Synthesis of chromene derivatives in the presence of mordenite zeolite/MIL‐101 (Cr) metal–organic framework composite as catalyst

In the present study, the synthesis of mordenite zeolite/MIL‐101(Cr) metal–organic framework (MOF) composite [MOR/MIL‐101(Cr)] using the ship in a bottle method was suggested. The properties of prepared composite and individual MOF and MOR zeolite were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption measurement, and thermogravimetric analysis (TGA). The XRD results indicated diffraction peaks for each compound (MOR and MOF) in composite. The SEM and TEM images showed the formation of plates MOR (with size of 2.5 × 3 μm) along with spherical particles MIL‐101. The Brunauer–Emmett–Teller results showed that the surface area of the composite was smaller than individual MOF and MOR zeolite. Based on TGA plots, the hybrid zeolite/MOF composite was more thermally stable compared with the isolated MIL‐101(Cr). The composite was functionalized by post‐synthetic modification to obtain acid–base bifunctionality (H‐MOR/MIL‐101‐ED) for the synthesis of chromene derivatives. The acidity from framework Al‐O(H)‐Si sites in MOR and basicity from amine groups in MIL‐101 were obtained by post‐synthetic modification.     

The Metal–Organic Framework MIL‐53(Al) Constructed from Multiple Metal Sources: Alumina,Aluminum Hydroxide,and Boehmite

Three aluminum compounds, namely alumina, aluminum hydroxide, and boehmite, are probed as the metal sources for the hydrothermal synthesis of a typical metal–organic framework MIL‐53(Al). The process exhibits enhanced synthetic efficiency without the generation of strongly acidic byproducts. The time‐course monitoring of conversion from different aluminum sources into MIL‐53(Al) is achieved by multiple characterization that reveals a similar but differentiated crystallinity, porosity, and morphology relative to typical MIL‐53(Al) prepared from water‐soluble aluminum salts. Moreover, the prepared MIL‐53(Al) constructed with the three insoluble aluminum sources exhibit an improved thermal stability of up to nearly 600 °C and enhanced yields. Alumina and boehmite are more preferable than aluminum hydroxide in terms of product porosity, yield, and reaction time. The adsorption performances of a typical environmental endocrine disruptor, dimethyl phthalate, on the prepared MIL‐53(Al) samples are also investigated. The improved structural stability of MIL‐53(Al) prepared from these alternative aluminum sources enables double‐enhanced adsorption performance (up to 206 mg g^?1) relative to the conventionally obtained MIL‐53(Al).     

Turning Redundant Ligands into Treasure: A New Strategy for Constructing MIL‐53(Al)@Nanoscale TiO2 Layers

A strategy for in situ fabrication of nanoscale‐thin layers of anatase TiO₂ coated on the metal–organic framework (MOF) material, MIL‐53(Al), is developed. The preparation conditions for crystallized TiO₂ are normally incompatible with the thermal and chemical stability of MOFs. Based on our strategy, we found that the redundant organic ligands (1,4‐benzenedicarboxylic acid, H₂BDC) within the pores of the as‐synthesized MOF play a key function in the protection and support of the framework during hydrothermal loading of the TiO₂ precursor, as well as in preventing the infiltration of the precursor into the pores. After annealing, a nanoscale‐thin layer of highly crystalline anatase TiO₂, with a thickness of 6–10 nm, was successfully attached to the external surface of the MIL‐53(Al) crystals, while the porous framework remains intact. The core–shell structure of the MOF@TiO₂ nanocomposite endows the resulting materials with additional optical response and enhanced moisture and chemical stability.     

A Systematic Study on the Stability of Porous Coordination Polymers against Ammonia

To establish a strategy for designing porous coordination polymers (PCPs) for ammonia capture, the first systematic study on the stability of PCPs against ammonia was conducted. Various types of PCPs were investigated by comparing their powder XRD patterns before and after treatment with ammonia. Among the PCPs tested, ZIF‐8, MIL‐53(Al), Al‐BTB, MOF‐76(M) (M=Y or Yb), MIL‐101(Cr), and MOF‐74(Mg) were stable up to 350 °C under an ammonia atmosphere at ambient pressure. The origin of the stability of PCPs is discussed from the viewpoint of their components, metal cations, and organic linkers. Furthermore, adsorption isotherm measurements show that the adsorptive behavior of PCPs is independent of their stability.     

Polystyrene‐Supported Core–Shell Beads with Aluminium MOF Coating for Extraction of Organic Pollutants

Aluminium‐based metal–organic framework (MOF) coatings on polystyrene bead surfaces were easily synthesized by reacting an intermediate metal hydroxide coating with an organic linker. Several different sizes of polystyrene beads were coated with aluminium metal hydroxide to construct Al@PS core–shell bead materials. The activated Al@PS core–shell beads were involved to make a homogenous MOF‐based layer in the presence of the organic linker. By using different sizes of the PS support the size of MOFs on the PS composites could be fine‐tuned under specific reaction conditions. MOF‐coated core–shell bead materials (Al‐1,4‐NDC@PS and MIL‐53(Al)@PS) were characterized using various analytical techniques. Al‐1,4‐NDC@PS and MIL‐53(Al)@PS were evaluated for solid‐phase microextraction (SPME) of hydrophobic polycyclic aromatic hydrocarbons (PAHs) and hydrophilic non‐steroidal anti‐inflammatory drugs (NSAIDs), respectively. Al‐1,4‐NDC@PS‐1000 displayed high extraction recoveries ranging from 79.2 % to 99.8 % in the SPME of PAHs. Meanwhile, MIL‐53(Al)@PS‐1000 showed 85.9–99.0 % extraction recoveries in the SPME of NSAIDs. These results show that the proposed approach holds potential to extract organic analytes on an industrial scale.     

Effect of Central Metal Ions of Analogous Metal–Organic Frameworks on Adsorption of Organoarsenic Compounds from Water: Plausible Mechanism of Adsorption and Water Purification

The adsorptive removal of organoarsenic compounds such as p‐arsanilic acid (ASA) and roxarsone (ROX) from water using metal–organic frameworks (MOFs) has been investigated for the first time. A MOF, iron benzenetricarboxylate (also called MIL‐100‐Fe) exhibits a much higher adsorption capacity for ASA and ROX than activated carbon, zeolite (HY), goethite, and other MOFs. The adsorption of ASA and ROX over MIL‐100‐Fe is also much more rapid than that over activated carbon. Moreover, the used MIL‐100‐Fe can be recycled by simply washing with acidic ethanol. Therefore, it is determined that a MOF such as MIL‐100‐Fe can be used to remove organoarsenic compounds from contaminated water because of its high adsorption capacity, rapid adsorption, and ready regeneration. Moreover, only one of three analogous MIL‐100 species (MIL‐100‐Fe, rather than MIL‐100‐Al or MIL‐100‐Cr) can effectively remove the organoarsenic compounds. This selective and high adsorption over MIL‐100‐Fe, different from other analogous MIL‐100 species, can be explained (through calculations) by the facile desorption of water from MIL‐100‐Fe as well as the large (absolute value) replacement energy (difference between the adsorption energies of the organoarsenic compounds and water) exhibited by MIL‐100‐Fe. A plausible adsorption/desorption mechanism is proposed based on the surface charge of the MOFs, FTIR results, calculations, and the reactivation results with respect to the solvents used in the experiments.     

Thermo‐Responsive MOF/Polymer Composites for Temperature‐Mediated Water Capture and Release

We report an in situ polymerization strategy to incorporate a thermo‐responsive polymer, poly(N‐isopropylacrylamide) (PNIPAM), with controlled loadings into the cavity of a mesoporous metal–organic framework (MOF), MIL‐101(Cr). The resulting MOF/polymer composites exhibit an unprecedented temperature‐triggered water capture and release behavior originating from the thermo‐responsive phase transition of the PNIPAM component. This result sheds light on the development of stimuli‐responsive porous adsorbent materials for water capture and heat transfer applications under relatively mild operating conditions.     

MIL‐101‐SO3H: A Highly Efficient Brønsted Acid Catalyst for Heterogeneous Alcoholysis of Epoxides under Ambient Conditions

For the first time, a ～100 % sulfonic acid functionalized metal–organic framework (MOF), MIL‐101‐SO₃H, with giant pores has been prepared by a hydrothermal process followed by a facile postsynthetic HCl treatment strategy. The replete readily accessible Lewis acidic and especially Brønsted acidic sites distributed throughout the framework as well as high stability endow the resultant MOF exceptionally high efficiency and recyclability, which surpass all other MOF‐based catalysts, for the ring opening of epoxides with alcohols (especially, methanol) as nucleophiles under ambient conditions.     

Well‐Defined Metal–Organic Framework Hollow Nanocages

Metal–organic frameworks (MOFs) have demonstrated great potentials in a variety of important applications. To enhance the inherent properties and endow materials with multifunctionality, the rational design and synthesis of MOFs with nanoscale porosity and hollow feature is highly desired and remains a great challenge. In this work, the formation of a series of well‐defined MOF (MOF‐5, Fe^II‐MOF‐5, Fe^III‐MOF‐5) hollow nanocages by a facile solvothermal method, without any additional supporting template is reported. A surface‐energy‐driven mechanism may be responsible for the formation of hollow nanocages. The addition of pre‐synthesized poly(vinylpyrrolidone)‐ (PVP) capped noble‐metal nanoparticles into the synthetic system of MOF hollow nanocages yields the yolk–shell noble metal@MOF nanostructures. The present strategy to fabricate hollow and yolk–shell nanostructures is expected to open up exciting opportunities for developing a novel class of inorganic–organic hybrid functional nanomaterials.     

The synthesis of metal–organic framework Al‐MIL‐53‐derived Brønsted acid catalyst and its application in the Mannich reaction

A metal–organic framework Al‐MIL‐53‐NH₂‐derived Brønsted acid catalyst (Al‐MIL‐53‐RSO₃H) has been synthesized employing a post‐synthetic modification strategy under mild conditions. The Al‐MIL‐53‐RSO₃H catalyst was successfully utilized in the nitro‐Mannich reaction taking advantage of its strong Brønsted acidity. Good to excellent yields of Mannich adducts were achieved for a variety of acylimine substrates in the presence of 0.1 mol% Al‐MIL‐53‐RSO₃H. Furthermore, the Al‐MIL‐53‐RSO₃H catalyst can be recycled five times without decreasing the yield and selectivity of Mannich adducts.     

Preparation and Gas Separation Properties of Metal‐Organic Framework Membranes

Continuous and intergrown metal‐organic framework (MOF) membranes, MIL‐100(In) (MIL represents Materials Institute Lavoisier), were prepared directly on porous anodic alumina oxide (AAO) membranes using an in situ crystallization method. The pore surface of MIL‐100(In) is conferred with polarity due to the presence of the 1, 3,5‐benzenetricarboxylic acid. The thickness of MIL‐100(In) membranes was tuned by varying the reactant concentration of indium chloride and 1, 3,5‐benzenetricarboxylic acid. Single gas permeation measurements on this MOF membrane indicate the large permeances of 0.90 × 10^–6 and 0.81 × 10^–6 mol · m^–2·s^–1·Pa^–1 for CO₂ and CH₄, and relatively high ideal selective factors of 3.75 and 3.38 for CO₂/N₂ and CH₄/N₂, respectively.     

Mechanochemical Immobilisation of Metathesis Catalysts in a Metal–Organic Framework

A simple, one‐step mechanochemical procedure for immobilisation of homogeneous metathesis catalysts in metal–organic frameworks was developed. Grinding MIL‐101‐NH₂(Al) with a Hoveyda–Grubbs second‐generation catalyst resulted in a heterogeneous catalyst that is active for metathesis and one of the most stable immobilised metathesis catalysts. During the mechanochemical immobilisation the MIL‐101‐NH₂(Al) structure was partially converted to MIL‐53‐NH₂(Al). The Hoveyda–Grubbs catalyst entrapped in MIL‐101‐NH₂(Al) is responsible for the observed catalytic activity. The developed synthetic procedure was also successful for the immobilisation of a Zhan catalyst.     

MIL‐53(Al) as a Versatile Platform for Ionic‐Liquid/MOF Composites to Enhance CO2 Selectivity over CH4 and N2

Five different imidazolium‐based ionic liquids (ILs) were incorporated into a metal–organic framework (MOF), MIL‐53(Al), to investigate the effect of IL incorporation on the CO₂ separation performance of MIL‐53(Al). CO₂, CH₄, and N₂ adsorption isotherms of the IL/MIL‐53(Al) composites and pristine MIL‐53(Al) were measured to evaluate the effect of the ILs on the CO₂/CH₄ and CO₂/N₂ selectivities of the MOF. Of the composite materials that were tested, [BMIM][PF₆]/MIL‐53(Al) exhibited the largest increase in CO₂/CH₄ selectivity, 2.8‐times higher than that of pristine MIL‐53(Al), whilst [BMIM][MeSO₄]/MIL‐53(Al) exhibited the largest increase in CO₂/N₂ selectivity, 3.3‐times higher than that of pristine MIL‐53(Al). A comparison of the CO₂ separation potentials of the IL/MOF composites showed that the [BMIM][BF₄]‐ and [BMIM][PF₆]‐incorporated MIL‐53(Al) composites both showed enhanced CO₂/N₂ and CO₂/CH₄ selectivities at pressures of 1–5 bar compared to composites of CuBTC and ZIF‐8 with the same ILs. These results demonstrate that MIL‐53(Al) is a versatile platform for IL/MOF composites and could help to guide the rational design of new composites for target gas‐separation applications.     

Formation of a Single‐Crystal Aluminum‐Based MOF Nanowire with Graphene Oxide Nanoscrolls as Structure‐Directing Agents

An innovative strategy is proposed to synthesize single‐crystal nanowires (NWs) of the Al³⁺ dicarboxylate MIL‐69(Al) MOF by using graphene oxide nanoscrolls as structure‐directing agents. MIL‐69(Al) NWs with an average diameter of 70±20 nm and lengths up to 2 μm were found to preferentially grow along the [001] crystallographic direction. Advanced characterization methods (electron diffraction, TEM, STEM‐HAADF, SEM, XPS) and molecular modeling revealed the mechanism of formation of MIL‐69(Al) NWs involving size‐confinement and templating effects. The formation of MIL‐69(Al) seeds and the self‐scroll of GO sheets followed by the anisotropic growth of MIL‐69(Al) crystals are mediated by specific GO sheets/MOF interactions. This study delivers an unprecedented approach to control the design of 1D MOF nanostructures and superstructures.     

Switch‐On Fluorescence of a Perylene‐Dye‐Functionalized Metal–Organic Framework through Postsynthetic Modification

A perylene dye was introduced directly as a linker into a metal–organic framework (MOF) during synthesis. Depending on the dye concentration in the MOF synthesis mixture, different fluorescent materials were generated. The successful incorporation of the dye was proven by using ¹³C and ²⁷Al MAS NMR spectroscopy, by solution NMR spectroscopy after digestion of the MOF sample, and by synthesizing a reference dye without connecting groups, which could coordinate on the metal–oxo cluster inside the MOF. Fluorescence quenching effects of the MOF linker, 2‐aminoterephthalate, were observed and overcome by postsynthetic modification with acetic anhydride. We show here for the first time that amino groups, which can be used as anchoring points for covalent attachment of other molecules, are responsible for fluorescence quenching. Thus, a very promising strategy to implement switchable fluorescence into MOFs is shown here.     

A Fluorescent Zirconium‐Based Metal‐Organic Framework for Selective Detection of Nitro Explosives and Metal Ions

In this work, a new porous Zr‐based metal‐organic framework (MOF ) with a large Brunner‐Emmet‐Teller (BET ) surface area was prepared by the solvothermal method using 4,4’‐(naphthalene‐1,4‐diyl)dibenzoic acid (NDDA ) as the organic ligand, and the luminescent detection performance was studied systematically. The experiments combing with computations indicate that the as‐synthesized material can sensitively and selectively detect nitro explosives and metal ions, especially for 2,4,6‐trinitrophenol (TNP ) and Fe³⁺, due to the possible electron transfer from inorganic moieties to organic moieties with naphthalene part. Interestingly, owing to its high porosity and large surface area, this Zr‐MOF showed quick luminescent response time (in 1 min) for TNP and Fe³⁺. The results obtained may provide useful information for the design of MOFs with the large permanent porosity in sensing applications for large molecules in the future.     

Encapsulation of a Porous Organic Cage into the Pores of a Metal–Organic Framework for Enhanced CO2 Separation

We present a facile approach to encapsulate functional porous organic cages (POCs) into a robust MOF by an incipient‐wetness impregnation method. Porous cucurbit[6]uril (CB6) cages with high CO₂ affinity were successfully encapsulated into the nanospace of Cr‐based MIL‐101 while retaining the crystal framework, morphology, and high stability of MIL‐101. The encapsulated CB6 amount is controllable. Importantly, as the CB6 molecule with intrinsic micropores is smaller than the inner mesopores of MIL‐101, more affinity sites for CO₂ are created in the resulting CB6@MIL‐101 composites, leading to enhanced CO₂ uptake capacity and CO₂/N₂, CO₂/CH₄ separation performance at low pressures. This POC@MOF encapsulation strategy provides a facile route to introduce functional POCs into stable MOFs for various potential applications.     

Homochiral MOF–Polymer Mixed Matrix Membranes for Efficient Separation of Chiral Molecules

Homochiral metal–organic framework (MOF) membranes have been recently reported for chiral separations. However, only a few high‐quality homochiral polycrystalline MOF membranes have been fabricated due to the difficulty in crystallization of a chiral MOF layer without defects on porous substrates. Alternatively, mixed matrix membranes (MMMs), which combine potential advantages of MOFs and polymers, have been widely demonstrated for gas separation and water purification. Here we report novel homochiral MOF–polymer MMMs for efficient chiral separation. Homochirality was successfully incorporated into achiral MIL‐53‐NH₂ nanocrystals by post‐synthetic modification with amino acids, such as l ‐histidine (l ‐His) and l ‐glutamic acid (l ‐Glu). The MIL‐53‐NH‐l ‐His and MIL‐53‐NH‐l ‐Glu nanocrystals were then embedded into polyethersulfone (PES) matrix to form homochiral MMMs, which exhibited excellent enantioselectivity for racemic 1‐phenylethanol with the highest enantiomeric excess value up to 100 %. This work, as an example, demonstrates the feasibility of fabricating diverse large‐scale homochiral MOF‐based MMMs for chiral separation.     

A Chromium Hydroxide/MIL‐101(Cr) MOF Composite Catalyst and Its Use for the Selective Isomerization of Glucose to Fructose

A metal–organic framework (MOF)‐based catalyst, chromium hydroxide/MIL‐101(Cr), was prepared by a one‐pot synthesis method. The combination of chromium hydroxide particles on and within Lewis acidic MIL‐101 accomplishes highly selective conversion of glucose to fructose in the presence of ethanol, matching the performance of optimized Sn‐containing Lewis acidic zeolites. Differently from zeolites, NMR spectroscopy studies with isotopically labeled molecules demonstrate that isomerization of glucose to fructose on this catalyst, proceeds predominantly via a proton transfer mechanism.