Cationic Metal-organic Framework Research Articles

99TcO4\u2212 removal from legacy defense nuclear waste by an alkaline-stable 2D cationic metal organic framework

Removal of 99TcO4− from legacy defense nuclear tank waste at Savannah River Site is highly desirable for the purpose of nuclear safety and environmental protection, but currently not achievable given the extreme conditions including high alkalinity, high ionic strength, and strong radiation field. Herein, we present a potential solution to this long-term issue by developing a two-dimensional cationic metal organic framework SCU-103, showing ultrahigh stability in alkaline aqueous media and great resistance to both β and γ radiation. More importantly, it is very effective for 99TcO4− separation from aqueous media as demonstrated by fast exchange kinetics, high sorption capacity, and superior selectivity, leading to the successful removal of 99TcO4− from actual Savannah River Site high level tank waste for the first time, to the best of our knowledge. In addition, the uptake mechanism is comprehensively elucidated by molecular dynamics simulation and density functional theory calculation, showing a unique chemical recognition of anions with low charge density.

Zwitterionic hybrid aerobeads of binary metal organic frameworks and cellulose nanofibers for removal anionic pollutants

Different adsorbents have been applied to remove various anionic pollutants in water treatment processes. However, the development of economic, sustainable, and high-performance adsorbents is still a challenge. Herein, we introduce a new strategy to produce highly porous (98.96%), very low density (0.015 g/cm3), and cost-effective spherical and nanostructured hybrid aerogels, termed aerobeads, from cellulose nanofibers (CNF) and metal-organic frameworks (MOFs). The zwitterionic MOFs@CNF aerobeads (with 10–50 wt% MOF loading) were synthesized via simple dropping of a cross-linked hydrogel containing CNF and a binary mixture of anionic and cationic MOFs in liquid nitrogen, followed by freeze-drying. The flexible aerobeads (diameter of 2–3 mm) with hierarchical porous structure demonstrated an outstanding adsorption capacity toward both diclofenac (121.20 mg/g) and methyl orange (49.21 mg/g). Moreover, the aerobeads were easily collected after use from the solution without any complicated separation methods or the formation of secondary pollutants.

A Water-Stable Cationic Metal-Organic Framework with Hydrophobic Pore Surfaces as an Efficient Scavenger of Oxo-Anion Pollutants from Water.

Water contamination due to heavy metal-based toxic oxo-anions (such as CrO42- and TcO4-) is a critical environmental concern that demands immediate mitigation. Herein, we present an effort to counter this issue by a novel chemically stable cationic metal-organic framework (iMOF-2C) with strategic utilization of a ligand with hydrophobic core, known to facilitate such oxo-anion capture process. Moreover, the compound exhibited very fast sieving kinetics for such oxo-anions and a very high uptake capacity for CrO42- (476.3 mg g-1) and ReO4- (691 mg g-1), while the latter being employed as a surrogate analogue for radioactive TcO4- anions. Notably, the compound showed excellent selectivity even in the presence of other competing anions such as NO3-, Cl-, SO42-, ClO4-. etc.. Furthermore, the compound possesses excellent reusability (up to 10 cycles) and is also employed to a stationary phase ion column to decontaminate the aforementioned oxo-anions from water.

A new porous cationic metal–organic framework: selective sorption of organic dyes and treatment on neural stem cells during spinal cord injury treatment

A novel metal–organic framework containing Co(II) of {(Me2NH2)4[Co12(OH)4(abtc)6 (H2O)12]·14H2O}n (1) has been synthesized via Co(NO3)2·6H2O to react with the 3,3′,5,5′-azobenzenetetracarboxylic acid (H4abtc) ligand under solvothermal conditions. Furthermore, methylene blue (MB) can easily replace free cations; after half a day, more than 90% of the MB (10−5 M) is absorbed selectively, and it makes the title compound become a good medium for the separation and adsorption of the dye. In biological section, the enhancement activity of the compound on the nerve growth factor for the spinal cord injury treatment was evaluated. The relative gene expression of trkA receptor was measured with reverse transcription polymerase chain reaction. In addition to this, the activation of PI3K/Akt signaling pathway in neural stem cells after treated by compound was evaluated with western blot. The results of potential binding models were predicted by molecular docking, and the binding poses provided possible binding mechanisms of the functional groups of the complex to the TRKA protein.

Selective Adsorption of Cationic Dyes for Stable Metal-Organic Framework ZJU-48.

A cationic metal–organic framework (MOF) ZJU-48 with one-dimensional pores of about 9.1 × 9.1 Å2 has been prepared from zinc ions, adenine, and carboxyl ligands. ZJU-48 displays excellent water stability for about one week, exhibiting its potential application for adsorption and separation of dyes. Cationic and anionic dyes with similar sizes are adopted to study the adsorbing and separating properties of ZJU-48. Cationic dyes are adsorbed better than anionic dyes because of the negatively charged zeta potential of the material surface, implying its selective adsorption to cationic dyes, and it is charge-based adsorption. Meanwhile, the adsorption ability of the MOF to cationic dyes with different sizes is also investigated. We find that the adsorbed amount decreases with increase in the size of organics ,indicating that it is size-based adsorption. Furthermore, the cationic dye methylene blue (MB) is employed and focused on for its suitable charge and fitting size to evaluate the maximum adsorption capacity and desorption progress of ZJU-48. The results show that the maximum loaded amount of MOF toward MB reaches 582.44 mg/g, and about 90% of loaded dyes can be released from frameworks in N,N-dimethylformamide with NaCl over 6 h, exhibiting satisfactory adsorptive property and possibility as a reusable adsorbent.

Novel multi-channel anion exchange membrane based on poly ionic liquid-impregnated cationic metal-organic frameworks

The “trade-off” effect between hydroxide conductivity and dimensional stability is challenging issue for anion exchange membrane fuel cells (AEMFCs). In this study, the framework of UiO-66-NH2 is for the first time applied to anion exchange membranes (AEMs). The robust pore walls of UiO-66-NH2 with mechanical and structural durabilities protect the membrane from the excessive swelling effects (a swelling ratio of 7%). In addition, the framework of UiO-66-NH2 is directly modified into (UiO-66-NH2)+Cl− as hydroxide conduction channels by anion stripping for the first time. And we construct well-organized ion nanochannels by the in-situ self-assembly of N,N,N′,N' -tetramethyl-1,6-hexanediamine (TMHDA) and allyl bromide within the highly ordered pores of (UiO-66-NH2)+Cl−. The obtained QA@(UiO-66-NH2)+Cl− then incorporated into pristine membrane (QAPPO) to fabricate the novel multi-channel AEMs. The hydroxide conductivity of QA@(UiO-66-NH2)+Cl−/PPO is up to 123 mS⋅cm−1 at 80 °C, which is greatly improved compared to QAPPO pristine membrane.

2D → 3D corrugated structure self‐assembled from 4,4′‐methylenebis(N‐(pyridin‐2‐ylmethylene)aniline and terephthalic acid: Crystal structure and selective anion separations via anion exchange

A new flexible cationic Zn(II)metal organic framework, {[Zn2(BDC)1.5(L)(DMF)]NO3·DMF·solvent}n, MOF 1, which is a corrugated two‐dimensional network, was synthesized by self‐assembly of Zn(NO3)2.6H2O with 4,4′‐methylenebis(N‐(pyridin‐2‐ylmethylene)aniline as a neutral ligand and terephthalic acid in dimethyl formamide (DMF) as solvent and characterized by X‐ray diffraction. Because of the presence of uncoordinated nitrate (NO3−) ions in the channels, the compound was employed for ion‐exchange applications. We report a detailed study of the host–guest interaction for a cationic metal–organic framework (MOF) that can reversibly capture nitrate. The recrystallization of the MOF was evaluated by monitoring the anion exchange dynamics using a combination of powder X‐ray diffraction and Fourier transform infrared spectra with various kinds of foreign anions. This MOF showed fast and highly efficient Cr2O72− and CrO42−, N3−, MnO4−, and SCN− exchange. The trapping capacities of Cr2O72−, CrO42−, N3−, MnO4−, and SCN− were 105,138, 44,104, and 25mg/g at 25°C after 3h, respectively, and there was good recyclability for capturing N3− and SCN−. {[Zn2(BDC)1.5(L)(DMF)]NO3}n exhibited anion exchange selectivity of SCN− in a solution containing a mixture of 0.025mmol N3−, SCN−, CrO4−2−, Cr2O72−, and MnO4− for 3h and exhibited anion exchange selectivity for SCN− and Cr2O72− in a solution containing a mixture of 0.001mmol N3−, SCN−, CrO42−, Cr2O72−, and MnO4−.

Highly Efficient Separation of Anionic Organic Pollutants from Water via Construction of Functional Cationic Metal–Organic Frameworks and Mechanistic Study

Organic anions possess various functional properties; however, their presence in wastewater causes environmental pollution. Thus, coupling the separation of such species with the resultant function could be highly desirable. Herein, we propose a "killing two birds with one stone" strategy for highly efficient separation of organic pollutant anions from water at room temperature through direct construction of functional cationic metal-organic frameworks (CMOFs) based on the organic anions as charge-balancing anions. To illustrate this strategy, 2,4,6-trinitrophenolate anion (PA-) is chosen as a typical anion, while 4,4'-azo-triazole (atrz) is strategically chosen as a suitable neutral ligand. The resultant positive framework exhibits a high adsorption capacity and selectivity for PA-. Remarkably, its adsorption capacity is 869.6 mg g-1, which is more than 30 times that of multiwalled carbon nanotubes and 15 times that of activated carbon. Its capacity is even higher than that of BUT-13 (865 mg g-1), the highest adsorbent ever known. 1H NMR and single-crystal X-ray diffraction show that the high capacity is attributed to strong electrostatic interaction between the positive framework and PA-, which leads to all the pores being completely occupied by PA- anions. 1H NMR titration reveals that the selectivity comes from stronger hydrogen-bonding interaction between the ligand of the positive framework and PA-, which is confirmed from the eight times length of the shifted signal of atrz due to the addition of PA- compared with the competing anions. The stronger interaction is further confirmed from the high stability of the resultant CMOF in high-concentration salt solutions containing the competing anions, particularly in 100-fold molar NaNO3 and Na2SO4 solutions. Meanwhile, first-principles simulation shows that the high binding energy between the positive framework and PA- contributes to enhancing the selectivity. Moreover, the resultant CMOF is a potential energetic material with an improved oxygen balance, high heat of formation, and heat of detonation.

Cationic metal-organic frameworks as an efficient adsorbent for the removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions

Metal-organic frameworks (MOFs) material with high surface area, good chemical stability and multi-functionality, has become an emerging adsorbent for water treatment. A novel kind of quaternary amine anionic-exchange MOFs UiO-66 namely UiO-66-NMe3+ was firstly synthesized for adsorptive removal of a widely used toxic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solutions. The well-prepared UiO-66-NMe3+ MOFs were fully characterized, and then the main parameters affecting the adsorption process including solution pH, adsorbent dosage and coexisting anions were systematically investigated. The maximum adsorption capacity of UiO-66-NMe3+ toward 2,4-D reached as high as 279 mg g−1, much higher than that of pristine UiO-66 and aminated UiO-66. The adsorption mechanism could be attributed to the electrostatic interactions efficiently enhanced by the functionalization of quaternary amine groups, combining with the π-π conjugations between the linkers in MOFs and 2,4-D molecules, leading to the better adsorption performance of UiO-66-NMe3+. Additionally, the UiO-66-NMe3+ could be well regenerated by simple solvent washing and exhibited a slight decline of adsorption capacity after seven successive recycle. Furthermore, satisfactory adsorption capacity and reusability of the MOFs in environmental water samples were attained. Comparing with reported activated carbon and resin materials, the UiO-66-NMe3+ MOFs possessed higher adsorption capacity and shorter equilibrium time, as well as good reusability and practicality. The developed ion-exchange functionalized MOFs provided an ideal alternative for efficient adsorptive-removal of 2,4-D from complicated aqueous environment.

Cationic metal-organic framework based mixed-matrix membrane for extraction of phenoxy carboxylic acid (PCA) herbicides from water samples followed by UHPLC-MS/MS determination

A novel kind of cationic metal-organic framework(MOF) based mixed-matrix membrane(MMM) namely cationic MOF-MMM was firstly designed and used for simultaneous dispersive membrane extraction(DME) of six phenoxy carboxylic acid(PCA) herbicides from water samples followed by determination using ultrahigh-performance liquid chromatography tandem mass spectrometry. The cationic MOF-MMM was synthesized by soaking the zirconium-based MOFs in a polyvinylidene fluoride(PVDF) solution and further functionalization with quaternary amine groups, viz., UiO-66-NMe3+ MMM. The well-prepared UiO-66-NMe3+ MMM was characterized by FT-IR, SEM, XRD, XPS, NMR and etc. Several main variables influencing the MMM based DME efficiency were investigated and optimized in detail, such as dosage ratio of MOF/PVDF, solution pH, extraction time, coexistent anions and ionic strength. Electrostatic interactions dominated adsorption mechanism between anionic PCAs and cationic UiO-66-NMe3+ MMM, along with ππ conjugation and cation-π bonding, leading to better adsorption performance. Low limits of detection in the range of 0.03–0.59 ng/L and satisfactory recoveries within 80.06–117.40 % for all the PCAs are a reliable witness to demonstrate supreme sensitivity and the applicability of the developed method. By relying on the obtained results, the present work implied cationic MOF-MMM based DME can be a versatile and worthy utility for extraction of pollutants from different water samples with high throughput.

A cationic Zr-based metal organic framework with enhanced acidic resistance for selective and efficient removal of CrO42−

A Zr-based cationic metal organic framework shows high acidic resistance and selectivity to the anion contaminant, CrO42−.

Highly effective and fast removal of anionic carcinogenic dyesviaan In3-cluster-based cationic metal–organic framework with nitrogen-rich ligand

A novel cationic MOFs (In-TATAB) built by In3-cluster and nitrogen-rich organic ligand with new (3,6)-c topology has been successfully designed and synthesized. It shows highly effective and rapid removal of anionic carcinogenic organic dye molecules.

Evaluation of materials for iodine and technetium immobilization through sorption and redox-driven processes.

Radioactive iodine-129 (129I) and technetium-99 (99Tc) pose a risk to groundwater due to their long half-lives, toxicity, and high environmental mobility. Based on literature reviewed in Moore et al. (2019) and Pearce et al. (2019), natural and engineered materials, including iron oxides, low-solubility sulfides, tin-based materials, bismuth-based materials, organoclays, and metal organic frameworks, were tested for potential use as a deployed technology for the treatment of 129I and 99Tc to reduce environmental mobility. Materials were evaluated with metrics including capacity for IO3- and TcO4- uptake, selectivity and long-term immobilization potential. Batch testing was used to determine IO3- and TcO4- sorption under aerobic conditions for each material in synthetic groundwater at different solution to solid ratios. Material association with IO3- and TcO4- was spatially resolved using scanning electron microscopy and X-ray microprobe mapping. The potential for redox reactions was assessed using X-ray absorption near edge structure spectroscopy. Of the materials tested, bismuth oxy(hydroxide) and ferrihydrite performed the best for IO3-. The commercial Purolite A530E anion-exchange resin outperformed all materials in its sorption capacity for TcO4-. Tin-based materials had high capacity for TcO4-, but immobilized TcO4- via reductive precipitation. Bismuth-based materials had high capacity for TcO4-, though slightly lower than the tin-based materials, but did not immobilize TcO4- by a redox-drive process, mitigating potential negative re-oxidation effects over longer time periods under oxic conditions. Cationic metal organic frameworks and polymer networks had high Tc removal capacity, with TcO4- trapped within the framework of the sorbent material. Although organoclays did not have the highest capacity for IO3- and TcO4- removal in batch experiments, they are available commercially in large quantities, are relatively low cost and have low environmental impact, so were investigated in column experiments, demonstrating scale-up and removal of IO3- and TcO4- via sorption, and reductive immobilization with iron- and sulfur-based species.

A cationic metal-organic framework for dye adsorption and separation based on column-chromatography

Dyes that are considered to be poisonous exist everywhere in our daily life. The most urgent task is to remove such dye molecules from effluents. In the present work, a cationic metal-organic framework, [Cd2(tib)(btb)(H2O)2]∙NO3∙2DMF (Cd-MOF), where charge neutrality is balanced by NO3−, was first synthesized to investigate its ability in the adsorption and separation of ionic dye molecules. It is found that anionic dye molecules can be efficiently adsorbed with a diverse adsorption rate, while neutral and cationic dye molecules cannot be adsorbed according to the color changes of Cd-MOF. Meanwhile, Cd-MOF serves as a column-chromatographic filler to adsorb and separate specific anionic dye molecules with visible effects. Furthermore, anionic dye molecules can be released gradually, and the release rate is faster in the presence of NaCl. It should be noted that Cd-MOF remains stable even after 6 cycles of adsorption and separation of ionic dye molecules, which implies that MOFs can be considered potential materials for dye adsorption and selective separation with the merits of convenience, rapidity and environmental friendliness.

Highly Selective Enamination of β‐ketoesters Catalyzed by Interlocked [Cu8] and [Cu18] Nanocages

AbstractInterlocking cages are of great interest due to their fascinating structures and potential applications. However, the interlocking of different cages has not been previously reported. Herein, quadruply interlocked [Cu8] and [Cu18] nanocages have been constructed and structurally characterized in cationic metal–organic framework {[CuICu4II(XN)4(PTA)4(H2O)4]0.5 SO4⋅5 H2O⋅EtOH}n (1). 1 can trap the anionic pollutant CrO42− and the radioactive‐contaminant simulant ReO4− with an uptake capacity of 83.2 and 218 mg g−1, respectively. Catalytic investigations reveal 1 is an efficient heterogeneous catalyst for the enamination of ethyl acetoacetate with aniline and the turnover frequency (TOF) can reach a record value of 4000 h−1. More importantly, 1 represents the first of a catalyst of enamination to exhibit excellent size selectivity on different substrates. The robust catalyst can be reused at least ten times without obvious loss in catalytic activity.

Highly Selective Enamination of β‐ketoesters Catalyzed by Interlocked [Cu8] and [Cu18] Nanocages

Interlocking cages are of great interest due to their fascinating structures and potential applications. However, the interlocking of different cages has not been previously reported. Herein, quadruply interlocked [Cu8 ] and [Cu18 ] nanocages have been constructed and structurally characterized in cationic metal-organic framework {[CuI Cu4 II (XN)4 (PTA)4 (H2 O)4 ]0.5 SO4 ⋅5 H2 O⋅EtOH}n (1). 1 can trap the anionic pollutant CrO4 2- and the radioactive-contaminant simulant ReO4 - with an uptake capacity of 83.2 and 218 mg g-1 , respectively. Catalytic investigations reveal 1 is an efficient heterogeneous catalyst for the enamination of ethyl acetoacetate with aniline and the turnover frequency (TOF) can reach a record value of 4000 h-1 . More importantly, 1 represents the first of a catalyst of enamination to exhibit excellent size selectivity on different substrates. The robust catalyst can be reused at least ten times without obvious loss in catalytic activity.

Integrating cationic metal-organic frameworks with ultrafiltration membrane for selective removal of perchlorate from Water

We design a novel cationic metal-organic framework hybrid ultrafiltration polyvinylidene fluoride membrane (PVA/Cu-iMOFs/PVDF-0.05) and report its unique capture of aqueous perchlorate (ClO4−) at ppm-level. This membrane outperformed traditional adsorption materials and exhibited a specific affinity toward ClO4− in the presence of various competing anions at greater levels (up to a concentration ratio of 20). In the batch experiment, the ClO4− removal ratio reached 99.6% over a wide pH range (3˜10). Membrane filtration by using a 12.56 cm2 PVA/Cu-iMOFs/PVDF-0.05 membrane could effectively treat 4.71 L of ClO4−-contaminated water before breakthrough occurred, while maintaining a satisfactory permeability (˜627.32 L/(m2 h bar)) and antifouling property. The exhausted membrane could easily be regenerated in aminoethanesulfonic acid solution for repeated use with a negligible decrease in capacity. Moreover, the membrane showed excellent long-term stability in a cross-flow filtration process due to the amido bond between the Cu-iMOFs and membrane surface as well as the "protection" of polyvinyl alcohol. Selective and reversible ion-exchange between the sulfonic acid (R-SO3) ligands of Cu-iMOFs and tetrahedral oxo-anionic species was verified to be the pathway for ClO4− trapping. Thus, other problematic elements that also occur in tetrahedral form in water can be removed by this method.

An unusual self-catenated cationic metal-organic framework for the selective adsorption of anionic dyes

Based on a tripodal N, O-donor ligand, an unusual self-catenated cationic metal-organic framework [Zn2(cdc)(tmpo)2]·2NO3·5DMF (H2cdc = 1,4‑cyclohexanedicarboxylic acid and tmpo = tris[4‑(2′‑methylimidazol‑yl)phenyl]phosphine oxide) has been synthesized and structurally characterized. This compound exhibits selective adsorption of anionic dyes.

A cationic metal-organic framework for the highly efficient removal of thiocyanate from water

The adsorption of thiocyanate (SCN−) from water is a challenging and urgent task. In this work, a cationic metal-organic framework [Ag-4, 4′-bipy+] [NO3−] (SBN) was successfully synthesized for the highly efficient removal of SCN−. A series of characterization results show that SBN has good hydrolytic stability and thermal stability. SBN shows higher adsorption capacity (174.2 mg g−1) for SCN− than any other previous adsorbents. Kinetic study shows that adsorption equilibrium can be achieved within 10 min. SBN has good stability in the range of pH 2–10, and the adsorption capacity is immobile with the change of pH. In addition, SBN has a good selectivity for SCN− in the presence of other ions. The increased concentration of NO3− during the adsorption verified that the mechanism of SBN for SCN− removal is ion exchange, which formed [Ag-4, 4′-bipy+] [SCN−] (SBS). The low Gibb's energy (ΔrG(T)) indicates that the ion exchange process is thermodynamically spontaneous. Elution experiments showed that no anions could successfully elute SCN−. This work used a metal-organic framework for the adsorption of SCN− for the first time, revealing a new method for the adsorption and immobilization of SCN− in aqueous solutions.

Ion exchange collaborating coordination substitution: More efficient Cr(VI) removal performance of a water-stable CuII-MOF material

An unusual water-stable cationic metal-organic framework {[Cu(L)0.5(bpe)(H2O)](NO3)•(H2O)0.5}n (1) (H4L = bis(3,5-dicarboxypyridinium)-p-xylylene) was synthesized, which was developed into an effective capture material for removal chromate from water. The results show that this material efficiently traps HCrO4- pollutant ions via single-crystal to single-crystal (SCSC) coordination substitution process. The HCrO4- uptake capacity of 1 is high to 190 mg/g. Meaningfully, the structure of 1-HCrO4 ({[Cu(L)0.5(bpe)(HCrO4)]}n) can be accurately obtained by single-crystal X-ray diffraction, where the chromate enter the framework to form stable coordination with central metal ions Cu2+. This is the first example of a stable coordination between chromate and the framework during the capture process. The captured HCrO4- are not dissociated easily into the solution due to the coordination bond. This interaction makes the enrichment of HCrO4- more stable and the capture capacity excellent. Furthermore, the HCrO4- releasing process displays good regeneration in a single crystal state, which further elaborates the reversible SCSC transformation. The mechanism of Cr(VI) removal was also confirmed by DFT calculation studies. This work provides a new way to design and develop efficient MOF capture materials.