Sunflower (Helianthus annuus) can potentially be used for uranium (U) phytoremediation. However, the factors influencing the absorption of U and its subsequent distribution within plant tissues remain unclear, including the effect of silicon (Si) which is known to increase metal tolerance. Here, using hydroponics, the effect of Si on the distribution and speciation of U in sunflower was examined using synchrotron-based X-ray fluorescence and fluorescence-X-ray absorption near-edge spectroscopy. It was found that ∼88 % of U accumulates within the root regardless of treatments. Without the addition of Si, most of the U appeared to bind to epidermis within the roots, whereas in the leaves, U primarily accumulated in the veins. The addition of Si alleviated U phytotoxicity and decreased U concentration in sunflower by an average of 60 %. In the roots, Si enhanced U distribution in cell walls and impeded its entry into cells, likely due to increased callose deposition. In the leaves, Si induced the sequestration of U in trichomes. However, Si did not alter U speciation and U remained in the hexavalent form. These results provide information on U accumulation and distribution within sunflower, and suggest that Si could enhance plant growth under high U stress.

Uranium pollution in aquatic ecosystems poses a threat to organisms. However, the metabolism and toxicity of uranium along aquatic food chains remain unknown. Here, we established an artificial aquatic ecosystem to investigate the fate of uranium along the food chain and reveal its potential toxicity. The results displayed a dose- and time-dependent toxicity of uranium on algae, leading to cell deformation and impeding cell proliferation. When uranium-exposed algae are ingested by fish, uranium tends to concentrate in the intestinal system and bones of fish. Comparatively, direct water uranium exposure resulted in a remarkable uranium accumulation in the head, skin, and muscles of fish, suggesting different toxicity depending on distinct exposure pathways. High-level uranium pollution (20 mg L-1) intensifies the toxicity to fish through food intake compared to direct water exposure. It has also revealed that approximately 25 % and 20 % of U(VI) were reduced to lower valence forms during its accumulation in algae and fish, respectively, and over 10 % of U(IV, VI) converted to U(0) ultimately, through which uranium toxicity was mitigated due to the lower solubility and bioavailability. Overall, this study provides new insights into the fate of uranium during its delivery along the aquatic food chain and highlights the risks associated with consuming uranium-contaminated aquatic products.

Uranium is the most important fuel for nuclear power operations, and the safe supply of its resources is the key to the development of nuclear power in China. Because of the complex seawater environment and extremely low uranium concentration, extracting uranium from natural seawater poses a significant challenge. In this study, a polyamidoxime-phosphorylated cellulose nanofibril composite aerogel was prepared as an adsorbent for uranium extraction from seawater. An adsorption kinetics test, equilibrium adsorption isotherm model fitting, an adsorption-desorption cycle test, and a selectivity test were carried out to evaluate the adsorption performance of the composite aerogel for uranium extraction. The adsorption capacities for the initial concentrations of 4 and 8 ppm in uranium-spiked pure water were 96.9 and 204.3 mg-U/g-Ads, respectively. The equilibrium uranium adsorption capacities of uranium-spiked simulated seawater were 38.9 and 51.7 mg-U/g-Ads, respectively. The distribution coefficient KD of uranium was calculated to be 2.5 × 107 mL/g. The results show that the polyamidoxime-phosphorylated cellulose nanofiber composite aerogels prepared in this study have the advantages of low cost and high uranium selectivity for uranium extraction from seawater.

Graphitic carbon nitride (CN) as an adsorbent exhibit promising potential for the removal of uranium in water. However, the lack of active sites seriously restricts its practical application. In contrast to the traditional method of introducing new ligands, we propose a strategy to activate original ligands on CN by injecting π electrons, which can be realized by grafting 4-phenoxyphenol (PP) on CN (PCN). Compared with CN, the maximum adsorption capacity of PCN for uranium increased from 150.9 mg/g to 380.6 mg/g. Furthermore, PCN maintains good adsorption properties over a wide range of uranium concentrations (1 ∼ 60 mg/L) and pH (4 ∼ 8). After 5 consecutive cycles, PCN exhibited sustained uranium removal performance with a little of losses. The experimental and theoretical results show that the enhancement of adsorption performance is mainly due to the ligands activation of CN by delocalization of π electrons from PP. Furthermore, this activation can be enhanced by irradiation, as the CN can be photoexcited to provide additional photoelectrons for PP. As a result, dormant ligands such as N-CN, C-O-C, C-N-H and N-(C)3 can be activated to participate in coordination with uranium. This work provides theoretical guidance for the design and preparation of high efficiency uranium adsorbent.

A rapid in situ synthesis of electrochromic covalent organic frameworks (EC-COFs) was proposed by using green electrochemical interface polymerization of N,N,N\',N\'-tetrakis(p-aminophenyl)p-phenylenediamine (TPDA) and 2,5-dihydroxy-p-phenylenedicarboxaldehyde (DHBD). The synthetized TPDA-DHBD films exhibit stable polymorphic colour variations under different applied potentials, which can be attributed to the redox state changes of bis(triphenylamine) and imine electroactive functional groups within the COFs skeleton. TPDA-DHBD represents markedly different electrochromisms from red to cyan due to the steric hindrance effect caused by the presence of UO22+, demonstrating the unique tunability of COFs materials. This work offers a new feasible idea for rapid EC-COFs synthesis and tunable EC-COFs realization.

Photocatalysis has emerged as a extremely promising green technology for the treatment of uranium-containing wastewater. This study focuses on the fabrication of Ti3C2Tx/Cd0.8Zn0.2S composites with Schottky junctions through the in-situ growth of Cd0.8Zn0.2S on Ti3C2Tx nanosheets, enabling efficient photoreduction of U(VI) without the requirement of sacrificial agents. The results demonstrate that the Ti3C2Tx/Cd0.8Zn0.2S composites achieve remarkable 99.48 % U(VI) reduction efficiency within 60 min in a 100 ppm uranium solution. Furthermore, the removal rate remains above 90 % after five cycles. The formation of Schottky heterojunctions by Ti3C2Tx and Cd0.8Zn0.2S leads to the generation of an internal electric field that significantly promotes the rapid separation and transfer of photogenerated carriers, thereby enhancing the photocatalytic reduction efficiency of Ti3C2Tx/Cd0.8Zn0.2S-3:100 (TC/CZS-3:100). A considerable amount of electrons accumulate on Ti3C2Tx via the Schottky barrier, effectively facilitating the reduction of U(VI) to U(IV). As a co-catalyst, Ti3C2Tx enhances the photocatalytic performance and stability of Cd0.8Zn0.2S. Moreover, the practical application in the waste liquid of rare earth tailings reveals that the removal rate can be as high as 91.24 %. This research is of significant value in the development of effective photocatalysts for the elimination of uranium from wastewater.

Uranium (U) contamination of rice is an urgent ecological and agricultural problem whose effective alleviation is in great demand. Sphingopyxis genus has been shown to remediate heavy metal-contaminated soils. Rare research delves into the mitigation of uranium (U) toxicity to rice by Sphingopyxis genus. In this study, we exposed rice seedlings for 7 days at U concentrations of 0, 10, 20, 40, and 80 mg L-1 with or without the Sphingopyxis sp. YF1 in the rice nutrient solution. Here, we firstly found YF1 colonized on the root of rice seedlings, significantly mitigated the growth inhibition, and counteracted the chlorophyll content reduction in leaves induced by U. When treated with 1.1 × 107 CFU mL-1 YF1 with the amendment of 10 mg L-1 U, the decrease of U accumulation in rice seedling roots and shoots was the largest among all treatments; reduced by 39.3% and 32.1%, respectively. This was associated with the redistribution of the U proportions in different organelle parts, leading to the alleviation of the U damage to the morphology and structure of rice root. Interestingly, we found YF1 significantly weakens the expression of antioxidant enzymes genes (CuZnSOD,CATA,POD), promotes the up-regulation of metal-transporters genes (OsHMA3 and OsHMA2), and reduces the lipid peroxidation damage induced by U in rice seedlings. In summary, YF1 is a plant-probiotic with potential applications for U-contaminated rice, benefiting producers and consumers.

In this study, we used 16S high-throughput sequencing to investigate the effects of uranium mining on the rhizospheric bacterial communities and functions of three local plant species, namely, Artemisia frigida, Acorus tatarionwii Schott., and Salix oritrepha Schneid. The results showed that uranium mining significantly reduced the diversity of rhizospheric bacteria in the three local plant species, including the Shannon index and Simpson index (P < 0.05). Interestingly, we found that Sphingomonas and Pseudotrichobacter were enriched in the rhizosphere soil of the three local plants from uranium mining areas, indicating their important ecological role. The three plants were enriched in various dominant rhizospheric bacterial populations in the uranium mining area, including Vicinamidobacteriaceae, Nocardioides, and Gaiella, which may be related to the unique microecological environment of the plant rhizosphere. The rhizospheric bacterial community of A. tatarionwii plants from tailings and open-pit mines also showed a certain degree of differentiation, indicating that uranium mining is the main factor driving the differentiation of plant rhizosphere soil communities on the plateau. Functional prediction revealed that rhizospheric bacteria from different plants have developed different functions to cope with stress caused by uranium mining activities, including enhancing the translational antagonist Rof, the translation initiation factor 2B subunit, etc. This study explores for the first time the impact of plateau uranium mining activities on the rhizosphere microecology of local plants, promoting the establishment of effective soil microecological health monitoring indicators, and providing a reference for further soil pollution remediation in plateau uranium mining areas.

Rare earth elements have garnered increasing attention due to their strategic properties and chronic toxicity to humans. To better understand the content, migration, and ecological risk of rare earth elements in a 180 cm depth sediment profile downstream of a decommissioned uranium hydrometallurgical site in South China, X-ray powder diffraction (XRD) and High-resolution transmission electron microscope (HRTEM) were additionally used to quantify and clarify the mineral composition features. The results showed a high enrichment level of total rare earth elements in the sediment depth profile (range: 129.6-1264.3 mg/kg); the concentration variation of light rare earth elements was more dependent on depth than heavy rare earth elements. Overall, there was an obvious enrichment trend of light rare earth elements relative to heavy rare earth elements and negative anomalies of Ce and Eu. The fractionation and anomaly of rare earth elements in sediments were closely related to the formation and weathering of iron-bearing minerals and clay minerals, as confirmed by the correlation analysis of rare earth elements with Fe (r2 = 0.77-0.90) and Al (r2 = 0.50-0.71). The mineralogical composition of sediments mainly consisted of quartz, feldspar, magnetite, goethite, and hematite. Pollution assessment based on the potential ecological risk index, pollution load index (PLI), enrichment factor, and geological accumulation index (Igeo) showed that almost all the sediments had varying degrees of pollution and a high level of ecological risk. This study implied that continued environmental supervision and management are needed to secure the ecological health in terms of rare earth elements enrichment around a decommissioned uranium hydrometallurgical site. The findings may provide valuable insights for other uranium mining and hydrometallurgical areas globally.

The high efficiency, economy, sustainability and no secondary pollution of U(VI) removal is an important and challenging topic for U(VI) wastewater treatment. Here, the regenerable biohybrids with xanthan gum (XG) stabilized biogenic mackinawite nanoparticles (BX-FeS) were prepared, where XG acted as carrier facilitated the Fe2+ attachment and induced the low size, high stability and activity of nearly spherical FeS nanoparticles. Results showed that BX-FeS kept high activity after storing two years and good performance for U(VI) removal in broad pH range and co-existence of ions, and had greater removal efficiency (97.9 %) than biogenic B-FeS (67.1 %). Moreover, BX-FeS preformed high adsorption capacity in uranium wastewater (658.0 mg/g), and lower cost compared with zerovalent-iron and silica gel. Importantly, BX-FeS maintained high activity within three regeneration cycles driven by Desulfovibrio desulfuricans, inhibited the secondary pollution (Fe3+, SO42-) of reaction. This study provides a new strategy for sustainable and efficient treatment of U(VI) wastewater.