Polymer-assisted synthesis of nanocrystalline copper-based metal–organic framework for amine oxidation

Synergistic Construction of Sub-Nanometer Channel Membranes through MOF-Polymer Composites: Strategies and Nanofiltration Applications

The selective separation of small molecules at the sub-nanometer scale has broad application prospects in the field, such as energy, catalysis, and separation. Conventional polymeric membrane materials (e.g., nanofiltration membranes) for sub-nanometer scale separations face challenges, such as inhomogeneous channel sizes and unstable pore structures. Combining polymers with metal-organic frameworks (MOFs), which possess uniform and intrinsic pore structures, may overcome this limitation. This combination has resulted in three distinct types of membranes: MOF polycrystalline membranes, mixed-matrix membranes (MMMs), and thin-film nanocomposite (TFN) membranes. However, their effectiveness is hindered by the limited regulation of the surface properties and growth of MOFs and their poor interfacial compatibility. The main issues in preparing MOF polycrystalline membranes are the uncontrollable growth of MOFs and the poor adhesion between MOFs and the substrate. Here, polymers could serve as a simple and precise tool for regulating the growth and surface functionalities of MOFs while enhancing their adhesion to the substrate. For MOF mixed-matrix membranes, the primary challenge is the poor interfacial compatibility between polymers and MOFs. Strategies for the mutual modification of MOFs and polymers to enhance their interfacial compatibility are introduced. For TFN membranes, the challenges include the difficulty in controlling the growth of the polymer selective layer and the performance limitations caused by the "trade-off" effect. MOFs can modulate the formation process of the polymer selective layer and establish transport channels within the polymer matrix to overcome the "trade-off" effect limitations. This review focuses on the mechanisms of synergistic construction of polymer-MOF membranes and their structure-nanofiltration performance relationships, which have not been sufficiently addressed in the past.

Guiding Metal Organic Framework Morphology via Monolayer Artificial Defect-Induced Preferential Facet Selection

Guiding metal organic framework (MOF) morphology, especially without the need for chemical additives, still remains a challenge. For the first time, we report a unique surface guiding approach in controlling the crystal morphology formation of zeolitic imidazole framework-8 (ZIF-8) and HKUST-1 MOFs on disrupted alkanethiol self-assembled monolayer (SAM)-covered Au substrates. Selective molecule removal is applied to generate diverse SAM matrices rich in artificial molecular defects in a monolayer to direct the dynamic crystal growth process. When a 11-mercaptoundecanol alkanethiol monolayer is ruptured, the hydroxyl tail groups of surface residue molecules act as nucleating sites by coordination with precursor metal ions. Meanwhile, the exposed alkane chain backbones stabilize a particular facet of MOF nuclei in the dynamic growth by slowing down their crystal growth rates along a specific direction. The competitive formation between the [110] and [100] planes of ZIF-8 ultimately regulates the crystal shapes from rhombic dodecahedron, truncated rhombic dodecahedron, and truncated cube to cube. Similarly, changeable morphologies of HKUST-1 crystals are also achieved from cube and tetrakaidekahedron to octahedron, originating from the competitive selection between the [100] and [111] planes. In addition to the artificial matrix preferred orientation of initial nucleation, parameters such as temperature also play a crucial role in the resulting crystal morphology. Standing on the additive-free MOF crystal morphology growth control, porous architectures prepared in this approach can act as templates for ligand-free metal (Au, Ag, and Cu) nanocluster synthesis. The nanocluster-embedded MOF structures represent distinct crystal morphology-dependent optical properties, and interestingly, their fluorescence emission can be highly enhanced by facet-induced nanocluster packing alignments. These findings not only provide a unique thought on MOF crystal morphology guidance but also pave a new route for the accompanied property investigation and further application.

Synthesis of Nano/Microsized MIL-101Cr Through Combination of Microwave Heating and Emulsion Technology for Mixed-Matrix Membranes

Nano/microsized MIL-101Cr was synthesized by microwave heating of emulsions for the use as a composite with Matrimid mixed-matrix membranes (MMM) to enhance the performance of a mixed-gas-separation. As an example, we chose CO₂/CH₄ separation. Although the incorporation of MIL-101Cr in MMMs is well-known, the impact of nanosized MIL-101Cr in MMMs is new and shows an improvement compared to microsized MIL-101Cr under the same conditions and mixed-gas permeation. In order to reproducibly obtain nanoMIL-101Cr microwave heating was supplemented by carrying out the reaction of chromium nitrate and 1,4-benzenedicarboxylic acid in heptane-in-water emulsions with the anionic surfactant sodium oleate as emulsifier. The use of this emulsion with the phase inversion temperature (PIT) method offered controlled nucleation and growth of nanoMIL-101 particles to an average size of <100 nm within 70 min offering high apparent BET surface areas (2,900 m² g^-1) and yields of 45%. Concerning the CO₂/CH₄ separation, the best result was obtained with 24 wt.% of nanoMIL-101Cr@Matrimid, leading to 32 Barrer in CO₂ permeability compared to six Barrer for the neat Matrimid polymer membrane and 21 Barrer for the maximum possible 20 wt.% of microMIL-101Cr@Matrimid. The nanosized filler allowed reaching a higher loading where the permeability significantly increased above the predictions from Maxwell and free-fractional-volume modeling. These improvements for MMMs based on nanosized MIL-101Cr are promising for other gas separations.

Introducing a dual-step procedure comprising microwave and electrical heating stages for the morphology-controlled synthesis of chromium-benzene dicarboxylate, MIL-101(Cr), applicable for CO2 adsorption

MIL-101(Cr) crystals were synthesized through a dual-step procedure consisting of a short term nucleation step in which the solution mixture was heated using microwave irradiation (MW phase) followed by a long-term growth step in which conventional electrical heating (CE phase) was used as a source of energy. The primary objective of such segregation is to increase the nuclei population at the end of the nucleation step. As a result of the high population density of nuclei, it is expected that the total time required to grow crystals in the CE phase decreases. The results showed that using the dual-step procedure led to a significant reduction in total synthesis time. The results also revealed that increasing pH from around 1.5 to 3 at the beginning of the CE phase resulted in producing octahedral crystals instead of a multifaceted sphere. Octahedral crystals exhibit higher CO₂ adsorption capacity than the multifaceted ones. Using the dual step procedure, one can not only control the morphology but also reduce the total synthesis time of MIL-101(Cr) crystals.

Synthesis and Characterization of Metal Organic Frameworks for Gas Storage

This research demonstrates the preparation of a metal-organic framework (MOF-199) using the solvothermal method. The solvothermal conditions for synthesis and activation were investigated by changing the synthesis time (24 - 48 h), the solvothermal temperatures (85 and 100 °C), and the effect of the ethanol: water solvent ratio (within the solvents range from 1:1 to 1:2 ratios). All synthesized samples were characterized using of x-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area (BET). The prepared MOF-199 at the optimal conditions (100 °C for 48 h, 1:1 of the ethanol: water) has up to 5518 m2/g m2/g surface area (BET), 0.693 cm3 g−1 specific volume, a 11.8 Å porous size, and 103 crystallinity. All MOF-199 samples were activated for 21 h at 60 °C.

Colloid-assisted growth of metal–organic framework nanoparticles

A new colloid-assisted approach is introduced to synthesize metal–organic framework (MOF) nanoparticles.

Block co-polyMOFs: morphology control of polymer-MOF hybrid materials

The hybridization of block copolymers and metal-organic frameworks (MOFs) to create novel materials (block co-polyMOFs, BCPMOFs) with controlled morphologies is reported. In this study, block copolymers containing poly(1,4-benzenedicarboxylic acid, H₂bdc) and morphology directing poly(ethylene glycol) (PEG) or poly(cyclooctadiene) (poly(COD)) blocks were synthesized for the preparation of BCPMOFs. Block copolymer architecture and weight fractions were found to have a significant impact on the resulting morphology, mediated through the assembly of polymer precursors prior to MOF formation, as determined through dynamic light scattering. Simple modification of block copolymer weight fraction allowed for tuning of particle size and morphology with either faceted and spherical features. Modification of polymer block architecture represents a simple and powerful method to direct morphology in highly crystalline polyMOF materials. Furthermore, the BCPMOFs could be prepared from both Zr⁴⁺ and Zn²⁺ MOFs, yielding hybrid materials with appreciable surface areas and tuneable porosities. The resulting Zn²⁺ BCPMOF yielded materials with very narrow size distributions and uniform cubic morphologies. The use of topology in BCPMOFs to direct morphology in block copolymer assemblies may open new methodologies to access complex materials far from thermodynamic equilibrium.

A novel copper(ii)–lanthanum(iii) metal organic framework as a selective catalyst for the aerobic oxidation of benzylic hydrocarbons and cycloalkenes

The synthesis and catalytic activity of a novel heteronuclear Cu^II and La^III metal organic framework (MOF) having pyridinedicarboxylic acid (CuLa-MOF) is reported.

Ligand-free N-arylation of heterocycles using metal–organic framework [Cu(INA)2] as an efficient heterogeneous catalyst

A metal–organic framework [Cu(INA)₂] was synthesized and used as a heterogeneous catalyst for arylation of a wide range of N–H heterocycles and aryl halides under ligand-free conditions.

Nanoscaled copper metal-organic framework (MOF) based on carboxylate ligands as an efficient heterogeneous catalyst for aerobic epoxidation of olefins and oxidation of benzylic and allylic alcohols

Aerobic epoxidation of olefins at a mild reaction temperature has been carried out by using nanomorphology of [Cu3(BTC)2] (BTC = 1,3,5-benzenetricarboxylate) as a high-performance catalyst through a simple synthetic strategy. An aromatic carboxylate ligand was employed to furnish a heterogeneous copper catalyst and also serves as the ligand for enhanced catalytic activities in the catalytic reaction. The utilization of a copper metal-organic framework catalyst was further extended to the aerobic oxidation of aromatic alcohols. The shape and size selectivity of the catalyst in olefin epoxidation and alcohol oxidation was investigated. Furthermore, the as-synthesized copper catalyst can be easily recovered and reused several times without leaching of active species or significant loss of activity.

Direct arylation of heterocycles through C–H bond cleavage using metal–organic-framework Cu2(OBA)2(BPY) as an efficient heterogeneous catalyst

Cu₂(OBA)₂(BPY) was showed to be an efficient heterogeneous catalyst for direct C-arylation of a variety of heterocycles by iodoarenes. The optimal conditions employed tBuOLi in dioxane at elevated temperature.

A reusable CuII based metal–organic framework as a catalyst for the oxidation of olefins

The metal–organic framework [Cu₂(bipy)₂(btec)]_∞ was used as a heterogeneous catalyst in the liquid phase oxidation of styrene and cyclohexene with tert-butylhydroperoxide (TBHP) as the oxidant either in water–dichloroethane or n-decane medium.

Facile synthesis of metal-organic framework films via in situ seeding of nanoparticles

A facile in situ nanoparticle seeding method is reported to prepare MIL-101(Cr) films on alumina supports. The in situ seeding of MIL-101(Cr) nanoparticles was promoted by use of dimethylacetamide (DMA). The generality of this approach is further demonstrated for Cu(3)(btc)(2) films by using a (poly)acrylate promoter.