A Membrane-Supported Bifunctional Poly(amidoxime-ethyleneimine) Network for Enhanced Uranium Extraction from Seawater and Wastewater

A sodium alginate gel bead adsorbent doping with amidoxime-modified hydroxyapatite for the efficient adsorption of uranium

In this work, the modified‑sodium alginate gel beads were prepared by sol-gel method. Due to the presence of water channels in the sodium alginate gel bead, amidoxime groups and PO43- were exposed to the surface of the adsorbent to the maximum extent, resulting in the excellent adsorption capacity of modified‑sodium alginate gel beads. The introduction of amidoxime-modified hydroxyapatite significantly improved the adsorption capacity and the adsorption rate of the gel beads. The adsorption capacity increased from 308.7 to 466.0 mg/g and the adsorption equilibrium time was shortened from 300 min to 120 min. The modified‑sodium alginate gel bead possessed the advantages of short adsorption time, high adsorption efficiency and large adsorption capacity, which could be regarded as a potential adsorbent for uranium. Moreover, the uranium removal ability on the modified gel beads was mainly attributed to the Coulomb force between PO43- and uranium and the complexation between uranium and amidoxime groups. In summary, this work would provide a new idea for the modification and application of sodium alginate-based materials.

Anodic Electrodepositing Bioinspired Cu-BDC-NH2@Graphene Oxide Membrane for Efficient Uranium Extraction

The challenge of removing trace levels of heavy metal ions, particularly uranium, from wastewater is a critical concern in environmental management. Uranium, a key element in long-term nuclear power generation, often poses significant extraction difficulties in wastewater due to its low concentration, interference from other ions, and the complexity of aquatic ecosystems. This study introduces an anodic electrodeposited hierarchical porous 2D metal-organic framework (MOF) Cu-BDC-NH2@graphene oxide (GO) membrane for effective uranium extraction by mimicking the function of the superb-uranyl-binding protein. This membrane is characterized by its hierarchical pillared-layer structures resulting from the controlled orientation of Cu-BDC-NH2 MOFs within the laminated GO layers during the electrodeposition process. The integration of amino groups from 2D Cu-BDC-NH2 and carboxylate groups from GO enables a high affinity to uranyl ions, achieving an unprecedented uranium adsorption capacity of 1078.4 mg/g and outstanding selectivity. Our findings not only demonstrate a breakthrough in uranium extraction technology but also pave the way for advancements in water purification and sustainable energy development, proposing a practical and efficient strategy for creating orientation-tunable 2D MOFs@GO membranes tailored for high-efficiency uranium extraction.

Enhanced uranium extraction from seawater: from the viewpoint of kinetics and thermodynamics

Uranium extraction from seawater (UES) is recognized as one of the seven pivotal chemical separations with the potential to revolutionize global paradigms. The forthcoming decade is anticipated to witness a surge in UES, driven by escalating energy demands. The oceanic reservoirs, possessing uranium quantities approximately 1000-fold higher than terrestrial mines, present a more sustainable and environmentally benign alternative. Empirical evidence from historical research indicates that adsorption emerges as the most efficacious process for uranium recovery from seawater, considering operational feasibility, cost-effectiveness, and selectivity. Over the years, scientific exploration has led to the development of a plethora of adsorbents with superior adsorption capacity. It would be efficient to design materials with a deep understanding of the adsorption from the perspective of kinetics and thermodynamics. Here, we summarize recent advancements in UES technology and the contemporary challenges encountered in this domain. Furthermore, we present our perspectives on the future trajectory of UES and finally offer our insights into this subject.

Global research trends of uranium-containing wastewater treatment based on bibliometric review

The generation of uranium-containing wastewater (UCW) during different stages of uranium mining, processing, and utilization presents a significant ecological and biospheric threat. Consequently, it is crucial for both sustainable development and the protection of human health to adopt appropriate methods for the treatment of UCW as well as the separation and enrichment of uranium. This study conducted a comprehensive search of the Web of Science Core Collection (WOSCC) database for publications related to UCW treatment between 1990 and 2022 to gain insight into current trends in the field. Subsequently, the annual publications, WOSCC categories, geographical distribution, major collaborations, prolific authors, influential journals, and highly cited publications were the subjects of a biliometric analysis that was subsequently carried out. The study findings indicate a significant rise in the overall number of publications in the research field between 1990 and 2022. China, India, and the USA emerged as the primary contributors in terms of publication count. The Chinese Academy of Sciences, the East China University of Technology, and the University of South China were identified as the key research institutions in this field. Furthermore, a majority of the publications in this field were distributed through prestigious journals with high impact factors, such as the Journal of Radioanalytical and Nuclear Chemistry. The top 3 journals were Radioanalytical and Nuclear Chemistry, Chemical Engineering Journal, and Journal of Hazardous Materials. The keyword co-occurrence and burst analysis revealed that the current research on UCW treatment mainly focuses on adsorption-based treatment methods, environmentally functional materials, uranium recovery, etc. Furthermore, the study of the adsorption efficiency of different adsorbent materials, as well as the strengthening and improvement of adsorbent material selectivity and capacity for the recovery of uranium, represents a research hotspot in the field of UCW treatment in the future. This study conducts a comprehensive overview of the current status and prospects of the UCW treatment, which can provide a valuable reference for gaining insights into the development trajectory of the UCW treatment.

Recent developments and challenges in uranium extraction from seawater through amidoxime-functionalized adsorbents

As per statistical estimations, we have only around 100 years of uranium life in terrestrial ores. In contrast, seawater has viable uranium resources that can secure the future of energy. However, to achieve this, environmental challenges need to be overcome, such as low uranium concentration (3.3 ppb), fouling of adsorbents, uranium speciation, oceanic temperature, and competition between elements for the active site of adsorbent (such as vanadium which has a significant influence on uranium adsorption). Furthermore, the deployability of adsorbent under seawater conditions is a gigantic challenge; hence, leaching-resistant stable adsorbents with good reusability and high elution rates are extremely needed. Powdered (nanostructured) adsorbents available today have limitations in fulfilling these requirements. An increase in the grafting density of functional ligands keeping in view economic sustainability is also a major obstacle but a necessity for high uranium uptake. To cope with these challenges, researchers reported hundreds of adsorbents of different kinds, but amidoxime-based polymeric adsorbents have shown some remarkable advantages and are considered the benchmark in uranium extraction history; they have a high affinity for uranium because of electron donors in their structure, and their amphoteric nature is responsible for effective uranium chelation under a wide range of pH. In this review, we have mainly focused on recent developments in uranium extraction from seawater through amidoxime-based adsorbents, their comparative analysis, and problematic factors that are needed to be considered for future research.

Efficient removal of uranium (VI) from water by a hyper-cross-linked polymer adsorbent modified with polyethylenimine via phosphoramidate linkers

Practical adsorbents with high efficiency are essential to effectively treating wastewater. Herein, a novel porous uranium adsorbent (PA-HCP) having a considerable amount of amine and phosphoryl groups was designed and synthesized by grafting polyethyleneimine (PEI) on a hyper-cross-linked fluorene-9-bisphenol skeleton via phosphoramidate linkers. Furthermore, it was used to treat uranium contamination in the environment. PA-HCP exhibited a large specific surface area (up to 124 m2/g) and a pore diameter of 2.5 nm. Batch uranium adsorptions on PA-HCP were investigated methodically. PA-HCP demonstrated a uranium sorption capacity of >300 mg/g in the pH range of 4-10 (C0 = 60 mg/L, T = 298.15 K), with its maximum capacity reaching 573.51 mg/g at pH = 7. The uranium sorption process obeyed the pseudo-second-order model and fitted well with the Langmuir isothermal. In the thermodynamic experiments, uranium sorption on PA-HCP was revealed to be an endothermic, spontaneous process. Even in the presence of competing metal ions, PA-HCP exhibited excellent sorption selectivity for uranium. Additionally, excellent recyclability can be achieved after six cycles. Based on FT-IR and XPS measurements, both the PO and -NH2 (and/or -NH-) groups on PA-HCP contributed to efficient uranium adsorption as a result of the strong coordination between these groups and uranium. Furthermore, the high hydrophilicity of the grafted PEI improved the dispersion of the adsorbents in water and facilitated uranium sorption. These findings suggest that PA-HCP can be used as an efficient and economical sorbent to remove U(VI) from wastewater.

N, N-bis (2-hydroxyethyl) malonamide based amidoxime functionalized polymer immobilized in biomembranes for highly selective adsorption of uranium(VI)

Amidoxime compounds have been widely used in metal separation and recovery because of their excellent chelating properties to metal ions, especially to uranium (VI). In this study, N, N-bis (2-hydroxyethyl) malonamide was obtained from ethanolamine and dimethyl malonate, and used to prepare a two-dimensional network polymer, then the obtained polymer was immobilized in an environmentally friendly chitosan biomembrane, which enhanced its stability and hydrophobicity, meanwhile the amidoxime functionalization was achieved by oximation reaction of bromoacetonitrile, the application of the material further extends to uranium (VI) separation in solutions. Due to the synergistic action of amide group and amidoxime group, poly (ethanolamine-malonamide) based amidoxime biomembranes (PEA-AOM) showed extraordinary adsorption effect on uranium (VI), among which the saturation adsorption capacity of PEA-AOM-2 was 748.64 mg/g. PEA-AOM-2 also had good reusability (following five cycles of adsorption-desorption, the recovery rate maintained at 88%) and selectivity for uranium (VI), showing satisfactory results in competitive ion coexistence system and simulated seawater experiments. This study demonstrated that PEA-AOM-2 provided a new option for uranium (VI) separation in complex environment and low-concentration uranium background.

Heterometallic uranyl (hydroxyethyl)iminodiacetic acid (heidi) complexes: Molecular models for U(VI) uptake in complex media

Amidoximated absorbents (AO-PAN) effectively remove U(VI) from aqueous solution, but previous studies reported more variability for complex natural waters that contain additional confounding ions and molecules. Ternary phases containing U(VI), M(III) (M = Fe(III), Al(III), Ga(III)), and organic molecules exist under these conditions and cause heterogeneous U(VI) uptake on AO-PAN. The goal of the current study is to provide additional insights into the structural features ternary complexes using N-(2-hydroxyethyl)-iminodiacetic acid (HEIDI) as the model organic chelator and explore the relevance of these species on U(VI) capture. Three model compounds ([(UO2)(Fe)2(μ3-O)(C6NO5H8)2(H2O)4] (UFe2), ([(UO2)(Al)2(μ2-OH)(C6NO5H8)2(H2O)3] (UAl2) and [(UO2)(Ga)2(μ2-OH)(C6NO5H8)2(H2O)3] (UGa2)) were characterized by single-crystal X-ray diffraction. Raman spectra of the model compounds were compared with solution data and the ternary phases were noted in the case of Al(III) and Ga(III), but not in the Fe(III) system. U(VI) adsorption onto AO-PAN was not impacted by the presence of HEIDI or the trivalent metal species.

A cradle to cradle approach towards remediation of uranium from water using carbonized arecanut husk fiber

Sustainable materials for remediation of pollutants from water is the need of the hour. In this study two carbonaceous adsorbents prepared through hydrothermal carbonisation and pyrolysis from arecanut husk fiber, an agricultural waste material were used for the adsorption of uranium from water. Batch adsorption data as interpreted using the Langmuir model showed adsorption capacities of 250 mg g^-1 and 200 mg g^-1 respectively at pH 6 for the hydrochar (AHFC) and the pyrochar (AHFT) exceeding that reported for most of the unmodified biochars. The adsorption followed pseudo-second order kinetics and was exothermic in nature. The high selectivity and excellent removal efficiencies on application to environmental ground water samples and good regeneration capacity make these sorbents promising eco-friendly materials for uranium remediation from water.

Uranium extraction from seawater: material design, emerging technologies and marine engineering

Uranium extraction from seawater (UES), a potential approach to securing the long-term uranium supply and sustainability of nuclear energy, has experienced significant progress in the past decade. Promising adsorbents with record-high capacities have been developed by diverse innovative synthetic strategies, and scale-up marine field tests have been put forward by several countries. However, significant challenges remain in terms of the adsorbents' properties in complex marine environments, deployment methods, and the economic viability of current UES systems. This review presents an up-to-date overview of the latest advancements in the UES field, highlighting new insights into the mechanistic basis of UES and the methodologies towards the function-oriented development of uranium adsorbents with high adsorption capacity, selectivity, biofouling resistance, and durability. A distinctive emphasis is placed on emerging electrochemical and photochemical strategies that have been employed to develop efficient UES systems. The most recent achievements in marine tests by the major countries are summarized. Challenges and perspectives related to the fundamental, technical, and engineering aspects of UES are discussed. This review is envisaged to inspire innovative ideas and bring technical solutions towards the development of technically and economically viable UES systems.

Electrospun tannin-rich nanofibrous solid-state membrane for wastewater environmental monitoring and remediation

Heavy metal, organic dyes, and bacterial contamination in water endanger human/animals' health, and therefore, the detection, adsorption, and capturing of contaminants are essential for environmental safety. Ligand-rich membranes are promising for sensors, adsorption, and bacterial decontamination. Herein, tannin (TA)-reinforced 3-aminopropyltriethoxysilane (APTES) crosslinked polycaprolactone (PCL) based nanofibrous membrane (PCL-TA-APTES) was fabricated via electrospinning. PCL-TA-APTES nanofibers possess superior thermal, mechanical, structural, chemical, and aqueous stability properties than the un-crosslinked membrane. It changed its color from yellowish to black in response to Fe^2+/3+ ions due to supramolecular iron-tannin network (FeTA) interaction. Such selective sensing has been noticed after adsorption-desorption cycles. Fe³⁺ concentration, solution pH, contact time, and ligand concentration influence FeTA coordination. Under optimized conditions followed by image processing, the introduced membrane showed a colorimetric linear relationship against Fe³⁺ ions (16.58 μM-650 μM) with a limit of detection of 5.47 μM. The PCL-FeTA-APTES membrane could restrain phenolic group oxidation and result in a partial water-insoluble network. The adsorption filtration results showed that the PCL-FeTA-APTES membrane can be reused and had a higher methylene blue adsorption (32.04 mg/g) than the PCL-TA-APTES membrane (14.96 mg/g). The high capture efficiency of nanocomposite against Fe³⁺-based S. aureus suspension than Fe³⁺-free suspension demonstrated that Fe³⁺-bounded bacterium adhered to the nanocomposite through Fe³⁺/TA-dependent biointerface interactions. Overall, high surface area, rich phenolic ligand, porous microstructure, and super-wetting properties expedite FeTA coordination in the nanocomposite, crucial for Fe^2+/3+ ions sensing, methylene blue adsorption-filtration, and capturing of Fe³⁺-bounded bacterium. These multifunctional properties could promise nanocomposite membrane practicability in wastewater and environmental protection.

Green Synthesis of Molecularly Imprinted Polymers for Dispersive Magnetic Solid-Phase Extraction of Erythrosine B Associated with Smartphone Detection in Food Samples

Monitoring synthetic colorants in foods is important due to their potential toxicity and pathogenicity. We propose here a new and simple method for the extraction and determination of erythrosine B (ERT-B) in food samples. A composite of polydopamine-based molecularly imprinted polymers coating magnetic nanoparticles (Fe₃O₄@PDA@MIP) was synthesized using a green approach and exploited for the magnetic dispersive solid-phase extraction (MDSPE) of ERT-B. Fe₃O₄@PDA@MIP provides a rapid extraction of ERT-B, exhibiting good reusability and preconcentration ability. Moreover, the MIP showed a relatively good imprinting factor (3.0 ± 0.05), demonstrating excellent selectivity against patent blue (an interfering dye) and other food matrix components. The proposed MDSPE was coupled to colorimetric smartphone-based detection that allowed us to obtain similar performances of UV-Vis spectroscopy detection. The smartphone-based optical detection facilitated the determination of ERT-B in the 0.5-10 mg/L range, with a limit of detection of 0.04 mg/L. The developed method was successfully employed to determine ERT-B in food samples (juice, candy, and candied cherries) with good recovery values (82-97%).

A high-flux antibacterial poly(amidoxime)-polyacrylonitrile blend membrane for highly efficient uranium extraction from seawater

Uranium is an important fuel for nuclear power, with 4.5 billion tons of it stored in the oceans, 1,000 times more than on land. Polymer membrane materials are widely used in the marine resources fields, due to their convenient collection, good separation and can work continuously. Herein, a poly(amidoxime)-polyacrylonitrile blend membrane (PCP) with high flux, excellent antibacterial properties and uranium adsorption performance has been prepared by using the phase inversion method, and the prepared membrane was used for highly efficient uranium extraction from seawater. In static adsorption experiments, the PCP membrane reached adsorption equilibrium after 48 h, and the adsorption capacity was 303.89 mg/g (C₀ =50 mg/L). In dynamic adsorption experiments, it was found that the lower flow rate and higher number of membrane layers were favorable for dynamic adsorption. In addition, the water flux of the PCP membrane was 7.4 times higher than that of the PAN membrane. The adsorption mechanism can be attributed to the chelation between amino and hydroxyl groups in CS, amidoxime group in poly(amidoxime) and uranyl ions. The simple preparation process coupled with the excellent adsorption performance indicated that the PCP membrane would be a promising material for the uranium extraction from seawater.

High-strength and anti-biofouling nanofiber membranes for enhanced uranium recovery from seawater and wastewater

Ultrathin fibers can increase the contact area between adsorbents and seawater during the uranium extraction process; however, their construction usually aggravates the complex spinning technology and lowers their mechanical strength. Meanwhile, high strength and antifouling ability are essential for ocean adsorbents to withstand the complex natural environment and microbial systems. Herein, we design high-strength and anti-biofouling poly(amidoxime) nanofiber membranes (HA-PAO NFMs) via a supramolecular crosslinking. Bacterial cellulose supplies the NFMs with ultrathin fiber structure, and large amounts of adsorption ligands are immobilized on the framework via the crosslinking with antibacterial ions. Thus, different from other fibers, HA-PAO NFMs achieve ultrathin diameter (20-30 nm), high BET area (51 m² g^-1), and excellent mechanical strength (13.6 MPa). The uranium adsorption capacity reaches to 409 mg-U/g-Ads in the simulated seawater, 99.2% uranium can be removed from the U-contained wastewater, and the adsorption process can be observed by the naked eye due to the significant color changes. The inhibition zones indicate their excellent anti-biofouling ability, which contributes to 1.83 times more uranium extraction amount from natural seawater than the non-antifouling adsorbents. Furthermore, they display a long service life and can be large-scale prepared, and the HA-PAO NFMs have potential in the massive uranium recovery.

Bismuth impregnated biochar for efficient uranium removal from solution: Adsorption behavior and interfacial mechanism

In this work, Bi₂O₃ doped horse manure-derived biochar was obtained by carbonizing the H₂O₂-modified horse manure loaded with bismuth nitrate under nitrogen atmosphere at 500 °C. The results showed that there was a sharp response between the as-prepared bismuth impregnated biochar and uranium(VI) species in solution, which resulted in a short equilibrium time (<80 min), a fast adsorption rate (about 5.0 mg/(g·min)), a high removal efficiency (93.9%) and a large adsorption capacity (516.5 mg/g) (T = 298 K, pH = 4, C_i = 10 mg/L and m/V = 0.1 g/L). Besides, the removal behavior of the bismuth impregnated biochar for uranium(VI) did not depend on the interfering ions and ion strength, except Al³⁺, Ca²⁺, CO₃^2- and PO₄^3-. These results indicated that the modified biochar might possess the potential of remediating the actual uranium(VI)-containing wastewater. Moreover, the interaction mechanism between Bi₂O₃ doped biochar and uranium(VI) species was further explored. The results demonstrated that the enrichment of uranium(VI) on the surface of the as-prepared biochar was controlled by various factors, such as surface complexation, ion exchange, electrostatic attraction, precipitation and reduction, which facilitated the adsorption of uranium(VI) on the bismuth impregnated biochar.