Amidoxime Research Articles

Synthesis and structural characterization of acrylonitrile/vinyl imidazole copolymers and their amidoximated derivatives

Recently, environmental applications of copolymers such as CO2 capture and separation have become of significant interest. The development of copolymers with basic functional groups, such as amidoxime (AO) groups, represents a successful approach for enhancing absorption and separation of acidic molecules, such as CO2. In this research, acrylonitrile/N-vinyl imidazole (AN/VIM) copolymers were first synthesized through a free radical copolymerization method using 2,2′-azobisisobutyronitrile (AIBN) as the initiator and dimethylformamide as the solvent. The synthesized copolymers were then functionalized using hydroxylamine hydrochloride (NH2OH · HCl), the result being amidoximated (AO) copolymers. The synthesized copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. The analytical results simply confirmed that the copolymers and their amidoximated derivatives had successfully been synthesized. A microstructural study of amidoximated polymers using NMR spectroscopy clearly showed the tautomerization of AO groups.

Amidoxime-functionalized tetraphenylethylene ladder polymer for efficient membrane-based gas separations

Recent advances in solution-processible polymers of intrinsic microporosity (PIM) have attracted extensive research efforts in membrane-based gas separations due to their significantly enhanced gas permeability originating from inefficient chain packing. However, PIM-based membrane materials exhibit typically only moderate gas-pair selectivity, which is often insufficient especially for challenging gas separations containing highly sorbing feed components such as CO2. More importantly, they suffer from CO2-induced polymer chain dilation commonly referred as plasticization, which leads to poor separation performance under aggressive CO2/CH4 mixed-gas testing conditions. In this work, we conducted amidoxime (AO)-functionalization on a microporous tetraphenylethylene-based ladder polymer (TPE-PIM) by reacting its nitrile groups with hydroxyl amine under reflux conditions. Because of strong inter-chain hydrogen bonding, AO-functionalized TPE polymer (AO-TPE) exhibited a tightened and rigidified microstructure with 64 % reduction in Brunauer-Emmett-Teller (BET) surface area (175 m2/g) as compared to TPE-PIM (485 m2/g) derived from N2 adsorption isotherms at 77 K. As a result, fresh AO-TPE showed decreased gas permeability concurrent with a two-fold increase in CO2/CH4 selectivity (from 18 to 40) compared to TPE-PIM. Under aggressive 50:50 CO2:CH4 mixed-gas testing conditions, AO-TPE showed a strong plasticization resistance with decreased CH4 permeability over total feed pressure ranging from 4 to 30 bar. At 20 bar total pressure, AO-TPE demonstrated a mixed-gas CO2/CH4 selectivity of 37.7 as compared to 14.5 for TPE-PIM. The simple AO functionalization strategy holds promise to be an effective post-modification method to increase gas selectivity and alleviate the detrimental effects from CO2-induced plasticization.

Hydrazide and amidoxime dual functional membranes for uranium extraction from seawater

Amidoxime (AO)-based adsorbents are currently regarded as the most promising materials for extracting uranium (U) from seawater, but have limited adsorption capacities.

High-strength ionic hydrogel constructed by metal-free physical crosslinking strategy for enhanced uranium extraction from seawater

Uranium is one of the most important elements in the nuclear industry, and efficient extraction of uranium from the ocean is conducive to the sustainable development of nuclear energy. In this work, rigid perylene tetracarboxylate anion (PTC4−) was introduced by physical (non-covalent) crosslinking strategy to obtain metal-free ionic hydrogel PAOIB-PTC. PTC4− not only increased the rigid structure content of ionic hydrogel, but also formed dynamic macrocycle AO-PTC with amidoxime (AO) through hydrogen bonds. Unlike reported heterogeneous additives, PTC4− did not undergo inhomogeneity or shedding. Therefore, PAOIB-PTC exhibited high strength (7.34 MPa), excellent solvent resistance and salinity tolerance. A large number of hydrophilic groups and multistage pore structure endowed PAOIB-PTC with high hydrophilicity, which facilitated U(VI) mass transfer and led to rapid adsorption rates (88.6 mg g−1 h−1, c0 = 250 ppm). Since the metal-free component enabled more adsorption sites to be utilized, the maximum adsorption capacity of PAOIB-PTC was as high as 1008.03 mg g−1, which exceeded most reported hydrogel-based uranium adsorbents. Experiments and DFT calculations proved that PAOIB-PTC possessed high adsorption selectivity through uranyl recognition via hydrogen bonding and synergistic coordination by supramolecular structure AO-PTC. The low-concentration uranium capture capability and excellent recycling performance demonstrated the practical application potential of PAOIB-PTC. This work provides an idea for the design of metal-free ionic hydrogels with high-strength, and the established PAOIB-PTC is expected to be a candidate material for enhanced uranium extraction from seawater.

Efficient removal of U(VI) from wastewater by a sponge-like 3D porous architecture with hybrid electrospun nanofibers

Removal of uranium(VI) from nuclear wastewater is urgent due to the global nuclear energy exploitation. This study synthesized novel sponge-like 3D porous materials for enhanced uranium adsorption by combining electrospinning and fibrous freeze-shaping techniques. The materials possessed an organic–inorganic hybrid architecture based on the electrospun fibers of polyacrylonitrile (PAN) and SiO2. As a supporting material, the surface of fibrous SiO2 could be further functionalized by cyano groups via (3-cyanopropyl)triethoxysilane. All the cyano groups were turned into amidoxime (AO) groups to obtain a amidoxime-functionalized sponge (PAO/SiO2-AO) through the subsequent amidoximation process. The proposed sponge exhibited enhanced uranium adsorption performance with a high removal capacity of 367.12 mg/g, a large adsorption coefficient of 4.0 × 104 mL/g, and a high removal efficiency of 97.59%. The UO22+ adsorption kinetics perfectly conformed to the pseudo-second-order reaction. The sorbent also exhibited an excellent selectivity for UO22+ with other interfering metal ions.

Porous block polymer composite membranes for uranium uptake

Adsorptive membranes are an effective solution to capture uranium from seawater and contaminated water supplies. Current fibrous membrane-based sorbents suffer from a low density of binding ligands at the solid–liquid interface and broad pore size distributions. These issues lead to problems such as low binding capacity and gradual breakthrough curves during flow-through adsorption. We sought to address these challenges by developing highly permeable (i.e., ∼3.5×104 L m−2 h−1 bar−1) amidoxime-functionalized polysulfone(Psf)/polystyrene-b-poly(acrylic acid) (PS-PAA) composite membranes. A surface-segregation and vapor-induced phase separation (SVIPS) method was used to fabricate membranes that have an interconnected pore structure with PAA-lined pore walls. The PAA brushes offer a high density of reactive carboxyl sites that enable the surface chemistry to be modified with nitrile groups and then converted to amidoxime (AO) ligands for high-capacity uranium adsorption. The functionalized Psf/PS-PAO membrane removes uranium from dilute solution with a capacity of 150 mg g−1. Flow-through experiments demonstrate rapid mass transfer of the membranes, which adsorb over 90% of the uranyl ions from flowing solutions at feed concentrations of 0.1 and 1.0 mg L−1. Batch sorption–desorption experiments also indicate reusability of membranes over several cycles. Therefore, this membrane-based sorbents offers a chemically tailored platform for high-efficient uranium capture under trace concentrations.

Self-assembled MOF microspheres with hierarchical porous structure for efficient uranium adsorption

Herein, the self-assembled zirconium (Zr)-MOF microspheres formed by the octahedral nano-building blocks (UiO-66 and its derivatives) to adsorb uranium (U) was presented for the first time. The self-assembled MOF microspheres achieved the growth across orders of magnitude from nanometers (∼50 nm) to micrometers (∼2.3 μm), and exhibited ordered hierarchical porous structure (from ∼0.6 nm to ∼340 nm). The self-assembled MOF microspheres combined the advantages of nanostructures with stability and microstructures with hierarchical porous structure for effective mass diffusion. The improved mass diffusion properties of amidoxime (AO)-appended MOF microspheres (P-UiO-66-AO) endowed them with superior adsorption performance and excellent selective adsorption of U compared with AO-appended MOF (UiO-66-AO) octahedron. The adsorption equilibrium was obtained within 1400 min, and the maximum adsorption capacity of U was 283.2 mg/g. The adsorption capacity of U in simulated seawater was determined to be 11.4 mg/g and the ratio of distribution coefficients of U and vanadium (V) (Kd/U/Kd/V) increased 1.75 times than that of UiO-66-AO octahedron, overcoming the challenge of competitive adsorption of U and V with MOF. Overall, the strategy to fabricate self-assembled MOF microspheres with nano-building blocks is expected to expand the diversity and range of potential applications of MOFs.

Highly efficient extraction of uranium from seawater by polyamide and amidoxime co-functionalized MXene

Uranium mainly exists in the form of uranyl carbonate in seawater. [UO2(CO3)3]4- has strong stability, which increases the difficulty of uranium extraction from seawater. Meanwhile, the complex marine environment, a large number of coexisting competing ions and biological pollution are all non-negligible disturbing factors. Herein, we introduced amidoxime (AO) groups into the surface of Ti3C2 and grafted polyamides (PA) by a simple one-step hydrothermal method to produce an efficient seawater uranium extraction adsorbent Ti3C2-AO-PA. Owing to the amidoxime groups, the material was highly selective for uranium. And the large number of amino groups in the polyamides gave it ideal resistance to biofouling. The possibility of Ti3C2-AO-PA as an adsorbent for uranium extraction from seawater was confirmed by various characterization techniques, numerous adsorption batch experiments, simulated seawater experiments and antibacterial performance tests. It was demonstrated that the uptake of [UO2(CO3)3]4- by Ti3C2-AO-PA showed fast reaction kinetics (about 120 min), brilliant absorption capacity (81.1 mg·g−1 at pH 8.3), significant high selectivity (32.8 mg-U/g-Ads) and outstanding anti-biological contamination performance (92.9% antibacterial rate). XPS and DFT further indicated that the high extraction ability of Ti3C2-AO-PA for uranium was mainly attributed to the strong complexation of AO and –NH2 with [UO2(CO3)3]4-. These conclusions showed that Ti3C2-AO-PA not only had an ideal application prospect for uranium extraction from seawater, but also provided an available strategy for rapid and selective uranium adsorption from real seawater.

Self-locomotive composites based on asymmetric micromotors and covalently attached nanosorbents for selective uranium recovery

Nanosized sorbents are widely used for uranium (VI) recovery due to their high specific surface area, but the research on the integration of micromotors with nanosorbents to establish self-locomotive composites is still worth exploring. Thus, self-locomotive composites PS@PDA@Ag/SiO2-AO (PPA/SA) based on asymmetric micromotors and covalently attached nanosorbents were designed for selective uranium recovery. Pickering emulsion, as an important micro-reactor, was firstly adopted to prepare Janus microspheres with chemically distinct structure (PS@PDA@Ag), on which one hemisphere was loaded with catalytic silver (Ag) nanoparticles. Then, amidoxime (AO) decorated SiO2 nanospheres were covalently attached onto another hemisphere of PS@PDA@Ag, anisotropic configuration of as-prepared PPA/SA avoided the overlap of catalytic and binding sites. The self-propelled motion of PPA/SA induced by asymmetrical bubble evolution by H2O2 was observed, and the maximum speed was about 25 μm s−1 in case of 5 % H2O2. The uranium adsorption onto PPA/SA achieved 92 % of the equilibrium amount (29.31 mg g−1) in the first 20 min, and this value increased to 38.71 mg g−1 under the condition of H2O2, suggesting that autonomous movement achieves rapid mixing and mass transportation. The maximum adsorption amount (Qm) is 114.0 mg g−1 at 298 K according to the Langmuir model. In addition, PPA/SA exhibited remarkable selectivity for uranium even in the presence of large amounts of Na+, Mg2+, K2+, Ca2+ and other ions in the simulated seawater solution.

In situ chemical oxidation-grafted amidoxime-based collagen fibers for rapid uranium extraction from radioactive wastewater

The development of an amidoxime (AO)-based biomass adsorbent offers a solution for uranium extraction from radioactive wastewater and seawater. It also provides a strategy for realizing environmental safety and resource sustainability. Here, an AO-based collagen fiber (CF) adsorbent (AO-CF) was fabricated via in situ oxidative grafting. The fibrous morphology enables AO-CF to realize faster adsorption rate and higher adsorption capacity. During batch adsorption, the adsorption capacity of AO-CF was 0.877 mmol g−1 (234.16 mg g−1) at 318 K and pH 5.0 when the initial concentration of UO22+ was 2.5 mmol/L, while the adsorption capacity of AO-CF at pH 8.2 was 1.128 mmol g−1 (301.18 mg g−1). Moreover, AO-CF exhibited high selectivity for UO22+ in bilateral mixed solutions, including NH4+, Zn2+, Cr3+, Mg2+, Al3+, Ca2+, Ni2+, Ba2+, and Sr2+. Furthermore, AO-CF demonstrated higher adsorption capacity of UO22+ than its major competing element, namely, VO2+, in seawater. The adsorption behavior of UO22+ in the nuclear fuel preparation wastewater on the AO-CF column showed that the breakthrough point was approximately 175.0 bed volume (BV), and the AO-CF column could be rapidly regenerated by using only 3.0 BV of 0.1 mol/L HCl solution, indicating excellent reapplication ability. This work presents a new technology for the synthesis of highly efficient adsorbents for the recovery of UO22+ from radioactive wastewater.

Mesoporous silica (SBA-15) with enriched amidoxime functionalities for pH-controlled anticancer drug delivery

Amidoxime (AMI), an amphoteric functional ligand, mesoporous silica material (SBA-15@AMI NPs) was prepared and the pH-responsive drug release behavior was examined using Dox as model anticancer drug. Further, the cytocompatibility and the cell uptake results revealed that SBA-15@AMI NPs could be applied as pH-responsive drug delivery applications in cancer therapy. • Developing pH- responsive drug delivery system is attracted a great concern. • An amphoteric ligand functionalized SBA-15@AMI NPs for pH-responsive drug delivery system has been proposed. • The SBA-15@AMI NPs is applicable for delivery of anticancer drugs in cancer therapy. Amidoxime (AMI) functionalized mesoporous silica material (SBA-15@AMI NPs) was synthesized by surface modification approaches. This method allows for the creation of a higher concentration of amidoxime ligand groups to the SBA-15's surface without affecting the morphology. The synthesized SBA-15@AMI NPs were verified using a range of instrumental characterizations. Further, the drug loading and pH-responsive release behavior of the SBA-15@AMI NPs were examined using Dox as model anticancer drug. The biocompatibility and cellular uptake behavior was studied using MCF-7 cell line. Overall, the prepared SBA-15@AMI NPs could be applied as pH-responsive drug delivery applications in cancer therapy.

Lithium-Rich Porous Aromatic Framework-Based Quasi-Solid Polymer Electrolyte for High-Performance Lithium Ion Batteries.

The development of solid polymer electrolytes (SPEs) with high ionic conductivity, wide electrochemical window, and high mechanical strength is the key factor to realize high-energy-density solid lithium ion batteries (SLIBs). Porous aromatic frameworks (PAFs) have the advantages of high porosity, easily functionalized molecular structure, and rigid stable framework, which fully meet the requirements of solid polymer electrolytes with high Li+ capacity, fast Li+ transport, and safety. Herein, a lithium-rich amidoxime (AO)-modified porous aromatic framework (PAF-170-AO) was obtained through the absorption of LiTFSI by amidoxime groups and abundant pores and then compounded with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to prepare a PAF-based quasi-solid polymer electrolyte (PAF-QSPE) with only tiny amounts of plasticizer (∼12 μL). The amidoxime groups of PAF-170-AO restricted the movement of the anions of LiTFSI through hydrogen bonding, which effectively promoted the dissociation and migration number of Li+ (tLi+), reduced the concentration polarization, and inhibited the growth of lithium dendrites. The PAF-QSPE exhibited a high ionic conductivity of 1.75 × 10-4 S cm-1 and tLi+ of 0.55 at room temperature. The activation energy was as low as 0.136 eV. Furthermore, the assembled SLIBs with the PAF-QSPE presented a discharge capacity of 163 mAh g-1 at 0.2 C and a capacity retention rate of 96% after 350 cycles, illustrating a stable cycling performance. This work demonstrated the great application potential of lithium-rich PAFs in QSPEs.

Self-Emulsifying air-in-water HIPEs-Templated construction of amidoxime functionalized and chain entanglement enhanced macroporous hydrogel for fast and selective uranium extraction

A convenient design of amidoxime (AO)-functionalized hydrogel sorbent containing interconnected pores is critical for facilitating fast and selective uranium extraction. To address this, air-in-water high internal phase emulsions (HIPEs) templated construction of AO functionalized macroporous hydrogel sorbents (GMPAO) is reported for highly efficient extraction of uranium from aqueous solution. Curled gelatin methacryloyl (GelMA) chains, as amphiphilic Pickering emulsifier and molecular surfactant, endow self-emulsifying ability to stabilize the air/water interface. GMPAO exhibits an open-cell structure (diameter is about 80 % between 200 µm and 300 µm) with interconnecting pores (distribution is about 70 % between 55 µm and 75 µm), and the chain entanglement between polyamidoxime (PAO) and GelMA enhances mechanical strength. Benefitting from the macroporous structure and abundant affinity sites, GMPAO displays a spontaneous uranium adsorption capacity of 386.61 mg g−1 at 298 K and faster uptake within 60 min, which are superior to better than the previously reported hydrogel sorbent. In addition, GMPAO hydrogel still achieves the highest capacity and remarkable removal rate of almost 100 % towards uranium in the presence of competitive ions, as well as excellent recyclability toward uranium capture. Except for the coordination between uranium with amidoxime groups, the carboxylates from GelMA also cooperate as a synergistic effect for uranium uptake by charge interaction, which enhances the binding affinity of the adsorbent to uranium. Most importantly, this work demonstrates a new strategy for preparing macroporous hydrogel sorbents with enough stability and provides a new perspective for recovering uranium from an aqueous solution.

Theory-Guided Design of a Method to Obtain Competitive Balance between U(VI) Adsorption and Swaying Zwitterion-Induced Fouling Resistance on Natural Hemp Fibers.

The competitive balance between uranium (VI) (U(VI)) adsorption and fouling resistance is of great significance in guaranteeing the full potential of U(VI) adsorbents in seawater, and it is faced with insufficient research. To fill the gap in this field, a molecular dynamics (MD) simulation was employed to explore the influence and to guide the design of mass-produced natural hemp fibers (HFs). Sulfobetaine (SB)- and carboxybetaine (CB)-type zwitterions containing soft side chains were constructed beside amidoxime (AO) groups on HFs (HFAS and HFAC) to form a hydration layer based on the terminal hydrophilic groups. The soft side chains were swayed by waves to form a hydration-layer area with fouling resistance and to simultaneously expel water molecules surrounding the AO groups. HFAS exhibited greater antifouling properties than that of HFAO and HFAC. The U(VI) adsorption capacity of HFAS was almost 10 times higher than that of HFAO, and the max mass rate of U:V was 4.3 after 35 days of immersion in marine water. This paper offers a theory-guided design of a method to the competitive balance between zwitterion-induced fouling resistance and seawater U(VI) adsorption on natural materials.

Highly amidoxime utilization ratio of porous poly(cyclic imide dioxime) nanofiber for effective uranium extraction from seawater

Fibrous adsorption material with amidoxime (AO) group is widely considered as the most prospect of industrial application in uranium (U) extraction from seawater. However, the challenge of the AO-based adsorbents is that the utilization of AO has encountered bottle-neck of less than 1/100, which is far from saturated for decades. Herein, we construct porous structure in raspberry-like nanofibers (NFs) with rearranged AO groups cyclic imide dioxime (CID) nanoparticles (CID NFs) to improve the AO utilization ratio during U adsorption. By adjusting the size of the CID nanoparticles in NF, the area of the functional groups can be maximum exposed, which resulted in a breakthrough of the AO utilization ratio with high adsorption capacity. In simulated seawater with a U concentration of 330 ppb, the highest AO utilization ratio can reach 1/31. After adsorption in natural seawater for 87 days, the adsorption capacity of U was determined to be 11.39 mg-U/g-ads with AO utilization ratio of 1/74. Furthermore, extended X-ray absorption fine structure (EXAFS) fits and nuclear magnetic resonance (NMR) spectra suggested that the mechanism of AO bind uranyl ion was a tridentate binding model with CID. Density functional theory (DFT) computational studies proved that the tridentate binding model was the most stable combination. Positron annihilation lifetime spectroscopy (PALS) found that the generation of smaller free-volume holes in CID NFs have a certain cooperative binding in space on U adsorption. The CID NFs with unique nano morphology, and special CID chemical structure provide a new idea and potentiality for a novel design of U adsorbents in future U extraction from seawater.

Cuttlefish ink loaded polyamidoxime adsorbent with excellent photothermal conversion and antibacterial activity for highly efficient uranium capture from natural seawater

Owing to the abundant uranium reserves in the oceans, the collection of uranium from seawater has aroused the widespread interest. Compared to the uranium extraction from ore, uranium collection from seawater is a more environmentally friendly strategy. The amidoxime (AO) functional group has been considered as one of the most efficient chelating groups for uranium capture. In this work, by drawing upon the photothermal character and antibacterial activity of cuttlefish ink, a cuttlefish ink loaded polyamidoxime (CI-PAO) membrane adsorbent is developed. Under one-sun illumination, the CI-PAO membrane shows a high extraction capacity of 488.76 mg-U/g-Ads in 500 mL 8 ppm uranium spiked simulated seawater, which is 1.24 times higher than PAO membrane. The adsorption rate of CI-PAO membrane is increased by 32.04%. Furthermore, exhibiting roughly 75% bacteriostatic rate in composite marine bacteria, the CI-PAO shows a dramatically antibacterial activity, which effectively prevents the functional sites on the adsorbent surface from being occupied by the biofouling blocks. After immersing in natural seawater for 4 weeks, light-irradiated CI-PAO gave high uranium uptake capacity of 6.17 mg-U/g-Ads. Hence, the CI-PAO membrane adsorbent can be considered as a potential candidate for the practical application for uranium extraction from seawater.

Uranium removal from waste water of the tailings with functional recycled plastic membrane

Plastic pollution has become one of the most pressing environmental issues. Meanwhile, developing highly efficient adsorbents for uranium removal from the wastewater of its tailings is also of great significance in environmental protection. In this study, wastes of the plastic membrane in daily life were recycled and functionalized to treat uranium pollution in the environment. Membrane adsorbent with amidoxime (AO) group was successfully prepared using recycled plastic membranes through two-step polymerization. A network of nano-holes and nanostructured particles were observed on the surface of the AO modified membrane (AO-membrane) adsorbent. The adsorption performances from uranium solution and uranium tailings wastewater were evaluated in batch and column adsorption experiments. AO-membrane exhibited good removal performance in a wide pH range from 2 to 8. After adsorption in uranium tailings wastewater, the equilibrium concentrations of uranium in solution were lower than 50 μg/L, meeting the national standard of uranium solution discharge (50 μg/L). AO-membrane could reach adsorption equilibrium within 5 h in uranium tailings wastewater and present uranium removal ratio of nearly 100%. These indicated that this AO-membrane could be used for deep purification of wastewater, especially with low uranium concentration. AO-membrane exhibited a remarkable reuse performance and long service life. During the 10 cycles of adsorption and desorption, AO-membrane exhibited almost 100% uranium removal ratio even after ten adsorption and desorption cycles. This work provides new insights into the technology of waste control by waste.

Vertically Aligned Polyamidoxime/Graphene Oxide Hybrid Sheets’ Membrane for Ultrafast and Selective Extraction of Uranium from Seawater

AbstractWith the continuous research and development of amidoxime (AO)‐based adsorbents, industrialization production of uranium from seawater gradually becomes a reality. However, the currently available AO‐based adsorbents still suffer from low adsorption rate and poor selectivity. Herein, vertically aligned polyamioxime–graphene oxide (VA‐PG) sheet membrane is fabricated by directional freeze casting. The run‐through microchannels contribute to the free diffusion of uranyl ions (UO22+), leading to the fast adsorption kinetics. Furthermore, partially reduced graphene oxide allows high photothermal conversion efficiency and rapid in‐plane heat transfer, resulting in the fast temperature rise under simulated sunlight irradiation. Because of the endothermic behavior of UO22+, light‐irradiated VA‐PG can simultaneously satisfy the requirements of high adsorption capacity (13.63 mg‐U g‐Ads−1), high adsorption rate (0.43 mg g−1 day−1), and excellent selectivity toward U(VI) over V(V) (U/V = 1.24) in natural seawater, indicating the right direction for a breakthrough in the field of uranium extraction from seawater.

Constructing an Amino-reinforced amidoxime swelling layer on a Polyacrylonitrile surface for enhanced uranium adsorption from seawater

Polyacrylonitrile (PAN)-based materials have been studied for decades as uranium (U(VI)) adsorbents, because the further products of abundant nitrile groups, amidoxime (AO) groups, show great affinity for U(VI) ions. However, excessive amidoximation could cause the shrinkage of PAN fibers, resulting in decreased adsorption performance. Hence, an amino-reinforced amidoxime (ARAO) swelling layer was constructed on the PAN fiber surface (PAN-NH2-AO) by modification of the strongly hydrophilic amino group to prevent shrinkage. The molecular chains in the ARAO swelling layer would be swelled due to the adsorption of a large amount of water. Simultaneously, U(Ⅵ) ions can penetrate into the ARAO swelling layer with water molecules and coordinate with amino or AO groups, leading to increased adsorption performance. PAN-NH2-AO exhibited maximum U(VI) and water adsorption capacities of 492.61 mg g−1 and 20.32 g g−1 at 25 ℃ with a swelling ratio of 20.73%, respectively. The adsorption capacity of PAN-NH2-AO was 0.312 mg g−1 after a 91-day immersion in Yellow Sea, China. The study of the adsorption thermodynamics and kinetics of PAN-NH2-AO showed that the adsorption process was spontaneous homogeneous chemical adsorption. This paper proposes a novel method to obstruct amidoximation induced shrinkage and to maximize the potential application of PAN-based materials.

UiO-66-NH-(AO) MOFs with a New Ligand BDC-NH-(CN) for Efficient Extraction of Uranium from Seawater.

Metal-organic frameworks (MOFs) with a high surface area and excellent stability are potential candidates for uranium (U) adsorption. Amidoxime (AO) is the most widely used functional group to extract U, which is usually introduced into MOFs by two-step post-synthetic methods (PSMs). Herein, MOF UiO-66-NH-(AO) was obtained by a one-step PSM with amidoximation from UiO-66-NH-(CN), which was synthesized by a new organic ligand of 2-cyano-terephthalic acid and whose morphology was octahedron and could be well controlled with the new ligand. The one-step PSM can greatly maintain the octahedron of the MOFs. What is more, UiO-66-NH-(AO) showed good adsorption performance for U, the adsorption equilibrium was obtained within 1500 min, and the adsorption capacity of U was calculated to be 134.1 mg/g according to the Langmuir model. It also had excellent selectivity for U in the presence of high concentrations of vanadium (V), ferrum (Fe), magnesium (Mg), calcium (Ca), and zirconium (Zr). The adsorption capacity of U in natural seawater was determined to be 5.2 mg/g within 8 days. The recyclability of UiO-66-NH-(AO) in simulated seawater was demonstrated for at least four adsorption/desorption cycles. The binding mechanism was investigated by the extended X-ray absorption fine structure spectroscopy, revealing that U binding occurs in a fashion η2 motif. This study provides a reliable idea for the modification of MOFs and the potential for MOF-based materials to extract U from seawater.