Metal–organic frameworks (MOFs), also known as porous coordination polymers (PCPs), synthesized by assembling metal ions with organic ligands have recently emerged as a new class of crystalline porous materials. The amenability to design as well as fine-tunable and uniform pore structures makes them promising materials for a variety of applications. Controllable integration of MOFs and functional materials is leading to the creation of new multifunctional composites/hybrids, which exhibit new properties that are superior to those of the individual components through the collective behavior of the functional units. This is a rapidly developing interdisciplinary research area. This review provides an overview of the significant advances in the development of diverse MOF composites reported till now with special emphases on the synergistic effects and applications of the composites. The most widely used and successful strategies for composite synthesis are also presented.

Metal–organic framework composites

Novel catalytic materials are highly demanded to perform a variety of catalytic organic reactions. MOFs combine the benefits of heterogeneous catalysis like easy post reaction separation, catalyst reusability, high stability and homogeneous catalysis such as high efficiency, selectivity, controllability and mild reaction conditions. The possible organization of active centers like metallic nodes, organic linkers, and their chemical synthetic functionalization on the nanoscale shows potential to build up MOFs particularly modified for catalytic challenges. In this review, we have summarized the recent research progress in heterogeneous catalysis by MOFs and their catalytic behavior in various organic reactions, highlighting the key features of MOFs as catalysts based on the active sites in the framework. Examples of their post functionalization, inclusion of active guest species and metal nanoparticles have been discussed. Finally, the use of MOFs as catalysts for asymmetric heterogeneous catalysis and stability of MOFs has been presented as separate sections.

Metal–organic frameworks: versatile heterogeneous catalysts for efficient catalytic organic transformations

The ex vivo application of enzymes in various processes, especially via enzyme immobilization techniques, has been extensively studied in recent years in order to enhance the recyclability of enzymes, to minimize enzyme contamination in the product, and to explore novel horizons for enzymes in biomedical applications. Possessing remarkable amenability in structural design of the frameworks as well as almost unparalelled surface tunability, Metal–Organic Frameworks (MOFs) have been gaining popularity as candidates for enzyme immobilization platforms. Many MOF–enzyme composites have achieved unprecedented results, far outperforming free enzymes in many aspects. This review summarizes recent developments of MOF–enzyme composites with special emphasis on preparative techniques and the synergistic effects of enzymes and MOFs. The applications of MOF–enzyme composites, primarily in transferation, catalysis and sensing, are presented as well. The enhancement of enzymatic activity of the composites over free enzymes in biologically incompatible conditions is emphasized in many cases.

Enzyme–MOF (metal–organic framework) composites

Metal organic frameworks (MOFs) offer the highest surface areas per gram of any known material. As such, they epitomise resource productivity in uses where specific surface area is critical, such as adsorption, storage, filtration and catalysis. However, the ability to control the position of MOFs is also crucial for their use in devices for applications such as sensing, delivery, sequestration, molecular transport, electronics, energy production, optics, bioreactors and catalysis. In this review we present the current technologies that enable the precise positioning of MOFs onto different platforms. Methods for permanent localisation, dynamic localisation, and spatial control of functional materials within MOF crystals are described. Finally, examples of devices in which the control of MOF position and functionalisation will play a major technological role are presented.

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MOF positioning technology and device fabrication

Enzymatic catalytic processes possess great potential in chemical manufacturing, including pharmaceuticals, fuel production and food processing. However, the engineering of enzymes is severely hampered due to their low operational stability and difficulty of reuse. Here, we develop a series of stable metal-organic frameworks with rationally designed ultra-large mesoporous cages as single-molecule traps (SMTs) for enzyme encapsulation. With a high concentration of mesoporous cages as SMTs, PCN-333(Al) encapsulates three enzymes with record-high loadings and recyclability. Immobilized enzymes that most likely undergo single-enzyme encapsulation (SEE) show smaller Km than free enzymes while maintaining comparable catalytic efficiency. Under harsh conditions, the enzyme in SEE exhibits better performance than free enzyme, showing the effectiveness of SEE in preventing enzyme aggregation or denaturation. With extraordinarily large pore size and excellent chemical stability, PCN-333 may be of interest not only for enzyme encapsulation, but also for entrapment of other nanoscaled functional moieties.

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Stable metal-organic frameworks containing single-molecule traps for enzyme encapsulation

A simple nanoporous metal organic framework (MOF) bioreactor preparation via a low energy 30 minute vortex as driving force to immobilize trypsin enzyme is presented. No chemical modifications were employed thus organic wastes were eliminated. The digestion efficiency of this trypsin bioreactor is exceptionally high, even when reused. This “green” synthesis procedure produced a “green” bioreactor.

Novel trypsin–FITC@MOF bioreactor efficiently catalyzes protein digestion

Trypsin‐Immobilized Metal–Organic Framework as a Biocatalyst In Proteomics Analysis

Metal–organic frameworks: new matrices for surface-assisted laser desorption–ionization mass spectrometry

Approaches to drug delivery: Confinement of aspirin in MIL-100(Fe) and aspirin in the de novo synthesis of metal–organic frameworks

An enzyme-NBD@MOF bioreactor with exemplary proteolytic performance, even after successive reuse and storage, was produced through a novel, rapid and simple multipoint immobilization technique without chemical modification of the solid support. Enzyme loading and distribution could be directly monitored from the fluorescence emission of the bioreactor. The dye molecular dimension plays a role in its overall performance.

Brenda Singco

Papers

Novel trypsin–FITC@MOF bioreactor efficiently catalyzes protein digestion

Trypsin‐Immobilized Metal–Organic Framework as a Biocatalyst In Proteomics Analysis

Metal–organic frameworks: new matrices for surface-assisted laser desorption–ionization mass spectrometry

Approaches to drug delivery: Confinement of aspirin in MIL-100(Fe) and aspirin in the de novo synthesis of metal–organic frameworks

Fast multipoint immobilized MOF bioreactor.