Fast Catalytic Esterification Using a Hydrophobized Zr‐MOF with Acidic Ionic Liquid Linkers

Ionic Liquids Functionalized MOFs for Adsorption

Metal-organic frameworks (MOFs) and ionic liquids (ILs) represent promising materials for adsorption separation. ILs incorporated into MOF materials (denoted as IL/MOF composites) have been developed, and IL/MOF composites combine the advantages of MOFs and ILs to achieve enhanced performance in the adsorption-based separation of fluid mixtures. The designed different ILs are introduced into the various MOFs to tailor their functional properties, which affect the optimal adsorptive separation performance. In this Perspective, the rational fabrication of IL/MOF composites is presented, and their functional properties are demonstrated. This paper provides a critical overview of an emergent class of materials termed IL/MOF composites as well as the recent advances in the applications of IL/MOF composites as adsorbents or membranes in fluid separation. Furthermore, the applications of IL/MOF in adsorptive gas separations (CO2 capture from flue gas, natural gas purification, separation of acetylene and ethylene, indoor pollutants removal) and liquid separations (separation of bioactive components, organic-contaminant removal, adsorptive desulfurization, radionuclide removal) are discussed. Finally, the existing challenges of IL/MOF are highlighted, and an appropriate design strategy direction for the effective exploration of new IL/MOF adsorptive materials is proposed.

Surface Hydrophobicity and Guest Permeability in Polydimethylsiloxane-Coated MIL-53 as Studied by Solid-State Nuclear Magnetic Resonance Spectroscopy

Experimental characterization of the hydrophobic porous materials at the atomic and molecular levels is of great significance, but exploring their hydrophobicity characteristics and interactions with guest molecules with distinct polarity is still challenging. In this work, solid-state NMR is employed to characterize the surface hydrophobicity and explore the guest solvent permeability in polydimethylsiloxane (PDMS)-coated MIL-53. It was found that the PDMS-coated MIL-53 was hydrophobic to water and infiltrated to methanol, acetone, benzene, toluene, and ethylbenzene solvents. In addition, two types of guest solvents (methanol, acetone, benzene, toluene, and ethylbenzene), inside the pore and outside the pore of PDMS-coated MIL-53, were clearly identified using two-dimensional 1H-1H homo-nuclear correlation NMR experiments. Moreover, the membrane thickness of the PDMS-coated MIL-53 could be determined from the analysis of the 1H-1H spin diffusion buildup curves. Furthermore, the permeability of benzene, toluene, and ethylbenzene at different PDMS coating levels was extracted from 1H MAS NMR. The increase of the hydrophobic PDMS layer resulted in a decrease of the penetration of aromatic guests to the internal pore of MIL-53. This work provides deep insights into the understanding of guest solvent permeability of hydrophobic layer-coated MOFs in the application fields of catalysis and separation.

Novel Magnetically-Recoverable Solid Acid Catalysts with a Hydrophobic Layer in Protecting the Active Sites from Water Poisoning

Three novel magnetically-recoverable solid acid catalysts (hydrophobic catalysts Fe3O4@SiO2-Me&PrSO3H, Fe3O4@SiO2-Oc&PrSO3H and hydrophilic catalyst Fe3O4@SiO2-PrSO3H) were synthesized by introducing organic propylsulfonic acid and alkyl groups to Fe3O4@SiO2 nanocomposites. We characterized these catalysts by FT-IR, EDS, XRD, VSM and SEM, and found that they had excellent core-shell structure and magnetic responsiveness. We also explored the impact of surface hydrophobicity on activity and stability of catalysts in ethyl acetate (EAC) synthesis reaction. The results indicated that: for reactivity and reusability, Fe3O4@SiO2-Oc&PrSO3H > Fe3O4@SiO2-Me&PrSO3H > Fe3O4@SiO2-PrSO3H. This was because octyl and methyl groups could build a hydrophobic layer on the surfaces of Fe3O4@SiO2-Oc&PrSO3H and Fe3O4@SiO2-Me&PrSO3H, and this could effectively prevent water molecules from poisoning active sites; the hydrophobicity of octyl was stronger than methyl. Fe3O4@SiO2-Oc&PrSO3H also showed higher catalytic activity in the external aqueous reaction system, which indicated that it had good water toleration. Moreover, we could easily separate Fe3O4@SiO2-Oc&PrSO3H from the reaction mixture with an external magnetic field, in the meanwhile, its reactivity could still remain above 80% after reusing 6 times.

High-Performance Heterogeneous Thermocatalysis Caused by Catalyst Wettability Regulation

Catalyst wettability regulation has emerged as an attractive approach for high catalytic performance for the past few years. By introducing appropriate wettability, the molecule diffusion of reactants and products can be enhanced, leading to high activity. Besides this, undesired molecules are isolated for high selectivity of target products and long-term stability of catalyst. Herein, we summarize wettability-induced high-performance heterogeneous thermocatalysis in recent years, including hydrophilicity, hydrophobicity, hybrid hydrophilicity-hydrophobicity, amphiphilicity, and superaerophilicity. Relevant reactions are further classified and described according to the reason for the performance improvement. It should be pointed out that studies of utilizing superaerophilicity to improve heterogeneous thermocatalytic performance have been included for the first time, so this is a comparatively comprehensive review in this field as yet.

Polydimethylsiloxane Membranes Incorporating Metal-Organic Frameworks for the Sustained Release of Antibacterial Agents

Cyclodextrin metal-organic frameworks (CD-MOFs) possess great potential in environmental applications due to their high specific surface area and good biocompatibility properties. However, the hydrophilicity of the CD-MOF hinders its ability to maintain a sustained release in water as a carrier. In this study, we prepared a CD-MOF that has codelivery ability for both phytochemicals [caffeic acid (CA)] and silver nanoparticles (Ag NPs) and further incorporated this material (CA@Ag@CD-MOF) into the polydimethylsiloxane (PDMS) matrix to construct a hybrid membrane. This hybrid membrane could effectively maintain the release capacity of the CD-MOF in water, while endowing PDMS with swelling ability in water. The hybrid membrane can achieve a sustained release for up to 48 h in water. In addition, the elastic modulus of the hybrid membrane increases by nearly 100%, and the swelling degree of the hybrid membrane in water increases by 42% compared with that of the pure PDMS membrane, indicating better mechanical properties. The hybrid membrane exhibits excellent antibacterial effects on Escherichia coli O157:H7 (E. coli O157:H7) and Staphylococcus aureus (S. aureus). We expect that this work will be beneficial to the delivery research of the CD-MOF in more environmental scenarios, especially in water treatment.

The applications and prospects of hydrophobic metal-organic frameworks in catalysis

In recent years, large numbers of hydrophobic/superhydrophobic metal-organic frameworks (MOFs) have been developed. These hydrophobic MOFs not only retain rich structural variety, highly crystalline frameworks, and uniform micropores, but they also have lower affinity towards water and boosted hydrolytic stability. Until now, there were two main strategies to prepare hydrophobic MOFs, including a one-step method and post-synthesis modification (PSM). PSM was an often-used strategy for preparing hydrophobic MOFs. Hydrophobic MOFs showed unique advantages when used as catalysts for various categories of reactions. Herein, recent research advances relating to hydrophobic MOFs in the catalytic field are presented. The catalytic activities of hydrophobic MOFs and corresponding hydrophilic ones are also compared, and the superiority of hydrophobic MOFs or MOF materials as catalysts in 10 reactions is discussed. Finally, the advantages of hydrophobic MOFs as catalysts or auxiliary materials are summarized and promising future developments of hydrophobic MOFs are highlighted.