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      Metal–organic frameworks to satisfy gas upgrading demands: fine-tuning the soc-MOF platform for the operative removal of H2S

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          Abstract

          Structure/properties relationships for a series of isostructural (MOFs) with the soc topology were explored for various gas separation applications.

          Abstract

          A cooperative experimental/modeling strategy was used to unveil the structure/gas separation performance relationship for a series of isostructural metal–organic frameworks (MOFs) with soc-topology (square-octahedral) hosting different extra-framework counter ions (NO 3 , Cl and Br ). In 3+-, Fe 3+-, Ga 3+- and the newly isolated Al( iii)-based isostructural soc-MOF were extensively studied and evaluated for the separation-based production of high-quality fuels ( i.e., CH 4, C 3H 8 and n-C 4H 10) and olefins. The structural/chemical fine-tuning of the soc-MOF platform promoted equilibrium-based selectivity toward C 2+ (C 2H 6, C 2H 4, C 3H 6 C 3H 8 and n-C 4H 10) and conferred the desired chemical stability toward H 2S. The noted dual chemical stability and gas/vapor selectivity, which have rarely been reported for equilibrium-based separation agents, are essential for the production of high-purity H 2, CH 4 and C 2+ fractions in high yields. Interestingly, the evaluated soc-MOF analogues exhibited high selectivity for C 2H 4, C 3H 6 and n-C 4H 10. In particular, the Fe, Ga and Al analogues presented relatively enhanced C 2+/CH 4 adsorption selectivities. Notably, the Ga and Al analogues were found to be technically preferable because their structural integrities and separation performances were maintained upon exposure to H 2S, indicating that these materials are highly tolerant to H 2S. Therefore, the Ga- soc-MOF was further examined for the selective adsorption of H 2S in the presence of CO 2- and CH 4-containing streams, such as refinery-off gases (ROG) and natural gas (NG). Grand canonical Monte Carlo (GCMC) simulations based on a specific force field describing the interactions between the guest molecules and the Ga sites supported and confirmed the considerably higher affinity of the Ga- soc-MOF for C 2+ (as exemplified by n-C 4H 10) than for CH 4. The careful selection of an appropriate metal for the trinuclear inorganic molecular building block (MBB), i.e., a Ga metal center, imbues the soc-MOF platform with the requisite hydrolytic stability, H 2S stability, and exceptional gas selectivity for ROG and NG upgrading. Finally, the soc-MOF was deployed as a continuous film on a porous support, and its gas permeation properties as a membrane were evaluated.

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          Most cited references 53

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          From Molecules to Crystal Engineering:  Supramolecular Isomerism and Polymorphism in Network Solids

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            Flexible metal-organic frameworks.

            Advances in flexible and functional metal-organic frameworks (MOFs), also called soft porous crystals, are reviewed by covering the literature of the five years period 2009-2013 with reference to the early pertinent work since the late 1990s. Flexible MOFs combine the crystalline order of the underlying coordination network with cooperative structural transformability. These materials can respond to physical and chemical stimuli of various kinds in a tunable fashion by molecular design, which does not exist for other known solid-state materials. Among the fascinating properties are so-called breathing and swelling phenomena as a function of host-guest interactions. Phase transitions are triggered by guest adsorption/desorption, photochemical, thermal, and mechanical stimuli. Other important flexible properties of MOFs, such as linker rotation and sub-net sliding, which are not necessarily accompanied by crystallographic phase transitions, are briefly mentioned as well. Emphasis is given on reviewing the recent progress in application of in situ characterization techniques and the results of theoretical approaches to characterize and understand the breathing mechanisms and phase transitions. The flexible MOF systems, which are discussed, are categorized by the type of metal-nodes involved and how their coordination chemistry with the linker molecules controls the framework dynamics. Aspects of tailoring the flexible and responsive properties by the mixed component solid-solution concept are included, and as well examples of possible applications of flexible metal-organic frameworks for separation, catalysis, sensing, and biomedicine.
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              MOF thin films: existing and future applications.

              The applications and potentials of thin film coatings of metal-organic frameworks (MOFs) supported on various substrates are discussed in this critical review. Because the demand for fabricating such porous coatings is rather obvious, in the past years several synthesis schemes have been developed for the preparation of thin porous MOF films. Interestingly, although this is an emerging field seeing a rapid development a number of different applications on MOF films were either already demonstrated or have been proposed. This review focuses on the fabrication of continuous, thin porous films, either supported on solid substrates or as free-standing membranes. The availability of such two-dimensional types of porous coatings opened the door for a number of new perspectives for functionalizing surfaces. Also for the porous materials themselves, the availability of a solid support to which the MOF-films are rigidly (in a mechanical sense) anchored provides access to applications not available for the typical MOF powders with particle sizes of a few μm. We will also address some of the potential and applications of thin films in different fields like luminescence, QCM-based sensors, optoelectronics, gas separation and catalysis. A separate chapter has been devoted to the delamination of MOF thin films and discusses the potential to use them as free-standing membranes or as nano-containers. The review also demonstrates the possibility of using MOF thin films as model systems for detailed studies on MOF-related phenomena, e.g. adsorption and diffusion of small molecules into MOFs as well as the formation mechanism of MOFs (101 references).
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                Author and article information

                Journal
                JMCAET
                Journal of Materials Chemistry A
                J. Mater. Chem. A
                Royal Society of Chemistry (RSC)
                2050-7488
                2050-7496
                2017
                2017
                : 5
                : 7
                : 3293-3303
                Article
                10.1039/C6TA09406F
                © 2017
                Product
                Self URI (article page): http://xlink.rsc.org/?DOI=C6TA09406F

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