Preparation and characterization of PVDF-montmorillonite mixed matrix hollow fiber membrane for gas–liquid contacting process

Porous PVDF-hydrophobic montmorillonite (MMT) mixed matrix membranes (MMMs) were fabricated via wet spinning method and used in membrane gas absorption process. The effects of hydrophobic MMT nano-clay loadings (1, 3 and 5 wt% of polymer) on the structure and performance were investigated. The fabricated membranes showed both finger-like and sponge-like structure with an increase in the length of finger-like pores in their cross-section, which resulted in higher permeability and lower mass transfer resistance compared to plain PVDF membrane. Also, significant improvements for surface hydrophobicity, critical entry pressure of water and porosity with the addition of filler were observed. The CO₂ absorption test was conducted through the gas–liquid membrane contactor and demonstrated a significant improvement in the CO₂ flux with MMT loading and the membrane with 5 wt% MMT presented highest performance. For example, at the liquid water velocity of 0.5 m s⁻¹, CO₂ flux of the MMM with 5 wt% MMT of 9.73 × 10⁻⁴ mol m⁻² s⁻¹ was approximately 56% higher than the PVDF membrane without nano-filler. In conclusion, MMMs with improved absorption properties can be a promising candidate for CO₂ absorption and separation processes through membrane contactors.     

Tailoring the separation performance of a carbon nanotube-based mixed matrix membrane decorated with metal–organic framework

Synthesis of mixed matrix membranes(MMM) using carbon nanotubes(CNTs) has shown great prospects for achieving excellent selective separation because of its special structure. Nevertheless, the preparation of highly selective MMM faces challenges, which is attributed to the obstacles encountered by CNTs dispersion in polymer matrix and elimination of interface defects. A novel CNT-based composite decorated with metal–organic framework(MOF) was synthesized and applied to the preparation of MMM. MO...     

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.     

Air–water interfacial synthesis of metal–organic framework hollow fiber membranes for water purification

In this study, we report a novel air–water interfacial self-crystallization (AWISC) method for scalable depositing continuous metal–organic framework (MOF) layers on modification-free polyvinylidene fluoride (PVDF) hollow fibers. Through importing MOF precursors into porous hollow fiber substrates with outer diameters of 1.2 mm and evaporating aqueous solutions under mild conditions, the metal ions and linkers close to solution surface can be concentrated firstly, thus the crystallization of MOFs will preferentially occur at interface of air and liquid precursors. The formed crystals can block off the pores of substrates to form defect-free MOF membranes. The prepared ZIF-8 membranes exhibit superior performance in molecular separation, with high rejections of 94.1 ∼ 99.5% for small molecules (molecular weight: 320 ∼ 800 Da) and large permeance up to 50 L m⁻² h⁻¹ bar⁻¹. Moreover, by combining AWISC and microfluidic processing, the high-performance ZIF-8 hollow fiber membranes with long length of 30 cm can be easily fabricated in scalability.     

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).     

Linkers and coordinated solvent molecules; the two effective factors on formation of zinc oxide nanoparticles from metal–organic frameworks

The host and the apohost frameworks of Zn₂(ndc)₂(DMF)₂ ∙(H₂O)₄ (1 ∙ DMF ∙ H₂O) and Zn₂(bdc)₂(H₂O)₂ ∙(DMF)₂ (2·H₂O·DMF), (H₂ndc = 2,6-naphthalene dicarboxylic acid, H₂bdc = benzene-1,4-dicarboxylic acid and DMF = N,N-Dimethylformamide), were synthesized, characterized and subsequently used for preparing of ZnO nanoparticles. The morphology of initial precursors has direct influence on agglomeration tendency of resulting ZnO nanoparticles. Linkers and coordinated solvent molecules are the two effective factors on the formation of zinc oxide nanoparticles from these metal–organic frameworks.     

UV-induced grafting of organic–inorganic antibacterial membrane on wool fiber

Wool fiber was modified by UV irradiation and then reacted with cross-linked chitosan-coated Ag-loading nano-SiO₂ (CCTS-SLS) composites to prepare antibacterial wool fiber. The results show the topography of wool surface was also modified along with the formation of active radicals during UV irradiation. These active groups were used to graft antibacterial materials CCTS-SLS. Compared with parent wool fiber, the antibacterial wool fiber was improved in dyeing property. The dyeing uptake increased by 98% in a dyeing time of 50 min. Also, the antifelting performance increased as a result of the decrease in directional frictional effect after UV irradiation modification.     

Synthesis and characterization of homo- and heterometallic metal–organic frameworks based on 1,2,4,5-benzenetetracarboxylate ligand

Two new three-dimensional metal–organic frameworks, [H₂N(CH₃)₂]₂[Zn(btec)]·DMF (1, H₄btec = 1,2,4,5-benzenetetracarboxylate acid) and [H₂N(CH₃)₂][ZnLi(btec)]·DMF (2), have been solvothermally synthesized and structurally characterized by single crystal X-ray diffraction. Compound 1 based on μ₄-btec features an anionic homometallic framework with 4-connected pts topology. Compound 2 is a heterometallic organic framework with rare (4, 4, 8)-connected network topology, which can be considered as constitute of a Li-btec (pts) net and a Zn-btec net. Moreover, the luminescent properties of two compounds are investigated in the solid state at room temperature.     

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.     

Use of molecular simulation for evaluating adsorption equilibrium of inhalation anaesthetic agents on metal–organic frameworks

Metal–organic frameworks (MOFs) were studied as alternatives to zeolites and activated carbon for adsorptive removal of wasted inhalation anaesthetic agents (IAA). Monte Carlo simulation was used to predict equilibrium adsorption isotherms of IAA on selected MOFs. Rather than generic forcefields (FFs), the all-atom FF parameters published by Arcario were used for IAA modelling. Continuous fractional component Monte Carlo (CFCMC) proved crucial for speedy simulation of large molecules. We found that allocating 70% probability to the CFlambdaSwap move gave optimum fits between simulation and experiment. The simulations provided us with an insight into the adsorption mechanisms of IAA in these structures. Heats of adsorption, Brauner-Emmet-Teller (BET) surface area, and total pore volume were deduced to be the crucial parameters for low, medium, and high range of relative pressures in the isotherm. Therefore, the chromium atoms in MIL-101-Cr are better adsorbers of IAA than MIL-100-Al at lower pressures despite the similarities in terms of the type of linkers and topology. Our simulation results corroborated the earlier published studies on the self-association behaviour of sevoflurane molecules based on the experimental isotherms reported for MOF-177-Zn. Finally, the high polarity of IAA is thought to explain good low-pressure simulation/experiment data agreement for the MOFs possessing coordinatively unsaturated sites (CUS) despite using generic DREIDING FF for the framework atoms. Our in-house parsing code helped realize that the grand-canonical Monte-Carlo simulation speed is not the same for all pressure points but decreases for higher pressure points. This can be explained by increased density of the adsorbates making successful trial moves less probable.     

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

Journal of Porous Materials -     

Preparation and characterization of polysulfone–cyclodextrin composite nanofiltration membrane: Solvent effect

α-Cyclodextrin membranes were prepared by the phase inversion method using four types of casting solvents such as N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc), and dimethyl formamide (DMF) herein-after termed as α-CD-NMP, α-CD-DMSO, α-CD-DMAc, and α-CD-DMF, respectively. The membranes were characterized by IR, XRD, TGA-DTA, DSC, and SEM analysis and show that solvents like NMP, DMA, DMF give good uniform morphological membranes and are better than that of DMSO. Thermal decompositions of the pure polymer and composite membranes indicate different range of thermal degradation of the membrane. This study reveals that the casting solvents NMP, DMF, DMAC have nearly same significant effect on morphology and other properties of the membranes. This is explained in terms of demixing behavior of the polymer and the combined effect of solvent volatility and polymer–solvent interactions as estimated from Hansen solubility parameter. Solvent hydrophobicity also affects the performance of the membrane and can be determined in terms of water permeability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Encapsulation and controlled release of fragrances from functionalized porous metal–organic frameworks

In the fragrance and perfume industry, the encapsulation and controlled release of fragrance is important to appeal to consumers and promote the quality of products. Here, we demonstrate that porous metal–organic frameworks (MOFs) can effectively encapsulate and release fragrant molecules in a controlled manner. The incorporation of functional groups into MOFs can improve the adsorption and release behavior of fragrant molecules. We find that polar ester-type fragrances exhibit higher adsorption on polar hydroxyl-functionalized MOF [UiO-66-(OH)₂] than on nonpolar MOF (UiO-66), while nonpolar terpenoid-type fragrances show no adsorption difference between these two MOFs. The release profiles show that UiO-66-(OH)₂ can prolong the release of polar fragrances compared with nonpolar fragrances. Both the experimental results and computer molecular modeling demonstrate that the hydroxyl groups in UiO-66-(OH)₂ can form strong hydrogen binding with different ester fragrances. The releasing kinetics indicates that pore diffusion is the rate-limiting step of fragrance release from MOFs. © 2018 American Institute of Chemical Engineers AIChE J, 65: 491–499, 2019     

Decoration of graphene network with metal–organic frameworks for enhanced electrochemical capacitive behavior

Well-intergrown nanocrystals of zeolitic imidazolate frameworks (ZIF-8) supported on three-dimensional (3D) graphene were prepared by a counter diffusion technique. The incorporation of ZIF-8 crystals greatly improves the surface areas of the graphene composites. The carbonized graphene–ZIF composites with hierarchical pore structures showed high electrochemical capacitance and good stability. This work provides an efficient method to synthesize porous carbon materials with high capacitance.     

Functionalized metal–organic frameworks with strong acidity and hydrophobicity as an efficient catalyst for the production of 5-hydroxymethylfurfural

In the dehydration of fructose to 5-hydroxymethyl furfural(HMF), in situ produced water weakens the acid strength of the catalyst and causes the rehydration of HMF, causing unsatisfactory catalytic activity and selectivity. In this work, a class of benzenesulfonic acid-grafted metal–organic frameworks with strong acidity and hydrophobicity is obtained by the direct sulfonation method using 4-chlorobenzenesulfonic acid as sulfonating agent. The resultant MOFs have a specific surface area of greater than 250 m~2·g~(-1), acid density above 1.0 mmol·g~(-1), and water contact angle up to 129°. The hydrophobic MOF-Ph SO_3 H exhibits both higher catalytic activity and selectivity than MOF-SO_3 H in the HMF synthesis due to its better hydrophobicity and olephilicity. Moreover, the catalyst has a high recycled stability. At last, fructose is completely converted, and 98.0% yield of HMF is obtained under 120 °C in a DMSO solvent system. The successful preparation of the hydrophobic acidic MOF provides a novel hydrophobic catalyst for the synthesis of HMF.     

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.     

The effect of mass transfer on reaction rates during immobilized β-galactosidase-catalyzed conversion of lactose in hollow fiber membrane

The mass transfer of substrates through a bio-catalytic membrane layer is a key issue in determining the performance of β-galactosidase-catalyzed conversion of lactose in a hollow fiber membrane reactor (HFMR) system. An investigation on the effect of solutes mass transfer through a bio-catalytic membrane layer was carried out using the coupled mass transfer-reaction model. Product formation was reduced at a trans-membrane pressure (TMP) of higher than 0.5?bar. Meanwhile, the concentration polarization modulus of solutes rapidly increased with higher TMP and this result suggests the formation of gel layer, which reduced bio-catalysis rate at higher applied TMP. The concentration profile of solutes or substrates on the bio-catalytic membrane surface, which determines the rate of reaction was reduced due to mass transfer limitation. This investigation highlights that the formation of substrate-β-gal complex in an immobilized system is influenced by the mass transfer behavior of its substrate.     

Molecular fingerprint and machine learning to accelerate design of high-performance homochiral metal–organic frameworks

Computational screening was employed to calculate the enantioseparation capabilities of 45 functionalized homochiral metal–organic frameworks (FHMOFs), and machine learning (ML) and molecular fingerprint (MF) techniques were used to find new FHMOFs with high performance. With increasing temperature, the enantioselectivities for (R,S)-1,3-dimethyl-1,2-propadiene are improved. The “glove effect” in the chiral pockets was proposed to explain the correlations between the steric effect of functional groups and performance of FHMOFs. Moreover, the neighborhood component analysis and RDKit/MACCS MFs show the highest predictive effect on enantioselectivities among the four ML classification algorithms with nine MFs that were tested. Based on the importance of MF, 85 new FHMOFs were designed, and a newly designed FHMOF, NO₂-NHOH-FHMOF, with high similarity to the optimal MFs achieved improved chiral separation performance, with enantioselectivities of 85%. The design principles and new chiral pockets obtained by ML and MFs could facilitate the development of new materials for chiral separation.