Rational Design of High-Performance Cationic Organic Network Adsorbents

Development of high-performance ionic organic network (ION) adsorbents is of great importance for water remediation. However, the research on IONs is still nascent, especially, the design philosophy regarding contaminant adsorption has rarely been explored. In this contribution, we optimized the adsorption efficiency of IONs by increasing the density of charged sites and improving their accessibility. We first produced a new cationic organic network (CON), CON-LDU4, with a high density of positive sites via synthesis from tetra(4-pyridyl)ethene. Compared to the analogue CON-LDU2 that synthesized from tetra(4-(4-pyridyl)phenyl)ethene, CON-LDU4 exhibited higher efficiency in adsorption of methyl blue, indicating that the higher ionic density results in the higher adsorption efficiency. To further improve the accessibility of the active sites, another new CON material (CON-LDU5) was synthesized by employing a hard template. CON-LDU5 exhibited a larger specific surface area than CON-LDU4, with clearly enhanced adsorption efficiency. Finally, CON-LDU5 was used to capture CrO42- ions in water with fast adsorption kinetics (k2 = 0.0328 g mg-1 min-1) and high adsorption capacity (369 mg g-1).

Research progress of metal organic frameworks and their derivatives for adsorption of anions in water: A review

Anion pollution in water has become a problem that cannot be ignored. The anion concentration should be controlled below the national emission standard to meet the demand for clean water. Among the methods for removing excess anions in water, the adsorption method has a unique removal performance, and the core of the adsorption method is the adsorbent. In recent years, the emerging metal-organic frameworks (MOFs) have the advantages of adjustable porosity, high specific surface area, diverse functions, and easy modification. They are very competitive in the field of adsorption of liquid anions. This article focuses on the adsorption of fluoride, arsenate, chromate, radioactive anions (ReO₄^-, TcO₄^-, SeO₄^2-/SeO₃^2-), phosphate ion, chloride ion, and other anions by MOFs and their derivatives. The preparation methods of MOFs are introduced in turn, the application of different types of metal-based MOFs to adsorb various anions were discussed in categories with their crystal structure and functional groups. The influence on the adsorption of anions is analyzed, including the more common and special adsorption mechanisms, adsorption kinetics and thermodynamics, and regeneration performance are briefly described. Finally, the current situation of MOFs adsorption of anions is summarized, and the outlook for future development is summarized to provide my own opinions for the practical application of MOFs.

Selective perrhenate/pertechnetate removal by a MOF-based molecular trap

Rational design of anion-exchange materials for selective elimination of radioactive anionic contaminants poses a great challenge. Rather than relying on a size-compatible effect, combination of nano-sieve pore, hydrophobic cationic cavity,...

Enhancement of Proton Conductivity in Fe-Metal-Organic Frameworks by Postsynthetic Oxidation and High-Performance Hybrid Membranes with Low Acidity

The postsynthetic oxidation (PSO) of metal nodes in metal-organic frameworks (MOFs) has received widespread attention because PSO can significantly improve the performance of materials without changing the framework. This study investigates the influence of PSO on the proton conductivity of MOFs. The PSO product {[Fe^III₃L₂(H₂O)₆]•3(OH)}_n (2) is obtained by oxidizing {[Fe^II₃L₂(H₂O)₆]•3H₂O}_n (1) with Cu(NO₃)₂. At 98% RH and 70 °C, the proton conductivity of 2 is 66 times higher than that of 1, indicating that PSO can promote proton conduction. In the PSO process, metal ions shuttle in the MOF framework to functionalize the pores, and the change in the guest molecule forms more host-guest collaborative hydrogen bonds. All of these have made a significant contribution to proton conduction. Because 2 exhibits high proton conductivity (2.66 × 10^-4 S·cm^-1) at 98% RH and 80 °C, we doped 2 into a highly economical poly(vinylidene fluoride) (PVDF)/polyvinylpyrrolidone (PVP) substrate to make a hybrid membrane. The resulting hybrid membrane exhibits a high proton conductivity of 1.77 × 10^-3 S·cm^-1 at 98% RH and 80 °C, which is 4 times higher than the proton conductivity of the PVDF/PVP membrane and 6.6 times higher than that of 2.

A copper(ii)-based porous metal-organic framework for the efficient and rapid capture of toxic oxo-anion pollutants from water

The efficient and selective capture of toxic oxo-anions is highly desirable for environmental retrieval and hazardous waste disposal. This has remained an important task and gained considerable scientific attention due to their harmful effects on the ecosystem and human health. Herein, a porous cationic metal-organic framework (MOF), namely, [Cu₃Cl(L)(H₂O)₂]·Cl·4DMA·8H₂O (1), was synthesized (H₄L = 1,4,8,11-tetrazacyclotetradecane-N,N',N'',N'''-tetramethylenecinnamic acid and DMA = N,N'-dimethylacetamide). 1 shows high stability in aqueous solution and represents an extraordinary example that is capable of efficiently capturing environmentally toxic Cr₂O₇^2- and MnO₄^- anions. Moreover, the removal of Cr₂O₇^2- and MnO₄^- anions from water was also explored in the presence of other competing anions.

A new 3D luminescent Ba-organic framework with high open metal sites: CO2 fixation, luminescence sensing, and dye sorption

A new synthesized 3D luminescent Ba-organic framework (1) may be used as a recyclable heterogeneous catalyst for fixation of CO₂ and has excellent response and sensitivity for pollutant ions. Moreover, 1 exhibits the particular selective sorption towards Congo red (CR) dye.

Crystal structure of 2-(5-(pyridin-3-yl)-4-(pyridin-4-yl)-4H-1,2,4-triazol-3-yl)pyridine, C17H12N6

C17H12N6, monoclinic, P21/n (no. 14), a = 5.8617(14) Å, b = 15.845(4) Å, c = 15.326(4) Å, β = 92.650(5)°, V = 1422.0(6) Å3, Z = 4, R gt(F) = 0.0449, wR ref(F 2) = 0.1132, T = 296(2) K.

A Highly Efficient Coordination Polymer for Selective Trapping and Sensing of Perrhenate/Pertechnetate

A porous cationic Ag(I) coordination polymer, [Ag(1,2,4,5-p4b)](SbF₆) (TJNU-302) with the ligand 1,2,4,5-p4b (1,2,4,5-tetra(pyridin-4-yl)benzene), is reported that shows high sorption capacity (211 mg g^-1) and distribution coefficient K_d (5.8 × 10⁵ mL g^-1) as well as outstanding selectivity in 500 times excess of CO₃^2- or PO₄^3- anion for perrhenate removal. TJNU-302 can act as a crystalline turn-off sensor for perrhenate upon UV radiation. In this way, a test paper strip for sensing ReO₄^- could be produced. In water solution, TJNU-302 shows an efficient fluorescence quenching response to ReO₄^- ion, with the highest quenching percentage (86%) among all reported ReO₄^- sensors. These results could be elucidated by the bonding properties of single-crystal structures of TJNU-302 before and after perrhenate sorption, as well as density functional theory (DFT) calculations.

A zwitterionic ligand-based water-stable metal–organic framework showing photochromic and Cr(vi) removal properties

A water-stable In-MOF based on the zwitterionic viologen ligand was synthesized. It exhibits photochromic property and Cr(vi) removal performance.

Ligand substitution induced single-crystal-to-single-crystal transformations in two Ni(ii) coordination compounds displaying consequential changes in proton conductivity

Two Ni(ii) coordination compounds can reversibly SC–SC transform into each other induced by ligand substitution, causing changes in their proton conductivities.

Dual-Functionalized Fluorescent Cationic Organic Network: Highly Efficient Detection and Removal of Dichromate from Water

Dichromate is a widespread contaminant in wastewater, threatening the health of humans and other organisms. Therefore, effective detection and removal of dichromate from water is of great significance. Herein, a tetraphenylethylene functionalized cationic organic network (CON-LDU2) was constructed via a facile quaternization reaction. CON-LDU2 was successfully integrated with both detection and removal functionalities toward dichromate. On the one hand, benefiting from the strong fluorescence, CON-LDU2 was employed as a chemosensor, it could efficiently and selectively probe Cr₂O₇^2- in water with "turn-off" fluorescent response. On the other hand, the cationic skeleton and free anions inside framework make CON-LDU2 an excellent adsorbent for Cr₂O₇^2-, it could capture Cr₂O₇^2- from water with rapid kinetics and high capacity. The kinetic constant for adsorption of Cr₂O₇^2- can reach up to 1.784 g mg^-1 min^-1, while the capacity is determined as 325 mg g^-1. Furthermore, CON-LDU2 displayed good recyclability and can be reused for at least 5 cycles. Therefore, CON-LDU2 can serve as an ideal candidate not only in detection but also in removal of Cr₂O₇^2- in water medium.

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.

Syntheses of three new isostructural lanthanide coordination polymers with tunable emission colours through bimetallic doping, and their luminescence sensing properties

Tuning the emissive color changes of lanthanide (Ln) complexes is an important and appealing project for promoting the applications of Ln-complexes. A solvothermal reaction of 4-cyano-3-methylbenzoic acid (HL) and Ln(NO3)3·6H2O affords three isostructural Ln-complexes [Eu(L)3(H2O)2]n (1-Ln) (Ln = Eu, Gd and Tb) with one-dimensional chain structures. 1-Eu and 1-Tb show bright red and green emissions with absolute quantum yields of 3.06% and 11.96%, respectively, and the energy transfer was analyzed in detail through combined calculations. Interestingly, a series of heterometallic doped 1-TbxEu1-x coordination polymers were also obtained by mixing different ratios of Eu3+ and Tb3+ ions, which possess continuous luminescent color changes from green to yellow, orange and red. In addition, 1-Eu exhibits high quenching efficiency and low detection limit (∼10-4 M) for the simultaneous sensing of MnO4-, CrO42- and Cr2O72- ions in water.

Successful Decontamination of 99 TcO4 - in Groundwater at Legacy Nuclear Sites by a Cationic Metal-Organic Framework with Hydrophobic Pockets

⁹⁹ Tc contamination at legacy nuclear sites is a serious and unsolved environmental issue. The selective remediation of ⁹⁹ TcO₄ ^- in the presence of a large excess of NO₃ ^- and SO₄ ^2- from natural waste systems represents a significant scientific and technical challenge, since anions with a higher charge density are often preferentially sorbed by traditional anion-exchange materials. We present a solution to this challenge based on a stable cationic metal-organic framework, SCU-102 (Ni₂ (tipm)₃ (NO₃ )₄ ), which exhibits fast sorption kinetics, a large capacity (291 mg g^-1 ), a high distribution coefficient, and, most importantly, a record-high TcO₄ ^- uptake selectivity. This material can almost quantitatively remove TcO₄ ^- in the presence of a large excess of NO₃ ^- and SO₄ ^2- . Decontamination experiments confirm that SCU-102 represents the optimal Tc scavenger with the highest reported clean-up efficiency, while first-principle simulations reveal that the origin of the selectivity is the recognition of TcO₄ ^- by the hydrophobic pockets of the structure.

Construction of a cationic organic network for highly efficient removal of anionic contaminants from water

A new cationic organic network is constructed by a facile method from commercially available precursors, and exhibits high efficiency for removal of water contaminants.

Ultra-highly selective trapping of perrhenate/pertechnetate by a flexible cationic coordination framework

This work presents a 3D cationic coordination framework, showing ultra-highly selective trapping of perrhenate/pertechnetate in the presence of sulfate 20 000 times in excess.

Mechanisms of Solvent-Mediated Structural Transformations for Dynamic Crystals of Supramolecular Coordination Systems

Thus far, reports about the transformations for dynamic crystals of supramolecular coordination systems mainly include single-crystal-to-single-crystal reactions, and solvent-mediated processes. This Concept focuses on the mechanisms for solvent-mediated structural transformations of dynamic crystals, which can be classified into two categories, that is, core-on-shell and core-to-core. The core-on-shell mechanism means that the core of the new crystal is generated from the shell of original crystal, being concomitant with the dissolution of the mother crystal. In contrast, for the core-to-core case, the growth of new crystal core and the dissolution of original crystal core will proceed simultaneously, but they are physically separated. Herein, the two mechanisms are elucidated in detail, with some typical examples from recent advances.

Metal-organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal-organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

Structural Transformations of Amino-Acid-Based Polymers: Syntheses and Structural Characterization

A discrete complex [Zn(tpro)₂(H₂O)₂] (1, Htpro = l-thioproline), and two structural isomers of coordination polymers, a 1D chain of [Zn(tpro)₂]_n (2) and a layered structure [Zn(tpro)₂]_n (3), were synthesized and characterized. The discrete complex 1 undergoes a temperature-driven structural transformation, leading to the formation of a 1D helical coordination polymer 2. Compound 3 is comprised of a 2D homochiral layer network with a (4,4) topology. These layers are mutually linked through hydrogen bonding interactions, resulting in the formation of a 3D network. When 1 is heated, it undergoes nearly complete conversion to the microcrystalline form, i.e., compound 2, which was confirmed by powder X-ray diffractions (PXRD). The carboxylate motifs could be activated after removing the coordinated water molecules by heating at temperatures of up to 150 °C, their orientations becoming distorted, after which, they attacked the activation sites of the Zn(II) centers, leading to the formation of a 1D helix. Moreover, a portion of the PXRD pattern of 1 was converted into the patterns corresponding to 2 and 3, and the ratio between 2 and 3 was precisely determined by the simulation study of in-situ synchrotron PXRD expriments. Consequently, such a 0D complex is capable of underdoing structural transformations and can be converted into 1D and/or 2D amino acid-based coordination polymers.

Incorporating cuprous-halide clusters and lanthanide clusters to construct Heterometallic cluster organic frameworks with luminescence and gas adsorption properties

A series of heterometallic cluster organic frameworks based on cuprous-halide Cu₄I₄ clusters and lanthanide clusters have been successfully synthesized under solvothermal conditions.

Extremely stable europium-organic framework for luminescent sensing of Cr2O72− and Fe3+ in aqueous systems

A novel Eu-MOF which is extremely stable in an aqueous system over a wide pH range is reported as a dual functional Cr₂O₇²⁻ and Fe³⁺ sensor in aqueous environments.

A bifunctional cationic metal–organic framework based on unprecedented nonanuclear copper(ii) cluster for high dichromate and chromate trapping and highly efficient photocatalytic degradation of organic dyes under visible light irradiation

A bifunctional cationic MOF showed fast and highly efficient Cr₂O₇²⁻ and CrO₄²⁻ trapping, and highly efficient photocatalytic activity.

Spatial confinement of a cationic MOF: a SC–SC approach for high capacity Cr(vi)-oxyanion capture in aqueous solution

Compound 1 could be used as a single crystal container to capture Cr(vi)-oxyanions via ion exchange with high capacity and selectivity. It is the first report that demonstrates that CrO₄²⁻ ions could be traced and confirmed through a single-crystal to single-crystal (SC–SC) pattern.

Syntheses, structures, and magnetic properties of two unique Cu(ii)-based coordination polymers involving a crystal-to-crystal structural transformation from a 1D chain to a 3D network

Promoted by the DMF solvent, the 1D chain structure of 1 can be irreversibly transformed into the 3D sod network structure of 2 in a crystal-to-crystal fashion, which is accompanied by a drastic magnetic change.