Poly(ionic liquid)-Functionalized UiO-66-(OH)2: Improved Interfacial Compatibility and Separation Ability in Mixed Matrix Membranes for CO2 Separation

Amino-ionic liquid-assisted highly compatible mixed matrix membranes of ZIF-8 and PIM-1 for efficient CO2/N2 separation

Mixed matrix membranes (MMMs), which incorporate metal-organic framework (MOF) nanofillers within a polymer matrix, offer a highly promising solution for CO2 capture and separation. However, poor interfacial compatibility and filler aggregation in MMMs pose significant challenges to enhancing CO2/N2 separation performance. Here, we present a novel approach using amino-ionic liquid modification to optimize MMMs, where the modified AFIL promotes the formation of ZIF-8 with well-defined facets and sharp edges and enhances the compatibility between ZIF-8 particles and PIM-1 polymer matrixes for favorable CO2 affinity and selective CO2 transport. The resulting 10 wt% AFIL@ZIF-8/PIM-1 exhibits exceptional gas separation performance with a CO2 permeability of 7864 ± 262.2 Barrer and a CO2/N2 selectivity of 29.66 ± 1.96. More importantly, the incorporation of AFIL into the ZIF-8 pores significantly enhances the thermal stability and aging resistance of AFIL@ZIF-8/PIM-1 MMMs via structural support and hydrogen bonding interactions. This work provides a practical approach for developing hybrid membranes for CO2/N2 separation, showcasing improved overall performance and strong interfacial compatibility.

Controlled Growth of Highly Defected Zirconium-Metal-Organic Frameworks via a Reaction-Diffusion System for Water Remediation

The relentless growth of metal-organic framework (MOF) chemistry is paralleled by the persistent urge to control the MOFs physical and chemical properties. While this control is mostly achieved by solvothermal syntheses, room temperature procedures stand out as more convenient and sustainable pathways for the production of MOF materials. Herein, a novel approach to control the crystal size and defect numbers of a dihydroxy-functionalized zirconium-based metal-organic framework (UiO-66(OH)2) at room temperature is reported. Through a reaction-diffusion method in a 1D system, zirconium salt was diffused into an agar gel matrix containing the organic linker to form nanocrystals of UiO-66(OH)2 with tailored structural features that include crystal size distribution, surface area, and defect number. By variation of the synthesis parameters of the system, hierarchical MOF nanocrystals with an average size ranging from 30 nm up to 270 nm and surface areas between 201 and 500 m2 g-1 were obtained in a one-pot synthetic route. To stress the importance of crystal size, morphology, and structural defects on the adsorption properties of UiO-66(OH)2, the adsorption capacity of the MOF toward methylene blue dye was tested with the largest and most defected crystals achieving the best performance of 202 mg/g. The distinctive structural characteristics including the hierarchical micromesoporous frameworks, the nanosized particles, and the highly defective crystals obtained by our synthesis procedure are deemed challenging through the conventional synthesis methods. This work paves the way for engineering MOF crystals with tunable physical and chemical properties, using a green synthesis procedure, for their advantageous use in many desirable applications.

Integration of metal organic framework nanoparticles into sodium alginate biopolymer-based three-dimensional membrane capsules for the efficient removal of toxic metal cations from water and real sewage

Sodium alginate (SA) biopolymer has been recognized as an efficient adsorbent material owing to their unique characteristics, including biodegradability, non-toxic nature, and presence of abundant hydrophilic functional groups. Accordingly, in the current research work, UiO-66-OH and UiO-66-(OH)2 metal organic framework (MOF) nanoparticles (NPs) have been integrated into SA biopolymer-based three-dimensional (3-D) membrane capsules (MCs) via a simple and facile approach to remove toxic metal cations (Cu2+ and Cd2+) from water and real sewage. The newly configured capsules were characterized by FTIR, SEM, XRD, EDX and XPS analyses techniques. Exceptional sorption properties of the as-developed capsules were ensured by evaluation of the pertinent operational parameters, i.e., contents of MOF-NPs (1-100 wt%), adsorbent dosage (0.001-0.05 g), content time (0-360 h), pH (1-8), initial concentration of metal cations (5-1000 mg/L) and reaction temperature (298.15-333.15 K) on the eradication of Cu2+ and Cd2+ metal cations. It was found that hydrophilic functional groups (-OH and -COOH) have performed an imperative role in the smooth loading of MOF-NPs into 3-D membrane capsules via intra/inter-molecular hydrogen bonding and van der waals potencies. The maximum monolayer uptake capacities (as calculated by the Langmuir isotherm model) of Cd2+ and Cu2+ by 3-D SGMMCs-OH were 940 and 1150 mg/g, respectively, and by 3-D SGMMCs-(OH)2 were 1375 and 1575 mg/g, respectively, under optimum conditions. The as-developed capsules have demonstrated superior selectivity against targeted metal cations under designated pH and maintained >80 % removal efficiency up to six consecutive treatment cycles. Removal mechanisms of metal cations by the 3-D SGMMCs-OH/(OH)2 was proposed, and electrostatic interaction, ion-exchange, inner-sphere coordination bonds/interactions, and aromatic ligands exchange were observed to be the key removal mechanisms. Notably, FTIR and XPS analysis indicated that hydroxyl groups of Zr-OH and BDC-OH/(OH)2 aromatic linkers played vital roles in Cu2+ and Cd2+ adsorption by participating in inner-sphere coordination interactions and aromatic ligands exchange mechanisms. The as-prepared capsules indicated >70 % removal efficiency of Cu2+ from real electroplating wastewater in the manifestation of other competitive metal ions and pollutants under selected experimental conditions. Thus, it was observed that newly configured 3-D SGMMCs-OH/(OH)2 have offered a valuable discernment into the development of MOFs-based water decontamination 3-D capsules for industrial applications.

Recent advances in the interfacial engineering of MOF-based mixed matrix membranes for gas separation

The membrane process stands as a promising and transformative technology for efficient gas separation due to its high energy efficiency, operational simplicity, low environmental impact, and easy up-and-down scaling. Metal-organic framework (MOF)-polymer mixed matrix membranes (MMMs) combine MOFs' superior gas-separation performance with polymers' processing versatility, offering the opportunity to address the limitations of pure polymer or inorganic membranes for large-scale integration. However, the incompatibility between the rigid MOFs and flexible polymer chains poses a challenge in MOF MMM fabrication, which can cause issues such as MOF agglomeration, sedimentation, and interfacial defects, substantially weakening membrane separation efficiency and mechanical properties, particularly gas separation. This review focuses on engineering MMMs' interfaces, detailing recent strategies for reducing interfacial defects, improving MOF dispersion, and enhancing MOF loading. Advanced characterisation techniques for understanding membrane properties, specifically the MOF-polymer interface, are outlined. Lastly, it explores the remaining challenges in MMM research and outlines potential future research directions.

Covalent connections between metal-organic frameworks and polymers including covalent organic frameworks

Hybrid composite materials combining metal-organic frameworks (MOFs) and polymers have emerged as a versatile platform for a broad range of applications. The crystalline, porous nature of MOFs and the flexibility and processability of polymers are synergistically integrated in MOF-polymer composite materials. Covalent bonds, which form between two distinct materials, have been extensively studied as a means of creating strong molecular connections to facilitate the dispersion of "hard" MOF particles in "soft" polymers. Numerous organic transformations have been applied to post-synthetically connect MOFs with polymeric species, resulting in a variety of covalently connected MOF-polymer systems with unique properties that are dependent on the characteristics of the MOFs, polymers, and connection modes. In this review, we provide a comprehensive overview of the development and strategies involved in preparing covalently connected MOFs and polymers, including recently developed MOF-covalent organic framework composites. The covalent bonds, grafting strategies, types of MOFs, and polymer backbones are summarized and categorized, along with their respective applications. We highlight how this knowledge can serve as a basis for preparing macromolecular composites with advanced functionality.

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.