High-performance Metal-organic Frameworks Research Articles

Mixed matrix membranes (MMMs) using an emerging metal-organic framework (MUF-15) for CO2 separation

Inorganic fillers can largely determine the ultimate performance of mixed matrix membranes (MMMs). The identification of new inorganic fillers is therefore crucial for the continued development of MMMs. MMMs that contain metal-organic framework (MOF) fillers have been extensively investigated. However, high-performance MOF fillers remain scarce and are in high demand. In this study, MUF-15 (Massey University Framework-15), an emerging MOF possessing exceptional physicochemical properties, was combined into MMM with PIM-1 for the first time. Owing to its intrinsic ability to discriminate different guest molecules, MUF-15 is an excellent filler that delivers MMMs with exceptional CO2 separation properties. Also, the layered structure of MUF-15 enabled the exfoliation of crystalline nanosheets leading to the significant enhancements of both CO2 permeability and selectivity even when only a small quantity of <5 wt% was incorporated. In addition, MUF-15 fillers could effectively inhibit the physical aging process of PIM-1 membranes. After 35 days, MMMs with a 2 wt% loading of MUF-15 nanosheets showed 155 % higher CO2 permeability, with identical CO2/N2 selectivity (25.5), relative to pristine PIM-1 membranes, which all still surpassed the 2008 upper bound. The isoreticular chemical modification of MUF-15 is proposed as a strategy to increase to further improve the MMM performance.

Ferrous metal-organic frameworks with strong electron-donating properties for persulfate activation to effectively degrade aqueous sulfamethoxazole

Three novel persulfate activators, Fe(II)-based metal-organic frameworks (MOFs) were synthesized for the degradation of sulfamethoxazole (SMX). The degradation experiment results showed that all the Fe(II)MOFs could effectively activate persulfate and degrade more than 97% SMX within 180 min, with higher than 77% persulfate decomposition efficiencies. It was found by Mössbauer spectra that the variation of organic ligands for synthesis have an influence on the content of Fe(II) of these MOFs, thus resulted in the order of activation capacities: Fe(Nic) > Fe(PyBDC) > Fe(PIP). It was demonstrated that the activation of persulfate was mainly ascribed to the heterogeneous process that accomplished by surface-bounded Fe(II) acted as the main active site to provided electrons for persulfate or dissolved oxygen. EPR and molecular probe studies confirmed the coexistence of SO4−, OH, and O2−, and differentiated their contributions in SMX degradation. Possible degradation pathways of SMX were proposed based on the detection results of intermediates by UPLC-MS/MS. This work provides a new prospect into the synthesis of high-performance MOFs with strong electron-donating properties as efficient persulfate activators, which may encourage the employ of MOFs in the wastewater treatment process.

Matrix Coordination-Induced Electrochemiluminescence Enhancement of Tetraphenylethylene-Based Hafnium Metal-Organic Framework: An Electrochemiluminescence Chromophore for Ultrasensitive Electrochemiluminescence Sensor Construction.

Here, we discovered that rigidifying the tetraphenylethylene (TPE)-based ligand H4TCBPE (H4TCBPE = 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene) into Hf-based metal-organic framework (Hf-TCBPE) could lead to a stronger electrochemiluminescence (ECL) emission in comparison to H4TCBPE aggregates and H4TCBPE monomers. Due to the lack of close-packed TCBPE chromophores in Hf-TCBPE, which was required for aggregation-induced ECL (AI-ECL) enhancement, we defined this unprecedented phenomenon as matrix coordination-induced ECL (MCI-ECL) enhancement. The strong ECL intensity of Hf-TCBPE not only originated from the fixation of the TCBPE ligand between Hf6 clusters that restricted the intramolecular free motions of TCBPE and suppressed the nonradiative relaxation but also stemmed from the high porosity of Hf-TCBPE that rendered both internal and external TCBPE chromophores able to be excited. Considering the unique ECL characteristic of Hf-TCBPE, we combined the new ECL indicator of Hf-TCBPE as well as the phosphate-terminal ferrocene (Fc)-labeled hairpin DNA (Fc-HP3) aptamer together as a signal probe (Hf-TCBPE/Fc-HP3), which was employed to construct a novel "off-on" ECL sensor for ultrasensitive mucin 1 (MUC1) detection with the assistance of the exonuclease III (Exo III)-assisted recycling amplification strategy. As expected, the ECL sensor displayed a desirable linear response range from 1 fg/mL to 1 ng/mL and the detection limit down to 0.49 fg/mL. The MCI-ECL enhancement demonstrated by the Hf-TCBPE developed a new and promising strategy to design and synthesize high-performance metal-organic framework (MOF)-based ECL materials for constructing ultrasensitive ECL sensors.

Machine-learning-assisted high-throughput computational screening of high performance metal–organic frameworks

The combination of machine learning and high-throughput computation for the screening of MOFs with high performance.

Stable Bimetal-MOF Ultrathin Nanosheets for Pseudocapacitors with Enhanced Performance.

Exploring high-performance metal-organic frameworks (MOFs) for pseudocapacitors is quite meaningful for energy storage. Herein a bimetal NiCo-MOF with ultrathin thickness was prepared via a simple hydrothermal method, which shows excellent electrochemical performance with specific capacitances of 1945.83 and 1700.40 F/g at current densities of 0.5 and 1 A/g, respectively, while maintaining good stability. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy spectra unravel that the strong coupling between Ni and Co species enhances the valence state of Ni2+ in the ultrathin nanosheets, which facilitates the charge transfer during the electrochemical reaction and results in greatly improved pseudocapacitive reactivity. This work provides guidance on the promising prospect of MOF materials for pseudocapacitor applications.

Inlaying Ultrathin Bimetallic MOF Nanosheets into 3D Ordered Macroporous Hydroxide for Superior Electrocatalytic Oxygen Evolution.

Controllable synthesis of ultrathin metal-organic framework (MOF) nanosheets and rational design of their nano/microstructures in favor of electrochemical catalysis is critical for their renewable energy applications. Herein, an in situ growth method is proposed to prepare the ultrathin NiFe MOF nanosheets with a thickness of 1.5 nm, which are vertically inlaid into a 3D ordered macroporous structure of NiFe hydroxide. The well-designed composite delivers an efficient electrocatalytic performance with a low overpotential of 270 mV at a current density of 10 mA cm-2 and stable electrolysis as long as 10 h toward the electrochemical oxygen evolution reaction, much superior to the state-of-the-art RuO2 electrocatalyst. A comprehensive analysis demonstrates that the excellent performance originates from the desirable combination of the highly exposed active centers in the ultrathin bimetallic MOF nanosheets, effective electron conduction between MOF nanosheets and ordered macroporous hydroxide, and efficient mass transfer across the hierarchically porous hybridization. This study sheds light on the exploration of powerful protocols to gain diverse high-performance MOF nanosheets and may open a perspective to achieve their efficient electrocatalytic performance.

Metal-organic framework-derived hollow Co3O4/carbon as efficient catalyst for peroxymonosulfate activation

Concurrently rational optimization and design of the structure and composition of catalysts are significant for improving its catalytic performance. In this report, a novel hollow carbon supported ultrafine Co3O4 nanoparticles (HCo3O4/C) with a diameter of 6–12 nm were prepared as an active catalyst for peroxymonosulfate (PMS) activation. Initially, the zeolitic-imidazole-framework (ZIF-67) was synthesized followed by top-down etching strategy to get the hollow structure. Finally, as prepared hollow ZIF-67 was used as a precursor to fabricate HCo3O4/C. To understand the effects of structure and final composition on catalytic performance, another material, solid carbon supported Co3O4 nanoparticles (SCo3O4/C) was synthesized for comparison. The catalytic efficiency in control experiments between HCo3O4/C and SCo3O4/C was identified; in which HCo3O4/C demonstrated more than two times improved catalytic efficiency as compared to a solid structure. Interestingly, the HCo3O4/C catalyst exhibits better efficiency for PMS activation to generate sulfate radicals (SO4−) and the results show that degradation rate of targeted pollutant bisphenol A (BPA) was achieved up to 97% in 4 min, which is higher than other reported catalysts. The other factors which could influence PMS activation were also analyzed as well, for instance, the solution pH, catalyst loading, pollutant (BPA) concentration, system temperature and effect of organic molecules. Moreover, the Liquid chromatography-mass spectrometry (LC–MS) was used to identify the BPA degraded intermediate products. This work provides a new prospect into the synthesis of high-performance metal-organic framework (MOF) derived catalysts with exceptional properties, which may encourage the employ of hollow MOF materials in more practical applications.

Towards High Performance Metal-Organic Framework-Microporous Polymer Mixed Matrix Membranes: Addressing Compatibility and Limiting Aging by Polymer Doping.

Membrane separation for gas purification is an energy-efficient and environment-friendly technology. However, the development of high performance membranes is still a great challenge. In principle, mixed matrix membranes (MMMs) have the potential to overcome current materials limitations, but in practice there is no straightforward method to match the properties of fillers and polymers (the main components of MMMs) in such a way that the final membrane performance reflects the high performance of the microporous filler and the processability of the continuous polymer phase. This issue is especially important when high flux polymers are utilized. In this work, we demonstrate that the use of small amounts of a glassy polymer in combination with high performance PIM-1 allow for the preparation of metal-organic framework (MOF)-based MMMs with superior separation properties and low aging rates under humid conditions, meeting the commercial target for post-combustion CO2 capture.

CO2 adsorption performance of functionalized metal-organic frameworks of varying topologies by molecular simulations

The mixed linker metal-organic frameworks (MOFs) consisting of a variety of organic linkers functionalized by multiple functional groups exhibit better performance in carbon capture due to the increased surface heterogeneity. In order to explore the influence of the framework topology and mixed functionalities on the carbon capture performance, in this work, Zr-MOFs in three topologies (csq, ftw, scu) with each composed by one of the three types of linkers of different lengths were constructed, which were then functionalized by three types of functional groups (F, NH2, OCH3), respectively. Grand canonical Monte Carlo (GCMC) simulations were used to investigate CO2 adsorption performance of all created MOFs. We revealed that among the parent MOFs consisted of identical building blocks but in different topologies, ftw-MOFs exhibit the highest CO2 working capacity and CO2/N2 selectivity due to the strong affinity towards CO2. Moreover, the CO2 adsorption performance of ftw-MOFs shows obvious dependence on the pore size, consistent with their host-adsorbate interaction energy, which is not the fact for csq-MOFs and scu-MOFs. The enhanced CO2 adsorption performance upon functionalization of MOFs displays pore-size dependence as well, especially for NH2 functionalized frameworks in csq and scu, which is mostly attributed to the enhanced host-adsorbate Coulombic interaction. The proposed effects of the topology, the pore size and the functional group on CO2 adsorption performance of MOFs obtained in this study may provide meaningful insight into the rational design of high-performing MOFs for carbon capture by tuning the topology, pore size and functionality of frameworks.

Fabrication of Metal Organic Framework Flexible All Solid State Supercapacitors By Electrophoretic Deposition

Two-dimensional (2D) materials exhibit remarkable properties that suggest many possibilities for electronic applications. Metal organic frameworks (MOFs) are 2D nanosheets materials, which are good candidates for applications in various electrochemical applications such as fuel cells, batteries, and supercapacitors. Herein we report the fabrication of Ni3(2,3,6,7,10,11-hexaaminotriphenylene)2 (Ni3(HITP)2) flexible all solid-state supercapacitors by electrophoretic deposition (EPD). The Ni3(HITP)2 films were electrophoretically deposited in a layer-by-layer fashion onto targeted substrates. The electrodes’ surface morphology characterized by SEM shows a porous surface, and a honeycomb morphology known for improving the capacitive performance. TEM pictures confirmed the ultrathin two-dimensional structure of the (Ni3 (HITP)2) electrodes. The electrochemical capacitive performance of the obtained symmetric Ni3(HITP)2 supercapacitor has been characterized using cyclic voltammetry measurements and galvanostatic charge-discharge tests. This work demonstrates an exciting potential of EPD for the fabrication of high performance MOFs for flexible solid state energy storage systems.

Metal-organic framework one-dimensional fibers as efficient catalysts for activating peroxymonosulfate

Metal-organic framework (MOF) nanocrystalline materials have received great attention because of their application in heterogeneous catalysis. However, they suffer from poor separation from reaction mixtures in practical applications. In this study, we report the first cobalt metal-organic framework containing zeolitic imidazolate framework (ZIF)-67 nanoparticles immobilized on electrospun polyacrylonitrile (PAN) nanofibers, which was used as a composite catalyst (ZIF-67/PAN) for activating peroxymonosulfate (PMS). Detailed characterization showed that the ZIF-67/PAN nanofibers possessed a flexible one-dimensional structure. To demonstrate the catalytic performance of the ZIF-67/PAN nanofibers, the activation of PMS for the catalytic degradation of acid yellow-17 (AY) was chosen as the model catalytic reaction. The results show that 95.1% of AY (500mgL−1) was removed by ZIF-67/PAN in 10min, which is much higher than many other PMS catalyst. More interestingly, the flexible ZIF-67/PAN composite nanofibers catalysts were not only easy to separate from solution but they also retained high catalytic stability. The influencing factors for PMS activation were also investigated, including the catalyst dosage, reaction temperature, solution pH, and doping with competing organic molecules. The degradation mechanism was elucidated by electron paramagnetic resonance experiments. This work provides a new sight into the fabrication of high-performance MOF catalysts with outstanding recycling properties, which may promote the use of MOF materials in more practical applications.

Two-Dimensional Metal-Organic Framework Nanosheets for Membrane-Based Gas Separation.

Metal-organic framework (MOF) nanosheets could serve as ideal building blocks of molecular sieve membranes owing to their structural diversity and minimized mass-transfer barrier. To date, discovery of appropriate MOF nanosheets and facile fabrication of high performance MOF nanosheet-based membranes remain as great challenges. A modified soft-physical exfoliation method was used to disintegrate a lamellar amphiprotic MOF into nanosheets with a high aspect ratio. Consequently sub-10 nm-thick ultrathin membranes were successfully prepared, and these demonstrated a remarkable H2 /CO2 separation performance, with a separation factor of up to 166 and H2 permeance of up to 8×10-7 mol m-2 s-1 Pa-1 at elevated testing temperatures owing to a well-defined size-exclusion effect. This nanosheet-based membrane holds great promise as the next generation of ultrapermeable gas separation membrane.

Metal–Organic Frameworks Constructed from a New Thiophene-Functionalized Dicarboxylate: Luminescence Sensing and Pesticide Removal

A family of thiophene-based metal-organic frameworks (MOFs), [Zn(L)(BBI)·(H2O)2] (1) (BBI = 1,1'-(1,4-butanediyl)bis(imidazole)) and [Cd(L)(TPOM)0.75]·xS (2) (TPOM = tetrakis(4-pyridyloxy-methylene) methane, S represents noncoordinated solvent molecules) was constructed by employing a new linear thiophene-functionalized dicarboxylic acid (benzo-(1,2;4,5)-bis(thiophene-2'-carboxylic acid, H2L) to assemble with d10 ions in the presence of a flexible ancillary ligand under solvothermal conditions, which exhibit diverse structures. Most strikingly, both compounds 1 and 2 could be efficient luminescent sensory materials that are highly selective and sensitive to environmental contaminants, especially for Hg(II), Cu(II), Cr(VI), and salicylaldehyde, and yet remain unaffected by other molecules that may coexit. Furthermore, this is the first report on MOF-based sensors capable of recyclable detection of Hg(II), Cr(VI), and salicylaldehyde so far. The luminescent sensing mechanism was studied in detail as well. In addition, compound 2 is one of the rare examples of high-performance MOFs trapping 2,4-dichlorophenol from the wasted methanol solution.

Rational Design of a Low-Cost, High-Performance Metal-Organic Framework for Hydrogen Storage and Carbon Capture.

We present the in silico design of a MOF-74 analogue, hereon known as M2(DHFUMA) [M = Mg, Fe, Co, Ni, Zn], with enhanced small-molecule adsorption properties over the original M2(DOBDC) series. Constructed from 2,3-dihydroxyfumarate (DHFUMA), an aliphatic ligand which is smaller than the aromatic 2,5-dioxidobenzene-1,4-dicarboxylate (DOBDC), the M2(DHFUMA) framework has a reduced channel diameter, resulting in higher volumetric density of open metal sites and significantly improved volumetric hydrogen (H2) storage potential. Furthermore, the reduced distance between two adjacent open metal sites in the pore channel leads to a CO2 binding mode of one molecule per two adjacent metals with markedly stronger binding energetics. Through dispersion-corrected density functional theory (DFT) calculations of guest–framework interactions and classical simulation of the adsorption behavior of binary CO2:H2O mixtures, we theoretically predict the M2(DHFUMA) series as an improved alternative for carbon capture over the M2(DOBDC) series when adsorbing from wet flue gas streams. The improved CO2 uptake and humidity tolerance in our simulations is tunable based upon metal selection and adsorption temperature which, combined with the significantly reduced ligand expense, elevates this material’s potential for CO2 capture and H2 storage. The dynamical and elastic stabilities of Mg2(DHFUMA) were verified by hybrid DFT calculations, demonstrating its significant potential for experimental synthesis.

Materials design by evolutionary optimization of functional groups in metal-organic frameworks.

A genetic algorithm that efficiently optimizes a desired physical or functional property in metal-organic frameworks (MOFs) by evolving the functional groups within the pores has been developed. The approach has been used to optimize the CO2 uptake capacity of 141 experimentally characterized MOFs under conditions relevant for postcombustion CO2 capture. A total search space of 1.65 trillion structures was screened, and 1035 derivatives of 23 different parent MOFs were identified as having exceptional CO2 uptakes of >3.0 mmol/g (at 0.15 atm and 298 K). Many well-known MOF platforms were optimized, with some, such as MIL-47, having their CO2 adsorption increase by more than 400%. The structures of the high-performing MOFs are provided as potential targets for synthesis.

Interfacial Design of Mixed Matrix Membranes for Improved Gas Separation Performance.

High-performance metal-organic framework (MOF)/polyimide (PI) mixed matrix membranes (MMMs) are fabricated by a facile strategy by designing the MOF/PI matrix interface via poly dopamine coating. The overall separation performance of the designed MMMs surpasses the state-of-the-art 2008 Robeson upper bound for the H2 /CH4 and H2 /N2 gas pairs and approaches the 2008 upper bound for the O2 /N2 gas pair.

Ab Initio Derived Force Fields for Predicting CO2 Adsorption and Accessibility of Metal Sites in the Metal–Organic Frameworks M-MOF-74 (M = Mn, Co, Ni, Cu)

Metal–organic frameworks (MOFs) are versatile nanoporous materials that have gained significant interest as low heat capacity, high selectivity sorbents for CO2 capture applications. Large-scale atomistic simulations for identifying high-performance MOFs are possible, but are limited to systems for which existing molecular mechanics force fields describe the interactions between the guest and framework atoms with sufficient accuracy. However, standard force fields are not applicable to cases involving coordinatively unsaturated metal centers that can strongly bind specific sorbate molecules. It has been previously shown that improved force fields can be derived from quantum mechanical calculations. In this work, we derived force fields for an isostructural series of MOFs, M-MOF-74, where M = Mn, Co, Ni, and Cu, from first principles. Monte Carlo calculations in the Gibbs ensemble were used to calculate the CO2 adsorption isotherms in order to assess the quality of the derived force field parameters and to determine a generally applicable procedure for obtaining a reliable force field for a targeted MOF and adsorbate system. The computed CO2 adsorption isotherms for the different M-MOF-74 members agree with experimental measurements at low loading and show that Ni-MOF-74 possesses the highest affinity toward CO2 and Cu-MOF-74 the weakest. In addition, we explored the source of open metal site and pore inaccessibility in these materials and quantified its impact on adsorption, especially the discrepancies often observed between experiments and simulations at high loadings.

Rapid and Accurate Machine Learning Recognition of High Performing Metal Organic Frameworks for CO2 Capture.

In this work, we have developed quantitative structure-property relationship (QSPR) models using advanced machine learning algorithms that can rapidly and accurately recognize high-performing metal organic framework (MOF) materials for CO2 capture. More specifically, QSPR classifiers have been developed that can, in a fraction of a section, identify candidate MOFs with enhanced CO2 adsorption capacity (>1 mmol/g at 0.15 bar and >4 mmol/g at 1 bar). The models were tested on a large set of 292 050 MOFs that were not part of the training set. The QSPR classifier could recover 945 of the top 1000 MOFs in the test set while flagging only 10% of the whole library for compute intensive screening. Thus, using the machine learning classifiers as part of a high-throughput screening protocol would result in an order of magnitude reduction in compute time and allow intractably large structure libraries and search spaces to be screened.

An Unconventional Rapid Synthesis of High Performance Metal–Organic Framework Membranes

Metal-organic frameworks (MOFs) are attractive for gas separation membrane applications due to their microporous channels with tunable pore shape, size, and functionality. Conventional MOF membrane fabrication techniques, namely in situ and secondary growth, pose challenges for their wider commercial applications. These challenges include reproducility, scalability, and high manufacturing cost. Recognizing that the coordination chemistry of MOFs is fundamentally different from the covalent chemistry of zeolites, we developed a radically different strategy for MOF membrane synthesis. Using this new technique, we were able to produce continuous well-intergrown membranes of prototypical MOFs, HKUST-1 and ZIF-8, in a relatively short period of time (tens of min). With a minimal consumption of precursors and a greatly simplified synthesis protocol, our new technique provides potential for a continuous, scalable, reproducible, and easily commercializable route for the rapid synthesis of MOF membranes. RTD-prepared MOF membranes show greatly improved gas separation performances as compared to those prepared by conventional solvothermal methods, indicating improved membrane microstructure.

Christopher Wilmer &amp; Omar Farha

When most graduate students speak about their doctoral research at scientific gatherings, the response is usually polite applause and some probing questions from faculty. But when Christopher E. Wilmer spoke about his graduate work as part of a presentation at the Rice Business Plan Competition in Houston this April, he and his colleagues from NuMat Technologies walked away with more than $850,000. “As a graduate student, I’m tickled that I got to talk to an audience of over 500 people about my Ph.D. research and have them be excited enough about it to give us that much money,” says Wilmer, NuMat’s chief technology officer. “That’s just the biggest validation that our business idea and business plan are very sound,” agrees Omar K. Farha, NuMat’s chief scientific officer. Since its incorporation in February, NuMat has been wowing investors with plans to design and make high-performance metal-organic frameworks, or MOFs. The company ...