Petroleum pitch-based porous aromatic frameworks with phosphonate ligand for efficient separation of uranium from radioactive effluents

Extraction of Uranium by a Cheap Phosphite-Derived Polymer under Light Condition

Uranium, as the main fuel of today's nuclear energy, is crucial to the development of nuclear energy. Therefore, the development of low-cost and powerful adsorbents is very important for the removal or recovery of uranium from uranium-containing solutions. Herein, we report the synthesis of a cheap phosphite-derived polymer for such use. Under visible-light irradiation, this phosphite-derived polymer was found to enable selective adsorption of uranium with an adsorption capacity as high as 1030 mg/g, suggesting its great potential in handling nuclear waste.

Functionalized hydrogen-bonded organic superstructures via molecular self-assembly for enhanced uranium extraction

Effective uranium extraction from water is essential for the development of nuclear power industry and the protection of human health and environment. Nevertheless, it still remains challenging to realize efficient and cost-effective uranium extraction. Herein, a fast and simple method for the direct fabrication of novel functionalized hydrogen-bonded organic superstructures via molecular self-assembly is reported. The as-constructed flower-like superstructures (MCP-5) can allow the exposure of adsorption sites and facilitate the transport of uranyl ions, while synergism between amino and phosphate groups can realize selective uranium extraction. Consequently, MCP-5 possesses excellent uranium adsorption ability with a high saturated adsorption capacity of 950.52 mg g-1, high utilization rate of adsorption sites and adsorption equilibrium time of simply 5 min in uranium-spiked aqueous solution. Furthermore, MCP-5 offers selective uranium adsorption over a broad range of metal ions. The facile synthesis and low-cost raw materials make it have promising potential for uranium capture. Simultaneously, this study opens a design avenue of functionalized hydrogen-bonded organic material for efficient uranium extraction.

Synthesis of pH responsive malononitrile functionalized metal organic framework MIL-100(Fe) for efficient adsorption of uranium U(VI) from real-life alkaline leach liquor

The porous framework of MIL-100(Fe) was functionalized using malononitrile (MN), through an in-situ Knoevenagel condensation reaction to introduce abundant -CN groups on the surface of the developed adsorbent. The resultant MN-functionalized MIL-100(Fe) exhibited excellent Uranium (U(VI)) removal capacity (i.e., 270 mg/g) at highly alkaline pH (⁓ 10). Different coexisting cations and anions show negligible influence on the U-removal and it was 92.1-99.7 % in presence of different co-ions, with the concentration from 10 to 50 mg/L. Moreover, MIL-100(Fe)_MN showed extremely selective U removal from the actual alkaline leach liquor (⁓ 97 %), without any pH adjustment and leaching of the constituent Fe. The surface-grafted -CN groups were predominantly active towards the coordinative interactions with the U(VI) ionic moieties, as evident from the XPS and FTIR analysis. The MIL-100(Fe)_MN adsorbent was also subjected to five consecutive adsorption-desorption cycles, with >90 % U removal after 5th cycle. Moreover, the regenerated MIL-100(Fe)_MN was structurally and functionally resilient, as observed from the morphological and crystallographic analysis. A convection-pore diffusion based transport model was used to analyze the optimized mass transfer parameters. Overall, the present study highlights the simple design and development of malononitrile-functionalized MIL-100(Fe) as an efficient and selective adsorbent for U(VI) removal from U-rich alkaline leach liquor.

Construction of an egg-like DTAB/SiO2 composite for the enhanced removal of uranium

For the past few years, the environmental safety problems of radioactive nuclides caused wide public concern. In this work, the dodecyl trimethyl ammonium bromide-modified silicon dioxide composite (DTAB/SiO₂) was synthesized for the elimination of uranium. The dodecyl trimethyl ammonium bromide can decorate the surface of the silicon dioxide and change its surface topography, which can offer more active sites and functional groups for the combination of U(VI). The removal capacity of U(VI) on DTAB/SiO₂ reached 78.1 mg/g, which was greater than that of the silicon dioxide nanopowder. In the adsorption process, the surface oxygen-containing functional groups formed surface complexation with uranium. The results may provide helpful content to eliminate U(VI) and expand the application of surfactant in radioactive nuclide cleanup.

Pitch-based porous polymer beads for highly efficient iodine capture

The efficient and safe capture of volatile radioiodine is of great significance in the reprocessing of spent fuel. Herein, the millimeter-scale pitch-based hyper-cross-linked porous polymers@polyethersulfone (PHCP@PES) composite beads were firstly synthesized for the removal of volatile iodine and methyl iodide. PHCP@PES beads exhibit high iodine vapor and methyl iodide uptake capacities of 770.0 mg/g and 186.5 mg/g, respectively. More impressively, the uptake capacities of PHCP@PES (744.5 mg/g for iodine vapor and 180 mg/g for methyl iodide) remained almost unchanged after treatment with 3 mol/L of nitric acid. The rich interconnected pore structure of PHCP@PES promotes the rapid physical capture of iodine and methyl iodide. Intrinsic features such as low-cost preparation, good mechanical properties as well as thermal, acid stability and excellent performance in iodine capture indicate that PHCP@PES can be used as a potential candidate for the removal of radioactive iodine in the exhaust gas stream of post-treatment plants.

A hyper-cross-linked polymer derived from pitch as an efficient adsorbent for VOCs

Hyper-cross-linked polymers (HCPs) have been attracted widespread attention as adsorbents in recent years. A series of HCPs (HCP-1, HCP-2 and HCP-3) were synthesized via a Friedel-Crafts reaction using low-cross-linked pitch as precursor and dichloromethane (DCM) as cross-linking reagent and solvent. The prepared HCPs were characterized by N2 adsorption, Fourier transform infrared (FI-IR), Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA) and static water contact angle. The resultant HCPs possess micro/meso pore structures and a high stability. The Brunauer-Emmett-Teller (BET) surface areas of HCP-1, HCP-2 and HCP-3 are 152 m2·g−1, 467 m2·g−1 and 447 m2·g−1, respectively. Their total pore volumes vary from 0.207 cm·g−1 to 0.545 cm3·g−1 and following the sequence of HCP-1<HCP-3<HCP-2. The FTIR spectra of HCPs suggests the DCM is successfully grafted onto the skeleton structure. Dynamic adsorption capacities of the prepared HCP-1, HCP-2 and HCP-3 were examined and the results show the adsorption properties of o-xylene on HCP-2 are significantly higher than that of the other HCPs. The adsorption amount of o-xylene on HCP-2 is 198.18 mg·g−1, which is higher than that of benzene, suggesting a strong adsorption selectivity for o-xylene over benzene. In addition, the effect of water vapor on the adsorption of o-xylene onto HCP-2 was investigated. The dynamic adsorption amount of o-xylene on HCP-2 decreases by 76.47% under the relative humidity (RH) of 30%, implying that the HCP-2 has poor hydrophobicity. The equilibrium adsorption capacity of o-xylene on HCP-2 shows a slight decline after five adsorption cycles.

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Biochar mediated uranium immobilization in magnetite rich Cu tailings subject to organic matter amendment and native plant colonization

Organic matter (OM) amendments and plant colonization can accelerate mineral weathering and soil formation in metal mine tailings for ecological rehabilitation. However, the weathering effects may dissolve uranium (U)-bearing minerals (e.g., ianthinite) and increase U dissolution in porewater and seepages. The present study aimed to characterize the U solubility and distribution among different fractions and investigate if biochar (BC) could decrease soluble U levels and facilitate U immobilization in the OM-amended and plant-colonized tailings. A native plant species, Red Flinders grass (Iseilema vaginiflorum) was cultivated in the tailings for four weeks, which were amended with sugarcane residue (SR) with or without BC addition. The results showed that OM amendment and plant colonization increased porewater U concentrations by almost 10 folds from ~ 0.2 mg L^-1 to > 2.0 mg L^-1. The BC addition decreased porewater U concentrations by 40%. Further micro-spectroscopic analysis revealed that U was immobilized through adsorption onto BC porous surfaces, via possibly complexing with oxygen-rich organic groups. Besides, the BC amendment facilitated U sequestration by secondary Fe minerals in the tailings. These findings provide important information about U biogeochemistry in Cu-tailings mediated by BC, OM and rhizosphere interactions for mitigating potential pollution risks of tailings rehabilitation.

A conveniently synthesized redox-active fluorescent covalent organic framework for selective detection and adsorption of uranium

Uranium is a key element in the nuclear industry and also a global environmental contaminant with combined highly toxic and radioactive. Currently, the materials based on post-modification of amidoxime have been developed for uranium detection and adsorption. However, the affinity of amidoxime group for vanadium is stronger than that of uranium, which is the main challenge hindering the practical application of amidoxime-based adsorbents. Herein, we synthesized a fluorescent covalent organic framework (TFPPy-BDOH) through integrating biphenyl diamine and pyrene unit into the π-conjugated framework. TFPPy-BDOH has an excellent selectivity to uranium due to the synergistic effect of nitrogen atom in the imine bond and hydroxyl groups in conjugated framework. It can achieve ultra-fast fluorescence response time (2 s) and ultra-low detection limit (8.8 nM), which may be attributed to its intrinsic regular porous channel structures and excellent hydrophilicity. More excitingly, TFPPy-BDOH can chemically reduce soluble U (VI) to insoluble U (IV), and release the binding site to adsorb additional U (VI), achieving high adsorption capacity of 982.6 ± 49.1 mg g^-1. Therefore, TFPPy-BDOH can overcome the challenges faced by current amidoxime-based adsorbents, making it as a potential adsorbent in practical applications.

Iron phosphonate for highly efficient capture of U(VI) from acidic solution

In this study, a novel, high surface area iron phosphonate (IP) for highly efficient adsorption of uranyl ion in acidic medium was described. The as-prepared IP was amorphous with its specific surface area and total pore volume as high as 268 m²/g and 1.04 cm³/g, respectively. Particularly, the as-prepared IP with ferrous ions and oxygen, nitrogen-bearing functional groups prove excellent U(VI) adsorption capacity (154.6 mg/g) as compared to that of amorphous FePO₄ (67.3 mg/g) and Fe₃(PO₄)₂(H₂O)₈ (33.8 mg/g). Surprising, the saturation adsorption capacity could achieve up to 353.9 mg/g. Besides, the IP also had a fast adsorption rate for attaining adsorption equilibrium within 20 min, and followed pseudo-second-order kinetic and Freundlich models. Moreover, both the Dubinin-Radushkevich isotherm adsorption model and the value of enthalpy indicated a chemisorption process. Otherwise, the Na⁺-independent U(VI) adsorption on IP and the adsorption-desorption isotherm studies revealed that inner-layer surface complexation is the control step for U(VI) adsorption process, and the adsorbent featured an irreversible adsorption process. The structure and functional groups of the adsorbent remained unchanged after capture of U(VI). Further, X-ray photoelectron spectra (XPS) analysis demonstrated that the capture mechanism of U(VI) on IP from acidic aqueous solution was due to not only redox reaction, but also ascribed to the coordinated chemical adsorption.

Efficient uranium adsorbent with antimicrobial function constructed by grafting amidoxime groups on ZIF-90 via malononitrile intermediate

Herein, a dual-function Zeolitic Imidazole Frameworks (ZIFs) ZIF-90 grafted with malononitrile by Knoevenagel reaction and following with an amidoximation reaction to form an efficient U (VI) adsorbent (ZIF-90-AO). The strong chelation power of amidoxime groups (AO) with uranium and ZIF-90's mesoporous structure afforded ZIF-90-AO high maximum uranium adsorption capacity of 468.3 mg/g (pH = 5). In addition, the factors affecting uranium adsorption process were investigated by a batch of adsorption tests under different adsorption conditions. ZIF-90-AO displayed good selectivity to UO₂²⁺ in the solution containing multiple co-existing ions and good regeneration property. More importantly, ZIF-90-AO showed excellent antimicrobial property against both E. coli and S. aureus. Therefore, ZIF-90-AO is a U-adsorbent with great application value for removing U (VI) from wastewater due to the high U (VI) adsorption capacity in weak acid condition and good anti-biofouling properties.

Enhancement of the heterogeneous adsorption and incorporation of uraniumVI caused by the intercalation of β-cyclodextrin into the green rust

The influence of intercalated anions on the structure and composition of green rusts supplies a theoretical possibility for the investigation of the structural modification of Fe^II/Fe^III (oxyhydr)oxide materials. β-Cyclodextrin was intercalated into the mixed-valent iron-based hydroxide layers to synthesize new green rust materials (β-CD GRs), pursuing high-capacity uranium^VI (U^VI) sorption. The molar ratios of Fe^II to Fe^III and the molar ratios of β-CD GR to Fe^II + Fe^III had a significant effect on the synthesis of β-CD GRs. The synthesis process was further optimized by the quadric predictor and desirability function in a central composite design in combination. Both strong acidity and alkalinity were harmful to the adsorption of β-CD GRs towards U^VI. The pseudo-first-order kinetic model and Langmuir isotherm model were appropriate in fitting the whole adsorption process. The maximum monolayer adsorption capacity of β-CD GRs was 2548.61 mg/g. The presence of mimic groundwater constituents explicitly deteriorated the interaction between β-CD GR and U^VI species. Nanoscale nodules and particles were formed on the β-CD GR after the adsorption experiments. The peaks at 1159 and 609 cm^-1 vanished with the band at 1103 cm^-1 being left-shifted to 1117 cm^-1 in the FTIR spectra of β-CD GR during the heterogeneous process. The intercalation of β-CD brought obvious enhancement of U^VI species sorption to the GR material, which was combinedly driven by several reaction pathways and different from the unmodified GRs.

Dual-signal amplification electrochemical sensing for the sensitive detection of uranyl ion based on gold nanoparticles and hybridization chain reaction-assisted synthesis of silver nanoclusters

Herein, a dual-signal amplification electrochemical sensing has been proposed for the ultrasensitive detection of uranyl ions (UO₂²⁺) by integration of gold nanoparticles (AuNPs) and hybridization chain reaction (HCR)-assisted synthesis of silver nanoclusters (AgNCs). In this sensing platform, AuNPs are used as an ideal signal amplification carrier, aiming at increasing the loads of UO₂²⁺-specific DNAzyme on the gold electrode. In the presence of UO₂²⁺, UO₂²⁺-specific DNAzyme can be activated, leading to the cleavage of substrate strands (S-DNA). Then, HCR is triggered to produce long dsDNA through hybridization the probe with the ssDNA on the electrode surface. As a result, an amplified electrochemical response can be detected by inserting a large amount of AgNCs generated in situ using dsDNA as template. Featured with amplification efficiency, good specificity and high sensitivity, the strategy could quantitatively detect UO₂²⁺ down to 6.2 pM with a linear calibration range from 20 pM to 5000 pM. The proposed sensing platform has been also successfully demonstrated the practical application of detecting UO₂²⁺, indicating that the developed method has the potential applications and can open up a new avenue for highly sensitive detection of UO₂²⁺ in environmental monitoring.

Thiol/methylthio-functionalized porous aromatic frameworks for simultaneous capture of aromatic pollutants and Hg(II) from water

Simultaneously capturing organic pollutants and heavy metal can greatly reduce the water remediation time and cost, however it is still a great challenge presently. Herein, two novel thiol/methylthio-functionalized porous aromatic frameworks were synthesized as sorbents via the Sonogashira-Hagihara reaction of 1,3,5-triethynylbenzene and 1,3,5-tris(4-bromophenyl) benzene, the subsequent chloromethylation of the phenyl rings, and the final nucleophile substitution of -Cl groups by NaSH/NaSMe. These two sorbents were characterized by FT-IR spectra, energy dispersive X-ray spectra, scanning electron microscope, nitrogen adsorption analysis, thermo-gravimetric analysis, and elemental analyses. Adsorption experiments displayed that new sorbents had high uptake abilities and fast adsorption kinetics for aromatic pollutants and mercury (II) (Hg(II)). The maximum adsorption capacity (Q_max) of toluene and m-xylene on both new sorbents were 531.9-571.4 mg/g with the kinetic binding rate constants (k_obs) of 0.00276-0.02422 g/mg/min, and the Q_max values of Hg(II) were 148.1-180.3 mg/g with k_obs of 0.00592-0.01573 g/mg/min. Moreover, new sorbents indicated high simultaneous uptake abilities for these pollutants with good reusability, and finally they were successfully applied to the simultaneous remediation of these pollutants in two simulated sewages with high and low concentration, indicating their great practical application potential in wastewater remediation.

Triazine-triphenylphosphine based porous organic polymer as sorbent for solid phase extraction of nitroimidazoles from honey and water

A triazine-based porous organic polymer was prepared by facile solvothermal polymerization with cyanuric chloride and triphenyl phosphine as functional monomers. The polymer was characterized and then used for the first time as the sorbent for the effective solid-phase extraction of some nitroimidazoles (NDZs) (metronidazole, ronidazole, secnidazole, dimetridazole and ornidazole). The main experimental influencing parameters for the extraction including the eluent solvent, eluent volume, sample loading rate, sample solution pH, salt concentration and sample volume were investigated. The adsorption kinetics and adsorption isotherms were investigated to elucidate the possible adsorption mechanism. With the triazine-based porous organic polymer as the SPE adsorbent, trace NDZs were effectively extracted. The good enrichment capability for the NDZs was mainly attributed to the hydrogen binding interactions by the aromatic 1,3,5-trizine rings. After the SPE, the extracted analytes were analyzed by high-performance liquid chromatograph with ultraviolet detection. Under the selected conditions, the method had a good linear response for the analytes in the range of 0.06-120 ng mL^-1 for water and 1.5-1200 ng g^-1 for honey samples. The limits of detections (S/N=3) fell in the range of 0.02-0.06 ng mL^-1 for water and 0.5-1.5 ng g^-1 for honey samples. The method recoveries for the analytes for spiked samples were in the range of 80.3-118%. The method can be applied for the determination of the NDZs from real samples.

Sulfonated perylene-based conjugated microporous polymer as a high-performance adsorbent for photo-enhanced uranium extraction from seawater

A sulfonated perylene-based adsorbent is prepared for photo-enhanced uranium extraction from seawater. Owing to the photo-enhanced effect, the uranium extraction capacity of PyB-SO₃H in seawater reaches 1989 mg g⁻¹, with 90% extraction efficiency.

Stable sp2 carbon-conjugated covalent organic framework for detection and efficient adsorption of uranium from radioactive wastewater

Uranium is an important element in the nuclear industry while the discharge of radioactive wastewater can cause serious damages to the environment. In this work, an ultra-stable sp² carbon-conjugated covalent organic framework (COF-PDAN-AO) is synthesized with amidoxime-substituted monomers for detection and efficient adsorption of uranium from radioactive wastewater. Abundant amidoxime groups laced on the open 1D channels of COF-PDAN-AO exhibit exceptional accessibility and the regular pores facilitate the mass transfer. Based on these features, COF-PDAN-AO achieves ultra-low detection limit of 6.5 nM, high uranium adsorption capacity (410 mg/g) and selective interaction with uranium. In addition, various spectroscopies verify COF-PDAN-AO possesses excellent radioresistance in acidic solution. Regeneration studies have shown that COF-PDAN-AO maintained good structural stability after seven cycles. These results indicate that our sp² carbon conjugated COF can be potentially used for practical detection and adsorption of uranium from radioactive wastewater. This strategy can be extended to detection and extraction of other contaminants by designing the target ligand.

Constructing amidoxime-modified porous adsorbents with open architecture for cost-effective and efficient uranium extraction

The dense structure of polymeric matrices exposes only 10–20% of adsorption (amidoxime) groups, thus detracting from the extraction efficiency of uranium from seawater. Herein, the amidoxime-modified building units were cross-linked via the Scholl reaction into porous aromatic frameworks (PAFs). Due to the formation of open architecture, PAF adsorbents reveal a larger utilization ratio (>60%) of amidoxime groups. Consequently, PAF samples enable an ultrahigh uranium capacity of 702 mg g⁻¹, which creates a 16-fold capacity enhancement and gains a 7-fold adsorption rate improvement compared with polymer-based adsorbents. Notably, PAF solids are able to be integrated into various devices, thus realizing versatile and efficacious uranium extraction from real seawater (meeting the commercial standard ∼6 mg g⁻¹ in 21 days). In addition, the final cost using our PAF-based adsorbent is US $189.77 per kg uranium, it is in accordance with the prevailing market cost ($100–335 per kg).

The dense structure of polymeric matrices exposes only 10–20% of adsorption (amidoxime) groups, thus detracting from the extraction efficiency of uranium from seawater.

Porous ionic liquid polymer: A reusable adsorbent with broad operating pH range for speciation of nitrate and nitrite

Ionic liquids (ILs) are a class of fluids with unique physicochemical properties employing polymeric substances emerging new materials. Solidification of ILs into porous materials generates porous ionic liquid polymers that combine the unique characteristics of ILs with common porous materials and polymers. In this study, it's the first time the porous ionic liquid polymer was chosen as a sorbent for extraction and speciation of nitrite and nitrate. Porous IL was prepared through polymerization of 1-allyl-3-methylimidazolium bromide monomers in the presence of azobisisobutyronitrile (AIBN) and crosslinking of ethylene glycol dimethyl acrylate (EGDMA). Parameters affecting the adsorbent performance were optimized. Under the optimal conditions, correlation coefficient (R²) was 0.9996 and LOD was 0.1 µg L^-1. This method presented the linearity in the concentration range between 0.1-100 µg L^-1 and the relative standard deviation was 3.2%. Finally, the adsorption behavior of the obtained sorbent for nitrate and nitrite determination in various real samples was evaluated. The result indicates that the porous ionic liquid polymer showed high adsorption capacity (233 mg g^-1). The convenient preparation of the porous ionic liquid material, as well as high adsorption capacity for anionic pollutants predicted its broad application potential in anion removal materials.

Symbiotic Aerogel Fibers Made via In-Situ Gelation of Aramid Nanofibers with Polyamidoxime for Uranium Extraction

The uranium reserve in seawater is enormous, but its concentration is extremely low and plenty of interfering ions exist; therefore, it is a great challenge to extract uranium from seawater with high efficiency and high selectivity. In this work, a symbiotic aerogel fiber (i.e., PAO@ANF) based on polyamidoxime (PAO) and aramid nanofiber (ANF) is designed and fabricated via in-situ gelation of ANF with PAO in dimethyl sulfoxide and subsequent freeze-drying of the corresponding fibrous gel precursor. The resulting flexible porous aerogel fiber possesses high specific surface area (up to 165 m²·g⁻¹), excellent hydrophilicity and high tensile strength (up to 4.56 MPa) as determined by BET, contact angle, and stress-strain measurements. The batch adsorption experiments indicate that the PAO@ANF aerogel fibers possess a maximal adsorption capacity of uranium up to 262.5 mg·g⁻¹, and the absorption process is better fitted by the pseudo-second-order kinetics model and Langmuir isotherm model, indicating an adsorption mechanism of the monolayer chemical adsorption. Moreover, the PAO@ANF aerogel fibers exhibit selective adsorption to uranium in the presence of coexisting ions, and they could well maintain good adsorption ability and integrated porous architecture after five cycles of adsorption–desorption process. It would be expected that the symbiotic aerogel fiber could be produced on a large scale and would find promising application in uranium ion extraction from seawater.