Search

Abstract Recent studies have shown that aqueous U(VI) ions can be transformed into U(VI) precipitates through electrocatalytic redox reactions for uranium recovery. However, there have been no reports of U(IV) solids, such as UO2, using electrochemical methods under ambient conditions since low-valence states of uranium are typically oxidized to U(VI) by O2 or H2O2. Here we developed a secondary metal ion-induced strategy for electrocatalytic production of U(IV) solids from U(VI) solutions using a catalyst consisting of atomically dispersed gallium on hollow nitrogen-doped carbon capsules (Ga-Nx-C). This method relies on the presence of secondary metal ions, e.g., alkaline earth metals, transition metals, lanthanide metals, and actinide metals, which promote the generation of UO2 or bimetallic U(IV)-containing oxides through a two-electron transfer process. No U(IV) solid products were generated in the presence of alkali metal ions. Mechanistic studies revealed that the strong binding affinity between U(IV) and alkaline earth metals (Ca2+/Mg2+/Sr2+/Ba2+), transition metals (Ni2+/Zn2+/Pb2+/Fe3+, etc.) and lanthanide/actinide metals (Ce4+/Eu3+/Th4+/La3+) suppressed re-oxidation of U(IV) to U(VI), leading to the generation of U(IV)O2 and Mx(M = Ce, Eu, Th, La)U(IV)yO2. This work provides fundamental insights into the electrochemical behavior of uranium in aqueous media, whilst guiding uranyl capture from nuclear waste and contaminated water.

Abstract Radioiodine capture from nuclear fuel waste and contaminated water sources is of enormous environmental importance, but remains technically challenging. Herein, we demonstrate robust covalent organic frameworks (COFs) with antiparallel stacked structures, excellent radiation resistance, and high binding affinities toward I2, CH3I, and I3 − under various conditions. A neutral framework (ACOF-1) achieves a high affinity through the cooperative functions of pyridine-N and hydrazine groups from antiparallel stacking layers, resulting in a high capacity of ~2.16 g/g for I2 and ~0.74 g/g for CH3I at 25 °C under dynamic adsorption conditions. Subsequently, post-synthetic methylation of ACOF-1 converted pyridine-N sites to cationic pyridinium moieties, yielding a cationic framework (namely ACOF-1R) with enhanced capacity for triiodide ion capture from contaminated water. ACOF-1R can rapidly decontaminate iodine polluted groundwater to drinking levels with a high uptake capacity of ~4.46 g/g established through column breakthrough tests. The cooperative functions of specific binding moieties make ACOF-1 and ACOF-1R promising adsorbents for radioiodine pollutants treatment under practical conditions.

Removing trace amounts of acetylene (C2H2) from ethylene (C2H4)-rich gas mixtures is vital for the supply of high-purity C2H4 to the chemical industry and plastics sector. However, selective removal of C2H2 is challenging due to the similar physical and chemical properties of C2H2 and C2H4. Here, we report a “single-molecule trap” strategy that utilizes electrostatic interactions between the one-dimensional (1D) channel of a covalent organic framework (denoted as COF-1) and C2H2 molecules to massively enhance the adsorption selectivity toward C2H2 over C2H4. C2H2 molecules are immobilized via interactions with the O atom of C=O groups, the N atom of C≡N groups, and the H atom of phenyl groups in 1D channels of COF-1. Due to its exceptionally high affinity for C2H2, COF-1 delivered a remarkable C2H2 uptake of 7.97 cm3/g at 298 K and 0.01 bar, surpassing all reported COFs and many other state-of-the-art adsorbents under similar conditions. Further, COF-1 demonstrated outstanding performance for the separation of C2H2 and C2H4 in breakthrough experiments under dynamic conditions. COF-1 adsorbed C2H2 at a capacity of 0.17 cm3/g at 2,000 s/g when exposed to 0.5 ml/min C2H4-rich gas mixture (99% C2H4) at 298 K, directly producing high-purity C2H4 gas at a rate of 3.95 cm3/g. Computational simulations showed that the strong affinity between C2H2 and the single-molecule traps of COF-1 were responsible for the excellent separation performance. COF-1 is also robust, providing a promising new strategy for the efficient removal of trace amounts of C2H2 in practical C2H4 purification.

Abstract The selective removal of the β‐emitting pertechnetate ion (99TcO4−) from nuclear waste streams is technically challenging. Herein, a practical approach is proposed for the selective removal of 99TcO4− (or its surrogate ReO4−) under extreme conditions of high acidity, alkalinity, ionic strength, and radiation field. Hollow porous N‐doped carbon capsules loaded with ruthenium clusters (Ru@HNCC) are first prepared, then modified with a cationic polymeric network (R) containing imidazolium‐N+ units (Ru@HNCC‐R) for selective 99TcO4− and ReO4− binding. The Ru@HNCC‐R capsules offer high binding affinities for 99TcO4−/ReO4− under wide‐ranging conditions. An electrochemical redox process then transforms adsorbed ReO4− to bulk ReO3, delivering record‐high removal capacities, fast kinetics, and excellent long‐term durability for removing ReO4− (as a proxy for 99TcO4−) in a 3 m HNO3, simulated nuclear waste‐Hanford melter recycle stream and an alkaline high‐level waste stream (HLW) at the U.S. Savannah River Site (SRS). In situ Raman and X‐ray absorption spectroscopy (XAS) analyses showed that adsorbed Re(VII) is electrocatalytically reduced on Ru sites to a Re(IV)O2 intermediate, which can then be re‐oxidized to insoluble Re(VI)O3 for facile collection. This approach overcomes many of the challenges associated with the selective separation and removal of 99TcO4−/ReO4− under extreme conditions, offering new vistas for nuclear waste management and environmental remediation.

Covalent organic frameworks (COFs) represent an emerging class of organic photocatalysts but it remains challenging to gain insight into photocatalytic active sites and reaction mechanisms. Herein, the authors construct a family of isoreticular crystalline hydrazide-based COF photocatalysts, with the optoelectronic properties and local pore characteristics of the COFs modulated using different linkers

Abstract Seawater contains uranium at a concentration of ≈3.3 ppb, thus representing a rich and sustainable nuclear fuel source. Herein, an adsorption–electrocatalytic platform is developed for uranium extraction from seawater, comprising atomically dispersed indium anchored on hollow nitrogen‐doped carbon capsules functionalized with flexible amidoxime moieties (In–Nx–C–R, where R denotes amidoxime groups). In–Nx–C–R exhibits excellent uranyl capture properties, enabling a uranium removal rate of 6.35 mg g−1 in 24 h, representing one of the best uranium extractants reported to date. Importantly, In–Nx–C–R demonstrates exceptional selectivity for uranium extraction relative to vanadium in seawater (8.75 times more selective for the former). X‐ray absorption spectroscopy (XAS) reveals that the amidoxime groups serve as uranyl chelating sites, thus allowing selective adsorption over other ions. XAS and in situ Raman results directly indicate that the absorbed uranyl can be electrocatalytically reduced to an unstable U(V) intermediate, then re‐oxidizes to U(VI) in the form of insoluble Na2O(UO3·H2O)x for collection, through reversible single electron transfer processes involving InNx sites. These results provide detailed mechanistic understanding of the uranium extraction process at a molecular level. This work provides a roadmap for the adsorption–electrocatalytic extraction of uranium from seawater, adding to the growing suite of technologies for harvesting valuable metals from the earth's oceans.

Fe2O3–ZrO2 catalysts with different morphologies (nanoplates (HZNPs), nanorods (HZNRs), nanocubes (HZNCs), and nanotubes (HZNTs)) were prepared by a hydrothermal method to investigate the effect of the morphology on the catalytic performance in the Fenton-like reaction for sulfamethazine (SMT) degradation. The Fe2O3–ZrO2 catalysts were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analysis. The H2O2 adsorption and the Fe2+ density sites on the Fe2O3–ZrO2 catalysts had a close relationship with the morphologies and exhibited an important effect on the ·OH formation in the Fenton-like reaction. Free ·OH radicals were the main oxidative species in the reaction, and the normalized ·OH concentration per surface area of the catalysts was 4.52, 2.24, 2.20, and 0.37 μmol/m2 for HZNPs, HZNRs, HZNCs, and HZNTs, respectively. The Fe2O3–ZrO2 catalysts with different morphologies showed good catalytic performance, and the order of SMT degradation was HZNPs > HZNRs > HZNCs > HZNTs. Total SMT removal was achieved in the Fenton-like reaction over HZNPs at pH 3.0 and 45 °C after 240 min.

Wheat (Triticum aestivum L.) is one of the most important staple food crops, and its sustained production and nutritional security have attracted much attention. Cadmium, a heavy metal toxic to plants and humans, can enter wheat in various ways. Foliar fertilization can reduce the cadmium content in plants, but how different fertilizers reduce the cadmium toxicity of plants is still unclear. In this study, the effects of foliar application of fertilizers on spring wheat yield, cadmium accumulation, and trace element contents were studied by applying three kinds of fertilizers (multi-element compound fertilizer, manganese-zinc micro fertilizer, and foliar silicon fertilizer) to spring wheat planted in mildly and moderately cadmium polluted areas. The results showed that the yield of wheat when fertilized with multi-element compound fertilizer, manganese-zinc micro fertilizer, and silicon fertilizer increased by 17.1%, 15.7%, and 16.9%, respectively, compared with the control. In addition, all three foliar fertilizers reduced the cadmium content in wheat grains to below the standard value of food pollutants (≤0.1mg/kg), and significantly reduced the transport of cadmium from glume to grain, among which manganesezinc micro fertilizer had the best effect, with a cadmium reduction rate of 41.7%. At the same time, manganese-zinc micro fertilizer significantly increased the absorption of trace elements in wheat organs. These results indicated that the foliar application of manganese-zinc micro fertilizer could be an effective way to increase wheat yield, inhibit cadmium accumulation, and increase nutrient absorption in mildly to moderately cadmium-polluted areas. [ABSTRACT FROM AUTHOR]