Heterogeneous heck coupling in multivariate metal–organic frameworks for enhanced selectivity

Highly selective heterogeneous Heck coupling has been demonstrated inside a series of metal–organic frameworks (MOFs). These MOFs, Zn₄O(BDC-NH₂)_n(BDC)_(3 − n) (n = 3, 2.4, 1.8, 1.2, 0.9, 0.75, 0.6, 0.3, and 0.15), have been synthesized with different amounts of 1,4-benzenedicarboxylate (BDC) and 2-amino-1,4-benzenedicarboxylate (BDC-NH₂) incorporated into their structure. The BDC-NH₂ is functionalized by covalent postmodification with salicylic aldehyde for binding catalytically active Pd(II) ions. The catalytic activity of the embedded Pd(II) ions was tested via heterogeneous Heck coupling to produce resveratrol trimethyl ether, a pharmaceutically relevant precursor. It is also found during catalytic testing that a trade-off exists between amount of metalation and pore blocking.     

Enhancement of permittivity in P(VDF-CTFE)/metal–organic frameworks mixed matrix membranes

A novel family of mixed matrix membranes (MMMs) with the combination of ferroelectric fluropolymers matrix (P(VDF-CTFE)) and ferroelectric MOFs fillers ([NH₃(CH₂)₄NH₃][M(HCOO)₃]₂(MCo^II, Mg^II, and Mn^II), have been synthesized and characterized, including the morphology, structures, and dielectric properties. Dielectric measurements revealed that the permittivity of the composites improved notablely with the introduction of ferroelectric MOFs fillers, while the dielectric loss was comparable to that of the polymer matrix. And also, interestingly, the enhancement of permittivity evidently dependent on the quantity and dielectric behavior of MOFs fillers, which may be valuable to the dielectric regulation of the polymer/MOFs MMMs. In addition, two different preparation methods were adopted respectively, including blending and electrospinning-hot pressing. The comparison of the two preparation methods revealed that the blending MMMs exhibit higher permittivity and higher dielectric loss than that of the electrospinning-hot pressing MMMs. To our knowledge, this is a novel research of high-ε_r dielectric MMMs fabricated by ferroelectric MOFs and ferroelectric fluropolymers, and this work may provide a new perspective on the further research of high-κ dielectric MMMs and the industrial application of ferroelectric MOFs.     

Vapor linker exchange of partially amorphous metal–organic framework membranes for ultra-selective gas separation

Metal–organic framework (MOF) membranes are promising for efficient separation applications. However, the uncontrollable pathways at atomic level impede the further development of these membranes for molecular separation. Herein we show that vapor linker exchange can induce partial amorphization of MOF membranes and then reduce their transport pathways for precisely molecular sieving. Through exchanging MOF linkers by incoming ones with similar topology but higher acidity, the resulted metal-linker bonds with lower strength cause the transformation of MOF membranes from order to disorder/amorphous. The linker exchange and partial amorphization can narrow intrinsic apertures and conglutinate grain boundary/crack defects of membranes. Because of the formation of ultra-microporous amorphous phase, the MOF composite membrane shows competitive H₂/CO₂ selectivity up to 2400, which is about two orders of magnitude higher than that of conventional MOF membranes, accompanied by high H₂ permeance of 13.4 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and good reproducibility and stability.     

Immobilization of lipase onto metal–organic frameworks for enantioselective hydrolysis and transesterification

Enzyme immobilization enhances the catalytic activity and stability of the enzyme, and also improves reusability. Metal–organic frameworks (MOFs), which possess diversified structures and porosity, have been used as excellent carriers for enzyme immobilization. Pseudomonas fluorescens lipase (PFL) has been successfully immobilized onto MOFs by covalent cross-linking to obtain a series of immobilized lipase (PFL@MOFs). PFL@MOFs are used for catalytic enantioselective hydrolysis of 2-(4-hydroxyphenyl) propionic acid ethyl ester enantiomers (2-HPPAEE) in aqueous medium and transesterification of 4-methoxymandelic acid enantiomers (4-MMA) in organic medium. The experimental results indicated that PFL@Uio-66(Zr) exhibits excellent enzymatic catalysis performances and high enantioselectives. In addition, to improve catalytic activity and reusability, PFL is modified by the polyethylene glycol (PEG) to prepare PEG-modified lipase (PFL-PEG), then PFL-PEG is immobilized onto Uio-66(Zr) to prepare PFL-PEG@Uio-66(Zr), demonstrating better reusability and catalytic activity compared with PFL@Uio-66(Zr).     

F3-functionalized nanoscale metal–organic frameworks for tumor-targeting combined chemotherapy and chemodynamic therapy

Nanoscale metal–organic frameworks (nMOFs) have attracted much attention as emerging porous materials as drug delivery carriers. Appropriate surface modification of them can greatly improve stability and introduce biocompatibility and cancer targeting functionality into drug delivery systems. Herein, we prepared nano-sized MIL-101(Fe)-N₃ and loaded anticancer drug doxorubicin (DOX) into it. The synthetic polymer layer Alkyne-PLA-PEG was then attached to the F3 peptide (labeled as Alkyne-PLA-PEG-F3), and the surface of DOX/MIL-101(Fe)-N₃ was covalently modified with it to obtain DOX/MIL-101-PLA-PEG-F3. Nano-sized MIL-101(Fe)-N₃ has high drug loading capacity and the modification of MIL-101(Fe)-N₃ by polymer Alkyne-PLA-PEG not only improved the dispersion, but also avoided the sudden release of the drugs and increased the biocompatibility of nanocarriers. The F3 peptide introduced into the nanocarriers also enabled it to specifically target tumor tissues and achieved active targeted drug delivery. As a nucleolin-mediated endocytosis drug delivery system, DOX/MIL-101-PLA-PEG-F3 can not only deliver anticancer drugs to tumors accurately, but also participate in Fenton-like reaction to generate hydroxyl radicals (•OH) for chemodynamic therapy (CDT), thus enabling combination therapy. It holds great promise as drug candidates to reduce systemic toxicity and improve the efficacy of cancer treatment.     

Correction to: Recent advances in the design of metal–organic frameworks for methane storage and delivery

Journal of Porous Materials -     

Immobilization of urease in metal–organic frameworks via biomimetic mineralization and its application in urea degradation

Enzyme immobilization has been accepted as an efficient technique for improving the stability and recyclability of enzymes. Herein, biomimetic mineralization strategy was employed to achieve the immobilization of urease in a type of metal–organic frameworks(zeolite imidazolate framework-8, ZIF-8), and the immobilized enzyme urease@ZIF-8 was systematically evaluated for its structure, activity, stability and recyclability, using the hydrolysis of urea as a model. The entrapment of urease was found to be realized in a synchronous manner with the formation of ZIF-8 crystal. The loading of urease in ZIF-8 was measured to be ca. 10.6% through the bicinchoninic acid(BCA) protein assay. The encapsulated urease could efficiently maintain its native conformation, which endowed the immobilized urease with excellent activity and stability, even in harsh conditions(e.g., in the presence of trypsin, acidic or alkali conditions, or at high temperature). Further, urease@ZIF-8 exhibited good recyclability during the degradation of urea, in which it could keep 58.86% of initial activity after being used for 5 cycles. Thus, biomimetic mineralization could be potentially utilized as a promising method to prepare immobilized ureases with superior activity, stability and recyclability, thereby facilitating the construction of efficient catalysts for industrial biocatalysis and biosensing.     

Double-layer structure,sorption and magnetism properties of metal–organic frameworks with trigonal planar ligand

A new double-layer metal–organic framework [Co₃(tcpt)₂(H₂O)₂] (1) has been synthesized using trigonal planar ligand 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine (H₃tcpt) as a bridging ligand and characterized by single-crystal X-ray diffraction, elemental analyses, IR, PXRD and TGA. Structure analysis reveals that compound 1 has a double-layer structure. Gas sorption measurements indicate that compound 1 exhibits selective adsorption capabilities for CO₂ over CH₄ and N₂. Furthermore, the magnetic studies of compound 1 show antiferromagnetic interactions between Co(II) ions.     

New composite membrane poly(vinyl alcohol)/graphene oxide for direct ethanol–proton exchange membrane fuel cell

This study investigated a simple synthesis of a crosslinked poly(vinyl alcohol)/ graphene oxide composite membrane with lower ethanol permeability membrane for passive direct ethanol–proton exchange membrane fuel cells (DE-PEMFCs). The chemical and physical structure, morphologies, ethanol uptake and permeability, ion exchange capacities, water uptake, and proton conductivities were determined and found that transport properties of the membrane were affected by the GO loading. The composite membrane with optimum GO content (15 wt %) exhibited the highest proton conductivity of 9.5 × 10⁻³ Scm⁻¹ at 30°C, 3.24 × 10⁻² Scm⁻¹ at 60°C, respectively and reduced ethanol permeability until 1.75 × 10⁻⁷ cm² s⁻¹. In the passive DE-PEMFC, the power density at 60°C were obtained as 5.84 mW cm⁻² higher than those by commercial Nafion 117 is 4.52 mW cm⁻². © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46928.     

In situ sol–gel route to novel sulfonated polyimide?SiO2 hybrid proton‐exchange membranes for direct methanol fuel cells

Polyimides (PIs) as high‐performance organic matrices are used in the preparation of PI composites because of their excellent mechanical, thermal and dielectric properties. The sol–gel method is a promising technique for preparing these PI composites due to the mild reaction conditions and the process being controllable. Although sulfonated polyimide (SPI) proton‐exchange membranes have attracted much attention recently, studies on preparing SPI‐based hybrid proton‐exchange membranes for fuel cells have been rare. A series of SPI? SiO₂ hybrid proton‐exchange membranes were prepared from amino‐terminated SPI pre‐polymers, 3‐glycidoxypropyltrimethoxysilane (KH‐560) and tetraethylorthosilicate through a co‐hydrolysis and condensation process using an in situ sol–gel method. The reactive silane KH‐560 was used to react with amino‐terminated SPI to form silane‐capped SPI in order to improve the compatibility between the polymer matrix and the inorganic SiO₂ phase. The microstructure and mechanical, thermal and proton conduction properties were studied in detail. The hybrid membranes were highly uniform without phase separation up to 30 wt% SiO₂. The storage modulus and tensile strength of the hybrid membranes increased with increasing SiO₂ content. The introduction of SiO₂ improved the methanol resistance while retaining good proton conductivity. The hybrid membrane with 30 wt% SiO₂ exhibited a proton conductivity of 10.57 mS cm^?1 at 80 °C and methanol permeability of 2.3 × 10^?6 cm² s^?1 possibly because the crosslinking structure and SiO₂ phases formed in the hybrids could retain water and were helpful to proton transport. Copyright © 2010 Society of Chemical Industry     

Mixed matrix metal–organic framework membranes for efficient CO2/N2 separation under humid conditions

Mixed matrix metal–organic framework (MOF) membranes show excellent application prospects in gas separation. However, their stability in various practical application scenarios is poor, especially under humid conditions. Herein, we encapsulated a hydrophobic ionic liquid (IL) into the cavity of MOFs, which effectively mitigated the competition between H₂O and CO₂ in humid gas mixtures, leading to stable and high-performance gas separation. For this reason, the resulting membranes using polymer of intrinsic miroporosity-1 (PIM-1) as a polymer matrix show good CO₂/N₂ separation performance and long-term test stability under humid environment. In particular, the 20 wt% IL-UiO/PIM-1 shows a high permeability of 13,778 Barrer and competitive CO₂/N₂ separation factor of ~35.2, transcending the latest upper bound. Besides, the according membrane module exhibits slightly decreased CO₂ permeability and selectivity, promoting the application of self-supporting membranes. This work provides a reliable strategy for the rational design of MOF-based hybrid membranes under extreme conditions.     

Preparation and investigation of acid–base composite membranes with modified graphitic carbon nanosheets for direct methanol fuel cells

The ethylenediamine-modified graphite oxide (EGO)-doped sulfonated poly (arylene ether ketone) (SPEEK) composite membranes have been prepared and developed for fuel cell applications in the present work. The base-modified EGO improves the dispersion of inorganic nanosheet in the polymer matrix and enhances proton conductivity by creating continuous conduction pathways. Furthermore, the methanol barrier property also be enhanced due to the nanosheet block the methanol-transport channels. EGO-filled membranes display improved dimensional stability, proton conductivity, and ethanol permeability than those using SPEEK control and graphite oxide (GO)-filled membranes. In the direct methanol fuel cells (DMFCs), the SPEEK/EGO-1.5 membrane displays the highest current density of 395.9 mA/cm² at 60°C, which is 1.6- and 1.4-fold higher than that of SPEEK (254.0 mA/cm²) and SPEEK/GO membrane (292.6 mA/cm²).     

Nonthermal plasma (NTP) activated metal–organic frameworks (MOFs) catalyst for catalytic CO2 hydrogenation

A systematic study of Ni supported on metal–organic frameworks (MOFs) catalyst (i.e., 15Ni/UiO-66) for catalytic CO₂ hydrogenation under nonthermal plasma (NTP) conditions was presented. The catalyst outperformed other catalysts based on conventional supports such as ZrO₂, representing highest CO₂ conversion and CH₄ selectivity at about 85 and 99%, respectively. We found that the turnover frequency of the NTP catalysis system (1.8 ± 0.02 s⁻¹) has a nearly two-fold improvement compared with the thermal catalysis (1.0 ± 0.06 s⁻¹). After 20 hr test, XPS and HRTEM characterizations confirmed the stability of the 15Ni/UiO-66 catalyst in the NTP-activated catalysis. The activation barrier for the NTP-activated catalysis was calculated as ~32 kJ mol⁻¹, being lower than the activation energy of the thermal catalysis (~70 kJ mol⁻¹). In situ DRIFTS characterization confirmed the formation of multiple carbonates and formates on catalyst surface activated by NTP, surpassing the control catalysts (e.g., 15Ni/α-Al₂O₃ and 15Ni/ZrO₂).     

Graphene oxide–TiO2 composite filtration membranes and their potential application for water purification

Graphene oxide-particle composite films with filtration function have been successfully synthesized by a two-step method. First, graphene oxide–TiO₂ composite sheets are prepared, which can form stable dispersion in water. Then, by assembling these composite sheets, graphene oxide–TiO₂ films are obtained. In these as-prepared films, dilated space and channels are desirably formed by introducing nanoparticles between these carbon sheets, making them promising separation membranes. We used these films as filtration membranes to remove dye molecules (methyl orange and rhodamine B) from water. The results show that apart from the adsorption capacities of these dyes, these graphene oxide–TiO₂ films can also capture additional amount of dye molecules, indicating their potential applications in water purification areas.     

Physical modification of polymeric support layer for thin film composite forward osmosis membranes by metal–organic framework-based porous matrix membrane strategy

Physical modification of support layers (SLs) for thin-film composite (TFC) forward osmosis (FO) membranes is the main goal of this study. Accordingly, the strategy of metal–organic framework (MOF)-based porous matrix membrane (PMM) was used for the fabrication of controllable SLs. Fourteen different TFC FO membranes were successfully fabricated by interfacial polymerization (IP) technique over the fourteen different SLs made of polyetherimide (PEI), polyethersulfone (PES), and twelve MOF-based PMM. The controllable MOF particles, fabricated SLs, and TFC membranes were characterized by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), dynamic light scattering (DLS), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle (CA), inductively coupled plasma (ICP), and developed SHN1 method. The results showed that the PMM strategy can lead to an increase in the degree of crosslinking of polyamide (PA) as a result of physical modification of the original SLs. Also, the PMM strategy reduced the structural parameters and hence the internal concentration polarization (ICP) was controlled. However, according to the characteristic curve, physical modification of the structure of PES and PEI by MOF-based PMM strategy caused a small and dramatic effect (respectively) on the performance of the TFC FO membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48672.     

Enhancing hydrophobicity via core–shell metal organic frameworks for high-humidity flue gas CO2 capture

Developing metal-organic framework(MOF) materials with the moisture-resistant feature is highly desirable for CO₂ capture from highly humid flue gas.In this work,a new core-shell MOF@MOF composite using Mg-MOF-74 with high CO₂ capture capacity as a functional core and hydrophobic zeolitic imidazolate framework-8(ZIF-8) as a protective shell is fabricated by the epitaxial growth method.Experimental results show that the CO₂ adsorption performance of the core-shell...