Functional Metal-organic Frameworks Research Articles

Highly-Efficient Sulfonated UiO-66(Zr) Optical Fiber for Rapid Detection of Trace Levels of Pb2.

Lead detection for biological environments, aqueous resources, and medicinal compounds, rely mainly on either utilizing bulky lab equipment such as ICP-OES or ready-made sensors, which are based on colorimetry with some limitations including selectivity and low interference. Remote, rapid and efficient detection of heavy metals in aqueous solutions at ppm and sub-ppm levels have faced significant challenges that requires novel compounds with such ability. Here, a UiO-66(Zr) metal-organic framework (MOF) functionalized with SOH group (SOH-UiO-66(Zr)) is deposited on the end-face of an optical fiber to detect lead cations (Pb) in water at 25.2, 43.5 and 64.0 ppm levels. The SOH-UiO-66(Zr) system provides a Fabry–Perot sensor by which the lead ions are detected rapidly (milliseconds) at 25.2 ppm aqueous solution reflecting in the wavelength shifts in interference spectrum. The proposed removal mechanism is based on the adsorption of [Pb(OH)] in water on SOH-UiO-66(Zr) due to a strong affinity between functionalized MOF and lead. This is the first work that advances a multi-purpose optical fiber-coated functional MOF as an on-site remote chemical sensor for rapid detection of lead cations at extremely low concentrations in an aqueous system.

Adsorptive removal of nitro- or sulfonate-containing dyes by a functional metal–organic framework: Quantitative contribution of hydrogen bonding

The removal of organic dyes from water is important from the perspective of sustainability. In this study, the adsorptive removal of four dyes having nitro or sulfonate groups was performed using highly porous metal–organic frameworks (MOFs, MIL101s) with or without further functionalization. In particular, a melamine-functionalized MOF (MIL101-Mela) was effective in the removal of martius yellow (MY), naphthol yellow S, orange G, and sunset yellow FCF. For example, the adsorbed quantity of MY over MIL101-Mela, even after the fourth recycle, was 6.9 times that over the fresh activated carbon. Moreover, MIL101-Mela showed higher adsorption capacity for the four studied dyes than previously reported any adsorbent. The adsorption results suggest the importance of the number of hydrogen donors and hydrogen acceptors in adsorbents and dyes, respectively, for improved performance in dye removal. Importantly, the mechanism of the dyes adsorption over the functionalized MIL101s is explained by the formation of six-membered rings between the studied MOFs and the dyes via hydrogen bonding. This work will pave the way toward the development of effective adsorbents for organics having high concentration of nitro or sulfonate groups.

Bioinspired Construction of Uranium Ion Trap with Abundant Phosphate Functional Groups.

Highly efficient extraction of radioactive uranium from aqueous solution remains a serious task in the nuclear energy field. To address this, we here create an effective uranium ion trap by using a novel and facile strategy that introduces bioinspired moiety phytic acid (PA) into highly robust PCN-222. The resultant metal-organic framework (MOF)-based uranium ion trap (PCN-222-PA) with a high density of accessible phosphate groups exhibits a remarkable U(VI) uptake capacity (401.6 mg·g-1), surpassing most of the reported phosphorus-modified MOFs and various other MOF adsorbents. Kinetics study reveals that PCN-222-PA can reduce the uranium concentration from 10 mg L-1 to 21 μg L-1, below the acceptable limit defined by the US Environmental Protection Agency. In addition, PCN-222-PA also shows good selectivity and high stability as well as excellent recyclability toward uranium capture. Our work demonstrates a new strategy to design functional MOFs with abundant phosphate groups and provides a new perspective for extracting uranium from aqueous solution.

Hierarchical ZIF-decorated nanoflower-covered 3-dimensional foam for enhanced catalytic reduction of nitrogen-containing contaminants

Metal Organic Frameworks (MOFs) represent a promising class of metallic catalysts for reduction of nitrogen-containing contaminants (NCCs), such as 4-nitrophenol (4-NP). Nevertheless, most researches involving MOFs for 4-NP reduction employ noble metals in the form of fine powders, making these powdered noble metal-based MOFs impractical and inconvenient for realistic applications. Thus, it would be critical to develop non-noble-metal MOFs which can be incorporated into macroscale and porous supports for convenient applications. Herein, the present study proposes to develop a composite material which combines advantageous features of macroscale/porous supports, and nanoscale functionality of MOFs. In particular, copper foam (CF) is selected as a macroscale porous medium, which is covered by nanoflower-structured CoO to increase surfaces for growing a cobaltic MOF, ZIF-67. The resultant composite comprises of CF covered by CoO nanoflowers decorated with ZIF-67 to form a hierarchical 3D-structured catalyst, enabling this ZIF-67@Cu foam (ZIF@CF) a promising catalyst for reducing 4-NP, and other NCCs. Thus, ZIF@CF can readily reduce 4-NP to 4-AP with a significantly lower Ea of 20 kJ/mol than reported values. ZIF@CF could be reused over 10 cycles and remain highly effective for 4-NP reduction. ZIF@CF also efficiently reduces other NCCs, such as 2-nitrophenol, 3-nitrophenol, methylene blue, and methyl orange. ZIF@CF can be adopted as catalytic filters to enable filtration-type reduction of NCCs by passing NCC solutions through ZIF@CF to promptly and conveniently reduce NCCs. The versatile and advantageous catalytic activity of ZIF@CF validates that ZIF@CF is a promising and practical heterogeneous catalyst for reductive treatments of NCCs.

Recyclable and Magnetically Functionalized Metal-Organic Framework Catalyst: IL/Fe3O4@HKUST-1 for the Cycloaddition Reaction of CO2 with Epoxides.

A recyclable and magnetic nanocomposite catalyst (IL/Fe3O4@HKUST-1) was synthesized via grafting ionic liquid (IL) [AEMIm]BF4 into magnetically functionalized metal-organic framework Fe3O4@HKUST-1 in a water-ethanol media. The properties of IL/Fe3O4@HKUST-1 were fully characterized by powder X-ray diffraction, electron microscopy, Fourier-transform infrared spectroscopy, nitrogen adsorption-desorption, density-functional theory, and a magnetic property measurement system. IL/Fe3O4@HKUST-1 showed high activity in the solvent-free cycloaddition of CO2 with epoxides under mild conditions. Furthermore, the catalyst can be easily separated from the reaction mixture, and the recycled catalyst maintained high performance for several cycles. The synergistic effect of the Lewis acid and base sites in IL/Fe3O4@HKUST-1 contributes to its greater reactivity than individual IL or HKUST-1.

Achieving Multifunctional Detection of Th4+ and UO22+ in the Post‐Synthetically Modified Metal–Organic Framework and Application of Functional MOF Membrane

AbstractThe field of post‐synthesis modification has aroused widespread concern from diverse perspectives, including chemistry, biology, and material science. Post‐synthesis modification can introduce rich functionality into metal–organic frameworks (MOFs) without destroying the main structure of MOFs. Based on this research status, a series of lanthanide metal–organic frameworks ([Ln2(NH2‐BDC)2.5(CH3COO)(DMA)(H2O)]•DMA, Ln = Pr, Nd, Sm, Eu, Gd and Tb, NH2‐BDC = 2‐aminoterephthalic acid, DMA = N,N‐Dimethylacetamide) with 3D network structures, are synthesized by hydrothermal synthesis. Due to the presence of uncoordinated amino groups in the ligands, a series of post‐synthesis modified compounds are successfully synthesized through aldimine condensation reaction. Based on the good fluorescence properties and stable structure of coordination polymers and post‐synthesis modified compounds in water or organic solvents, they are able to be used as potential fluorescence sensor for the detection of Th4+, UO22+, and Cr2O72−, and the calculation result shows that the post‐synthesis modified compounds are more sensitive to the detection of analytes (Th4+, UO22+ and Cr2O72−) than coordination polymers. In addition, the MOF membrane prepared by self‐assembly of [Eu2(NH2‐BDC)2.5(CH3COO)(DMA)(H2O)]•DMA and ternary soap‐free copolymer (VAc‐AA‐BA) emulsion can be used first for detecting aldehyde vapors.

Metal–Organic Frameworks as Versatile Platforms for Organometallic Chemistry

Metal–organic frameworks (MOFs) are emerging porous materials with highly tunable structures developed in the 1990s, while organometallic chemistry is of fundamental importance for catalytic transformation in the academic and industrial world for many decades. Through the years, organometallic chemistry has been incorporated into functional MOF construction for diverse applications. Here, we will focus on how organometallic chemistry is applied in MOF design and modifications from linker-centric and metal-cluster-centric perspectives, respectively. Through structural design, MOFs can function as a tailorable platform for traditional organometallic transformations, including reaction of alkenes, cross-coupling reactions, and C–H activations. Besides, an overview will be made on other application categories of organometallic MOFs, such as gas adsorption, magnetism, quantum computing, and therapeutics.

Large-Area Assembly of Metal-Organic Layered Ultrathin Films at the Liquid/Liquid Interface.

Two-dimensional functional metal-organic frameworks and coordination polymers have attracted much attention and have been successfully prepared in solutions and at interfaces through the coordination of ligands to metal ions. However, the preparation of large-area ultrathin ordered films is still a challenge. Here, a modified liquid/liquid interfacial epitaxial growth method has been developed. A planar liquid/liquid interface between a chloroform solution of bipyridine derivatives and pure water was constructed first, and then an aqueous solution of Eu3+ or Cu2+ ions was added dropwise into the water phase. A layered ultrathin film with the size of several hundreds of square micrometers appeared at the liquid/liquid interface after a certain time. The monitoring results showed that the formation of ultrathin films was a result of continuous epitaxial growth of the adsorbed species due to the synergistic effects of hydrophobic effects of the alkyl chains, coordination bonds between the ligands and metal ions, π-π interactions between the ligands, and the restriction of the interface on the vertical growth. This offers a way to fabricate more large-area thin films of amphiphilic molecules.

Efficient adsorption separation of methane from CO2 and C2–C3 hydrocarbons in a microporous closo-dodecaborate [B12H12]2- pillared metal–organic framework

A closo-dodecaborate [B12H12]2- functionalized metal organic framework (MOF), BSF-3, constructed by the self-assembly of the Cu(II) cation, 1,4-di(pyridin-4-yl)benzene linker and cluster [B12H12]2- pillar was investigated for the adsorption separation of light hydrocarbons. The activated MOF exhibited efficient uptake of CO2 and C2–C3 hydrocarbons with high separation selectivity of C3H8 (138), C2H2 (205), C2H4 (23), C2H6 (13) and CO2 (9) over CH4, outperforming many popular MOFs. The practical gas separation ability for C2H2/CH4, CO2/CH4 and C3H8/C2H6/CH4 was confirmed by mixed gas breakthrough experiments with no capacity loss after 7 cycles, indicating its potential for purification of methane from natural gas and pyrolysis gas. The gas bonding sites within the framework were further studied by modelling studies, which indicated that the anionic [B12H12]2- pillar contributed the most to capturing hydrocarbon molecules by multiple B-Hδ-···Hδ+-C interactions.

Metal-bipyridine/phenanthroline-functionalized porous crystalline materials: Synthesis and catalysis

Abstract Bipyridine(bpy)/phenanthroline(phen)-based ligands have been utilized widely to coordinate metals for homogeneous organic catalysis. The immobilization of M(bpy)/M(phen) active sites into porous supports is an intriguing approach to combine the appealing activities of homogeneous catalysts with the heterogeneity of the host materials. Herein we review the recent research progress of M(bpy)/M(phen)-functionalized metal–organic frameworks (MOFs) and covalent organic frameworks (COFs). Emphasis is focused on the synthetic strategies of these porous materials, as well as their catalytic performances in thermocatalysis, photocatalysis and electrocatalysis.

Reversible Diels-Alder and Michael Addition Reactions Enable the Facile Postsynthetic Modification of Metal-Organic Frameworks.

Functionalization of metal-organic frameworks (MOFs) is critical in exploring their structural and chemical diversity for numerous potential applications. Herein, we report multiple approaches for the tandem postsynthetic modification (PSM) of various MOFs derived from Zr(IV), Al(III), and Zn(II). Our current work is based on our efforts to develop a wide range of MOF platforms with a dynamic functional nature that can be chemically switched via thermally triggered reversible Diels-Alder (DA) and hetero-Diels-Alder (HDA) ligations. Furan-tagged MOFs (furan-UiO-66-Zr) were conjugated with maleimide groups bearing dienophiles to prepare MOFs with a chemically switchable nature. As HDA pairs, phosphoryl dithioester-based moieties and cyclopentadiene (Cp)-grafted MOF (Cp-MIL-53-Al) were utilized to demonstrate the cleavage and rebonding of the linkages as a function of temperature. In addition to these strategies, the Michael addition reaction was also applied for the tandem PSM of IRMOF-3-Zn. Maleimide groups were postsynthetically introduced in the MOF lattice, which were further ligated with cysteine-based biomolecules via the thiol-maleimide Michael addition reaction. On the basis of the versatility of the herein presented chemistry, we expect that these approaches will help in designing a variety of sophisticated functional MOF materials addressing diverse applications.

Engineering Nanoscale Metal‐Organic Frameworks for Heterogeneous Catalysis

Metal‐organic frameworks (MOFs) are porous crystalline materials composed of metal ions (or clusters) and organic ligands. Targeted preparation of nanoscale MOFs has been successfully achieved through numerous synthetic methods and is beneficial to improve the utilization of catalytic sites. On one hand, the dynamic bonds and rich selection of both metal centers and organic molecules enable broadening the types and functions of MOFs, thus offering the basis for rational design of heterogeneous catalysts at the molecular level. On the other hand, the reversible nature of connections between metal centers and organic ligands brings serious challenges about its stability under harsh reaction conditions. To optimize the catalytic performance of MOFs, considerable efforts have been devoted to tune the chemical environment of active sites by introducing electronic or channel confinement effect as well as controlling their size growth at nanoscale for increasing the surface coordination unsaturated sites. In this review, the state‐of‐the‐art development of nanoscale MOFs is summarized and particular focus is placed on regulation strategies of catalytic sites. The authors also propose the current challenges, the problems awaiting to be solved and opportunities in the future.

Metal-organic frameworks and their derivatives-modified photoelectrodes for photoelectrochemical applications

Artificial photosynthesis based on photoelectrochemical (PEC) strategy is another solar-to-chemical energy conversion method besides photocatalysis. Owing to the diversity of structure and the adjustability of synthesis, the metal-organic frameworks (MOFs) can enrich this important research field in the form of constructing a photoelectrode. In addition to solving the problems of difficult recovery for powder and the easy recombination for carriers in photocatalysis, MOFs and their derivatives-modified photoelectrodes can reasonably adjust the PEC activity at the molecular level and increase the contact area between the electrolyte and electrode, thereby facilitating the diffusion of electrolyte and reaction substrate in the electrode. In this review, we comprehensively reviewed representative studies in this area. Firstly, functions of MOFs in photoelectrodes are outlined, and the various synthesis strategies of MOFs-modified photoelectrodes are elaborated. Subsequently, special attention has been paid to the application and mechanism of MOFs-modified photoelectrodes (MIL, ZIF, UiO and PCN) in photo-electrochemistry. And we discuss the stability, reproducibility and reusability of MOFs-modified photoelectrodes. Finally, the challenges and improvements of MOFs-modified photoelectrodes in promoting practical application are proposed. Overall, MOFs and their derivatives-modified photoelectrodes achieved the integration of adsorption, photocatalysis and electrocatalysis. Notably, the research in this field is in infancy, many improvements are required before practical applications.

One-Step Encapsulation of ortho-Disulfides in Functionalized Zinc MOF. Enabling Metal-Organic Frameworks in Agriculture.

Application of natural products as new green agrochemicals with low average lifetime, low concentration doses, and safety is both complex and expensive due to chemical modification required to obtain desirable physicochemical properties. Transport, aqueous solubility, and bioavailability are some of the properties that have been improved using functionalized metal–organic frameworks based on zinc for the encapsulation of bioherbicides (ortho-disulfides). An in situ method has been applied to achieve encapsulation, which, in turn, led to an improvement in water solubility by more than 8 times after 2-hydroxypropyl-β-cyclodextrin HP-β-CD surface functionalization. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HR HAADF-STEM) and integrated differential phase contrast (iDPC) imaging techniques were employed to verify the success of the encapsulation procedure and crystallinity of the sample. Inhibition studies on principal weeds that infect rice, corn, and potato crops gave results that exceed those obtained with the commercial herbicide Logran. This finding, along with a short synthesis period, i.e., 2 h at 25 °C, make the product an example of a new generation of natural-product-based herbicides with direct applications in agriculture.

Supramolecular control of MOF pore properties for the tailored guest adsorption/separation applications

This work mainly focuses to review the recent progress of MOFs in different sorption and separation, and highlight the control approaches of the pore properties of MOFs on the capture and separation of the tailored guest molecules by various supramolecular interactions for the first time. • This review introduced the inherent pore properties of MOFs. • Some specific strategies are presented to improve the capture/separation of MOFs. • The supramolecular interactions are discussed between adsorbates and adsorbents. • The review prospected the sorption/separation applications of porous MOF materials. Because the adsorption/separation process plays a great role in chemical, petrochemical, pharmaceutical, environmental protection and many other fields, it has received extensive concern in both scientific research and practical applications. However, due to the new requirements and specific applications, it is a great necessity and urgency to explore new-type porous materials or maximize the adsorption capacity and improve the separation efficiency through endowing the adsorbent functionality to enable its special interactions with the adsorbates. The crystalline metal–organic framework (MOF) materials have shown great potentials in gas/liquid phase capture and separation due to their enormous porosities, tunable void properties, and easier modification, etc. Although there are lots of excellent reviews about functional MOFs in different fields, this review introduces the influence of MOF pore properties on the capture and separation of tailored guest molecules from the control of the supramolecular interactions for the first time. Some specific strategies are thus presented to enhance the adsorption/separation performance, and the relationships of the supramolecular interactions are well discussed between the adsorbates and adsorbents. Finally, the applications of porous MOF materials in adsorption/separation are further prospected and provided by the recent relevant studies.

The Role of Metal-Organic Frameworks in Electronic Sensors.

MOFs have a highly ordered self-assembled nanostructure, high surface area, nanoporosity with tunable size and shape, reliable host-guest interactions, and responsiveness to physical and chemical stimuli which can be exploited to address critical issues in sensor applications. On the one hand, the nanoscale pore size of MOFs ranging from less than 1 nm to ≈ 10 nm not only allows the diffusion of small molecules into the pores or through the MOF layer, but also excludes other larger molecules depending on the size, shape, and conformation of MOFs. On the other hand, MOFs with flexible structure exhibit a dynamic response to external stimuli, including guest molecules, temperature, pressure, pH, and light. Due to the unsaturated coordination metal sites and active functional groups, the interaction between certain analytes and active sites results in high selectivity. In this review, we summarize the latest studies on MOF-based electronic sensors in terms of the function of MOFs, discuss challenges, and suggest perspectives.

Integrated Microfluidic Synthesis of Aptamer Functionalized Biozeolitic Imidazolate Framework (BioZIF-8) Targeting Lymph Node and Tumor.

Targeted delivery of therapeutic molecules using nanomaterials is desired to elicit specific responses toward diseases. Such an integrated synthesis of functional material using a microfluidic approach is a great challenge. Functional metal organic frameworks (MOFs) with unique structural diversity possess a complicated synthesis procedure thereby requiring a modest, straightforward approach to synthesize size-controllable MOFs. Here, we develop an integrated microfluidic chip to synthesize the aptamer-modified biozeolitic imidazolate framework (BioZIF-8) to target the lymph node and tumor. The first stage of the microfluidic chip forms the ZIF-8 encapsulating biomolecules (bovine serum albumin, small interfering ribonucleic acid, and doxorubicin). The second stage modifies the surface of BioZIF-8 with the aptamer. Our approach reduces the overall synthesis time (∼3 mg/10 min against 15 h for the conventional two-step method) and encapsulates a higher number of biomolecules. The microfluidic approach realizes the rapid and fine-tuned synthesis of functional MOFs integrated into one-step.

2D Copper Tetrahydroxyquinone Conductive Metal-Organic Framework for Selective CO2 Electrocatalysis at Low Overpotentials.

Metal-organic frameworks (MOFs) are promising materials for electrocatalysis; however, lack of electrical conductivity in the majority of existing MOFs limits their effective utilization in the field. Herein, an excellent catalytic activity of a 2D copper (Cu)-based conductive MOF, copper tetrahydroxyquinone (CuTHQ), is reported for aqueous CO2 reduction reaction (CO2 RR) at low overpotentials. It is revealed that CuTHQ nanoflakes (NFs) with an average lateral size of 140nm exhibit a negligible overpotential of 16mV for the activation of this reaction, a high current density of ≈173mA cm-2 at -0.45V versus RHE, an average Faradaic efficiency (F.E.) of ≈91% toward CO production, and a remarkable turnover frequency as high as ≈20.82 s-1 . In the low overpotential range, the obtained CO formation current density is more than 35 and 25 times higher compared to state-of-the-art MOF and MOF-derived catalysts, respectively. The operando Cu K-edge X-ray absorption near edge spectroscopy and density functional theory calculations reveal the existence of reduced Cu (Cu+ ) during CO2 RR which reversibly returns to Cu2+ after the reaction. The outstanding CO2 catalytic functionality of conductive MOFs (c-MOFs) can open a way toward high-energy-density electrochemical systems.

Facile fabrication of a noval melamine derivative-doped UiO-66 composite for enhanced Co(II) removal from aqueous solution

In this study, a novel melamine derivative (TABC)-doped metal-organic framework (MOF) composite UiO-66-TABC was synthesised, with an attempt to remove Co(II) from aqueous solution. All analysis results characterised by SEM, XRD, FT-IR, EDS, and N2 adsorption–desorption experiments confirmed that TABC was successfully encapsulated into UiO-66. Compared to initial MOFs, the doped composite exhibited a remarkable decrease in both the surface area and pore volume due to the incorporation of TABC nanoparticles into the cages of the UiO-66. The adsorption experiments showed that the adsorption performance of UiO-66-TABC to Co(II) was significantly superior to that of UiO-66, with a maximum adsorption capacity of 137.0 mg/g at 298 K. The adsorption process was spontaneous and endothermic, and can be well described by the Langmuir and pseudo-second-order kinetic models. The regeneration experiments also demonstrated that UiO-66-TABC was highly stable and could be recycled with relatively stable adsorption ability. This study provides a facile method for preparing functional MOFs by doping approach to improve their adsorption capacity, which will improve the applicability of MOFs without grafted atoms or groups.

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF