The targeted incorporation of defects into crystalline matter allows for the manipulation of many properties and has led to relevant discoveries for optimized and even novel technological applications of materials. It is there- fore exciting to see that defects are now recognized to be similarly useful in tailoring properties of metal-organicframeworks (MOFs). For instance, heterogeneous catalysis crucially depends on the number of active catalytic sites as well as on diffusion limitations. By the incorporation of missing linker and missing node defects into MOFs, both parameters can be accessed, improving the catalytic properties. Furthermore, the creation of defects allows for adding properties such as electronic conductivity, which are inherently absent in the parent MOFs. Herein, progress of the rapidly evolving field of the past two years is overviewed, putting a focus on properties that are altered by the incorporation and even tailoring of defects in MOFs. A brief account is also given on the emerging quantitative understanding of defects and heterogeneity in MOFs based on scale-bridging computational modeling and simulations.
Metal-organicframeworks (MOFs), assembled from metal ions and organic linkers via coordination chemistry, have wide potentials in catalysis [1-5], energy [6-8], and biomedical applications [9, 10]. As a new type of porous crystalline material, MOF building blocks can themselves be functional, which is different from the other nanomaterials. In particular, the tunable porosity, controlled structure, and readily chemical functionalizability of MOFs make them good examples as nanocarriers in biomedical applications . From bulk phase to nanoscale phase, the discovery of abundant applicable properties of MOFs has led to new applications in biomedicine, especially at nanoscale size. During the past few years, preparation of various uniform nanoscale MOFs has provided a significant platform to explore structure-orientated functions of MOFs . From nanocarriers to nanocargoes, MOFs have been able to make themselves a functional entity by controlling their assembling units. As a consequence, multifunctional MOFs have been extensively studied via direct synthesis or post-synthesis modification for
Highly porous metal–organicframeworks (MOFs), which have undergone exciting developments over the past few decades, show promise for a wide range of applications. However, many studies indicate that they suffer from significant stability issues, especially with respect to their interactions with water, which severely limits their practical potential. Here we demonstrate how the presence of
Metal-organicframeworks (MOFs) are currently the focus of intense scientific interest due to their wide range of potential applications in gas storage 1,2 and separation, 3 catalysis, 4,5 drug delivery, 6-8 and as thermo-active, 9 conducting 10,11 and electronic 12,13 materials. Of particular interest to us is the potential of MOFs to store and purify fuel and exhaust gases. 14 For industrial scale applications, MOFs must not only possess the desired functionality and properties, but their synthesis and processing must be scalable at low cost to give products in high yield and purity. Increasing environmental awareness and commercial constraints mean that synthetic processes must be as green as possible, and water is thus an attractive solvent for the synthesis of MOFs. 15,16
Crystallographic studies in which adsorbed gas molecules are allocated within the pores of MOFs (or other porous mate- rials) present significant experimental and structure refine- ment challenges. However, such studies have been successfully conducted on a range of metal–organicframeworks using both single-crystal and powder diffraction, and employing both X- rays and neutrons (Table 1). These studies have enabled important structural information on the position of gas molecules contained within these porous materials to be determined and the nature of the interactions involved in holding these molecules in place to be investigated. This knowledge can now be applied to help design the next generation of porous materials. As diffraction capabilities continue to advance, it is anticipated that crystallographic characterization of gas molecules adsorbed within MOFs and related porous materials will become more routinely under- taken. Such studies will continue to make important contri- butions not only to the development of MOFs and related materials, but in driving crystallography towards new frontiers.
Supramolecular organocatalysis is an interdisciplinary research area that includes elements from organic chemistry, supramo- lecular chemistry and biochemistry. 1,2 The design of a supra- molecular catalyst is based on using hydrogen bonding and other intermolecular interactions in recognition and activation of substrates for triggering a variety of chemical trans- formations. 3,4 However, supramolecular catalysis oen suﬀers from drawbacks such as the lack of catalyst recycling and low eﬃciency due to the self-aggregation (self-quenching) of the catalyst. 3 The heterogenization of supramolecular organo- catalysts may be a logical solution to overcome these obstacles in extending the applicability of these systems. 5 –7 Recently, metal-organicframeworks (MOFs) were introduced as prom- ising candidates for applications in diverse areas. 8–10 Compared to other porous materials, MOFs have given chemists the opportunity to tune the topology, pore size and functionality by rational selection of organic linkers and inorganic metal centers. Owing to this feature, MOFs with uniform and permeable pores and channels have shown to be particularly promising for catalysis. 11–14 According to the catalytically active sites, these frameworks may be categorized into four distinct groups, namely metal-organicframeworks with coordinatively
3 Figure 1.1: Zeolite structure FAU (faujasite Y). It has a 3-dimensional pore structure made of secondary building units 4, 6, and 6-6.
Extensive research on zeolites and the evolution of porous materials has led onto a new family of materials, known as coordination polymers (CP) and metal-organicframeworks (MOFs), which are built up of organic and inorganic components. These allow the pore size and chemical properties to be widely tuned. IUPAC 8 defined coordination networks as a subset of coordination polymers, and MOFs a further subset of coordination networks. The network of a MOF should contain potential voids as part of its assembly, while all other coordination compounds can be named as coordination polymers. Another characteristic that makes them different is that MOFs are by definition crystalline, whereas coordination polymers do not need to be. 9
1.1 Metalorganic frameworks and the concept of reticular synthesis
Metalorganic frameworks (MOFs), also referred to as metalorganic coordination networks, coordination polymers, hybrid organic inorganic materials or organic “zeolite analogues” with unavoidable overlap 15 are a new kind of material consisting of metal ions or clusters linked together by rigid organic molecules to form one, two or threedimensional networks. The term “zeolite analogues” does not imply that the full functionality of zeolites should be reproduced, but refers instead to the ability of the materials to act as molecular sieves. Metalorganic frameworks are materials that have a good permeability, high void volumes, and well defined tailorable cavities of uniform size. These are precisely the qualities needed for catalysis, separation and storagerelease applications. In the past ten years, the interest in Metalorganic frameworks has grown dramatically and a number of recent review articles cover the various aspects of this field of hybrid inorganic
It is clear that adsorbent materials are key in the development of heat transformation technologies. In this respect, the discovery of new materials applicable for adsorption-desorption working fluid is still a fundamental research of which the development of this technology is ongoing.[16-19] Porous coordination polymers (PCPs) also well known as metal-organicframeworks (MOFs) demonstrated excellent properties as adsorbent and are explored for heat transformation applications. Due to their huge surface (having micro- to macro-pores), chemical and physicochemical variability tunable composition/properties can be designed. Moreover, MOFs consist of both hydrophilic and hydrophobic moieties in the same structure which possess some unique adsorption properties. Compared with a vast number of natural and synthetic adsorbents, MOF materials have a high potential for heat transformation applications because of their high ability in adsorption of guest molecules, including water (working fluid), and thermal stability.[16, 20] Additionally, MOFs possessing hydrophilic properties have an advantage over silica gel, they exhibit a non-limited water uptake at high relative pressure values reaching their maximum capacity. Initially, the demonstration of MOFs as adsorbent materials was carried out by investigating the capability of solid-gas adsorption applications for energy transformation.
Over the last 20 years, a number of different nanoparticle-based strategies have been developed to improve the efficacy of conventional drug delivery. 1,2 Porous and tunable hybrid materials, metalorganicframeworks (MOFs), are promising candi- dates as potential drug carriers, because of their remarkably large surface areas and excessively high porosities. 3,4 The adjustment of the framework’s functional groups and pore size make it advantageous over rigid nanoparticle carriers in biomedical applications. 5 Although several types of organic carriers at a nanoscale level such as micelles, liposomes, and dendrimers 6–9 have been employed for drug delivery, the drug release is difficult to control with an absence of tunable porosity. 10 In contrast, MOF nanoparticles have a high loading capacity and controlled drug release properties. 2
* Correspondence: firstname.lastname@example.org (N.R.); email@example.com (E.M.)
Abstract: The composition and topology of metal-organicframeworks (MOFs) are exceptionally tailorable; moreover, they are extremely porous and represent an excellent Brunauer–Emmett–Teller (BET) surface area ( ≈ 3000–6000 m 2 · g −1 ). Nanoscale MOFs (NMOFs), as cargo nanocarriers, have increasingly attracted the attention of scientists and biotechnologists during the past decade, in parallel with the evolution in the use of porous nanomaterials in biomedicine. Compared to other nanoparticle-based delivery systems, such as porous nanosilica, nanomicelles, and dendrimer- encapsulated nanoparticles, NMOFs are more flexible, have a higher biodegradability potential, and can be more easily functionalized to meet the required level of host–guest interactions, while preserving a larger and fully adjustable pore window in most cases. Due to these unique properties, NMOFs have the potential to carry anticancer cargos. In contrast to almost all porous materials, MOFs can be synthesized in diverse morphologies, including spherical, ellipsoidal, cubic, hexagonal, and octahedral, which facilitates the acceptance of various drugs and genes.
There has been extensive research on the sensing of explosive nitroaromatic compounds (NACs) using ﬂuorescent metal-organicframeworks (MOFs). However, ambiguity in the sensing mechanism has hampered the development of ef ﬁcient explosive sensors. Here we report the synthesis of a hydroxyl-functionalized MOF for rapid and ef ﬁcient sensing of NACs and examine in detail its ﬂuorescence quenching mechanisms. In chloroform, quenching takes place primarily by exciton migration to the ground-state complex formed between the MOF and the analytes. A combination of hydrogen-bonding interactions and π–π stacking interactions are responsible for ﬂuorescence quenching, and this observation is supported by single-crystal structures. In water, the quenching mechanism shifts toward resonance energy transfer and photo-induced electron transfer, after exciton migration as in chloroform. This study provides insight into ﬂorescence-quenching mechanisms for the selective sensing of NACs and reduces the ambiguity regarding the nature of interactions between the MOF and NACs.
KEYWORDS: nanocon ﬁnement, lithium-ion batteries, metal−organicframeworks, dendrites, quasi-solid electrolytes
Metal −organicframeworks (MOFs) are hybrid porous solids, obtained by reticular synthesis, through which inorganic metal ions or clusters are coordinated by organic linkers to form a multidimensional framework. 1 Due to the high ﬂexibility in terms of chemical nature, size, and geometry of the components, more than 90,000 MOF structures are available in the Cambridge Structural Database (CSD) 2 as of March 2021. 3 The organic unit typically possesses a ditopic or polytopic functionality (often carboxylate) which is anchored to metal ions or clusters to yield a (often) robust crystalline MOF structure with a porosity degree typically higher than 50%. By tuning the metal ions and linkers, ultrahigh porosity may be achieved with pore diameters in the micro −meso domain, namely, lower than 10 nm. This results in surface area values larger than 7000 m 2 g −1 with a theoretical upper limit of 14,600 m 2 g −1 , 4 exceeding those typically observed in other class of porous materials such as zeolites and porous carbons. 5 In addition, MOF thermal and chemical stabilities allow postsynthesis functionalization, which enable their use in a wide range of applications, from gas storage, separation, and adsorption to catalysis and ion and/or electron conduction. 1
Metal–organicframeworks (MOFs) are highly porous crystalline materials consisting of metal ions or clusters bridged by organic ligands, 1 and their value arises from the void space within their structure (up to 90%), 2 which drives applications in gas storage and separation, 3 catalysis, 4 sensors, 5 and as supercapacitors. 6 Typically MOFs are prepared by solvothermal batch reactions whereby the reactants are heated above the boiling point of the solvent and retained under autogenous pressure for up to one week. 7 The duration and energy requirement of these reactions has led to a restriction in the adoption of MOFs for industrial applications owing to their high product cost. A critical need exists for technologies that reduce the time and cost of manu- facture of MOFs 8 in order for their industrial potential to be fully realised.
Chapter 1 outlined the potential of nitric oxide, carbon monoxide and hydrogen sulfide as therapeutics, and how metal-organicframeworks represent a potential delivery method. The storage and delivery of nitric oxide from some MOFs has been well characterised, but whether suitable amounts of hydrogen sulfide and carbon monoxide can be released from MOFs is currently unknown. In order for these materials to be used for the storage and delivery of these gases, more needs to be known about the physical properties of the framework materials; how much of each gas each material can store; whether all of the stored gas can be delivered, and at what rate; and whether the frameworks degrade over storage periods. Ideally, these questions should be answered with reference to the structural properties of the material and how gases interact with the structure. Therefore, the main objective of this thesis is to gain a greater understanding of the way in which nitric oxide, carbon monoxide and hydrogen sulfide interact with metal-organicframeworks in order to assess their potential as gas storage and release media.
Natural gas is major resource in UAE, constitute about 90% methane and as compared to other fossil fuels, it is more environmentally friendly. Energy demand from natural gas can be projected to exceed two hundred exajoules per year in 2040. In the UAE, many natural gas filling stations are already built for utilizing natural gas as a vehicle transportation fuel where these materials have potential applications to store and deliver this fuel. This research aims to study various kinds of Metal-OrganicFrameworks, and to investigate adsorption properties for the storage of natural gas and its delivery. MOFs possess porous material that exhibits a high deliverable capacity of gases. These are synthesized using strategies such as crystal engineering with varying organic groups such as linker length and hydrophilicity, pore shape, and phase changes. The main challenges in designing MOFs for methane storage are understanding the mechanical properties, developing thermal management solutions, and the effect of impurities on the working capacity as well as the manufacturing costs of MOFs. This thesis gives pathway to tackle such problems. Overall, HKUST-1 showed promising results for the various MOFs tested. Synthesis and characterization were done by scanning electron microscope, thermogravimetric analysis, X-ray diffraction, and nitrogen adsorption. Adsorption process, reaction heat, and total heat involved in the process were studied using Tian-Calvet calorimeter and gas chromatography. A significant part of this research was dedicated to designing and setting up the calorimeter used in obtaining the heat of adsorption. Moreover, the adsorption properties and separation of the gaseous mixture are also studied using the gas chromatography with some equipment modifications. Designing of MOFs, a class of adsorbents, is described considering the thermodynamics of adsorption of these porous materials for natural gas and methane storage. The thermodynamics of adsorption governs the adsorption isotherm and, therefore the deliverable capacity of stored natural gas and methane. Calorimetric and gas chromatography studies indicated that HKUST-1 has the best adsorbent among the tested MOFs.
MAXSORB) as well as metal-organicframeworks (MOFs)have been extensively considered and investigated for CO 2 capture and separation under different conditions. However, there are some distinct limitations for these solid physical adsorbents. Firstly, the weak affinity and relatively low adsorption capacity such as activated carbons and carbon fibers. Secondly, the degradation phenomenon of the adsorbents, for example, the CaO is easily to degrade after several carbonation-calcination cycles at high temperature. Thirdly, zeolites and silica materials are moisture sensitive which is unavailable for wet streams. Lastly, due to the complex topology of HTLCs compounds and silica materials as well as the poor thermal stability, these adsorbents confront great challenges for recycling and renewal in the regeneration step. Thus, recent research attentions have been drawn to overcome these shortcomings (Alhamami, Doan & Cheng 2014; Chałupnik et al. 2013; Miller, Akbar &
Commun. 2007, 2820
14 D. Cunha, M. B. Yahia, S. Hall, S. R. Miller, H. Chevreau, E. Elkaïm, G. Maurin, P. Horcajada, and C. Serre, “Rationale of drug encapsulation and release from biocompatible porous metal–organicframeworks,” Chem. Mater. 25(14), 2767 (2013).
15 Y. Liu, J. F. Eubank, A. J. Cairns, J. Eckert, V. C. Kravtsov, R. Luebke, and M. Eddaoudi, “Assembly of metal–organicframeworks (MOFs) based on indium-trimer building blocks: A porous MOF with soc topology and high hydrogen storage,”
Figure 1. Structure of ligands H 2 1 (a) and H 2 2 (b). c) Paddlewheel SBU, with DMF coordinated in the axial positions. d) X-ray crystal structure showing layered structure of Zn(1)(DMF).
In our work we seek to design new layered MOFs which incorporate features intended to enhance their exfoliation and stabilize the resulting MONs in suspension. We recently communicated a study reporting the liquid exfoliation of Cu(1)(DMF), a layered MOF incorporating weakly interacting methoxy-propyl chains designed to aid exfoliation of the layers into nanosheets. [13g] The nanosheets are based on the popular metal-paddlewheel secondary building unit (SBU) which has a labile, lewis acidic axial coordination site which makes it ideal for a wide range of sensing, catalytic, electronic, separation and storage applications. [2c, 3b, 6b, 6c, 6e] We hypothesized that liquid exfoliation of layered metal-organicframeworks functionalized with either hydrophobic or hydrophilic functionalities would produce nanosheets with different concentrations, stabilities and thicknesses in different solvents. To investigate this, we compared the liquid exfoliation of the relatively hydrophilic methoxy-propyl functionalized MOF with an isostructural MOF incorporating a more hydrophobic pentyl-chain in a wide range of different solvents. We then investigated the molecular and nanoscopic structure of the resulting nanosheets in selected solvents under different conditions in order to understand and optimize the exfoliation process.
Scope: metal-organicframeworks for separating hydrocarbons mixture
Priority application: french patent application FR0803245 filed on June 11, 2008 and entitled « Solide hybride cristallin poreux réductible pour la séparation de mélanges de molécules ayant des degrés et / ou un nombre d’insaturations différents »