Post-synthetic Modification Of Metal-organic Frameworks Research Articles

Investigation of synergistic effects using alkanolamines on post-synthetic modification of metal-organic framework and CO2 adsorption capacity

The net global carbon balance is a key modern and even existential environmental issue to humans. Therefore, developing highly efficient gas separation technologies, e.g. based on the application of solid adsorbents, is critically important. Among the advanced solid adsorbents metal-organic frameworks (MOFs), especially MIL-101(Cr), which offers superior physicochemical properties, have proven to be highly promising porous materials for such purposes. In this approach, MIL-101(Cr) nanoadsorbent was functionalized using four alkanolamines (MIL-101(Cr)-alkanolamine) to enhance its CO2 adsorption capacity by increasing the polarity of its pores. Additionally, the synergistic effects of steric hindrance (-CH3 and –CH2CH2OH) and the basicity strength (pKa) of alkanolamines on post-synthetic modification (PSM) of MIL-101(Cr) were investigated. Alkanolamines were selected as the organic ligands because their nitrogen atoms (amino group) coordinate with the chromium ion in MIL-101(Cr), while the hydroxyl groups increase pore polarity and improve the CO2 adsorption capacity through creating weak hydrogen bonding (H-bonding) interactions, resulting in reduced energy consumption during regeneration. In this study, PXRD, IR, and FE-SEM results demonstrated that the crystal structure and morphology of nanoadsorbents remained intact after modification. CHN and ICP analyses were additionally employed to calculate the Nalkanolamine/Cr ratios. CO2 adsorption capacities of all MIL-101(Cr)-alkanolamine nanoadsorbents (∼30–∼45 %) and their selectivity profile (CO2:CH4 and CO2:N2) exhibited significant improvement as opposed to MIL-101(Cr). Investigations revealed that the adsorption capacities of all nanoadsorbents negligibly changed after five adsorption-desorption cycles.

Synthesis and evaluation of gene delivery vectors based on PEI-modified metal-organic framework (MOF) nanoparticles.

Zirconium-based metal-organic frameworks (MOFs) nanostructures, due to their capability of easy surface modification, are considered interesting structures for delivery. In the present study, the surfaces of UIO-66 and NH2-UIO-66 MOFs were modified by polyethyleneimine (PEI) 10000 Da, and their efficiency for plasmid delivery was evaluated. Two different approaches, were employed to prepare surface-modified nanoparticles. The physicochemical characteristics of the resulting nanoparticles, as well as their transfection efficiency and cytotoxicity, were investigated on the A549 cell line. The sizes of DNA/nanocarriers for PEI-modified UIO-66 (PEI-UIO-66) were between 212-291 nm and 267-321 nm for PEI 6-bromohexanoic acid linked UIO-66 (PEI-HEX-UIO-66). The zeta potential of all was positive with the ranges of +16 to +20 mV and +23 to +26 mV for PEI-UIO-66 and PEI-HEX-UIO-66, respectively. Cellular assay results showed that the PEI linking method had a higher rate of gene transfection efficiency with minimal cytotoxicity than the wet impregnation method. The difference between transfection of modified nanoparticles compared to the PEI 10 kDa was not significant but the PEI-HEX-UIO-66 showed less cytotoxicity. The present study suggested that the post-synthetic modification of MOFs with PEI 10000 Da through EDC/NHS+6-bromohexanoic acid reaction can be considered as an effective approach for modifying MOFs' structure in order to obtain nanoparticles with better biological function in the gene delivery process.

Magnetic Nitrogen-Rich UiO-66 Metal-Organic Framework: An Efficient Adsorbent for Water Treatment.

The postsynthetic modification of metal-organic frameworks (MOFs) has opened up a promising area to widen their water treatment application. However, their polycrystalline powdery state still restricts their widespread industrial-scale applications. Herein, the magnetization of UiO-66-NH2 is reported as a promising approach to facilitate the separation of the used MOFs after water treatment. A two-step postmodification procedure employing 2,4,6-trichloro-1,3,5-triazine (TCT) and 5-phenyl-1H-tetrazole (PTZ) agents was introduced to level up the adsorption performance of the magnetic nanocomposite. Despite a decrement in porosity and specific surface area of the designed MOFs (m-UiO-66-TCT) compared to neat UiO-66-NH2, it outweighs in adsorption capacity. It was observed that m-UiO-66-TCT has an adsorption capacity of ≈298 mg/g for methyl orange (MO) with facile MOF separation using an external magnet. Pseudo-second-order kinetic model and Freundlich isotherm models suitably interpret the experimental data. Thermodynamic studies showed that MO removal using m-UiO-66-TCT is spontaneous and thermodynamically favorable at higher temperatures. The m-UiO-66-TCT composite exhibited easy separation, high adsorption capacity, and good recyclability, rendering it an attractive candidate for the adsorptive removal of MO dye from aqueous environments.

Pressure-induced postsynthetic cluster anion substitution in a MIL-53 topology scandium metal-organic framework.

Postsynthetic modification of metal-organic frameworks (MOFs) has proven to be a hugely powerful tool to tune physical properties and introduce functionality, by exploiting reactive sites on both the MOF linkers and their inorganic secondary building units (SBUs), and so has facilitated a wide range of applications. Studies into the reactivity of MOF SBUs have focussed solely on removal of neutral coordinating solvents, or direct exchange of linkers such as carboxylates, despite the prevalence of ancillary charge-balancing oxide and hydroxide ligands found in many SBUs. Herein, we show that the μ2-OH ligands in the MIL-53 topology Sc MOF, GUF-1, are labile, and can be substituted for μ2-OCH3 units through reaction with pore-bound methanol molecules in a very rare example of pressure-induced postsynthetic modification. Using comprehensive solid-state NMR spectroscopic analysis, we show an order of magnitude increase in this cluster anion substitution process after exposing bulk samples suspended in methanol to a pressure of 0.8 GPa in a large volume press. Additionally, single crystals compressed in diamond anvil cells with methanol as the pressure-transmitting medium have enabled full structural characterisation of the process across a range of pressures, leading to a quantitative single-crystal to single-crystal conversion at 4.98 GPa. This unexpected SBU reactivity - in this case chemisorption of methanol - has implications across a range of MOF chemistry, from activation of small molecules for heterogeneous catalysis to chemical stability, and we expect cluster anion substitution to be developed into a highly convenient novel method for modifying the internal pore surface and chemistry of a range of porous materials.

Interfacial self-healing performance of carbon fiber/epoxy based on postsynthetic modification of metal-organic frameworks

The interfacial self-healing of fiber/matrix materials is an efficient strategy for extend the service life of composites. Here, we constructed the interfacial self-healing carbon fiber/epoxy composites system based on Diels-Alder reaction. Metal-organic frameworks (MOF) after postsynthetic modification (PSM), i.e., UiO-66-maleimide (UiO-66-M) is not only in-situ grafted on carbon fiber (CF) surface, but also used as nanofillers to disperse epoxy resin to fabricate UiO-66-M/epoxy nanocomposites. After growth MOF, the surface energy of CF enhanced from 38.34 to 58.90 mN m−1, the IFSS and ILSS increased by 39.43% and 16.62%, respectively. UiO-66-M rigid structure plays a key role for strengthening the mechanical interlocking. The interface between UiO-66-M-CF and UiO-66-M-EP can be healed three times and the best self-healing efficiency was 90.60%. In addition, UiO-66-M-EP resin can be reprocessed due to the Diels-Alder bonds.

Recent advancements in metal-organic frameworks composites based electrochemical (bio)sensors.

Metal-organic frameworks (MOFs) are a novel class of crystalline materials which find widespread applications in the field of microporous conductors, catalysis, separation, biomedical engineering, and electrochemical sensing. With a specific emphasis on the MOF composites for electrochemical sensor applications, this review summarizes the recent construction strategies on the development of conductive MOF composites (post-synthetic modification of MOFs, in situ synthesis of functional materials@MOFs composites, and incorporating electroactive ligands). The developed composites are revealed to have excellent electrochemical sensing activity betterthan their pristine forms. Notably, the applicable functionalized MOFs to electrochemical sensing/biosensing of various target species are discussed. Finally, we highlight the perspectives and challenges in the field of electrochemical sensors and biosensors for potential directions of future development.

Remodelling a shp: Transmetalation in a Rare-Earth Cluster-Based Metal-Organic Framework.

Postsynthetic modification of metal-organic frameworks (MOFs) is an important strategy for accessing MOF analogues that cannot be easily synthesized de novo. In this work, the rare-earth (RE) cluster-based MOF Y-CU-10 with shp topology was modified through transmetalation using a series of RE ions, including La(III), Nd(III), Eu(III), Tb(III), Er(III), Tm(III), and Yb(III). In all cases, metal exchange higher than 70% was observed, with reproducible results. All transmetalated materials were fully characterized and compared to the parent MOF Y-CU-10 with regard to crystallinity, surface area, and morphology. Additionally, single-crystal X-ray diffraction measurements were performed to provide further evidence of transmetalation occurring in the nonanuclear cluster nodes of the MOF.

Postsynthetic Modification of Metal-Organic Frameworks by Vapor-Phase Grafting.

A vapor-phase grafting strategy is developed for the postsynthetic modification of metal-organic frameworks (MOFs). On the basis of the Schotten-Baumann reaction between acyl chloride (-COCl) and amino (-NH2) groups and hydrolysis of -COCl, the carboxylated MOFs could be prepared through simple exposure in vaporized acyl chloride molecules and immersion in water. The modified MOFs have well-maintained crystalline structures and porosities and show substantially improved fluoride removal performance.

Ratiometric fluorescent sensing for phosphate based on Eu/Ce/UiO-66-(COOH)2 nanoprobe

The sensing of phosphate anion (PO43−) is an important subject for human health and environmental monitoring. Herein, a unique ratiometric fluorescent nanoprobe based on postsynthetic modification of metal-organic frameworks (MOF) UiO-66-(COOH)2 with Eu3+ and Ce3+ ions toward PO43− was proposed (designated as Eu/Ce/Uio-66-(COOH)2). The Eu/Ce/Uio-66-(COOH)2 nanoprobe exhibits three emission peaks at 377 nm, 509 nm, and 621 nm with the single excitation wavelength at 250 nm, respectively. The strong coordinating interaction between Ce3+ and O atoms in the PO43− group can result in the fluorescence quenching at 377 nm, while the fluorescence of 621 nm almost remains unchanged. Such a useful phenomenon is exploited for the construction of a ratiometric fluorescence platform for the detection of PO43−. The assay exhibited a good linear response in the 0.3–20 μM concentration range with the detection limit of 0.247 μM. In addition, this ratiometric fluorescent sensing method not only can be applied to read out PO43− concentration in real water samples, but also shows higher sensitivity, easier preparation and sensing procedures than other detection strategies.

Vapor-phase linker exchange of metal-organic frameworks.

Metal-organic frameworks (MOFs) have been attracting intensive attention because of their commendable potential in many applications. Postsynthetic modification for redesigning chemical characteristics and pore structures can greatly improve performance and expand functionality of MOF materials. Here, we develop a versatile vapor-phase linker exchange (VPLE) methodology for MOF modification. Through solvent-free and environment-friendly VPLE processing, various linker analogs with functional groups but not for straightforward MOF crystallization are inserted into frameworks as daughter building blocks. Besides single exchange for preparing MOFs with dual linkers, VPLE can further be performed by multistage operations to obtain MOF materials with multiple linkers and functional groups. The halogen-incorporated ZIFs exhibit good porosity, tunable molecular affinity, and impressive CO2/N2 and CH4/N2 adsorption selectivities up to 31.1 and 10.8, respectively, which are two to six times higher than those of conventional adsorbents. Moreover, VPLE can substantially enhance the compatibility of MOFs and polymers.

Tb post-functionalized La (III) metal organic framework hybrid probe for simple and highly sensitive detection of acetaldehyde

A novel highly fluorescent hybrid system called Tb@La-MOF (Tb@{[La(hisp)(Hhisp)(H2O)2]·2H2O}n) has been synthesized via post-synthetic modification of metal-organic framework centered on inert lanthanum ion. With excellent luminescent properties, Tb@La-MOF is developed as a fluorescent probe for acetaldehyde detection, notably, it can distinguish acetaldehyde specifically from a series of other organic molecules. More importantly, water-stable Tb@La-MOF exhibits advantages like low detection limit (0.00058% for water with acetaldehyde, volume fraction), rapid response, and resistance to decompose over a wide range of pH values (3.35–11.75). Therefore, it is expected to be a promising candidate for both practical sensing on liquid acetaldehyde and simple detection of acetaldehyde vapor. Besides, the possible sensing mechanism is discussed.

Fabrication of a Luminescence-Silent System Based on a Post-Synthetic Modification Cd-MOFs: A Highly Selective and Sensitive Turn-on Luminescent Probe for Ascorbic Acid Detection.

A unique three-dimensional luminescent metal-organic framework (Cd-MOFs), [Cd(tpbpc)2]·2H2O·DMF (Htpbpc = 4'-[4,2';6',4″]-terpyridin-4'-yl-biphenyl-4-carboxylic acid; DMF = dimethylformamide), was synthesized and structurally characterized; it exhibits excellent luminescent property and structural stability in aqueous solutions. Interestingly, an unparalleled luminescence-silent system CrO42-@Cd-MOFs was successfully fabricated by postsynthetic modification of metal-organic frameworks. This luminescence-silent system represents a highly selective and sensitive turn-on luminescent responding to ascorbic acid. First, this advanced fluorescent sensor displays excellent performance for CrO42- ions with a quenching of fluorescence intensity originating from fluorescence resonance energy transfer (FRET) mechanism. What's more, the fluorescent intensity of CrO42-@Cd-MOFs system can be recovered (turn-on) for sensing ascorbic acid because of the elimination of FRET process. Such a novel fabrication strategy should offer the guidance to develop various MOFs-implicated luminescence-silent systems as "turn-on" sensors for detection of specific chemicals.

Post-synthetic Modification of Metal-Organic Framework through Urethane Formation

An octahedral metal-organic framework (MOF), UiO-68, with two hydroxymethyl groups (UiO68-hyd) was synthesized for the first time and the hydroxy groups were post-synthetically modified with iso(th...

Incorporating Heavy Alkanes in Metal-Organic Frameworks for Optimizing Adsorbed Natural Gas Capacity.

Metal-organic frameworks (MOFs) as methane adsorbents are highly promising materials for applications such as methane-powered vehicles, flare gas capture, and field natural gas separation. Pre- and post-synthetic modification of MOFs have been known to help improve both the overall methane uptake as well as the working capacity. Here, a post-synthetic modification strategy to non-covalently modify MOF adsorbents for the enhancement of the natural gas uptake for the MOF material is introduced. In this study, PCN-250 adsorbents were doped with C10 alkane and C14 fatty acid and their impact on the methane uptake capabilities was investigated. It was found that even trace amounts of heavy hydrocarbons could considerably enhance the raw methane uptake of the MOF while still being regenerable. The doped hydrocarbons are presumably located at the mesoporous defects of PCN-250, thus optimizing the framework-methane interactions. These findings reveal a general approach that can be used to modify the MOF absorbents, improving their ability to be sustainable and renewable natural gas adsorption platforms.

Postsynthetic Modification of Metal-Organic Frameworks through Nitrile Oxide-Alkyne Cycloaddition.

Postsynthetic modification of metal-organic frameworks is an important method to tailor their properties. We report on the nitrile oxide-alkyne cycloaddition (NOAC) as a modification tool, a reaction requiring neither strained alkynes nor a catalyst. This is demonstrated with the reaction of nitrile oxides with PEPEP-PIZOF-15 and -19 at room temperature. PIZOF-15 and -19 are porous Zr-based MOFs (BET surface areas 1740 and 960 m2 g-1, respectively) consisting of two mutually interpenetrating UiO-type frameworks with linkers of the type -O2C[PE-P(R1,R2)-EP]CO2- (P, phenylene; E, ethynylene; R1 and R2, side chains at the central benzene ring with R1 = R2 = OCH2C≡CH or R1 = OCH2C≡CH and R2 = O(CH2CH2O)3Me). Their syntheses, using benzoic acid as a modulator, and their characterization are reported herein. The propargyloxy (OCH2C≡CH) side chains contain the ethyne moieties needed for NOAC. Formation of nitrile oxides through oxidation of oximes in aqueous ethanolic solution in the presence of PEPEP-PIZOF-15 and -19 resulted in the reaction of 96-100% of the ethyne moieties to give isoxazoles. Thereby the framework was preserved. The type of nitrile oxide RCNO was greatly varied with R being isopentyl, tolyl, 2-pyridyl, and pentafluorophenyl. A detailed NMR spectroscopic investigation showed the formation of the 3,5-disubstituted isoxazole to be clearly favored (≥96%) over that of the constitutional isomeric 3,4-disubstituted isoxazole, except for one example.

Realizing uniform dispersion of MnO2 with the post-synthetic modification of metal-organic frameworks (MOFs) for advanced lithium ion battery anodes.

MnO2 nanoparticles were uniformly loaded on the surface of zeolitic imidazolate frameworks (ZIF-67 and ZIF-8) with ligand modification via a facile method with no other impurities introduced, with an average diameter of less than 10 nm. The MnO2/ZIF-COOH composites with stable structures can effectively alleviate expansion tension and provide a fast ion transport channel during electrochemical performance tests. The introduction of carboxyl (-COOH) increases the specific capacity due to Li insertion, enhances the conductivity with ionization, and improves stability through the formation of H-bonds. When used as an anode for lithium ion batteries, the MnO2/ZIF-67-COOH composite exhibits an excellent rate performance (1208 mA h g-1 at 50 mA g-1, 931 mA h g-1 at 100 mA g-1, 828 mA h g-1 at 200 mA g-1, 684 mA h g-1 at 500 mA g-1, 566 mA h g-1 at 1000 mA g-1, 431 mA h g-1 at 2000 mA g-1, and 242 mA h g-1 at 5000 mA g-1) and high cycle stability even at high rates (a high capacity of 664 mA h g-1 is achieved at 1000 mA g-1 and is maintained at approximately 100% after 100 cycles).

Anchorage of Au3+ into Modified Isoreticular Metal\u2013Organic Framework-3 as a Heterogeneous Catalyst for the Synthesis of Propargylamines

Postsynthetic modification of metal-organic framework is a general and practical approach to access MOF-based catalysts bearing multiple active sites. The isoreticular metal–organic framework-3 (IRMOF-3) was modified with lactic acid through condensation reaction of the carboxyl group of lactic acid and amino group present in IRMOF-3 frameworks. Au3+ was subsequently anchored onto the metal–organic framework IRMOF-3 using postsynthetic modification. The synthezized IRMOF-3-LA-Au (LA = lactic acid) was characterized by powder X-ray diffraction, N2 adsorption-desorption, infrared spectroscopy, liquid-state nuclear magnetic resonance, thermogravimetric analysis, H2-temperature programmed reduction, transmission electro microscopy, and inductively coupled plasma–optical emission spectrometry. IRMOF-3-LA-Au acted as an efficient heterogeneous catalyst in the synthesis of propargylamines by three-component coupling reaction of aldehyde, alkyne, and amine. Moreover, the catalyst is applicable to various substituted substrates, including aromatic and aliphatic aldehydes, alkyl- and aryl-substituted terminal alkynes, and alicyclic amines. In addition, the catalyst can be easily separated from the mixture and can be reused for four consecutive cycles.

Multi-functional sites catalysts based on post-synthetic modification of metal-organic frameworks

Metal-organic frameworks (MOFs) are a unique class of porous crystalline materials that have shown promise for a wide range of applications. MOFs have been explored as a new type of heterogeneous catalytic materials, because of their high surface area, uniform and tunable pores, facile functionalization and incorporation of catalytic active sites. The use of multi-functional sites MOF materials as catalysts for synergistic catalysis and tandem reactions has attracted increasing attention. In this review, we aim to introduce the construction of bi- or multi-functional MOF catalysts with cooperative or cascade functions via post-synthetic modification (PSM).

Functional dual hydrophilic dendrimer-modified metal-organic framework for the selective enrichment of N-glycopeptides.

Analysis of protein glycosylation remains a significant challenge due to the low abundance of glycoproteins or N-glycopeptides. Here we have synthesized an amino-functionalized metal-organic framework (MOF) MIL-101(Cr)-NH2 whose surface is grafted with a hydrophilic dendrimer poly(amidoamine) (PAMAM) for N-glycopeptide enrichment based on the hydrophilic interactions. The selected substrate MOF MIL-101(Cr) owns high surface area which provides nice support for peptide adsorption. In addition, the MOF displayed a good hydrophilic property after being modified with amino groups. Most importantly, the grafted hydrophilic dendrimer PAMAM was firstly applied in the postsynthetic modification of MOFs. And this functionalization route using macromolecular dendrimer opens a new perspective in MOFs design. Owing to its long dendritic chains and abundant amino groups, our material displayed dual hydrophilic property. In the enrichment of standard glycoprotein HRP digestion, the functional MOF material was shown to have low detection limit (1 fmol/μL) and good selectivity when the concentration of nonglycopeptides was 100 fold higher than the target N-glycopeptides. All the results proved that MIL-101(Cr)-NH2 @PAMAM has great potential in the glycoproteome analysis.

X-ray crystallographic insights into post-synthetic metalation products in a metal-organic framework.

Post-synthetic modification of metal-organic frameworks (MOFs) facilitates a strategic transformation of potentially inert frameworks into functionalized materials, tailoring them for specific applications. In particular, the post-synthetic incorporation of transition-metal complexes within MOFs, a process known as 'metalation', is a particularly promising avenue towards functionalizing MOFs. Herein, we describe the post-synthetic metalation of a microporous MOF with various transition-metal nitrates. The parent framework, 1: , contains free-nitrogen donor chelation sites, which readily coordinate metal complexes in a single-crystal to single-crystal transformation which, remarkably, can be readily monitored by X-ray crystallography. The presence of an open void surrounding the chelation site in 1: prompted us to investigate the effect of the MOF pore environment on included metal complexes, particularly examining whether void space would induce changes in the coordination sphere of chelated complexes reminiscent of those found in the solution state. To test this hypothesis, we systematically metalated 1: with first-row transition-metal nitrates and elucidated the coordination environment of the respective transition-metal complexes using X-ray crystallography. Comparison of the coordination sphere parameters of coordinated transition-metal complexes in 1: against equivalent solid- and solution-state species suggests that the void space in 1: does not markedly influence the coordination sphere of chelated species but we show notably different post-synthetic metalation outcomes when different solvents are used.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.