Assembly Of Metal-organic Frameworks Research Articles

Electrostatic assembly of metal organic frameworks nanocubes on electrochemically exfoliated graphene nanoflakes: Superior role in flame retardance

The extensive usage of epoxy resin (EP) is facing the head-scratching challenge of high fire hazard. As such, the electrostatic assembly of metal organic frameworks (MOFs) nanocubes on electrochemically exfoliated graphene nanoflakes is performed to acquire the hybrid of PG@UIO. The corresponding role and behavior in flame retardance are explored in detail. By adding 2.0 wt% PG@UIO, the reductions in peak heat release rate, total heat release, peak smoke production rate, peak CO yield, peak CO2 yield reach 49.2 %, 44.3 %, 56.1 %, 57.7 % and 51.3 %. The in-situ volatiles analysis points out the reductions of 35.1 %, 29.4 %, 50.8 %, 32.5 % in the maximal intensities of aromatic compounds, ethers, CO and HCN. The mechanical interlocking area between PG@UIO nanostructures and EP molecular chains contributes to the enhanced mechanical performances. Specifically, by adding 2.0 wt% PG@UIO, the flexural strength is increased by 50.3 %. This work enables a new paradigm for fabricating fire-safe polymer composites with the judicious design of MOFs based flame retardant.

Synergistic bimetallic nanozymes of Ni/ZIF-8 and Cu/ZIF-8 as carbonic anhydrase mimics

The remarkable diversity of metal nodes and ligands, coupled with the extensive array of connection modes, enables the precise design and assembly of metal-organic frameworks (MOFs), which have garnered significant attention in the field of nanozyme. In this study, the synthesis of zeolite imidazole framework materials (ZIFs) with varying Zn2+ and Ni2+ or Cu2+ concentrations were investigated and regulated by methanol, aiming to mimic the CO2 hydration activity of carbonic anhydrase (CA). The materials were comprehensively characterized using TEM, XRD, FTIR, UV-Vis DRS, XPS, and subsequently the catalytic performance of the materials was assessed. The results demonstrated that the structural characteristics of bimetallic Ni/ZIF-8 and Cu/ZIF-8 were influenced by varying concentrations of metal ions. Notably, ZIF-8 doped with lower metal content exhibited enhanced stability, while a precursor containing nickel and copper ions exceeding 50% hindered the formation of the desired ZIFs, resulting in an unstable cluster structure. However, methanol can counteract the inhibitory effect of metal ions on the structure. The bimetallic synergies of doped metals in ZIFs CA mimics can simultaneously expedite both two rate-limiting steps in the CO2 hydration process. The esterase activity of ZIF-8 doped with a small quantity of Ni2+ or Cu2+ can be achieved at a level comparable to that of human carbonic anhydrase (hCA II) at 80 °C, along with remarkable catalytic performance and hydrothermal stability. Specifically, Cu66%/ZIF-8 exhibited an activity of 0.31 U·mg−1 at 25 °C, which was 2.31 times higher than that of ZIF-8, moreover, the esterase activity at 80 °C was approximately 2.21 times greater than that of ZIF-8 under the same condition. While the relative activity of Ni50%/ZIF-8 and Cu50%/ZIF-8 still exceeding 50% even after five repeated utilization cycles. The bimetallic Ni/ZIF-8 and Cu/ZIF-8 can be easily synthesized using a simple method, resulting in enhanced catalytic activity. Therefore, it holds great potential for future applications in CO2 capture.

Assembling 99% MOFs into Bioinspired Rigid-Flexible Coupled Membrane with Significant Permeability: The Impacts of Defects.

Assembling metal-organic frameworks (MOFs) into high-performance macroscopic membranes is crucial but still challenging. MOF-containing hybrid membranes can effectively integrate the advantages of flexible guest materials and MOFs. Nevertheless, the inherent limitations in fully harnessing the distinct characteristics of MOFs persist due to the substantial guest material content necessitated in membrane fabrication. Herein, inspired by the rigid and flexible structures in biological systems, rigid MIP-202(Zr) and defective MIP-202(Zr) (D-MIP-202(Zr)) modified flexible graphene oxide (GO) sheets are synthesized in situ and then assembled into a rigid-flexible coupled MOF-based membrane. The defects in D-MIP-202(Zr) are introduced by using acetic acid as the modulation agent. The obtained GO@MIP-202(Zr) membrane possesses a hierarchical porous structure with a 99 wt% MOF proportion, which is higher than the GO@D-MIP-202(Zr) (75 wt%) membrane with a compact bulge-structured surface. The water permeability of the GO@MIP-202(Zr) membrane attains remarkedly 5762.92 L h-1 m-2 bar-1 , which is 960 and 2.6 times higher than that of the GO membrane and GO@D-MIP-202(Zr) membrane. Additionally, benefiting from the superhydrophilicity and underwater superoleophobicity, the resultant membrane not only demonstrates high rejection for oil-water emulsions but also exhibits exceptional recyclability and anti-fouling ability. These findings provide valuable insights into the assembly of MOFs into high-performance membranes.

“Matryoshka Doll” Heterostructures Induce Electromagnetic Parameters Fluctuation to Tailor Electromagnetic Wave Absorption

Components manipulation and structure engineering have shown powerful approaches for tailoring electromagnetic (EM) parameters. However, the integration of controllable architectural and compositional complexity into one multiple‐layer heterostructure seems significantly effective but remains a considerable challenge, and correlative quantized modulation of EM parameters is scarce. Herein, three types of metal–organic frameworks (MOFs) hybrids and derived sulfides are ingeniously fabricated by MOF architecture engineering and solvothermal sulfuration. Compared to the random assembly of MOFs in the “Chaotic” structure (Structure 1), the regular arrangement of MOF‐on‐MOF heterostructures in the “Matryoshka doll” structure (Structure 2) guarantees improved lattice strain and defect arising from abundant heterointerfaces in core–shell heterostructure. Impressively, such aforementioned advantages together with sufficiently exposed defect sites and conductivity display an interesting “quantized state” between “0 state” and “1 state” in the subsequent ion exchange process for “Matryoshka doll” structured Zn–Co sulfides, benefiting EM parameters “quantization” and boost electromagnetic wave (EMW) absorption. Further, introducing metal ions in a cation‐doped “Matryoshka doll” structure (Structure 3) subtly optimizes composition and defect, leading to enhanced impedance matching and effective absorption bandwidth of 7.8 GHz at 2.6 mm. This study highlights the significant effect of multiple‐layer heterostructures on EM parameters fluctuation, which is in synergy with lattice defect, sulfur vacancy, and conductivity to tailor desirable EMW absorption capacity.

Assembly of graphene-wrapped ZIF-8 microspheres and confined carbonization for energy storage applications

Metal–organic frameworks (MOFs) are widely used as sacrificial templates to prepare MOF-derived porous carbons for energy storage applications. Herein, we discuss three critical issues in the synthesis of MOF-derived carbons: 1) the collapse and aggregation of carbonized MOFs, 2) the low electrical conductivity of MOF-derived sp3-dominated amorphous carbons, and 3) the controlled assembly of MOFs into a microspherical powder form. This study demonstrates a novel approach to simultaneously resolve these challenges, which includes intimately wrapping ZIF-8 with GO sheets, assembling the GO-wrapped ZIF-8 into microspheres via spray drying, and performing the confined carbonization of ZIF-8. The GO sheets act as both a structural and conductive scaffold to support the ZIF-8, thereby maintaining morphological stability, preventing aggregation during carbonization, and improving electrical conductivity. Notably, the microspherical assembly of carbonized ZIF-8 and reduced graphene oxide (rGO) shows a high compressive strength of 380 MPa, indicating that rGO as the structural scaffold reinforces the structural integrity of the microspherical assembly. Furthermore, electrochemical tests demonstrate the improved textural properties of the assembly. Our novel strategy provides a convenient yet efficient solution to the common critical issues with MOF-derived carbons for important energy storage applications.

Assembly of Metal-Organic Frameworks on Transition Metal Phosphides as Self-Supported Electrodes for High-Performance Hybrid Supercapacitors.

In this work, the composite electrode composed of metal-organic frameworks and transition metal phosphides is first assembled on the nickel foam substrate. The as-prepared NiCo-MOF-74@Ni12P5/NF exhibits excellent performances with ultrahigh specific capacitance (12.8 F/cm2 at 1 mA/cm2), stable charge-discharge rate (82.8%), and excellent cycling stability (reserve 73.90% after 5000 charge and discharge cycles at 30 mA/cm2), which are better than those of NiCo-MOF-74@NF without phosphating treatment of nickel foam. The corresponding hybrid supercapacitor (SC) device (NiCo-MOF-74@Ni12P5/NF//AC) delivers high storage capability (44.33 W·h/kg at 800 W/kg) and distinguished operating durability (83.04% after 5000 cycles). In addition, an all-solid-state hybrid SC successfully lit the LED for more than 2 min, which means that there is viable potential for practical applications in energy storage. The improved electrical properties are mainly due to the 3D heterostructure, the positive cooperative binding of nickel and cobalt elements, and the excellent electrical conductivity of the phosphide. As a result, this study proves the possibility of practical applications of NiCo-MOF-74@Ni12P5/NF electrodes for energy storage in hybrid SCs.

Nanosheet-state cobalt-manganese oxide with multifarious active regions derived from oxidation-etching of metal organic framework precursor for catalytic combustion of toluene

For the first time, a nanosheet-state CoMnx mixed oxide with multifarious active regions was synthesized by oxidation-etching assembly of metal organic framework (MOF) precursor and applied for catalytic combustion of toluene at low temperatures. The obtained optimum catalyst denoted as CoMn6 showed excellent performance, which achieved 90% conversion of 1,000 ppm toluene under a weight hourly space velocity (WHSV) of 60,000 mL/(g·h) at 219 °C. While, it also exhibited long-term stability with strong water resistance property. The characterizations of physicochemical properties indicated that the oxidation-etching assembly process built an abundant mesoporous structure in the CoMnx catalyst, which greatly increased the specific surface area (SSA). Especially, potassium permanganate as oxidant and manganese source led to uniform dispersion and assembling of cobalt atoms, which caused the generation of low-crystallinity CoMnx mixed oxide with abundant dislocations, vacancies, phase interfaces and amorphous structures, resulting in excellent low-temperature reducibility, outstanding lattice oxygen mobility and abundant active species such as Mn3+, Co3+ and adsorbed oxygen species. Density functional theory (DFT) calculations demonstrated that gaseous oxygen with the longer bond length (1.406 Å) and stronger adsorption energy (−4.443 eV) could be adsorbed and activated well on the MnCo2O4.5 (311) plane, which is beneficial for the toluene oxidation. In situ diffuse reflectance infrared spectroscopy (DRIFTS) technique was applied to track the intermediates of toluene combustion under different atmospheres, which further deduced the contributions of different active regions and oxidation mechanism over the CoMnx catalyst. The present facile strategy of oxidation-etching assembly of the MOF precursor for the creating of novel catalyst with high performance could be applied in a wide variety of materials besides VOC combustion catalysts.

Nanoemulsion-directed growth of MOFs with versatile architectures for the heterogeneous regeneration of coenzymes

As one of the most appealing strategies for the synthesis of nanomaterials with various architectures, emulsion-directed methods have been rarely used to control the structure of metal-organic frameworks (MOFs). Herein, we report a versatile salt-assisted nanoemulsion-guided assembly to achieve continuous architecture transition of hierarchical Zr-based MOFs. The morphology of nanoemulsion can be facilely regulated by tuning the feed ratio of a dual-surfactant and the introduced amount of compatible hydrophobic compounds, which directs the assembly of MOFs with various architectures such as bowl-like mesoporous particle, dendritic nanospheres, walnut-shaped particles, crumpled nanosheets and nanodisks. The developed dendritic nanospheres with highly open and large mesochannels is successfully used as matrix for the co-immobilization of coenzymes and corresponding enzymes to realize the in situ heterogeneous regeneration of NAD+. This strategy is expected to pave a way for exploring sophisticated hierarchical MOFs which can be competent for practical applications with bulk molecules involved.

Versatility vs stability. Are the assets of metal–organic frameworks deployable in aqueous acidic and basic media?

Exploring the deployment of metal–organic frameworks (MOFs) in a plethora of applications is a growing research area. More importantly, this evolving class of solid materials has attracted recent interest in relevant applications that involve aqueous acids or bases. This mounting interest, mainly at a low readiness level, is driven by the high degree of structural tunability of MOFs vs other families of solid-state materials. However, the advantage of organic–inorganic hybridization in MOFs, for fine-tuning the structural properties-performances, is very often limited by their degree of chemical and hydrolytic stability. Herein, we offer an overview of the progress made in the design and assembly of MOFs with potential robustness in harsh aqueous acidic and basic media. In this review, we analyze critically the different works carried out on the use of MOFs as separation and catalytic agents in neutral and acidic-basic conditions. Prominently, this work finely evaluates the impact of different chemical, functional and topological parameters on the robustness of the resultant MOF frameworks. Future directions that guide material chemists towards designing frameworks with long-term stability in harsh liquid phases will also be debated.

Ordered structure of interlayer constructed with metal-organic frameworks improves the performance of lithium-sulfur batteries

Lithium-sulfur (Li-S) battery has attracted intensive attention in the realm of energy storage owing to its high theoretical capacity and energy density. However, the shuttle effect of soluble lithium polysulfides (LiPSs) between electrodes results in rapid capacity degradation. Herein, a strategy which combines the design of both chemical interaction and microstructure of interlayer was proposed to suppress the shuttle effect. The chemical interaction between different functionalized MOFs and LiPSs was systematically studied to find the best candidate. Furthermore, an interlayer with ordered structure was constructed via the layer-by-layer assembly of metal-organic frameworks (MOFs) on graphene (UiO-66-NH2@graphene) to create sinuous channels which can better impede the diffusion process of LiPSs by the strong adsorption of MOF toward LiPSs. Consequently, in comparison to the battery with a bare separator, the ordered interlayer increased the initial discharge capacity of battery by 28.98% at 1.0 C and lowered the capacity decay rate remarkably from 0.10% to 0.067% per cycle, indicating that the design of chemical interaction and microstructure paves the way for high-performance Li-S batteries.

Determination of total iron‐binding capacity of transferrin using metal organic framework‐based surface‐enhanced Raman scattering spectroscopy

AbstractWe report the rapid and sensitive determination of the total iron‐binding capacity of transferrin (Tf) in human serum using surface‐enhanced Raman scattering (SERS) spectroscopy. Herein, metal organic framework (MOF)–gold nanoparticle (AuNP) complexes were used as the SERS substrate. The highly porous MOF preconcentrates the reporter molecules and accelerates the approach of the reporter molecules to the vicinity of the AuNPs on the surface of the MOF. As a result, a significant number of reporter molecules are trapped close to SERS‐active “hot spots,” and their Raman signals are greatly enhanced. Additionally, Tf acts as an anchor to form a three‐dimensional assembly of MOF–AuNP units via specific binding to the Fe(III) ions of adjacent MOF units when MOF–AuNP complexes are added to human serum. This leads to further enhancement of the Raman signals of Raman reporter molecules with increasing Tf concentration. Quantitative estimation of Tf is possible by monitoring the variations in the intensity of the Raman signal of Raman reporter molecules adsorbed on MOF–AuNP complexes as a function of the Tf concentration. In this work, SERS‐based analysis using the MOF–AuNP complexes was performed to determine the concentration of Tf in the human serum for diagnosing iron deficiency. The limit of detection of Tf was determined to be 0.51 μM in spiked human serum. This SERS‐based analysis of Tf using MOF–AuNPs provides new insight for the rapid and sensitive diagnosis of iron deficiency in human serum.

Highly conductive skeleton Graphitic-C3N4 assisted Fe-based metal-organic frameworks derived porous bimetallic carbon nanofiber for enhanced oxygen-reduction performance in microbial fuel cells

Rational design and assembly of metal-organic frameworks (MOFs) is an effective strategy to develop high-performance electrocatalysts for oxygen reduction reaction in the microbial fuel cells (MFCs). In this work, a novel strategy to fabricate hierarchically porous bimetallic-carbon nanofibers (Mn–Fe@g-C3N4) via pyrolyzing Mn-doped g-C3N4 assisted Fe-based MOFs (MIL-101) is proposed. The Mn–Fe@g-C3N4 exhibits superior oxygen reduction reaction (ORR) onset potential (0.393 V vs. Ag/AgCl) and half-wave potential (−0.042 V vs. Ag/AgCl) under neutral condition, exceeding the state-of-the-art Pt/C catalyst. Mn–Fe@g-C3N4 displays a direct four-electron-transfer pathway, excellent stability and methanol tolerance in alkaline media. Mn–Fe@g-C3N4 cathode exhibits the ohmic resistance (8.07 Ω) and charge transfer resistance (5.44 Ω), which is slightly lower than Pt/C catalyst. Mn–Fe@g-C3N4 catalyst is an outstanding air-cathode in MFC with a power density of 413 ± 7 mW m−2, outperforms the MFC with 20 wt% Pt/C catalyst (333 ± 9 mW m−2). The outstanding catalytic activity for Mn–Fe@g-C3N4 is mainly due to 3D interconnected porous architectures, highly conductive framework and the synergistic effects between nitrogen and metal ion center. The present work not only provides an efficient conductive-skeleton-assisted synthetic strategy to construct high-performance electrocatalyst, but also improves the electrochemical performance of MOF-derived materials for practical MFCs application.

Highly Transparent, Flexible, and Mechanically Strong Nanopapers of Cellulose Nanofibers @Metal-Organic Frameworks.

Freestanding nanopapers were fabricated by the assembly of metal-organic frameworks (MOFs) onto cellulose nanofibers (CNFs). The CNFs are wrapped by continuously nucleated MOF layers (CNF@MOF) by interfacial synthesis, with the charge density on the surface of the CNFs and the dosage of the surfactant polyvinylpyrrolidone (PVP) being carefully adjusted. The obtained CNF@MOF nanofibers with long-range, continuous, hybrid nanostructures were very different to the composites formed by aggregation of MOF nanoparticles on the substrates. Four typical MOFs (HKUST-1, Al-MIL-53, Zn-MOF-74, ZIF-CO3 -1) were successfully grown onto CNFs in aqueous solutions and further fabricated into freestanding nanopapers. Because of their unique nanostructures and morphologies, the corresponding flexible nanopapers exhibit hierarchical meso-micropores, high optical transparency, high thermal stability, and high mechanical strength. A proof-of-concept study shows that the CNF@MOF nanopapers can be used as efficient filters to separate volatile organic compounds (VOCs) from the air. This work provides a new path for structuring MOF materials that may boost their practical application.

Electrospun metal-organic framework nanoparticle fibers and their derived electrocatalysts for oxygen reduction reaction

The rational design of assembled metal-organic frameworks (MOFs) derived carbon materials with rapid mass transport properties and stable porous structure is highly desirable yet a great challenge to date. In this work, MOFs-derived Co/N-doped porous carbon fibers with high electrochemical performance can be prepared simply by carbonizing MOFs nanofibers, which were fabricated by the electrospinning-assisted assembly of bimetallic zeolitic imidazolate framework nanoparticles (BMZIFs) based on ZIF-8 and ZIF-67. The effects of assembly and Zn/Co ratios on the oxygen reduction reaction (ORR) performances of the electrospun fibers derivatives were systematically studied. As expected, compared to the non-electrospun samples, such doped porous carbon nanofibers exhibited excellent electrocatalytic performances without any etching or other activating processes, and the sample with the molar ratio of Zn: Co= 5:1 even showed comparable ORR performance with the commercial Pt/C catalyst under the same conditions. The high catalytic performances root in the dense assembly of MOFs within the electrospun fibers, which was beneficial to endow the derivatives with the high surface area as well as uniform N and Co doping. Besides, the one-dimensional porous structure significantly promoted the mass transfer and exposure of active sites.

Nucleation and growth of oriented metal-organic framework thin films on thermal SiO2 surface

Assembly of metal-organic framework (MOF) thin-films with well-ordered growth directions enables many practical applications and is likely part of the future of functional nanomaterials. Insights into the formation pathway of the MOF thin films would allow better control over the growth directions and possibly the amount of guest molecules absorbed into the MOF pores. Here, we investigate the nucleation and growth of oriented Cu3(BTC)2∙xH2O MOF (HKUST-1, BTC = benzene-1,3,5-tricarboxylic acid) thin films on the thermal SiO2 surface using a room temperature stepwise layer-by-layer (LBL) method. Initial stages of LBL growth were characterized with X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analysis in order to understand nucleation and growth kinetics. HKUST-1 thin films with preferred growth along the [111] direction on the thermal SiO2 surface were obtained in the absence of not only a gold substrate, but also organic-based self-assembled monolayers (SAMs). It is found that the formation of HKUST-1 is initiated by deposition of copper acetate on the thermal SiO2 surface followed by ligand exchange between coordinated acetate from the copper precursor and the BTC ligands. As the LBL growth cycle is increased, HKUST-1 crystals on the thermal SiO2 surfaces are continuously forming and growing and finally the crystallites coalesce into a continuous film. Highly oriented HKUST-1 thin films on thermal SiO2 surface with complete surface coverage and ~90 nm thickness were obtained at ~80 cycles of LBL growth under the conditions used in this study.

Development of metal-organic framework composites in sample pretreatment

In recent years, a new type of multi-functional porous material, metal-organic frameworks (MOFs), is emerging. MOFs are formed by coordination of metal ions or metal clusters with oxygen or nitrogen and contain organic ligands porous skeleton structure. Compared with other traditional inorganic porous materials, MOFs have many advantages such as high specific surface area, large porosity, good thermal stability and diversified structure and function. They are widely used in the fields of gas storage, catalysis, adsorption and separation. In recent years, the applications of MOF composites in sample pretreatment have aroused great interest and widespread concern. Due to the assembly of MOFs and different functional materials, such as polymers, carbon-based materials and magnetic materials, the performance of MOF composites are better than the original MOFs. This review summarizes the applications of MOF composites in sample pretreatment technique in recent years, focuses on the applications of MOFs composites in solid phase microextraction (SPME), solid phase extraction (SPE) and magnetic solid phase extraction (MSPE).

In Situ Growth of Self-Assembled ZIF-8-Aminoclay Nanocomposites with Enhanced Surface Area and CO2 Uptake.

Self-assembly of metal-organic framework (MOF) nanoparticles (NPs) with a functional material can result in MOF nanocomposites having new and advanced properties along with the fabrication of new nanoscopic structures. However, such assembly of MOFs has not been realized to date. Here we report self-assembled nanocomposites of the zeolitic imidazolate framework (ZIF-8) and layered aminoclay (AC) for the first time, and the ZIF-8@AC composites exhibit significantly enhanced adsorption properties in comparison to those of pristine ZIF-8 nanoparticles. Four different composites denoted as ZIF-8@AC-1, ZIF-8@AC-2, ZIF-8@AC-3, and ZIF-8@AC-4 were synthesized by varying the clay content, and their AC contents were found to be 12.1, 18.3, 22.2, and 27.2 wt %, respectively. The composites were thoroughly characterized by PXRD, FTIR, Raman, and various microscopic techniques (FESEM, TEM, and STEM). The formation of the composites is driven by the specific interaction between unsaturated Zn(II) sites of ZIF-8 nanoparticles and NH2 groups of the aminoclay, which was validated from ζ potential and Raman spectroscopic measurements. The adsorption studies of the desolvated composites were also carried out in detail. The best performance is achieved with one of the composites, which exhibits a 42% increase in BET surface area while CO2 uptake at 298 K is doubled in comparison to the ZIF-8 nanoparticles.

Polymerization of Alkylsilanes on ZIF-8 to Hierarchical Siloxane Microspheres and Microflowers

The use of metal-organic frameworks (MOFs) in the polymerization field remains comparatively rare up to now, let alone studies on the fabrication of polymer microstructures through a MOFs-catalyzed assembly process. Zeolitic imidazolate framework-8 (ZIF-8), a well-known MOF for its chemical and thermal stabilities, was used to induce a polymerization reaction of saturated alkylsilanes for the first time. The reaction temperature was found to be critical for morphology control of the polymerized ZIF-siloxane composites. The polymerization of alkylsilanes by ZIF-8 at room temperature resulted in siloxane microspheres while rose petal-like microstructures were obtained at higher temperature. The effects of the reaction time on the structures of the polymerization products were also investigated and the polymerization reaction process was proposed. This work expands the field of MOFs’ applications and develops a reasonable method for the multidimensional assembly of MOFs building blocks into required structures or platforms for designing new kinds of hierarchical morphologies, which to our knowledge has not been previously investigated.

Layer-by-Layer Assembly of Metal-Organic Frameworks in Macroporous Polymer Monolith and Their Use for Enzyme Immobilization.

New monolithic materials comprising zeolitic imidazolate framework (ZIF-8) located on the pore surface of poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith previously functionalized with N-(3-aminopropyl)-imidazole have been prepared via a layer-by-layer self-assembly strategy. These new ZIF-8@monolith hybrids are used as solid-phase carriers for enzyme immobilization. Their performance is demonstrated with immobilization of a model proteolytic enzyme trypsin. The best of the conjugates enable very efficient digestion of proteins that can be achieved in mere 43 s.

Assembly of MOF Microcapsules with Size-Selective Permeability on Cell Walls.

The assembly of metal-organic frameworks (MOFs) into microcapsules has attracted great interest because of their unique properties. However, it remains a challenge to obtain MOF microcapsules with size selectivity at the molecular scale. In this report, we used cell walls from natural biomaterials as non-toxic, stable, and inexpensive support materials to assemble MOF/cell wall (CW) microcapsules with size-selective permeability. By making use of the hollow structure, small pores, and high density of heterogeneous nucleation sites of the cell walls, uniform and continuous MOF layers could be easily obtained by inside/outside interfacial crystallization. The prepared MOF/CW microcapsules have excellent stability and enable the steady, slow, and size-selective release of small molecules. Moreover, the size selectivity of the microcapsules can be adjusted by changing the type of deposited MOF.