion of uranyl ions, it is ideally suited as an advanced platform for the selective extraction and efficient reduction of U(VI). Remarkably, H-CTF-NSs demonstrated an unprecedented uranium extraction capacity of 3230.3 mg/g, which is almost 1.71 times that of its bulk counterpart H-CTF, making it one of the best uranium-trapping photocatalysts known to date.

Synergistic enhancement of NC-GCN/Ag2O photocatalytic reduction of uranium by D-A and p-n junction structures

Recently, how to improve the photocatalytic uranium removal performance of Graphite-phase carbon nitride (GCN) has always been a hot research topic. In this paper, a new strategy based on p-n junction and D-A structure is proposed to improve the photocatalytic performance. And as a result, a novel cyano modified photocatalytic material NC-GCN/Ag2O was designed and prepared for the reduction of U(VI). Interestingly, the material shows better adsorption performance for U(VI) in the dark treatment stage, and its removal of U(VI) is close to 70 % under the initial U(VI) concentration of 20 ppm and the solid–liquid ratio of 0.2 g/L. And the adsorption is in accordance with the Langmuir model and Pseudo second order model. After 30 min of illumination, the removal rate of U(VI) can reach 93.2 %, significantly higher than that of GCN (13.6 %) and NC-GCN10(37.7 %). It’s worth mentioning that photocatalytic reduction dominated the adsorption-reduction process for U(VI) removal after light exposure. In addition, after four cycles, the removal of U(VI) from the composite material decreased by only 5 % with no change in the crystal structure, i.e., it has good reusability and stability. Meanwhile, there was no significant interference with other ions except for Cu2+ and V5+, which had a weak interference. Finally, a new mechanism for U(Ⅵ) reduction was proposed.