Fluorinated Metal Organic Framework Research Articles

A microporous fluorinated MOF for efficient separation of C2H2 from C2H2/CO2 and C2H2/C2H4 mixtures

Acetylene (C2H2)-adsorbed physisorbents are promising in addressing significant yet challenging industrial separation processes, such as the purification of C2H2 from carbon dioxide (CO2) and ethylene (C2H4) from C2H2. Herein, we report a fluorinated metal–organic framework (MOF), QDU-MOF-1, featuring micropores full of fluorinated anions, which enables preferential C2H2 adsorption over CO2 and C2H4. QDU-MOF-1 exhibits a high C2H2 adsorption capacity of 141.03 cm3/g at 298 K and 1 bar. Dynamic breakthrough experiments demonstrate a C2H2 capture capacity of 127.76 cm3/g for equimolar C2H2/CO2 mixtures. Strong affinity was revealed by density functional theory calculations between C2H2 and SiF62- in pores through hydrogen bonding, contributing to high C2H2 adsorption capacity. QDU-MOF-1 also shows good air stability and recyclability, making it potential for the C2H2/CO2 and C2H2/C2H4 separation applications. This study underscores the strength of discovering advanced physisorbents for challenging gas separations with low energy footprints.

Leveraging synergistic polar and nonpolar binding sites in a fluorinated metal–organic framework for efficient ethane/ethylene separation

Constructing favorable C2H6-selective adsorbents for one-step C2H4 purification from C2H6/C2H4 mixtures is a matter of considerable significance, but is still a very challenging task in the field of petrochemical industry. Herein, we report a well-designed ant-type metal–organic framework (NUM-16) with appropriate pore size and pore environment for preferential trapping C2H6. NUM-16a (activated NUM-16) performs a high C2H6 uptake of 4.39 mmol/g and a good adsorption selectivity for C2H6/C2H4 (10:90, v/v) mixture at 298 K and 1 bar. The separation mechanism, as unveiled by the grand canonical Monte Carlo simulations and density functional theory calculations, is mainly attributed to synergistic polar and nonpolar binding sites on the pore surface of NUM-16a, which provide stronger affinities to C2H6 than C2H4. Under ambient conditions, dynamic breakthrough experiments revealed that NUM-16a demonstrates the enormous potential for actual C2H6/C2H4 separation and is expected to be applied to the correlative industrial process. Both experiments and theoretical calculations distinctly demonstrated that the reasonable integration of polar and nonpolar binding sites in C2H6-preferred MOFs is a feasible strategy for efficient C2H6/C2H4 separation. This work afforded some useful insights into designing and developing high-powered MOF adsorbents to solve tricky industrial separation challenges.

Superhydrophobic fluorinated metal–organic framework (MOF) devices for high-efficiency oil–water separation

A series of fluorinated UiO-66 was prepared using the bottom-up method. The composites of 2CF3-UiO-66 and cotton show excellent oil–water separation efficiency (up to 99.66%).

Fluorinated Metal–Organic Framework–Polymer Mixed Matrix Membrane with Tunable Hydrophobic Channel for Efficient Pervaporation of Butanol/Water

The permeability–selectivity trade‐off of membrane is a major challenge limiting the development of pervaporation (PV) technology. Rational design of high‐performance mixed matrix membranes (MMMs) has the potential to break off the trade‐off. Herein, a solvent‐assisted linker exchange‐based strategy is reported to introduce fluoroalkyl into metal–organic framework‐808 (MOF‐808). The pore size of fluorinated MOF‐808 can be adjusted with fluoroalkyl of different chain length (like trifluoromethyl and pentafluoropropyl). Then, the fluorinated MOF‐808/polyether block amide (PEBA) MMMs are prepared for the PV of n‐butanol/water. Compared with pristine PEBA membrane, 20 wt% 3F‐MOF‐808(P)/PEBA MMMs (3F = ‐CF3 group; P = postmodification method) exhibit 69% increase in permeation flux and 33% increase in separation factor in the PV of 2.5 wt% n‐butanol aqueous solutions at 70 °C. Based on Grand Canonical Monte Carlo and molecular dynamics simulations, fluorinated MOF‐808 shows better butanol affinity (pull effect) and stronger water repulsion ability (push effect). And the “push–pull effect” between fluorinated MOF‐808 with butanol/water is helpful to enhance the PV performance of MMMs. The application of “push–pull effect” provides a new strategy for the rational design of high‐performance MMMs, which is of great significance for the in‐depth research and application of PV technology.

Enhanced Intermolecular Electron Transfer in Fluorinated Metal–Organic Framework Photocatalysts for Efficient CO2 Reduction

AbstractEfficient electron transfer from photosensitizer to catalytic sites is crucial for effective artificial photosynthesis, yet it remains a significant challenge. Herein, it is reported that simple fluorination of the organic linkers in the MIL‐101(Fe) photocatalyst results in a remarkable threefold increase in the photocatalytic CO2‐to‐CO conversion rate (688 µmol g−1 h−1) compared to the pristine counterpart (230 µmol g−1 h−1). It is unveiled that, instead of directly modifying the electron structure of MIL‐101(Fe), the fluorinated linkers enhance the interaction between the discrete photocatalyst and photosensitizer ([Ru(bpy)3]2+, bpy = 2,2'‐bipyridine) via hydrogen bonding, thereby facilitating their intermolecular electron transfer. Most importantly, it is also demonstrated that this performance boosting strategy can be applied to other Fe‐based metal–organic frameworks (MOFs) photocatalysts such as MIL‐53(Fe) and MIL‐88(Fe). The present work not only underscores the fluorination of organic linkers as a generic promising approach to enhance the photocatalytic performance of MOF‐based catalysts, but also holds significant implications for photosynthesis and catalytic processes reliant on intermolecular electron transfer as an important step.

Ethane-selective permeation in mixed matrix membranes containing fluorinated carboxylic acid functionalized metal-organic frameworks

Membrane technology based on ethane-selective permeation materials is highly imperative for energy-efficient separating C2H6 and C2H4 mixture. Herein, we rationally constructed a fluorinated metal–organic framework based mixed matrix membrane (MMM), which can selectively permeate ethane from a C2H6/C2H4 mixture. The unique structure of MOF-808 allows functionalization of fluorinated carboxylic acid (FCA) in the MOF framework to construct various fluorinated MOFs via a facile post-synthetic strategy. As a proof of concept, four FCAs with different fluorocarbon chain lengths, including trifluoroacetic acid (TFA), pentafluoropropionic acid (PFPA), heptafluorobutyric acid (HFBA), and perfluorovaleric acid (PFVA), were used to create fluorinated MOFs and corresponding MMMs. The typical HFBA-MOF/PIM-1 hybrid membrane exhibits a high C2H6/C2H4 selectivity of about 2.3 with C2H6 permeability of 4246 Barrer at 253 K and 6 bar. Computational simulations confirm that the reversed permeation behavior is attributed to the strong affinity of C2H6 within the fluorinated pore environment, mediated by multiple hydrogen bonds.

Efficient C2H2/CO2 and C2H2/C2H4 separations in a novel fluorinated metal–organic framework

Separating acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) presents a significant challenge in the industry due to their closely similar physical properties. Herein, we synthesized a novel [NbOF5]2- pillared microporous metal–organic framework ZNU-11 with abundant electronegative sites for efficient C2H2/CO2 and C2H2/C2H4 adsorption separation. The uncoordinating fluorine atoms in the confined pores selectively capture C2H2 from CO2 and C2H4 by hydrogen bonding interactions. The C2H2 capacity of ZNU-11 is 45.5 cm3/g at 298 K and 100 kPa, over three folds of the C2H4 uptake and two folds of the CO2 uptake. The relatively modest C2H2 adsorption heat of 36.1 kJ/mol facilitates the straightforward desorption and regeneration of ZNU-11. Furthermore, density functional theory (DFT) calculations confirmed the stronger binding of C2H2 compared to CO2 and C2H4. Experimental breakthroughs with C2H2/CO2 and C2H2/C2H4 gas mixtures, coupled with excellent recyclability, validated the practical separation performance of ZNU-11. Notably, the dynamic separation factor of 4.2 for equimolar C2H2/CO2 mixture rivals those of many benchmark materials.

Partially fluorinated UiO-66-NH2(Zr): Positive effect of the fluorine moiety on the adsorption capacity for environmental pollutants of metal–organic frameworks

Increasing the stability of materials and affinity to the target has always been the pursuit. In this paper, the strategy of partially fluorinated metal–organic framework materials (MOFs) was introduced into the field of sample preparation for the first time, and the potential of this method to prepare materials with improved stability and extraction performance against environmental pollutants was verified. The UiO-66-(NH2)0.58(4F)0.42 coating was successfully prepared on carboxyl functionalized stainless steel fiber through covalent bonding method. Owing to the introduction of F element, the UiO-66-(NH2)0.58(4F)0.42 coating exhibited enhanced metal node acidity, hydrophobicity and stability, thus its extraction performance for phthalates (PAEs) was higher than that of pure UiO-66-NH2 and commercial fiber coatings. The UiO-66-(NH2)0.58(4F)0.42-coated fiber was coupled with GC–MS to detect PAEs, and the wide linear range (0.03–1000 ng/L), good correlation coefficients (0.9732–0.9998) and low detection limit (0.0039–0.016 ng/L) were obtained. The established method had also been successfully applied to detection of trace PAEs in plastic bags packed milk and bottled liquor with satisfactory recoveries (83.7 ± 5.1–118.1 ± 4.1 %). This research provides a new path for the preparation of environmental pollutant enrichment and removel materials with good performance.

Adsorption in Reversed Order of C2 Hydrocarbons on an Ultramicroporous Fluorinated Metal-Organic Framework.

Metal-organic frameworks have been widely studied in the separation of C2 hydrocarbons, which usually preferentially bind unsaturated hydrocarbons with the order of acetylene (C2 H2 )>ethylene (C2 H4 )>ethane (C2 H6 ). Herein, we report an ultramicroporous fluorinated metal-organic framework Zn-FBA (H2 FBA=4,4'-(hexafluoroisopropylidene)bis(benzoic acid)), shows a reversed adsorption order characteristic for C2 hydrocarbons, that the uptake for C2 hydrocarbons of the framework and the binding affinity between the guest molecule and the framework follows the order C2 H6 >C2 H4 >C2 H2 . Density-functional theory calculations confirm that the completely reversed adsorption order behavior is attributed to the close van der Waals interactions and multiple cooperative C-H⋅⋅⋅F hydrogen bonds between the framework and C2 H6 . Moreover, Zn-FBA exhibits a high selectivity of about 2.9 for C2 H6 over C2 H4 at 298 K and 1 bar. The experimental breakthrough studies show that the high-purity C2 H4 can be obtained from C2 H6 and C2 H4 mixtures in one step.

Determination of anionic perfluorinated compounds in water samples using cationic fluorinated metal organic framework membrane coupled with UHPLC–MS/MS

Global concerns stem from the environmental crisis have compelled researchers to develop selective and sensitive methods for the identification and measurement of emerging pollutants in the environmental matrices. The cationic F-TMU-66+Cl-/polyvinylidene fluoride metal-organic frameworks (MOFs) mixed matrix membrane (F-TMU-66+Cl-/PVDF MMM) was synthesized and used as a versatile adsorbent with multiple binding sites for the simultaneous extraction of twelve anionic perfluorinated compounds (PFCs) from reservoir water samples. The physical and chemical characteristics of the materials, as well as adsorption mechanism were fully surveyed by various instrumental techniques. Important extraction parameters, including amount of MOFs, pH, desorption conditions, and salinity were systematically investigated and optimized. The combination of dispersive membrane solid extraction based on F-TMU-66+Cl-/PVDF MMM with ultra-high performance liquid chromatography-tandem mass spectrometry provided ultra-low limit of detections within the range of 0.03–0.48 ng/L. By virtue of the simplicity and robustness of the extraction procedure, high sensitivity of detection scheme, good stability and selectivity of the F-TMU-66+Cl-/PVDF MMM, the developed method exhibits excellent practicability for ultra-trace analysis of anionic PFCs in water samples.

Fluorinated metal organic frameworks, MFFIVE-Ni-L (M = Fe/Al, L = pyr), with coordinatively unsaturated metal site for CO2 separation from flue gas in the presence of humidity by computational methods.

The anthropogenic emission of greenhouse gases, mainly CO2, is considered to be one of the most challenging environmental threats related to global climatic change. Herein, for the first time, we accurately interpreted the interaction of guest molecules such as H2O, CO2 and N2, the main constituent of flue gas, to a coordinatively unsaturated (CUS) square pillared fluorinated metal organic framework (MOF) using a grand canonical Monte Carlo (GCMC) simulation with the help of a specific forcefield. This specific forcefield is derived from the interaction energy profile of the guest molecules to the framework attained from the periodic-density functional theory (DFT) calculations. The DFT-derived forcefield effectively safeguarded the ability of the coordinatively unsaturated square pillared fluorinated MOF for CO2 separation in the presence of moisture.

Understanding the transport mechanism of seawater through FMOF-1 and its derivative via molecular dynamics simulation

The instability of most metal organic frameworks (MOFs) in water limits their application in seawater desalination. The fluorinated metal organic framework has a suitable pore size and excellent water stability and is expected to be a new generation desalination material. In this work, the desalination performance of FMOF-1 and FMOF-CH3 was evaluated by non-equilibrium molecular dynamics simulation. The water permeability is 16.18 L·cm−2·day−1·MPa−1, which is one to two orders of magnitude greater than that of conventional reverse osmosis membranes, and the ion rejection is greater than 95%. At the same time, the effect of different hydrophobic groups in FMOF membranes on desalination was explored, and the transport mechanism of water molecules passing FMOF membranes was further investigated.

Tuning the Ultra-Micropore Size of Fluorinated MOFs (M′F6-Ni-L) for CO2 Capture from Flue Gases by Advanced Computational Methods

The CO2 capture capability of ultra-microporous pillared square grid fluorinated metal–organic framework (MOF), i.e., [(M′F6)M(L)2]n, (where M′, M, and L are pillared metal ion, divalent cation, an...

Fluorinated metal-organic framework as bifunctional filler toward highly improving output performance of triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) with high power-generating performance always attract much attention as one emerging green energy technology. To pursue higher triboelectricity of triboelectric materials and improve output performance of TENGs, various nano/micro-materials with high charge-trapping capabilities were introduced into TENGs as fillers, but challenges remained in single functionality of the fillers. Herein, an unconventional filler, fluorinated metal-organic framework (F-MOF), with bifunctionality (both high charge-inducing and charge-trapping capabilities) was incorporated into polydimethylsiloxane (PDMS) matrix to highly improve negative triboelectricity, charge-trapping property and hydrophobicity of composite films. With such an optimized composite film and an Al foil as the triboelectric pair, TENGs were assembled and showed an 11-time increase in the output power density. The working mechanism of the F-MOF in the composite film was discussed through elaborate experimental and theoretical analysis. Besides, F-MOF fillers also worked well when other polymer matrices (Poly(vinylidene fluoride), (PVDF) silicone rubber (Si- rubber), Polytetrafluoroethylene (PTFE), Polyurethane (PU) and Polyacrylonitrile (PAN))were used as the substitutes for PDMS, proving that the F-MOF can be used as the universal filler for improving output performance of TENGs. The successful attempt to introduce MOF as a filler paved a promising way to enhance the output performance of TENGs and enlarge the materials pool to choose for TENGs.

Metal–organic framework derived porous 2D semiconductor C/ZnO nanocomposite with the high electrical conductivity

In this work, we report a simple method for synthesis of the C/ZnO semiconductor nanocomposite with the high porosity (732 m2/g) from fluorinated metal–organic framework (F-MOF), namely [Zn2(hfibba)2(L1)]n.DMF (TMU-44) where (L1 = N,N'-bis-pyridin-4-ylmethylene-benzene-1,5-diamine and H2hfibba = 4,4′-(hexafluoroisopropylidene) bis(benzoic acid)) with the limited porosity. The C/ZnO nanocomposite was characterized by powder X-ray diffraction; Brunauer-Emmett-Teller (BET) surface area, FE-SEM, and EDX mapping analysis. Furthermore, the as-synthesized C/ZnO nanocomposite showed favorable electrical conductivity at room temperature.

Natural gas upgrading using a fluorinated MOF with tuned H2S and CO2 adsorption selectivity

The process used to upgrade natural gas, biogas and refinery-off-gas directly influences the cost of producing the fuel and often requires complex separation strategies and operational systems to remove contaminants such as hydrogen sulfide (H2S) and carbon dioxide (CO2). Here we report a fluorinated metal–organic framework (MOF), AlFFIVE-1-Ni, that allows simultaneous and equally selective removal of CO2 and H2S from CH4-rich streams in a single adsorption step. The simultaneous removal is possible for a wide range of H2S and CO2 compositions and concentrations of the gas feed. Pure component and mixed gas adsorption, single-crystal X-ray diffraction and molecular simulation studies were carried out to elucidate the mechanism governing the simultaneous adsorption of H2S and CO2. The results suggest that concurrent removal of CO2 and H2S is achieved via the integrated favourable sites for H2S and CO2 adsorption in a confined pore system. This approach offers the prospect of simplifying the complex schemes for removal of acid gases. Contaminants such as CO2 and H2S present in natural gas and biogas streams must be removed before use; existing strategies to do so can be rather complex. Here, the authors use a fluorinated porous metal–organic framework to remove CO2 and H2S from CH4-rich feeds in a single step, potentially simplifying the process.

CO2 Capture Using the SIFSIX-2-Cu-i Metal–Organic Framework: A Computational Approach

The adsorption of carbon dioxide and its separation from mixtures with methane using the recently synthesized SIFSIX-2-Cu-i metal–organic framework has been systematically studied by employing a variety of molecular simulation techniques. Quantum density functional theory calculations have been combined with force-field based Monte Carlo and molecular dynamics simulations in order to provide a deeper insight on the molecular-scale processes controlling the thermodynamic and dynamic adsorption selectivity of carbon dioxide over methane, giving particular emphasis to the mechanisms underlying the diffusion of the confined molecules in this hybrid porous material. The diffusion process was revealed to be mainly controlled by both (i) the residence dynamics around some specific interaction sites of the fluorinated metal–organic framework and (ii) the dynamics related to the process where faster molecules overtake slower ones in the narrow one-dimensional channel of SIFSIX-2-Cu-i. We further unveiled a 1-dimen...

A Fluorinated Metal–Organic Framework for High Methane Storage at Room Temperature

A fluorinated metal–organic framework NOTT-108 with single pure-phase has been synthesized for the first time, which has enabled us to examine the effect of the substituted fluorine atoms on the methane storage. The activated NOTT-108a shows a permanent porosity comparable to its isoreticular NOTT-101a but exhibits a higher volumetric methane storage capacity of 247 cm3 (STP) cm–3 and a working capacity of 186 cm3 (STP) cm–3 (at 298 K and 65 bar) than 237 cm3 (STP) cm–3 and 181 cm3 (STP) cm–3 of NOTT-101a, attributed to the higher polarity/dipole moment of C–F bonds compared to that of C–H bonds for the enhanced electrostatic interaction with methane molecules.

Green Synthesis of a Microporous, Partially Fluorinated ZnII Paddlewheel Metal–Organic Framework: H2/CO2 Adsorption Behavior and Solid‐State Conversion to a ZnO–C Nanocomposite

AbstractA microporous, partially fluorinated metal–organic framework consisting of ZnII dimeric paddlewheel units, formulated as [Zn(hfipbba)(4bpdb)0.5]·H2O (1) [hfipbba = 4,4′‐(hexaflouroisopropylene)bis(benzoic acid); 4bpdb = 1,4‐bis(4‐pyridyl)‐2,3‐diaza‐1,3‐butadiene], was synthesized by room‐temperature self‐assembly and characterized structurally by single‐crystal XRD. Compound 1 adopts a 3D microporous framework structure constituted by six‐connected ZnII dimeric paddlewheel nodes with {44.610.8}‐net topology. Further, rapid synthesis of phase‐pure 1 by green synthetic approaches such as mechanochemical and sonochemical routes was achieved. The 3D framework of 1 houses 1D helical channels with narrow pore dimensions of about 3.11 × 4.17 Å and exhibits interesting gas‐uptake (H2/CO2) properties. The isosteric heats of adsorption Qst for H2 and CO2 were estimated to be 8.8 and 36.4 kJ mol–1, respectively. Interestingly, solid‐state conversion of 1 to phase‐pure hexagonal ZnO nanocrystals of 6.1 ± 0.63 nm in size, embedded in carbonaceous layers to form a ZnO–C nanocomposite (NC), occurred on heating of 1 to 600 °C under vacuum for 2 h. The ZnO–C NC was characterized by XRD, UV/Vis, energy‐dispersive X‐ray, and TEM analyses. The as‐synthesized ZnO–C NC exhibits good photocatalytic activity for the degradation of methylene blue.

Investigating H₂ Sorption in a Fluorinated Metal-Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering.

Simulations of H2 sorption were performed in a metal-organic framework (MOF) consisting of Zn(2+) ions coordinated to 1,2,4-triazole and tetrafluoroterephthalate ligands (denoted [Zn(trz)(tftph)] in this work). The simulated H2 sorption isotherms reported in this work are consistent with the experimental data for the state points considered. The experimental H2 isosteric heat of adsorption (Qst) values for this MOF are approximately 8.0 kJ mol(-1) for the considered loading range, which is in the proximity of those determined from simulation. The experimental inelastic neutron scattering (INS) spectra for H2 in [Zn(trz)(tftph)] reveal at least two peaks that occur at low energies, which corresponds to high barriers to rotation for the respective sites. The most favorable sorption site in the MOF was identified from the simulations as sorption in the vicinity of a metal-coordinated H2O molecule, an exposed fluorine atom, and a carboxylate oxygen atom in a confined region in the framework. Secondary sorption was observed between the fluorine atoms of adjacent tetrafluoroterephthalate ligands. The H2 molecule at the primary sorption site in [Zn(trz)(tftph)] exhibits a rotational barrier that exceeds that for most neutral MOFs with open-metal sites according to an empirical phenomenological model, and this was further validated by calculating the rotational potential energy surface for H2 at this site.