This review summarizes the use of metal–organic frameworks (MOFs) as a versatile supramolecular platform to develop heterogeneous catalysts for a variety of organic reactions, especially for liquid-phase reactions. Following a background introduction about catalytic relevance to various metal–organic materials, crystal engineering of MOFs, characterization and evaluation methods of MOF catalysis, we categorize catalytic MOFs based on the types of active sites, including coordinatively unsaturated metal sites (CUMs), metalloligands, functional organic sites (FOS), as well as metal nanoparticles (MNPs) embedded in the cavities. Throughout the review, we emphasize the incidental or deliberate formation of active sites, the stability, heterogeneity and shape/size selectivity for MOF catalysis. Finally, we briefly introduce their relevance into photo- and biomimetic catalysis, and compare MOFs with other typical porous solids such as zeolites and mesoporous silica with regard to their different attributes, and provide our view on future trends and developments in MOF-based catalysis.

Applications of metal–organic frameworks in heterogeneous supramolecular catalysis

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

Metal–organic frameworks (MOFs) are porous crystalline materials constructed from metal ions or clusters and multidentate organic ligands. Recently, the use of MOFs or MOF composites as catalysts for synergistic catalysis and tandem reactions has attracted increasing attention due to their tunable open metal centres, functional organic linkers, and active guest species in their pores. In this review, the applications of MOFs with multiple active sites in synergistic organic catalysis, photocatalysis and tandem reactions are discussed. These multifunctional MOFs can be categorized by the type of active centre as follows: (i) open metal centres and functional organic linkers in the MOF structure, (ii) active guest sites in the pores and active sites in the MOF structure, and (iii) bimetallic nanoparticles (NPs) on MOF supports. The types of synergistic catalysis and tandem reactions promoted by multifunctional MOFs and their proposed mechanisms are presented in detail. Here, catalytic MOFs with a single type of active site and MOFs that only serve as supports to enhance substrate adsorption are not discussed.

Multifunctional metal–organic framework catalysts: synergistic catalysis and tandem reactions

Metal–organic frameworks (MOFs), established as a relatively new class of crystalline porous materials with high surface area, structural diversity, and tailorability, attract extensive interest and exhibit a variety of applications, especially in catalysis. Their permanent porosity enables their inherent superiority in confining guest species, particularly small metal nanoparticles (MNPs), for improved catalytic performance and/or the expansion of reaction scope. This is a rapidly developing interdisciplinary research field. In this review, we provide an overview of significant progress in the development of MNP/MOF composites, including various preparation strategies and characterization methods as well as catalytic applications. Special emphasis is placed on synergistic effects between the two components that result in an enhanced performance in heterogeneous catalysis. Finally, the prospects of MNP/MOF composites in catalysis and remaining issues in this field have been indicated.

Metal–organic frameworks meet metal nanoparticles: synergistic effect for enhanced catalysis

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

A new series of alkaline-alkaline earth fluoride carbonates (KSrCO(3)F, RbSrCO(3)F, KCaCO(3)F, RbCaCO(3)F, CsCaCO(3)F, and Cs(3)Ba(4)(CO(3))(3)F(5)) were synthesized by spontaneous crystallization with molten fluxes. Their crystal structures, except for Cs(3)Ba(4)(CO(3))(3)F(5), exhibit the stacking of [AF](∞) (A = K, Rb, Cs) and [B(CO(3))](∞) (B = Ca, Sr) layers, and the coplanar alignment of [CO(3)] triangles. The results from the UV-vis diffuse reflectance spectroscopy study of the powder samples indicated that the short-wavelength absorption edges were all below 200 nm, except for Cs(3)Ba(4)(CO(3))(3)F(5), which is about 210 nm. Second-harmonic generation (SHG) on polycrystalline samples was measured using the Kurtz and Perry technique, which indicated that these carbonates are all phase-matchable materials in both visible and the UV region, and their measured SHG coefficients were about 3.33, 3.33, 3.61, 1.11, 1.11, and 1.20 times as large as that of d(36) (KDP), respectively.

Alkaline-alkaline earth fluoride carbonate crystals ABCO3F (A = K, Rb, Cs; B = Ca, Sr, Ba) as nonlinear optical materials.

The new nonlinear optical (NLO) crystal BaGa4S7 for the mid-infrared (IR) has been grown by a Bridgman-Stockbarger technique. Polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S as the initial materials by solid-state reactions. The ultraviolet (UV) and IR transmittance of the crystal was determined with polished crystal pieces. The UV and IR optical absorption edges were found to be at 350 nm and 13.7 μm, respectively. From optical measurements of second harmonic generation on powders, the NLO coefficient d33 was determined to be 12.6 pm/V. The laser damage threshold of a single crystal reached about 1.2 J/cm2 at 1.064 μm. The Vickers-hardness value of the crystal is 327.5 HV5, which is equivalent to Mohs’ hardness of about 5.

Growth and Characterization of BaGa4S7: A New Crystal for Mid-IR Nonlinear Optics

Scintillation based X-ray detection has received great attention for its application in a wide range of areas from security to healthcare. Here, we report highly efficient X-ray scintillators with state-of-the-art performance based on an organic metal halide, ethylenebis-triphenylphosphonium manganese (II) bromide ((C38H34P2)MnBr4), which can be prepared using a facile solution growth method at room temperature to form inch sized single crystals. This zero-dimensional organic metal halide hybrid exhibits green emission peaked at 517 nm with a photoluminescence quantum efficiency of ~ 95%. Its X-ray scintillation properties are characterized with an excellent linear response to X-ray dose rate, a high light yield of ~ 80,000 photon MeV−1, and a low detection limit of 72.8 nGy s−1. X-ray imaging tests show that scintillators based on (C38H34P2)MnBr4 powders provide an excellent visualization tool for X-ray radiography, and high resolution flexible scintillators can be fabricated by blending (C38H34P2)MnBr4 powders with polydimethylsiloxane. Scintillation-based X-ray detection is promising for applications in various areas ranging from security to healthcare, and low-cost and eco-friendly scintillation materials would be beneficial. Here the authors report a facile solution growth of organic manganese halide for efficient X-ray scintillation.

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Highly efficient eco-friendly X-ray scintillators based on an organic manganese halide.

Scintillators are utilized for X-ray detection in many important fields ranging from homeland security to health care. Developing low-cost, high-performance scintillation materials to address the i...

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Xinsong Lin

Papers

Alkaline-alkaline earth fluoride carbonate crystals ABCO3F (A = K, Rb, Cs; B = Ca, Sr, Ba) as nonlinear optical materials.

Growth and Characterization of BaGa4S7: A New Crystal for Mid-IR Nonlinear Optics

Highly efficient eco-friendly X-ray scintillators based on an organic manganese halide.

Highly Stable Organic Antimony Halide Crystals for X-ray Scintillation

BaGa2GeX6(X=S, Se): New mid-IR nonlinear optical crystals with large band gaps