Defect-Induced Method for Preparing Hierarchical Porous Zr–MOF Materials for Ultrafast and Large-Scale Extraction of Uranium from Modified Artificial Seawater

Defect-enabling zirconium-based metal-organic frameworks for energy and environmental remediation applications

This comprehensive review explores the diverse applications of defective zirconium-based metal-organic frameworks (Zr-MOFs) in energy and environmental remediation. Zr-MOFs have gained significant attention due to their unique properties, and deliberate introduction of defects further enhances their functionality. The review encompasses several areas where defective Zr-MOFs exhibit promise, including environmental remediation, detoxification of chemical warfare agents, photocatalytic energy conversions, and electrochemical applications. Defects play a pivotal role by creating open sites within the framework, facilitating effective adsorption and remediation of pollutants. They also contribute to the catalytic activity of Zr-MOFs, enabling efficient energy conversion processes such as hydrogen production and CO2 reduction. The review underscores the importance of defect manipulation, including control over their distribution and type, to optimize the performance of Zr-MOFs. Through tailored defect engineering and precise selection of functional groups, researchers can enhance the selectivity and efficiency of Zr-MOFs for specific applications. Additionally, pore size manipulation influences the adsorption capacity and transport properties of Zr-MOFs, further expanding their potential in environmental remediation and energy conversion. Defective Zr-MOFs exhibit remarkable stability and synthetic versatility, making them suitable for diverse environmental conditions and allowing for the introduction of missing linkers, cluster defects, or post-synthetic modifications to precisely tailor their properties. Overall, this review highlights the promising prospects of defective Zr-MOFs in addressing energy and environmental challenges, positioning them as versatile tools for sustainable solutions and paving the way for advancements in various sectors toward a cleaner and more sustainable future.

Simultaneous size and defect control of metal-organic framework by deep eutectic solvent for efficient perfluoroalkyl substances adsorption: Delving into mechanism

This study reports an environment-friendly protocol to prepare a metal-organic framework (MOF) with simultaneously controlled particle size and open metal site for adsorption removal of perfluoroalkyl substances (PFASs). The successful preparation of UiO-66 with defect and crystal size modulation was achieved using a green and straightforward method, adjusting the components and molar ratios of ammonium salt/glycolic acid deep eutectic solvents (DESs). The corresponding modulation mechanism primarily relied on the combined regulation of the deprotonation and competitive coordination abilities of the eutectic solvent components. The adsorption process was thoroughly examined using spectral analyses, adsorption behavior profiling, and ab initio molecular dynamics simulations. The results revealed that PFAS adsorption is driven by combined capturing effects, such as CF-π, acid/base coordination, C-F⋯Zr, hydrogen bonding, and hydrophobic interactions. Our findings were not thus that the smaller the crystal size of MOF and the higher the defect concentration in the material, the better the PFAS adsorption performance. The result demonstrated the combined effect of these adsorbent features on PFAS mixtures. Furthermore, they revealed unique differences in sorption properties between these targets with different carbon chain lengths. Extensive defects in DES-based UiO-66 led to larger pores, increasing the availability of many adsorption sites and aiding in PFAS adsorption and diffusion. Nevertheless, the surplus of larger pores in the substance increased the competitive adsorption, reducing the total quantity of PFASs absorbed. Furthermore, various interactions and a less restrictive configuration increased the contact of functional groups with adsorbates, substantially enhancing the adsorption. This study investigates the basic questions about how PFAS molecules are adsorbed on DES-based MOFs and the relationship among the structure, properties, and performance to improve the efficiency of this novel adsorbent.

Adsorption of perfluoroalkyl substances on deep eutectic solvent-based amorphous metal-organic framework: Structure and mechanism

Perfluoroalkyl substances (PFASs) are a class of emerging organic pollutants characterized by high toxicity, environmental persistence, and widespread detection in water sources. The removal of PFASs from water is a matter of global concern, given their detrimental impact on both the environment and public health. Many commonly used PFAS adsorbents demonstrate limited adsorption capacities and/or slow adsorption kinetics. Therefore, there is an urgent need for the development of efficient adsorbents. For the first time, this work systematically investigated the performance of a deep eutectic solvent (DES)-based amorphous metal-organic framework (MOF) for the adsorption of PFASs with different carbon-chain lengths under the state of the mixture in aquatic environments. The adsorption mechanism was probed by a suite of adsorption kinetics studies, adsorption isotherm profiling, spectral characterization, and ab initio molecular dynamics (AIMD) simulations, revealing that PFAS adsorption is driven by synergistic capturing effects including acid/base coordination, CF-π (carbon-fluorine-π), hydrogen bonding, and hydrophobic interactions. Furthermore, the adsorption processes of short-chain and long-chain targets were found to involve different rate-controlling steps and interaction sites. Hydrophobic interactions facilitated the swift arrival of long-chain PFASs at the coordinatively interacting sites between carboxyl termini and Lewis acid Zr unsaturated sites, thanks to their lower reaction barriers. On the other hand, the adsorption of short-chain PFASs primarily relied on a Zr hydroxyl-based ligand exchange force, which would take place at Brønsted acid sites. The existence of massive structural disorder in amorphous UiO-66 led to the development of larger pores, thus improving the accessibility of abundant adsorption sites and facilitating adsorption and diffusion. The presence of multiple types of interactions and flexible structure in defect-rich amorphous UiO-66 significantly increased the exposure of functional groups to the adsorbates. Additionally, this material possessed outstanding regeneration efficiency and outperformed other MOF-based adsorbents with high affinity for targets. It enhances our understanding of the adsorption performances and mechanisms of amorphous materials toward PFASs, thereby paving the way for designing more efficient PFAS adsorbents.

Electrospun of functionalized mesoporous UiO-66 as the selective coating of solid phase microextraction Arrow for the determination of nine alkylphenols

A solid-phase microextraction (SPME) Arrow and high-performance liquid chromatography-UV detector (HPLC-UV, detection at 225 nm) based method was developed for the selective determination of nine alkylphenols (APs) in milk. The functionalized mesoporous UiO-66 (4-meso-UiO-66) was utilized as the new coating material, which was synthesized by post-modification of pore-expanded UiO-66-NH2 by an esterification reaction with 4-pentylbenzoic acid. It was fully characterized by X-ray photoelectron spectroscopy (XPS), fourier transformation infrared spectrometry, nitrogen sorption-desorption test, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. The characterization results showed the ester groups and benzene rings were introduced into the 4-meso-UiO-66, and the mesoporous structure was predominant in the 4-meso-UiO-66. The extraction mechanism of 4-meso-UiO-66 to APs is the synergistic effect of Zr-O electrostatic interaction and the size exclusion effect resulting from XPS, selectivity test, and nitrogen sorption-desorption test. The electrospinning technique was utilized to fabricate the 4-meso-UiO-66 coated SPME Arrow and polyacrylonitrile (PAN) was used as the adhesive. The mass rate of 4-meso-UiO-66 to PAN and the electrospinning time were evaluated. The extraction and desorption parameters were also studied. The linear range of this method was 0.2-1000 μg L-1 with a coefficient of determination greater than 0.9989 under the optimal conditions. The detection limits were 0.05-1 μg L-1, the inter-day and intra-day precision (RSD) were 2.8-11.5%, and the recovery was 83.6%-112%. The reusability study showed that the extraction performance of this new SPME Arrow could be maintained after 80 adsorption-desorption cycles. This method showed excellent applicability for the selective determination of APs in milk.

Emerging Nanomaterials toward Uranium Extraction from Seawater: Recent Advances and Perspectives

Nuclear energy holds great potential to facilitate the global energy transition and alleviate the increasing environmental issues due to its high energy density, stable energy output, and carbon-free emission merits. Despite being limited by the insufficient terrestrial uranium reserves, uranium extraction from seawater (UES) can offset the gap. However, the low uranium concentration, the complicated uranium speciation, the competitive metal ions, and the inevitable marine interference remarkably affect the kinetics, capacity, selectivity, and sustainability of UES materials. To date, massive efforts have been made with varying degrees of success to pursue a desirable UES performance on various nanomaterials. Nevertheless, comprehensive and systematic coverage and discussion on the emerging UES materials presenting the fast-growing progress of this field is still lacking. This review thus challenges this position and emphatically focuses on this topic covering the current mainstream UES technologies with the emerging UES materials. Specifically, this review elucidates the causality between the physiochemical properties of UES materials induced by the intellectual design strategies and the UES performances and further dissects the relationships of materials-properties-activities and the corresponding mechanisms in depth. This review is envisaged to inspire innovative ideas and bring technical solutions for developing technically and economically viable UES materials.

Significance of MOF adsorbents in uranium remediation from water

Uranium is considered as one of the most perilous radioactive contaminants in the aqueous environment. It has shown detrimental effects on both flora and fauna and because of its toxicities on human beings, therefore its exclusion from the aqueous environment is very essential. The utilization of metal-organic frameworks (MOFs) as an adsorbent for the removal of uranium from the aqueous environment could be a good approach. MOFs possess unique properties like high surface area, high porosity, adjustable pore size, etc. This makes them promising adsorbents for the removal of uranium from contaminated water. In this paper, sources of uranium in the water environment, human health disorders, and application of the different types of MOFs as well as the mechanisms of uranium removal have been discussed meticulously.

Dual-Ligand ZIF-8 Bearing the Cyano Group for Efficient and Selective Uranium Capture from Seawater

Uranium extraction from seawater is a potential technique that will change the world. Adsorption capacity, selectivity, and antibacterial ability for high-performance uranium adsorbents remain the major challenges. In this study, a dual-ligand zeolitic imidazolate framework 8 (ZIF-8) decorated with cyano groups (ZIF-8-CN) is prepared via a facile blend strategy at room temperature. Owing to the abundant mesopores and nitrogen functional groups, ZIF-8-CN shows an extremely high uranium uptake of 1000 mg/g at pH = 6, which is 2.42 times that of pristine ZIF-8. Noteworthily, ZIF-8-CN possesses a 16.2 mg/g uranium adsorption in natural seawater within 28 days, and the distribution coefficient (Kd = 3.25 × 106 mL/g) is far greater than that for other coexisting metal ions, demonstrating a marked preference for uranyl ions. Except for the coordination between uranium and nitrogen in imidazole, the cyano groups provide additional adsorption sites and preferentially bind to uranyl, thereby strengthening the affinity for uranyl. Notably, ZIF-8-CN displays ultrastrong antimicrobial ability against both Escherichia coli and Staphylococcus aureus, which is greatly desired for the scale-up marine tests. Our study demonstrates the high potential of ZIF-8-CN in uranium capture and provides a wide scope for the application of mixed-ligand MOFs.

Energetic Systematics of Metal-Organic Frameworks: A Case Study of Al(III)-Trimesate MOF Isomers

Thermal stability and thermodynamic properties of aluminum(III)-1,3,5-benzenetricarboxylate (Al-BTC) metal-organic frameworks (MOFs), including MIL-96, MIL-100, and MIL-110, have been investigated through a suite of calorimetric and X-ray techniques. In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC) revealed that these MOFs undergo thermal amorphization prior to ligand combustion. Thermal stabilities of Al-BTC MOFs follow the increasing order MIL-110 < MIL-96 < MIL-100, based on estimated amorphization temperatures. Their thermodynamic stabilities were directly measured by high-temperature drop combustion calorimetry. Normalized (per mole of Al) enthalpies of formation (ΔH*_f) of MIL-96, MIL-100, and MIL-110 from Al₂O_3, H₃BTC, and H₂O (only Al₂O₃ and H₃BTC for MIL-100) were determined to be -56.9 ± 13.7, -36.2 ± 17.9, and 62.8 ± 11.6 kJ/mol·Al, respectively. Our results demonstrate that MIL-96 and MIL-100 are thermodynamically favorable, while MIL-110 is metastable, in agreement with thermal and hydrothermal stability trends. The enthalpic preferences of MIL-96 and MIL-100 may be attributed to their shared trinuclear μ³-oxo-bridged (Al₃(μ₃-O)) secondary building units (SBUs) promoting stabilization of Al polyhedra by the ligands within these frameworks, in comparison to the sterically strained Al₈ octamer cluster cores formed in MIL-110. Furthermore, similar ΔH*_f of MIL-96 and MIL-100 explain their concurrent formation as physical mixtures often encountered during synthesis, implying the importance of kinetic factors that may facilitate the formation of Al-BTC framework isomers. More importantly, the normalized formation enthalpies of Al-BTC MOF isomers follow a negative correlation with the ratio of charged coordinated substituents to linkers (normalized per mole of Al within the MOF formula unit), with enthalpic preference given to systems with smaller (O^2- + OH^-)/ligand ratios. This trend has been successfully extended to the previously measured ΔH*_f of several Zn₄O-based frameworks (e.g., MOF-5, MOF-5(DEF), MOF-177, UMCM-1), all of which have been found to be metastable with respect to their dense phases (ZnO, H₂O, and ligands). The result suggests that carboxylate MOFs with higher metal coordination environments attain more enthalpic stabilization from the coordinated ligands. Thus, the formation of some lanthanide/actinide, transition metal, and main group carboxylate frameworks may be energetically more favored, which, however, requires further studies.

Metal-Organic Framework-Based Materials for Adsorption and Detection of Uranium(VI) from Aqueous Solution

The steady supply of uranium resources and the reduction or elimination of the ecological and human health hazards of wastewater containing uranium make the recovery and detection of uranium in water greatly important. Thus, the development of effective adsorbents and sensors has received growing attention. Metal-organic frameworks (MOFs) possessing fascinating characteristics such as high surface area, high porosity, adjustable pore size, and luminescence have been widely used for either uranium adsorption or sensing. Now pertinent research has transited slowly into simultaneous uranium adsorption and detection. In this review, the progress on the research of MOF-based materials used for both adsorption and detection of uranium in water is first summarized. The adsorption mechanisms between uranium species in aqueous solution and MOF-based materials are elaborated by macroscopic batch experiments combined with microscopic spectral technology. Moreover, the application of MOF-based materials as uranium sensors is focused on their typical structures, sensing mechanisms, and the representative examples. Furthermore, the bifunctional MOF-based materials used for simultaneous detection and adsorption of U(VI) from aqueous solution are introduced. Finally, we also discuss the challenges and perspectives of MOF-based materials for uranium adsorption and detection to provide a useful inspiration and significant reference for further developing better adsorbents and sensors for uranium containment and detection.

Confinement effect of layered double hydroxide on intercalated pyromellitic acidic anions and highly selective uranium extraction from simulated seawater

The oxygen-rich pyromellitic acidic anions (PMA4-) have been intercalated into MgAl-layered double hydroxide to fabricate the MgAl-PMA-LDH (abbr. PMA-LDH) composite, exhibiting excellent adsorption performance toward uranium (U(VI)). Benefiting from the...

Phosphate group functionalized magnetic metal-organic framework nanocomposite for highly efficient removal of U(VI) from aqueous solution

The phosphate group functionalized metal-organic frameworks (MOFs) as the adsorbent for removal of U(VI) from aqueous solution still suffer from low adsorption efficiency, due to the low grafting rate of groups into the skeleton structure. Herein, a novel phosphate group functionalized metal-organic framework nanoparticles (denoted as Fe₃O₄@SiO₂@UiO-66-TPP NPs) designed and prepared by the chelation between Zr and phytic acid, showing fast adsorption rate and outstanding selectivity in aqueous media including 10 coexisting ions. The Fe₃O₄@SiO₂@UiO-66-TPP was properly characterized by TEM, FT-IR, BET, VSM and Zeta potential measurement. The removal performance of Fe₃O₄@SiO₂@UiO-66-TPP for U(VI) was investigated systematically using batch experiments under different conditions, including solution pH, incubation time, temperature and initial U(VI) concentration. The adsorption kinetics, isotherm, selectivity studies revealed that Fe₃O₄@SiO₂@UiO-66-TPP NPs possess fast adsorption rates (approximately 15 min to reach equilibrium), high adsorption capacities (307.8 mg/g) and outstanding selectivity (S_u = 94.4%) towards U(VI), which in terms of performance are much better than most of the other magnetic adsorbents. Furthermore, the adsorbent could be reused for U(VI) removal without obvious loss of adsorption capacity after five consecutive cycles. The research work provides a novel strategy to assemble phosphate group-functionalized MOFs.

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.

Metal-organic frameworks as superior porous adsorbents for radionuclide sequestration: Current status and perspectives

Efficient separation of hazardous radionuclides from radioactive waste remains a challenge to the global acceptance of nuclear power due to complex nature of the waste, high radiotoxicities and presence of large number of interfering elements. Sorption of radioactive elements from liquid phase, gas phase or their solid particulates on various synthetic organic, inorganic or biological sorbents is looked as one of the options for their remediation. In this context, highly porous materials, termed as metal-organic frameworks (MOFs), have shown promise for efficient capturing of various types of radioactive elements. Major advantages that have been advocated for the application of MOFs in radionuclide sorption are their excellent chemical stability, and their large surface area due to abundant functional groups, and porosity. In this review, recent developments on the application of MOFs for radionuclide sequestration are briefly discussed. Focus has been devoted to address the separation of few crucial radioactive elements such as Th, U, Tc, Re, Se, Sr and Cs from aqueous solutions, which are important for liquid radioactive waste management. Apart from these radioactive metal ions, removal of radionuclide bearing gases such as I₂, Xe, and Kr are also discussed. Aspects related to the interaction of MOFs with the radionuclides are also discussed. Finally, a perspective for comprehensive investigation of MOFs for their applications in radioactive waste management has been outlined.

Abundant defects of zirconium-organic xerogels: High anhydrous proton conductivities over a wide temperature range and formic acid impedance sensing

There exists a challenge to develop solid-state proton conductors with high conductivity not only at high working temperatures (>353 K) but at start-up temperature and even at subzero temperature (<273 K) in cold climates or high-altitude drones. Here we present a series of zirconium-organic xerogels (Zr/Fum-xerogels) with porosity and defectivity, supported by N₂ sorption, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS), exhibiting a high anhydrous proton conductivity over the temperature range of 233 to 433 K. The anhydrous conductivity of Zr/Fum-xerogel-0.04 reaches 5.68 × 10^-4 (233 K) and 2.5 × 10^-2 S cm^-1 (433 K), situating in the leading level of all anhydrous conductors reported to date. Further, the defective effects on acidities and conductive mechanisms of xerogels, especially structural changes of water clusters generated by varying temperatures are investigated by ion exchange capacity (IEC), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of NH₃ (NH₃-TPD) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The zirconium-organic xerogels with outstanding conducting performance is further implemented as impedance sensor towards formic acid.

Nanocellulose aerogel for highly efficient adsorption of uranium (VI) from aqueous solution

Cellulose nanofibers (CNFs) aerogel was prepared via simple covalent crosslinking and freeze-drying method. The porous cellulose aerogel possessed high specific surface area and high metal-chelating capacity, which showed fast adsorption kinetics and high adsorption capacity (440.60 mg g^-1) in static uranium adsorption process. In the dynamic filtration system, the maximum adsorption capacity reached 194 mg g^-1 with the initial concentration of 10 mg L^-1. In addition, the CNFs aerogel possessed excellent selectivity and good regeneration ability for uranium adsorption. The integrated analyses of attenuated total reflection Fourier transform infrared (ATR-FTIR), X-Ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) suggested that the predominant UO₂²⁺ species formed inner-sphere surface complexes with two active carboxyl groups in the coordination model. This strategy may provide a sustainable route for development of efficient biomass-based adsorbents for selective uranium removal from aqueous solution.

Metal-Organic-Framework Based Functional Materials for Uranium Recovery: Performance Optimization and Structure/Functionality-Activity Relationships

Uranium recovery has profound significance in both uranium resource acquisition and pollution treatment. In recent years, metal-organic frameworks (MOFs) have attracted much attention as potential uranium adsorbents owing to their tunable structural topology and designable functionalities. This review explores the research progress in representative classic MOFs (MIL-101, UiO-66, ZIF-8/ZIF-67) and other advanced MOF-based materials for efficient uranium extraction in aqueous or seawater environments. The uranium uptake mechanism of the MOF-based materials is refined, and the structure/functionality-property relationship is further systematically elucidated. By summarizing the typical functionalization and structure design methods, the performance improvement strategies for MOF-based adsorbents are emphasized. Finally, the present challenges and potential opportunities are proposed for the breakthrough of high-performance MOF-based materials in uranium extraction.

Defect Engineering in Metal‒Organic Frameworks as Futuristic Options for Purification of Pollutants in an Aqueous Environment

Clean water scarcity is becoming an increasingly important worldwide issue. The water treatment industry is demanding the development of novel effective materials. Defect engineering in nanoparticles is among the most revolutionary of technologies. Because of their high surface area, structural diversity, and tailorable ability, Metal‒Organic Frameworks (MOFs) can be used for a variety of purposes including separation, storage, sensing, drug delivery, and many other issues. The application in wastewater treatment associated with water stable MOF‒based materials has been an emerging research topic in recent decades. Defect engineering is a sophisticated technique used to manufacture defects and to change the geometric framework of target compounds. Since MOFs have a series of designable structures and active sites, tailoring properties in MOFs by defect engineering is a novel concept. Defect engineering can excavate hidden active sites in MOFs, which can lead to better performance in many fields. Therefore, this technology will open new opportunities in water purification processes. However, there has been little effort to comprehensively discuss this topic. In this review, we provide an overview of the development of defect engineered MOFs for water purification processes. Furthermore, we discuss the potential applications of defect engineered materials.

Synthesis of macroscopic monolithic metal-organic gels for ultra-fast destruction of chemical warfare agents

The potential threat that has originated from chemical warfare agents (CWAs) has promoted the development of advanced materials to enhance the protection of civilian and military personnel. Zr-based metal–organic frameworks (Zr-MOFs) have recently been demonstrated as excellent catalysts for decomposing CWAs, but challenges of integrating the microcrystalline powders of Zr-MOFs into monoliths still remain. Herein, we report hierarchically porous monolithic UiO-66-X xerogels for the destruction of CWAs. We found that the UiO-66-NH₂ xerogel with a larger pore size and a higher surface area than the UiO-66-NH₂ powder possessed better degradability of 2-chloroethyl ethyl sulfide (2-CEES), which is a sulfur mustard simulant. These UiO-66-X xerogels exhibit outstanding performance for decomposing CWAs. The half-lives of vesicant agent sulfur mustard (HD) and nerve agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) are as short as 14.4 min and 1.5 min, respectively. This work is, to the best of our knowledge, the first report on macroscopic monolithic UiO-66-X xerogels for ultrafast decomposition of CWAs.

For the first time, we report hierarchically porous monolithic UiO-66-X xerogels for ultra-fast destruction of chemical warfare agents. The half-lives of the vesicant agent sulfur mustard (HD) and of the nerve agent VX are as short as 14.4 min and 1.5 min, respectively.

Exonuclease III-Driven Dual-Amplified Electrochemical Aptasensor Based on PDDA-Gr/PtPd@Ni-Co Hollow Nanoboxes for Chloramphenicol Detection

Herein, a hierarchically porous Zr-MOF-labeled electrochemical aptasensor based on the composite of PtPd@Ni-Co hollow nanoboxes (PtPd@Ni-Co HNBs) and poly (diallyldimethylammonium chloride)-functionalized graphene (PDDA-Gr) was developed for ultrasensitive detection of chloramphenicol (CAP). PtPd@Ni-Co HNBs have excellent conductivity and provide binding sites for aptamers; the functionalized PDDA-Gr improves its dispersibility and conductivity as a substrate material, which can be successfully used to increase the electrode surface area and support more PtPd@Ni-CoHNBs. Besides, hierarchically porous Zr-MOFs (HP-UiO-66) were utilized as signal probes and showed a stronger load capacity for signal molecules than conventional UiO-66. In the presence of CAP, two ingeniously designed Exo III-assisted cyclic amplification strategies further improved the sensitivity of the aptasensor: CAP causes cycle I to release a large amount of trigger DNA (Tr DNA), and then, Tr DNA initiated cycle II, which causes the exposed capture DNA to further bind the signal probes. With these advantages, the constructed aptasensors performed with satisfactory sensitivity in a wide linear range (10 fM-10 nM) and a detection limit of 0.985 fM. Several signal amplification strategies adopted in this study have effectively improved the performance of the sensor, providing a new avenue for the development of ultrasensitive sensors in the food analysis field.

Supramolecularly Poly(amidoxime)-Loaded Macroporous Resin for Fast Uranium Recovery from Seawater and Uranium-Containing Wastewater

Uranium is an extremely abundant resource in seawater that could supply nuclear fuel for over the long-term, but it is tremendously difficult to extract. Here, a new supramolecular poly(amidoxime) (PAO)-loaded macroporous resin (PLMR) adsorbent has been explored for highly efficient uranium adsorption. Through simply immersing the macroporous resin in the PAO solution, PAOs can be firmly loaded on the surface of the nanopores mainly by hydrophobic interaction, to achieve the as-prepared PLMR. Unlike existing amidoxime-based adsorbents containing many inner minimally effective PAOs, almost all the PAOs of PLMR have high uranium adsorption efficiency because they can form a PAO-layer on the nanopores with molecular-level thickness and ultrahigh specific surface area. As a result, this PLMR has highly efficient uranium adsorbing performance. The uranium adsorption capacity of the PLMR was 157 mg/g (the U_PAO in the PLMR was 1039 mg/g), in 32 ppm uranium-spiked seawater for 120 h. Additionally, uranium in 1.0 L 100 ppb U-spiked both water and seawater can be removed quickly and the recovery efficiency can reach 91.1 ± 1.7% and 86.5 ± 1.9%, respectively, after being filtered by a column filled with 200 mg PLMR at 300 mL/min for 24 h. More importantly, after filtering 200 T natural seawater with 200 g PLMR for only 10 days, the uranium-uptake amount of the PLMR reached 2.14 ± 0.21 mg/g, and its average uranium adsorption speed reached 0.214 mg/(g·day) which is very fast among reported amidoxime-based adsorbents. This new adsorbent has great potential to quickly and massively recover uranium from seawater and uranium-containing wastewater. Most importantly, this work will provide a simple but general strategy to greatly enhance the uranium adsorption efficiency of amidoxime-functionalized adsorbents with ultrahigh specific surface area via supramolecular interaction, and even inspire the exploration of other adsorbents.

Investigation of a modified metal-organic framework UiO-66 with nanoscale zero-valent iron for removal of uranium (VI) from aqueous solution

A novel composite material (nZVI/UiO-66) of nanoscale zero-valent iron (nZVI) with a functionalized metal-organic framework was synthesized by this study via a coprecipitation method, which was used for the efficient removal of U(VI) in the aqueous solution. The nZVI/UiO-66 had an excellent removal capacity of 404.86 mg g^-1 with an initial U(VI) concentration of 80 mg L^-1, 313 K and pH = 6. The transmission electron microscopy (TEM) revealed that nZVI particles were inhomogeneously distributed on the surface of UiO-66. The analysis by the X-ray diffraction (XRD) has further illustrated that the introduction of nZVI did not change the structure of UiO-66. The adsorption process closely followed the pseudo-second-order kinetic and the Freundlich isotherm model. The removal process of U(VI) by nZVI/UiO-66 was spontaneous and endothermic. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses have illustrated that the mechanism was mainly related to adsorption of U(VI) from UiO-66 and reduction of U(VI) by nZVI. The Zr-O bonds were shown to play a vital role in the uranium removal. nZVI/UiO-66 could be recycled. The uptake rate could be maintained at around 80% after 5 cycles of use. Therefore, these results manifested that the nZVI/UiO-66 is a promising sorbent for the efficient and selective removal of U(VI) in radioactive wastewaters.

Anti-Biofouling and Water-Stable Balanced Charged Metal Organic Framework-Based Polyelectrolyte Hydrogels for Extracting Uranium from Seawater

Metal-organic frameworks (MOFs) are diffusely defined as a promising class of porous material for uranium extraction from seawater, but there are still challenges in their stability and anti-biofouling performance. Herein, a water-stable and anti-biofouling ZIF-67/SAP_0.45 composite hydrogel was reported by the sequential processes of electrostatic interactions between the oppositely charged polymer, ionic gelation, and template growth of ZIF-67 crystals. Entanglement of positively charged polyethyleneimine (PEI) and negatively charged sodium alginate (SA) polymer chains provided external porosities, anti-biofouling properties, and mechanical support for the hydrogels and further reduced the possibility of ZIF-67 aggregation. The neutral composite hydrogel possessed the least Nitzschia on the surface after 7 days contact, which endows the adsorbent with a high uranium uptake capacity of 2107.87 ± 41.64 μg g^-1 at 1 mg L^-1 uranium-containing seawater with 8.6 × 10⁵ mL^-1 Nitzschia. Additionally, this adsorbent showed water stability with an uranium uptake capacity of 232.88 ± 8.02 mg g^-1 even after five adsorption-desorption cycles because of the excellent preparation method. Benefitting from the distinctive hierarchical structure and large accessible surface area, the resultant adsorbent achieved a high uranium capacity of 6.99 ± 0.26 mg g^-1 in real seawater. This flexible and scalable approach made the MOF/SAP composite hydrogel a highly desirable uranium adsorbent.

Modulated self-assembly of metal-organic frameworks

Exercising fine control over the synthesis of metal-organic frameworks (MOFs) is key to ensuring reproducibility of physical properties such as crystallinity, particle size, morphology, porosity, defectivity, and surface chemistry. The principle of modulated self-assembly - incorporation of modulator molecules into synthetic mixtures - has emerged as the primary means to this end. This perspective article will detail the development of modulated synthesis, focusing primarily on coordination modulation, from a technique initially intended to cap the growth of MOF crystals to one that is now used regularly to enhance crystallinity, control particle size, induce defectivity and select specific phases. The various mechanistic driving forces will be discussed, as well as the influence of modulation on physical properties and how this can facilitate potential applications. Modulation is also increasingly being used to exert kinetic control over self-assembly; examples of phase selection and the development of new protocols to induce this will be provided. Finally, the application of modulated self-assembly to alternative materials will be discussed, and future perspectives on the area given.

Bio-inspired antibacterial cellulose paper-poly(amidoxime) composite hydrogel for highly efficient uranium(vi) capture from seawater

A bio-inspired cellulose paper-poly(amidoxime) composite hydrogel is explored via UV-polymerization. This hydrogel has a highly efficient uranium capture capacity of up to 6.21 mg g^-1 for W_U/W_dry gel and 12.9 mg g^-1 for W_U/W_{poly(amidoxime)} in seawater for 6 weeks, due to its enhanced hydrophilicity, good hydraulic/ionic conductivity and broad-spectrum antibacterial performance.

Grafting functional groups in metal–organic frameworks for U(vi) sorption from aqueous solutions

Recent highlights of the organic groups-functionalized MOFs for uranium extraction from aqueous solution are discussed.

Porous Fe@C Composites Derived from Silkworm Excrement for Effective Separation of Anisole Compounds

Silkworm excrement is a very useful biomass waste, composed of layer-structured fats and proteins, which are great precursors for carbon composite materials. In this work, new porous composites derived from silkworm excrement were prepared for selective separation of flavor 4-methylanisole from the binary 4-methylanisole/4-anisaldehyde mixture. In particular, the silkworm excrement, possessing a unique nanosheet structure, is converted into a graphite-like carbon by a simple calcination strategy followed by a metal-ion-doping procedure. This Fe@C composite exhibits a special nano-spongy morphology, anchoring Fe₃C/Fe₅C₂ on the carbon nanosheets. Density functional theory simulations showed that 4-methylanisole presents a stronger π-π interaction and attraction forces with sp² carbon nanosheets in Fe@C composites than 4-anisaldehyde. The selective adsorption experiments further confirmed that the Fe@C composites exhibited a 4-methylanisole capacity of 7.3 mmol/g at 298 K and the highest selectivity of 17 for an equimolar 4-methylanisole/4-anisaldehyde mixture among the examined adsorbents including MOFs and commercial activated carbon materials, which demonstrates the potential of this low-cost and eco-friendly porous carbon material as a promising sustainable adsorbent.

Metal–organic framework-based materials for the recovery of uranium from aqueous solutions

This review focuses on the recent progress in MOFs and MOF-based materials as superior adsorbents for the efficient removal of uranium from aqueous solutions.