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Recent Submissions

  • A new Titanium Metal Organic Framework with visible-light responsive photocatalytic activity.

    Cadiau, Amandine; Kolobov, Nikita; Srinivasan, Sivaranjani; Goesten, Maarten Gerard; Haspel, Henrik; Bavykina, Anastasiya; Tchalala, Mohamed; Maity, Partha; Goryachev, Andrey; Poryvaev, Artem; Eddaoudi, Mohamed; Fedin, Matvey; Mohammed, Omar F.; Gascon, Jorge (Angewandte Chemie (International ed. in English), Wiley, 2020-04-22) [Article]
    We report the one step synthesis and characterization of a new and robust titanium-based Metal Organic Framework, ACM-1 . In this new structure, based on infinite Ti-O chains and 4,4',4″,4″'-(pyrene-1,3,6,8-tetrayl) tetrabenzoic acid as a photosensitizer ligand, the combination of highly mobile photogenerated electrons and a strong hole localization at the organic linker results in large charge separation lifetimes. The suitable energies for band gap and CBM offer great potential for a wide range of photocatalytic reactions, from hydrogen evolution to the selective oxidation of organic substrates.
  • Reticular Chemistry 3.2: Typical Minimal Edge-Transitive Derived and Related Nets for the Design and Synthesis of Metal–Organic Frameworks

    Chen, Zhijie; Jiang, Hao; Li, Mian; O’Keeffe, Michael; Eddaoudi, Mohamed (Chemical Reviews, American Chemical Society (ACS), 2020-04-17) [Article]
    Reticular chemistry has proven as a notable/distinctive discipline aimed at the deliberate assembly of periodic solids, offering great opportunities to effectively deploy the gained knowledge on net-topologies as a guide and toolbox for designed syntheses, based on the assembly of molecular building blocks into targeted and anticipated structures of crystalline extended solids. The effective practice of reticular chemistry has enriched the repertoire of crystal chemistry and afforded notable accelerating development of crystalline extended frameworks, especially metal−organic frameworks (MOFs). Here, we review a special class of trinodal MOF structures based on the reticulation of special minimal edgetransitive nets (nets with transitivity [3 2], three distinct nodes and two kind of edges) derived from edge-transitive nets (one kind of edge). The rationale for deriving these special minimal edge-transitive nets is reviewed, and their associated net-coded building (net-cBUs) for the design of trinodal MOFs is presented and discussed. The resultant inclusive list of the enumerated minimal edge-transitive nets provides a unique toolbox for the material’s designer as it offers ideal blueprints for the deliberate design and rational assembly of building blocks with embedded multiple branch points into intricate trinodal MOFs
  • Realization of an Ultrasensitive and Highly Selective OFET NO2 Sensor: The Synergistic Combination of PDVT-10 Polymer and Porphyrin–MOF

    Yuvaraja, Saravanan; Surya, Sandeep Goud; Chernikova, Valeriya; Vijjapu, Mani Teja; Shekhah, Osama; Bhatt, Prashant; Chandra, Suman; Eddaoudi, Mohamed; Salama, Khaled N. (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2020-04-13) [Article]
    Organic field-effect transistors (OFETs) are emerging as competitive candidates for gas sensing applications due to the ease of their fabrication process combined with the ability to readily fine-tune the properties of organic semiconductors. Nevertheless, some key challenges remain to be addressed, such as material degradation, low sensitivity, and poor selectivity toward toxic gases. Appropriately, a heterojunction combination of different sensing layers with multifunctional capabilities offers great potential to overcome these problems. Here, a novel and highly sensitive receptor layer is proposed encompassing a porous 3D metal-organic framework (MOF) based on isostructural-fluorinated MOFs acting as an NO2 specific preconcentrator, on the surface of a stable and ultrathin PDVT-10 organic semiconductor on an OFET platform. Here, with this proposed combination we have unveiled an unprecedented 700% increase in sensitivity toward NO2 analyte in contrast to the pristine PDVT-10. The resultant combination for this OFET device exhibits a remarkable lowest detection limit of 8.25 ppb, a sensitivity of 680 nA/ppb, and good stability over a period of 6 months under normal laboratory conditions. Further, a negligible response (4.232 nA/%RH) toward humidity in the range of 5%-90% relative humidity was demonstrated using this combination. Markedly, the obtained results support the use of the proposed novel strategy to achieve an excellent sensing performance with an OFET platform.
  • Molecular enhancement of heterogeneous CO2 reduction

    Nam, Dae-Hyun; De Luna, Phil; Rosas-Hernández, Alonso; Thevenon, Arnaud; Li, Fengwang; Agapie, Theodor; Peters, Jonas C.; Shekhah, Osama; Eddaoudi, Mohamed; Sargent, E. (Nature Materials, Springer Science and Business Media LLC, 2020-02-25) [Article]
    The electrocatalytic carbon dioxide reduction reaction (CO2RR) addresses the need for storage of renewable energy in valuable carbon-based fuels and feedstocks, yet challenges remain in the improvement of electrosynthesis pathways for highly selective hydrocarbon production. To improve catalysis further, it is of increasing interest to lever synergies between heterogeneous and homogeneous approaches. Organic molecules or metal complexes adjacent to heterogeneous active sites provide additional binding interactions that may tune the stability of intermediates, improving catalytic performance by increasing Faradaic efficiency (product selectivity), as well as decreasing overpotential. We offer a forward-looking perspective on molecularly enhanced heterogeneous catalysis for CO2RR. We discuss four categories of molecularly enhanced strategies: molecular-additive-modified heterogeneous catalysts, immobilized organometallic complex catalysts, reticular catalysts and metal-free polymer catalysts. We introduce present-day challenges in molecular strategies and describe a vision for CO2RR electrocatalysis towards multi-carbon products. These strategies provide potential avenues to address the challenges of catalyst activity, selectivity and stability in the further development of CO2RR.
  • Methanol and Humidity Capacitive Sensors Based on Thin Films of MOF Nanoparticles

    Andrés, Miguel A.; Vijjapu, Mani Teja; Surya, Sandeep Goud; Shekhah, Osama; Salama, Khaled N.; Serre, Christian; Eddaoudi, Mohamed; Roubeau, Olivier; Gascón, Ignacio (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2020-01-07) [Article]
    The successful development of modern gas sensing technologies requires high sensitivity and selectivity coupled to cost effectiveness, which implies the necessity to miniaturize devices while reducing the amount of sensing material. The appealing alternative of integrating nanoparticles of a porous metal−organic framework (MOF) onto capacitive sensors based on interdigitated electrode (IDE) chips is presented. We report the deposition of MIL-96(Al) MOF thin films via the Langmuir−Blodgett (LB) method on the IDE chips, which allowed the study of their gas/ vapor sensing properties. First, sorption studies of several organic vapors like methanol, toluene, chloroform, etc. were conducted on bulk MOF. The sorption data revealed that MIL-96(Al) presents high affinity toward water and methanol. Later on, ordered LB monolayer films of MIL-96(Al) particles of ∼200 nm were successfully deposited onto IDE chips with homogeneous coverage of the surface in comparison to conventional thin film fabrication techniques such as drop-casting. The sensing tests showed that MOF LB films were selective for water and methanol, and short response/recovery times were achieved. Finally, chemical vapor deposition (CVD) of a porous thin film of Parylene C (thickness∼250−300 nm) was performed on top of the MOF LB films to fabricate a thin selective layer. The sensing results showed an increase in the water selectivity and sensitivity, while those of methanol showed a huge decrease. These results prove the feasibility of the LB technique for the fabrication of ordered MOF thin films onto IDE chips using very small MOF quantities
  • Made-to-order porous electrodes for supercapacitors: MOFs embedded with redox-active centers as a case study.

    Mallick, Arijit; Liang, Hanfeng; Shekhah, Osama; Jia, Jiangtao; Mouchaham, Georges; Shkurenko, Aleksander; Belmabkhout, Youssef; Alshareef, Husam N.; Eddaoudi, Mohamed (Chemical communications (Cambridge, England), Royal Society of Chemistry (RSC), 2020) [Article]
    In this work, a pre-designed Zr-based-MOF encompassing an organic linker with a redox active core is synthesized and its structure-property relationship as a supercapacitor electrode is investigated. An enhanced performance is revealed by the combination of this MOF's high porosity and redox core incorporation, which alters its double-layer and pseudocapacitance, respectively. An increase in the capacitance performance by a factor of two is achieved via post-synthetic structure rigidification using organic pillars.
  • Toward New 2D Zirconium-Based Metal–Organic Frameworks: Synthesis, Structures, and Electronic Properties

    Cadiau, Amandine; Xie, Lilia S.; Kolobov, Nikita; Shkurenko, Aleksander; Qureshi, Muhammad; Tchalala, Mohammed; Park, Sarah S.; Bavykina, Anastasiya; Eddaoudi, Mohamed; Dincǎ, Mircea; Hendon, Christopher H.; Gascon, Jorge (Chemistry of Materials, American Chemical Society (ACS), 2019-12-18) [Article]
    Nowadays, zirconium metal-organic frameworks attract more attention because of their robustness and their easier predictability in terms of topology. Herein, we have been able to control synthetic parameters in order to construct two new 2D MOFs with the same sql topology. Both materials, ACM-10 and ACM-11, have been characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and UV-vis spectroscopy. Their textural, electrochemical, and conductivity properties are presented along with the opportunities that these new topologically interesting scaffolds offer for the design of new structures.
  • MXene Derived Metal–Organic Frameworks

    Wu, Hao; Almalki, Maram M.; Xu, Xiangming; Lei, Yongjiu; Ming, Fangwang; Mallick, Arijit; Roddatis, Vladimir; Lopatin, Sergei; Shekhah, Osama; Eddaoudi, Mohamed; Alshareef, Husam N. (Journal of the American Chemical Society, American Chemical Society (ACS), 2019-12-11) [Article]
    Synthesis of nanoscale metal−organic frameworks (MOFs) is a highly challenging task because conventional soluble metal salt precursors are not easy to manipulate spatially, thus normally leading to bulk MOFs. In the present work, V2CTx MXene is demonstrated for the first time as a metal precursor to fabricate twodimensional (2D) MOF nanosheets, whose thickness (6 to 18 nm) can be tuned by varying the reaction temperature. The highly electronegative surface atoms of MXene and sufficient accessible attacking sites for ligands are responsible for the evolution of 2D MOF nanosheets. Moreover, highly oriented and smooth MOF thin films have been grown based on these nanosheets using a convenient spin coating process. With the impregnation of nonvolatile H3PO4, the MOF thin film exhibits a protonconducting property. This study demonstrates that highquality 2D MOF sheets and thin films are enabled by 2D MXene precursors. We believe that the high-quality MOF films prepared in this study pave the way for many device applications.
  • Enriching the Reticular Chemistry Repertoire with Minimal Edge-Transitive Related Nets: Access to Highly Coordinated Metal-Organic Frameworks Based on Double Six-Membered Rings as Net-Coded Building Units.

    Chen, Zhijie; Thiam, Zeynabou; Shkurenko, Aleksander; Weselinski, Lukasz Jan; Adil, Karim; Jiang, Hao; Alezi, Dalal; Assen, Ayalew Hussen Assen; O'Keeffe, Michael; Eddaoudi, Mohamed (Journal of the American Chemical Society, American Chemical Society (ACS), 2019-12-03) [Article]
    Minimal edge-transitive nets are regarded as suitable blueprints for the successful practice of reticular chemistry, and par excellence ideal for the deliberate design and rational construction of highly coordinated metal-organic frameworks (MOFs). We report the systematic generation of the highly connected minimal edge-transitive related nets (transitivity [32]) from parent edge-transitive nets (transitivity [21] or [11]), and their use as a guide for the deliberate design and directional assembly of highly coordinated MOFs from their associated net-coded building units (net-cBUs), 12-connected (12-c) double six-membered ring (d6R) building units. Notably, the generated related nets enclose the distinctive highly coordinated d6R (12-c) due to the subsequent coordination number increase in one node of the resultant new related net; that is, the (3,4,12)-c kce net is the (4,6)-c soc-related net, and the (3,6,12)-c kex and urx nets are the (6,6)-c nia-related nets. Intuitively, the combination of 12-connected hexagonal prismatic rare-earth (RE) nonanuclear [RE9(μ3-O)2(μ3-OH)12(O2C-)12] carboxylate-based clusters with purposely chosen organic or organic-inorganic hybrid building units led to the formation of the targeted highly coordinated MOFs based on selected minimal edge-transitive related nets. Interestingly, the kex-MOFs can alternatively be regarded as a zeolite-like MOF (ZMOF) based on the zeolite underlying topology afx, by considering the dodecacarboxylate ligand as a d6R building unit, delineating a new avenue toward the construction of ZMOFs through the composite building units as net-cBUs. This represents a significant step toward the effective discovery and design of novel minimal edge-transitive and highly coordinated materials using the d6Rs as net-cBUs.
  • Computationally Assisted Assessment of the Metal-Organic Framework/Polymer Compatibility in Composites Integrating a Rigid Polymer

    Tavares, Sergio Rodrigues; Ramsahye, Naseem Ahmed; Adil, Karim; Eddaoudi, Mohamed; Maurin, Guillaume; Semino, Rocio (Advanced Theory and Simulations, Wiley, 2019-08-16) [Article]
    Density functional theory (DFT) calculations and subsequent classical molecular dynamics (MD) simulations are combined to build and further characterize the interface structure of three binary metal-organic framework (MOF)/polymer composite materials made of ultra-small pore MOFs with distinct surface morphologies, namely, MIL-69, ftw-MOF-ABTC, and ftw-MOF-BPTC, and the 6-FDA-DAM polymer. It is found that the three composites exhibit percolated or independent microvoids of different degrees of interconnectivity, sizes, and positions at the MOF/polymer interface that contribute to decrease the polymer surface coverage, a signature of a relatively poor adhesion between the two components. The ftw-MOF-BPTC-based composite, however, shows a partial penetration of the polymer in the MOF first pore layer, hinting a slightly higher affinity between the MOF and the polymer. These results suggest that even when considering MOFs surfaces with drastically different morphologies, finding a highly compatible MOF/polymer pair for rigid polymers remains challenging.
  • The Growth of Photoactive Porphyrin-Based MOF Thin Films Using the Liquid-Phase Epitaxy Approach and their Optoelectronic Properties.

    Ngongang Ndjawa, Guy Olivier; Tchalala, Mohamed R; Shekhah, Osama; Khan, Jafar Iqbal; Mansour, Ahmed E; Czaban-Jozwiak, Justyna; Weselinski, Lukasz Jan; Ait Ahsaine, Hassan; Amassian, Aram; Eddaoudi, Mohamed (Materials (Basel, Switzerland), MDPI AG, 2019-08-01) [Article]
    This study reports on the optoelectronic properties of porphyrin-based metal-organic framework (MOF) thin films fabricated by a facile liquid-phase epitaxy approach. This approach affords the growth of MOF thin films that are free of morphological imperfections, more suitable for optoelectronic applications. Chemical modifications such as the porphyrin ligand metallation have been found to preserve the morphology of the grown films making this approach particularly suitable for molecular alteration of MOF thin film optoelectronic properties without compromising its mesoscale morphology significantly. Particularly, the metallation of the ligand was found to be effective to tune the MOF bandgap. These porphyrin-based MOF thin films were shown to function effectively as donor layers in solar cells based on a Fullerene-C60 acceptor. The ability to fabricate MOF solar cells free of a liquid-phase acceptor greatly simplifies device fabrication and enables pairing of MOFs as light absorbers with a wide range of acceptors including non-fullerene acceptors.
  • Imaging defects and their evolution in a metal–organic framework at sub-unit-cell resolution

    Liu, Lingmei; Chen, Zhijie; Wang, Jianjian; Zhang, Daliang; Zhu, Yihan; Ling, Sanliang; Huang, Kuo-Wei; Belmabkhout, Youssef; Adil, Karim; Zhang, Yuxin; Slater, Ben; Eddaoudi, Mohamed; Han, Yu (Nature Chemistry, Springer Science and Business Media LLC, 2019-05-13) [Article]
    Defect engineering of metal–organic frameworks (MOFs) offers promising opportunities for tailoring their properties to specific functions and applications. However, determining the structures of defects in MOFs—either point defects or extended ones—has proved challenging owing to the difficulty of directly probing local structures in these typically fragile crystals. Here we report the real-space observation, with sub-unit-cell resolution, of structural defects in the catalytic MOF UiO-66 using a combination of low-dose transmission electron microscopy and electron crystallography. Ordered ‘missing linker’ and ‘missing cluster’ defects were found to coexist. The missing-linker defects, reconstructed three-dimensionally with high precision, were attributed to terminating formate groups. The crystallization of the MOF was found to undergo an Ostwald ripening process, during which the defects also evolve: on prolonged crystallization, only the missing-linker defects remained. These observations were rationalized through density functional theory calculations. Finally, the missing-cluster defects were shown to be more catalytically active than their missing-linker counterparts for the isomerization of glucose to fructose.
  • Cyclodextrin-functionalized asymmetric block copolymer films as high-capacity reservoir for drug delivery

    Huang, Tiefan; Manchanda, Priyanka; Zhang, Liwen; Shekhah, Osama; Khashab, Niveen M.; Eddaoudi, Mohamed; Peinemann, Klaus-Viktor (Journal of Membrane Science, Elsevier BV, 2019-04-22) [Article]
    Asymmetric block copolymer membranes can be facilely prepared via non-solvent induced phase separation combined with self-assembly. The membrane is characterized by a thin layer of highly ordered and uniform cylindrical nano-channels on top of a non-ordered macroporous sponge-like layer. Up to date, most studies concerning block copolymer membranes are focused on separation applications. In this work, highly adsorptive and adhesive isoporous block copolymer membranes have been fabricated. Because of the functionalization with cyclodextrin, the membrane shows excellent affinity to guest molecules. Moreover, the membrane is biocompatible and is adhesive to various substrates (e.g. glass, silicon, gold and stainless steel). Triclosan as a model drug was utilized to demonstrate the applicability of the membranes as a drug reservoir. A high loading capacity (305.5 μg cm−2) was achieved. The release behavior was investigated under various pH values in vitro. A long-time extended drug release was achieved without showing an initial burst effect. Furthermore, pH-responsive release behavior was observed. The triclosan-loaded membrane exhibited a significant antibacterial effect due to the triclosan release; the diffusion out of the membrane was evaluated using a disc diffusion assay. This study provides great potential for isoporous block copolymer membranes as a delivery platform for a wide variety of biomedical applications
  • Unprecedented ultralow detection limit of amines using a thiadiazole-functionalized Zr(IV)-based metal-organic framework

    Mallick, Arijit; El-Zohry, Ahmed; Shekhah, Osama; Yin, Jun; Jia, Jiangtao; Aggarwal, Himanshu; Emwas, Abdul-Hamid M.; Mohammed, Omar F.; Eddaoudi, Mohamed (Journal of the American Chemical Society, American Chemical Society (ACS), 2019-04-15) [Article]
    A luminescent Zr(IV)-based MOF, with the underlying fcu topology, encompassing a π-conjugated organic ligand with a thiadiazole functionality, exhibits an unprecedented low detection limit of 66 nanomolar (nM) for amines in aqueous solution. Markedly, this ultra-low detection is driven by the hydro-gen bonding interactions between the linker and amines. This observation is fully supported by Density Functional Theory (DFT) calculations which clearly corroborate the suppression of the twisting motion of the thiadiazole core in the presence of amine, reducing significantly the non-radiative recombination pathways and subsequently enhancing the emission intensity. Credibly, nicotine regarded as a harmful chemical and bearing an amine pending group is also detected with high sensitivity, positioning this MOF as a potential sensor for practical environmental applications. This finding not only provides an unprecedented low detection limit, but also serves as a benchmark to understand the sensing mechanism in MOFs.
  • Conductive Metal–Organic Frameworks Selectively Grown on Laser-Scribed Graphene for Electrochemical Microsupercapacitors

    Wu, Hao; Zhang, Wenli; Kandambeth, Sharath; Shekhah, Osama; Eddaoudi, Mohamed; Alshareef, Husam N. (Advanced Energy Materials, Wiley, 2019-04-15) [Article]
    Conductive 2D metal–organic frameworks (MOFs) have merits beyond traditional MOFs for electrochemical applications, but reports on using MOFs as electrodes for electrochemical microsupercapacitors (MSCs) are practically non-existent. In this work, a Ni-catecholate-based MOF (Ni-CAT MOF) having good conductivity and exhibiting redox chemistry in the positive and negative voltage windows is developed. A novel process is developed to selectively grow the conductive Ni-CAT MOF on 3D laser scribed graphene (LSG). The LSG with its superior wettability serves as a functional matrix-current collector for the hybridization of conductive Ni-CAT MOF nanocrystals. Impressively, MSCs fabricated using the hybrid LSG/Ni-CAT MOF show significant improvement compared with MOF-free LSG electrodes. Specifically, the LSG/Ni-CAT MOF electrodes can deliver MSCs with a wide operating voltage (1.4 V), high areal capacitance (15.2 mF cm−2), energy density (4.1 µWh cm−2), power density (7 mW cm−2), good rate performance, and decent cycling stability. This work opens up an avenue for developing electrochemical microsupercapacitors using conductive MOF electrodes.
  • Fluorinated MOF platform for selective removal and sensing of SO2 from flue gas and air

    Tchalala, Mohammed; Bhatt, Prashant; Nanaiah, Karumbaiah Chappanda; Tavares, S R; Adil, Karim; Belmabkhout, Youssef; Shkurenko, Aleksander; Cadiau, Amandine; Heymans, N; De Weireld, G; Maurin, G; Salama, Khaled N.; Eddaoudi, Mohamed (Nature Communications, Springer Nature, 2019-03-22) [Article]
    Conventional SO2 scrubbing agents, namely calcium oxide and zeolites, are often used to remove SO2 using a strong or irreversible adsorption-based process. However, adsorbents capable of sensing and selectively capturing this toxic molecule in a reversible manner, with in-depth understanding of structure-property relationships, have been rarely explored. Here we report the selective removal and sensing of SO2 using recently unveiled fluorinated metal-organic frameworks (MOFs). Mixed gas adsorption experiments were performed at low concentrations ranging from 250 p.p.m. to 7% of SO2. Direct mixed gas column breakthrough and/or column desorption experiments revealed an unprecedented SO2 affinity for KAUST-7 (NbOFFIVE-1-Ni) and KAUST-8 (AlFFIVE-1-Ni) MOFs. Furthermore, MOF-coated quartz crystal microbalance transducers were used to develop sensors with the ability to detect SO2 at low concentrations ranging from 25 to 500 p.p.m.
  • A Tailor-Made Interpenetrated MOF with Exceptional Carbon-Capture Performance from Flue Gas

    Liang, Weibin; Bhatt, Prashant; Shkurenko, Aleksander; Adil, Karim; Mouchaham, Georges; Aggarwal, Himanshu; Mallick, Arijit; Jamal, Aqil; Belmabkhout, Youssef; Eddaoudi, Mohamed (Chem, Elsevier BV, 2019-03-07) [Article]
    Metal-organic frameworks (MOFs) have attracted significant attention as sorbents for low-energy separation of CO2 from flue gas. Herein, we report the use of an interpenetration approach to developing a fluorinated MOF with the appropriate pore system to enable the efficient capture of CO2 from flue gas at 298 K. The MOF, dptz-CuTiF6, exhibits excellent volumetric and gravimetric CO2 uptakes at 10% CO2 and 298 K, which are superior to those of the reference aqueous amine technique, with significantly lower energy input for regeneration (38 kJ mol−1 versus 105 kJ mol−1). In cyclic breakthrough experiments, dptz-CuTiF6 achieves complete CO2 desorption at 298 K under inert gas purging. Single-crystal X-ray diffraction studies demonstrate that the exceptional CO2 adsorption capacity, moderate CO2 heat of adsorption, and high CO2-N2 selectivity are due to the optimal packing of the CO2 molecules within the MOF as well as the favorable thermodynamics and kinetics from cooperative host-guest interactions.
  • Highly tunable sulfur hexafluoride separation by interpenetration control in metal organic frameworks

    Skarmoutsos, Ioannis; Eddaoudi, Mohamed; Maurin, Guillaume (Microporous and Mesoporous Materials, Elsevier BV, 2019-03-03) [Article]
    The separation of fluid SF6/N2 mixtures using the recently synthesized metal-organic framework SIFSIX-2-Cu and its interpenetrated polymorph SIFSIX-2-Cu-i has been systematically studied by employing Monte Carlo and Molecular Dynamics simulations. These predictions revealed that SIFSIX-2-Cu shows a high thermodynamic adsorption selectivity for SF6 over N2 combined with one of the highest SF6 uptakes reported so far for an adsorbent. On the other hand, the smaller pore dimensions of the interpenetrated network cause a molecular sieving effect, allowing only the adsorption of N2. Furthermore, the self-diffusivity of the adsorbed SF6 molecules in the SIFSIX-2-Cu framework was predicted to be significantly lower than the one corresponding to N2, while the smaller pore channel network of SIFSIX-2-Cu-i decreases the self-diffusivity of N2 by a factor of about 6. This study revealed that controlling the interpenetration in MOFs is an efficient way to tune their separation performances for strategic gas mixtures.
  • Tunable Twisting Motion of Organic Linkers via Concentration and Hydrogen-Bond Formation

    El-Zohry, Ahmed; Alturki, Abdullah; Yin, Jun; Mallick, Arijit; Shekhah, Osama; Eddaoudi, Mohamed; Ooi, Boon S.; Mohammed, Omar F. (The Journal of Physical Chemistry C, American Chemical Society (ACS), 2019-02-20) [Article]
    Benzothiadiazole dibenzoic acid (BTDB) derivative is a well-known organic linker in various metal–organic framework structures as well as a fluorescent probe in biological systems. Here, we demonstrate that the radiative and nonradiative decay channels of BTDB can be interplayed and precisely controlled through concentration and hydrogen-bond interactions as directly evidenced experimentally and theoretically. This leads to excited-state structural changes that significantly suppress the torsional motion around the benzothiadiazole moiety, leading to an enormous increase in the emission quantum yields from ∼1 to 70%. These changes are associated with the existence of two equilibria, where dimers and small oligomers form in dimethylformamide (DMF), with high formation constants of 18 000 M–1 and 1.2 × 1013 M–3, respectively. These evolving species, i.e., the dimers and oligomers, are formed via hydrogen bonds between carboxylic acid groups present at the far edge of the rodlike BTDB molecules. The estimated repeating number for this small-oligomer formation via bonded monomers is eight in DMF, as shown by emission spectra analysis. With deprotonation as a control experiment, these associated species can easily collapse with the initial monomer species, confirming the role of the hydrogen-bond formation in the observed phenomena. Theoretical studies and NMR experiments not only confirm the existence of the dimers, but also demonstrate the important role of the hydrogen bonds in the excited-state dynamics. These new findings provide a better understanding of the photophysical behaviors of organic linkers used in a wide range of chemical and biological applications.
  • Conformation-Controlled Molecular Sieving Effects for Membrane-Based Propylene/Propane Separation

    Liu, Yang; Chen, Zhijie; Liu, Gongping; Belmabkhout, Youssef; Adil, Karim; Eddaoudi, Mohamed; Koros, William (Advanced Materials, Wiley, 2019-02-15) [Article]
    Membrane-based separation is poised to reduce the operation cost of propylene/propane separation; however, identifying a suitable molecular sieve for membrane development is still an ongoing challenge. Here, the successful identification and use of a metal-organic framework (MOF) material as fillers, namely, the Zr-fum-fcu-MOF possessing an optimal contracted triangular pore-aperture driving the efficient diffusive separation of propylene from propane in mixed-matrix membranes are reported. It is demonstrated that the fabricated hybrid membranes display a high propylene/propane separation performance, far beyond the current trade-off limit of polymer membranes with excellent properties under industrial conditions. Most importantly, the mechanism behind the exceptional high propylene/propane selectivity is delineated by exploring theoretically the efficiency of sieving of different conformers of propane through the hypothesized triangular rigid pore-aperture of Zr-fum-fcu-MOF.

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