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.

Interfacial alloying between lead halide perovskite crystals and hybrid glasses.

The stellar optoelectronic properties of metal halide perovskites provide enormous promise for next-generation optical devices with excellent conversion efficiencies and lower manufacturing costs. However, there is a long-standing ambiguity as to whether the perovskite surface/interface (e.g. structure, charge transfer or source of off-target recombination) or bulk properties are the more determining factor in device performance. Here we fabricate an array of CsPbI3 crystal and hybrid glass composites by sintering and globally visualise the property-performance landscape. Our findings reveal that the interface is the primary determinant of the crystal phases, optoelectronic quality, and stability of CsPbI3. In particular, the presence of a diffusion "alloying" layer is discovered to be critical for passivating surface traps, and beneficially altering the energy landscape of crystal phases. However, high-temperature sintering results in the promotion of a non-stoichiometric perovskite and excess traps at the interface, despite the short-range structure of halide is retained within the alloying layer. By shedding light on functional hetero-interfaces, our research offers the key factors for engineering high-performance perovskite devices.

Recent advances in enzymatic biofuel cells enabled by innovative materials and techniques.

The past few decades have seen increasingly rapid advances in the field of sustainable energy technologies. As a new bio- and eco-friendly energy source, enzymatic biofuel cells (EBFCs) have garnered significant research interest due to their capacity to power implantable bioelectronics, portable devices, and biosensors by utilizing biomass as fuel under mild circumstances. Nonetheless, numerous obstacles impeded the commercialization of EBFCs, including their relatively modest power output and poor long-term stability of enzymes. To depict the current progress of EBFC and address the challenges it faces, this review traces back the evolution of EBFC and focuses on contemporary advances such as newly emerged multi or single enzyme systems, various porous framework-enzyme composites techniques, and innovative applications. Besides emphasizing current achievements in this field, from our perspective part we also introduced novel electrode and cell design for highly effective EBFC fabrication. We believe this review will assist readers in comprehending the basic research and applications of EBFCs as well as potentially spark interdisciplinary collaboration for addressing the pressing issues in this field.

Metal-organic framework glass composites.

The melting phenomenon in metal-organic frameworks (MOFs) has been recognised as one of the fourth generation MOF paradigm behaviours. Molten MOFs have high processibility for producing mechanically robust glassy MOF macrostructures, and they also offer highly tunable interfacial characteristics when combined with other types of functional materials, such as crystalline MOFs, inorganic glass and metal halide perovskites. As a result, MOF glass composites have emerged as a family of functional materials with dynamic properties and hierarchical structural control. These nanocomposites allow for sophisticated materials science studies as well as the fabrication of next-generation separation, catalysis, optical, and biomedical devices. Here, we review the approaches for designing, fabricating, and characterising MOF glass composites. We determine the key application opportunities enabled by these composites and explore the remaining hurdles, such as improving thermal and chemical compatibility, regulating interfacial properties, and scalability.

Phase control of ZIF-7 nanoparticles via mechanochemical synthesis.

Mechanochemical synthesis is a greener synthesis route to form functional metal organic frameworks (MOFs) compared to the typical solvothermal method. Here we demonstrate the crystal phase control of a widely functional zeolitic imidazolate framework, ZIF-7, and its variations via the mechanochemical synthesis route.

Stabilizing bienzymatic cascade catalysis via immobilization in ZIF-8/GO composites obtained by GO assisted co-growth.

Enzyme catalysis has clear advantages in the process of oxidizing glucose to produce gluconic acid. In the enzyme cascade, the improvement of the cascade efficiency is desired but challenging. Graphene oxide (GO) and ZIF-8 composites as enzyme support offer the promising opportunity that not only the cascade efficiency can be improved by control the distance between two enzymes, but also the stability can be improved. Here, a new strategy of GO assisted co-growth of ZIF-8 and enzyme was carried in a one-pot synthesis. Glucose oxidase&catalase immobilized in the ZIF-8/GO composites can obtain 98% residual activity after 15 days of storage with almost no enzyme shedding. The residual activity is still higher than 75% after 5 repeated uses. The presented method of controllable growth of metal organic frameworks on 2D nanosheet can also be extended for renewable energy devices, gas storage and separation of small molecules.

Binder-free mechanochemical metal-organic framework nanocrystal coatings.

The practical applications of metal-organic frameworks (MOFs) usually require their assembly into mechanically robust structures, usually achieved via coating onto various types of substrates. This paper describes a simple, scalable, and versatile mechanochemical technique for producing MOF nanocrystal coatings on various non-prefunctionalised substrates, including ZrO2, carbon cloth, porous polymer, nickel foam, titanium foil and fluorine-doped tin oxide glass. We revealed the detailed mechanisms that ensure the coating's stability, and identified the coating can facilitate the interfacial energy transfer, which allowed the electrocatalysis application of the MOF coating on conductive substrates. We further demonstrated that coatings can be directly generated in a one-pot fashion by ball milling MOF precursors with substrates.

Mechanochemically Synthesised Flexible Electrodes Based on Bimetallic Metal-Organic Framework Glasses for the Oxygen Evolution Reaction.

The melting behaviour of metal-organic frameworks (MOFs) has aroused significant research interest in the areas of materials science, condensed matter physics and chemical engineering. This work first introduces a novel method to fabricate a bimetallic MOF glass, through melt-quenching of the cobalt-based zeolitic imidazolate framework (ZIF) [ZIF-62(Co)] with an adsorbed ferric coordination complex. The high-temperature chemically reactive ZIF-62(Co) liquid facilitates the formation of coordinative bonds between Fe and imidazolate ligands, incorporating Fe nodes into the framework after quenching. The resultant Co-Fe bimetallic MOF glass therefore shows a significantly enhanced oxygen evolution reaction performance. The novel bimetallic MOF glass, when combined with the facile and scalable mechanochemical synthesis technique for both discrete powders and surface coatings on flexible substrates, enables significant opportunities for catalytic device assembly.

Liquid-phase sintering of lead halide perovskites and metal-organic framework glasses.

Lead halide perovskite (LHP) semiconductors show exceptional optoelectronic properties. Barriers for their applications, however, lie in their polymorphism, instability to polar solvents, phase segregation, and susceptibility to the leaching of lead ions. We report a family of scalable composites fabricated through liquid-phase sintering of LHPs and metal-organic framework glasses. The glass acts as a matrix for LHPs, effectively stabilizing nonequilibrium perovskite phases through interfacial interactions. These interactions also passivate LHP surface defects and impart bright, narrow-band photoluminescence with a wide gamut for creating white light-emitting diodes (LEDs). The processable composites show high stability against immersion in water and organic solvents as well as exposure to heat, light, air, and ambient humidity. These properties, together with their lead self-sequestration capability, can enable breakthrough applications for LHPs.

Improved adenylate cyclase activity via affinity immobilization onto co-modified GO with bio-inspired adhesive and PEI.

Adenylate cyclase (AC) can efficiently catalyze the conversion of adenosine triphosphate (ATP) to cyclic adenosine-3', 5'-monophosphate (cAMP). However, AC directly immobilized on substrate is not desirable due to enzyme inactivation. Herein, bio-inspired adhesive of polydopamine and polyethyleneimine (PDA/PEI) was used as flexible chains to graft on graphene oxide (GO), and the AC was directionally immobilized through affinity between metal ions and his-tags of AC. The properties of modified GO and the activity of immobilized AC were studied in detail. PDA/PEI layers have been proved to improve the amino density of GO surface for affinity groups decoration and adjust the interaction between AC and support. And modified GO by this novel method contributes to subsequent grafting and immobilization of AC by affinity. AC immobilized on modified GO exhibited high activity recovery with about 90 % of free AC, while enzyme immobilized on unmodified GO has been inactivated. This study offers a versatile approach for support modification and enzyme oriented immobilization. PDA/PEI functionalized GO can be used as a promising carrier to immobilize other his-tagged enzymes.

Iron Phthalocyanine/Two-Dimensional Metal-Organic Framework Composite Nanosheets for Enhanced Alkaline Hydrogen Evolution.

Hydrogen evolution reaction (HER) in alkaline medium is currently under scientific spotlight for generating clean H2 fuel from electrochemical water splitting. However, alkaline HER suffers from sluggish reaction kinetics because of the additional energy required for water dissociation from catalysts in contrast to acidic HER. Herein, we report the development of two-dimensional metal-organic framework (2D MOF) Ni-1,4-benzenedicarboxylic acid-based composite nanosheets for superior performance in HER electrocatalysis. Iron phthalocyanine (FePc) molecules are uniformly anchored on the ultrathin 2D Ni-MOF, showing a substantially increased current density, improved activity, and enhanced durability in alkaline HER. On account of the ultralarge specific surface of Ni-MOF and the coupling effects between FePc and 2D MOFs, the resultant nanosheet catalyst FePc@Ni-MOF exhibits a low overpotential (334 mV) and satisfactory long-term stability (10 h) at a current density of 10 mA·cm-2, which outperform those of pristine FePc, Ni-MOF, and the counterpart FePc@bulk-MOF. This study provides new insights into the synthesis of robust MOF-based nanosheet composites with high performance in catalysis.

Mitigating the Agglomeration of Nanofiller in a Mixed Matrix Membrane by Incorporating an Interface Agent.

Nanodiamonds (ND) have recently emerged as excellent candidates for various applications including membrane technology due to their nanoscale size, non-toxic nature, excellent mechanical and thermal properties, high surface areas and tuneable surface structures with functional groups. However, their non-porous structure and strong tendency to aggregate are hindering their potential in gas separation membrane applications. To overcome those issues, this study proposes an efficient approach by decorating the ND surface with polyethyleneimine (PEI) before embedding it into the polymer matrix to fabricate MMMs for CO2/N2 separation. Acting as both interfacial binder and gas carrier agent, the PEI layer enhances the polymer/filler interfacial interaction, minimising the agglomeration of ND in the polymer matrix, which is evidenced by the focus ion beam scanning electron microscopy (FIB-SEM). The incorporation of PEI into the membrane matrix effectively improves the CO2/N2 selectivity compared to the pristine polymer membranes. The improvement in CO2/N2 selectivity is also modelled by calculating the interfacial permeabilities with the Felske model using the gas permeabilities in the MMM. This study proposes a simple and effective modification method to address both the interface and gas selectivity in the application of nanoscale and non-porous fillers in gas separation membranes.

The utilization of micro-mesoporous carbon-based filler in the P84 hollow fibre membrane for gas separation.

This research involved carrying out a unique micro-mesoporous carbon particle incorporation into P84 co-polyimide membrane for improved gas separation performance. The carbon filler was prepared using a hard template method from zeolite and known as zeolite-templated carbon (ZTC). This research aims to study the loading amount of ZTC into P84 co-polyimide toward the gas separation performance. The ZTC was prepared using simple impregnation method of sucrose into hard template of zeolite Y. The SEM result showing a dispersed ZTC particle on the membrane surface and cross-section. The pore size distribution (PSD) of ZTC revealed that the particle consists of two characteristics of micro and mesoporous region. It was noted that with only 0.5 wt% of ZTC addition, the permeability was boosted up from 4.68 to 7.06 and from 8.95 to 13.15 barrer, for CO2 and H2 respectively when compared with the neat membrane. On the other hand, the optimum loading was at 1 wt%, where the membrane received thermal stability boost of 10% along with the 62.4 and 35% of selectivity boost of CO2/CH4 and H2/CH4, respectively. It was noted that the position of the filler on the membrane surface was significantly affecting the gas transport mechanism of the membrane. Overall, the results demonstrated that the addition of ZTC with proper filler position is a potential candidate to be applicable in the gas separation involving CO2 and H2.

Interfacial engineering of a polymer-MOF composite by in situ vitrification.

Non-stoichoimetric crystalline ZIF-62 was used as the filler for a 6FDA-DAM polyimide-based composite membrane. In situ melting and vitrification of ZIF-62 was then performed, to yield the ZIF-62 glass phase (agZIF-62), within the polymer matrix. Focus ion beam scanning electron microscopy (FIB-SEM), thermal characterisation and membrane separation tests demonstrate the filling of voids at the MOF/polymer interface from the liquid phase of ZIF-62.

Halogenated Metal-Organic Framework Glasses and Liquids.

The synthesis of four novel crystalline zeolitic imidazolate framework (ZIF) structures using a mixed-ligand approach is reported. The inclusion of both imidazolate and halogenated benzimidazolate-derived linkers leads to glass-forming behavior by all four structures. Melting temperatures are observed to depend on both electronic and steric effects. Solid-state NMR and terahertz (THz)/far-IR demonstrate the presence of a Zn-F bond for fluorinated ZIF glasses. In situ THz/far-IR spectroscopic techniques reveal the dynamic structural properties of crystal, glass, and liquid phases of the halogenated ZIFs, linking the melting behavior of ZIFs to the propensity of the ZnN4 tetrahedra to undergo thermally induced deformation. The inclusion of halogenated ligands within metal-organic framework (MOF) glasses improves their gas-uptake properties.

Ionic Liquids as the MOFs/Polymer Interfacial Binder for Efficient Membrane Separation.

Obtaining strong interfacial affinity between filler and polymer is critical to the preparation of mixed matrix membranes (MMMs) with high separation efficiency. However, it is still a challenge for micron-sized metal organic frameworks (MOFs) to achieve excellent compatibility and defect-free interface with polymer matrix. Thin layer of ionic liquid (IL) was immobilized on micron-sized HKUST-1 to eliminate the interfacial nonselective voids in MMMs with minimized free ionic liquid (IL) in polymer matrix, and then the obtained IL decorated HKUST-1 was incorporated into 4,4'-(hexafluoroisopropylidene)diphthalic anhydride-2,3,5,6-tetramethyl-1,3-phenyldiamine (6FDA-Durene) to fabricate MMMs. Acting as a filler/polymer interfacial binder, the favorable MOF/IL and IL/polymer interaction can facilitate the enhancement of MOF/polymer affinity. Compared to MMM with only HKUST-1 incorporation, MMM with IL decorated HKUST-1 succeeded in restricting the formation of nonselective interfacial voids, leading to an increment in CO2 selectivity. The IL decoration method can be an effective approach to eliminate interfacial voids in MMMs, extending the filler selection to a wide range of large-sized fillers.

Mixed-Matrix Membranes with Metal-Organic Framework-Decorated CNT Fillers for Efficient CO2 Separation.

Carbon nanotube (CNT) mixed-matrix membranes (MMMs) show great potential to achieve superior gas permeance because of the unique structure of CNTs. However, the challenges of CNT dispersion in polymer matrix and elimination of interfacial defects are still hindering MMMs to be prepared for high gas selectivity. A novel CNT/metal-organic framework (MOF) composite derived from the growth of NH2-MIL-101(Al) on the surface of CNTs have been synthesized and applied to fabricate polyimide-based MMMs. Extra amino groups and active sites were introduced to external surface of CNTs after MOF decoration. The good adhesion between the synthesized CNT-MIL fillers and polymer phase was observed, even at a high filler loadings up to 15%. Consequently, MMMs containing the synthesized MOF/CNT composite exhibit not only a large CO2 permeability but also a high CO2/CH4 selectivity; the combined performance of permeability and selectivity is even above the Robeson upper bound. The strategy of growing MOFs on CNTs can be further utilized to develop a more effective approach to further improve MMM performance through the decoration of MOFs on existing fillers that have high selectivity to specific gas.

Synthesis and characterization of three amino-functionalized metal-organic frameworks based on the 2-aminoterephthalic ligand.

The incorporation of Lewis base sites and open metal cation sites into metal-organic frameworks (MOFs) is a potential route to improve selective CO2 adsorption from gas mixtures. In this study, three novel amino-functionalized metal-organic frameworks (MOFs): Mg-ABDC [Mg3(ABDC)3(DMF)4], Co-ABDC [Co3(ABDC)3(DMF)4] and Sr-ABDC [Sr(ABDC)(DMF)] (ABDC = 2-aminoterephthalate) were synthesized by solvothermal reactions of 2-aminoterephthalic acid (H2ABDC) with magnesium, cobalt and strontium metal centers, respectively. Single-crystal structure analysis showed that Mg-ABDC and Co-ABDC were isostructural compounds comprising two-dimensional layered structures. The Sr-ABDC contained a three-dimensional motif isostructural to its known Ca analogue. The amino-functionalized MOFs were characterized by powder X-ray diffraction, thermal gravimetric analysis and N2 sorption. The CO2 and N2 equilibrium adsorption capacities were measured at different temperatures (0 and 25 °C). The CO2/N2 selectivities of the MOFs were 396 on Mg-ABDC, 326 on Co-ABDC and 18 on Sr-ABDC. Both Mg-ABDC and Co-ABDC exhibit high heat of CO2 adsorption (>30 kJ mol(-1)). The Sr-ABDC displays good thermal stability but had a low adsorption capacity resulting from narrow pore apertures.

Mixed matrix membranes with strengthened MOFs/polymer interfacial interaction and improved membrane performance.

MOFs-based mixed matrix membranes (MMMs) have attracted extensive attention in recent years due to their potential high separation performance, the low cost, and good mechanical properties. However, it is still very challenging to achieve defect-free interface between micrometer-sized MOFs and a polymer matrix. In this study, [Cd2L(H2O)]2·5H2O (Cd-6F) synthesized using 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) as an organic ligand was introduced into the 6FDA-ODA polyimide matrix to achieve novel MOF MMMs. A specific interfacial interaction between MOF crystals and polymer chains was innovatively targeted and achieved through in situ polymerization procedure. The enhanced adhesion between MOF particles and polymer phase was observed, and the improved interfacial interaction between Cd-6F and the 6FDA-ODA polyimide matrix was confirmed by detailed characterizations including FTIR and NMR. In the meantime, the gas permeance and selectivity of the MMMs are strongly dependent on their morphology. The MMM derived from in situ polymerization presents excellent interfaces between micrometer-sized MOF crystals and the polymer matrix, resulting in increased permeability and selectivity. The strategy shown here can be further utilized to select the MOF/polymer pair, eliminate interfacial voids, and improve membrane separation performance of MOFs-based MMMs.

Design of a viscose based solid amine fiber: effect of its chemical structure on adsorption properties for carbon dioxide.

A solid amine fiber VF-AM-TETA was designed with viscose (VF) substrate for efficient CO2 capture, where its hydroxyl groups could serve synergizing effect in CO2-amine reaction. When grafting modification and subsequent amination were applied to VF, effect of structures of grafting monomers as well as amines on its CO2 adsorption properties was taken into account. Amines with different 1° and 2° amine ratios were investigated as amination agents in terms of amine efficiency, so as to afford the fibrous adsorbent with maximum effective reactive amine sites for CO2 capturing. Results suggested that higher content in primary amine can facilitate CO2 adsorption onto the fiber by stronger basicity and smaller steric hindrance. Consequently, optimal chemical structure provided VF-AM-TETA with satisfactory adsorption capacity of 4.08 mmol/g when amine content was 8.74 mmol/g. Constant adsorption behavior within 6 adsorption-desorption cycles indicated its desirable regeneration performance in practical use due to excellent mechanical properties of VF-AM-TETA.