SYSTEMATIC POSTSYNTHETIC MODIFICATION OF NANOPOROUS ORGANIC FRAMEWORKS AND THEIR PERFORMANCE EVALUATION FOR SELECTIVE CO2 CAPTURE

Porous organic polymers (POPs) with high physicochemical stability have attracted significant attention from the scientific community as promising platforms for small gas separation adsorbents. Although POPs have amorphous morphology in general, with the help of organic chemistry toolbox, ultrahigh surface area materials can be synthesized. In particular, nitrogen-rich POPs have been studied intensively due to their enhanced framework-CO2 interactions. Postsynthetic modification (PSM) of POPs has been instrumental for incorporating different functional groups into the pores of POPs which would increase the CO2 capture properties. We have shown that functionalizing the surface of POPs with nitro and amine groups increases the CO/N2 and CO2/CH4 selectivity significantly due to selective polarization of CO2 molecule. In addition, controlled postsynthetic nitration of NPOF-1, a nanoporous organic framework constructed by nickel(0)-catalyzed Yamamoto coupling of 1,3,5-tris(4-bromophenyl)benzene, has been performed and is proven to be a promising route to introduce nitro groups and to convert mesopores to micropores without compromising surface area. Reduction of the nitro groups yields aniline-like amine-functionalized NPOF-1-NH2. Adequate basicity of the amine functionalities leads to modest isosteric heats of adsorption for CO2, which allow for high regenerability. The unique combination of high surface area, microporous structure, and amine-functionalized pore walls enables NPOF-1-NH2 to have remarkable CO2 working capacity values for removal from landfill gas and flue gas. Benzimidazole-linked polymers have also been shown to have promising CO2 capture properties. Here, an amine functionalized benzimidazole-linked polymer (BILP-6-NH2) was synthesized via a combination of pre- and postsynthetic modification techniques in two steps. Experimental studies confirm enhanced CO2 uptake in BILP-6-NH2 compared to BILP-6, and DFT calculations were used to understand the interaction modes of CO2 with BILP-6-NH2. Using BILP-6-NH2, higher CO2 uptake and CO2/CH4 selectivity was achieved compared to BILP-6 showing that this material has a very promising working capacity and sorbent selection parameter for landfill gas separation under VSA settings. Additionally, the sorbent evaluation criteria of different classes of organic polymers have been compared in order to reveal structure-property relationships in those materials as solid CO2 adsorbents

Benzothiazolium-functionalized NU-1000 : a versatile material for carbon dioxide adsorption and cyanide luminescence sensing

The benzothiazolium-decorated NU-1000-BzTz MOF is a versatile material for carbon dioxide storage and cyanide luminescence sensing in aqueous solutions

Computer-aided discovery of a metal-organic framework with superior oxygen uptake.

Current advances in materials science have resulted in the rapid emergence of thousands of functional adsorbent materials in recent years. This clearly creates multiple opportunities for their potential application, but it also creates the following challenge: how does one identify the most promising structures, among the thousands of possibilities, for a particular application? Here, we present a case of computer-aided material discovery, in which we complete the full cycle from computational screening of metal-organic framework materials for oxygen storage, to identification, synthesis and measurement of oxygen adsorption in the top-ranked structure. We introduce an interactive visualization concept to analyze over 1000 unique structure-property plots in five dimensions and delimit the relationships between structural properties and oxygen adsorption performance at different pressures for 2932 already-synthesized structures. We also report a world-record holding material for oxygen storage, UMCM-152, which delivers 22.5% more oxygen than the best known material to date, to the best of our knowledge

Observation of Reduced Thermal Conductivity in a Metal-Organic Framework Due to the Presence of Adsorbates

Whether the presence of adsorbates increases or decreases thermal conductivity in metal-organic frameworks (MOFs) has been an open question. Here we report observations of thermal transport in the metal-organic framework HKUST-1 in the presence of various liquid adsorbates: water, methanol, and ethanol. Experimental thermoreflectance measurements were performed on single crystals and thin films, and theoretical predictions were made using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases by 40 – 80% depending on the adsorbate, a result that cannot be explained by effective medium approximations. Our findings demonstrate that adsorbates introduce additional phonon scattering in HKUST-1, which particularly shortens the lifetimes of low-frequency phonon modes. As a result, the system thermal conductivity is lowered to a greater extent than the increase expected by the creation of additional heat transfer channels. Finally, we show that thermal diffusivity is even more greatly reduced than thermal conductivity by adsorption

Benign by Design: Green and Scalable Synthesis of Zirconium UiO-Metal–Organic Frameworks by Water-Assisted Mechanochemistry

We present a solvent-free, green, and rapid mechanochemical route for the synthesis of a series of zirconium metal–organic frameworks (MOFs) composed of Zr6 cluster nodes, UiO-66, UiO-66-NH2, MOF-801, and MOF-804, both on a laboratory scale and by scalable and flow mechanochemical processing. The methodology, based on the use of a nonconventional zirconium dodecanuclear acetate cluster and a minute amount of water as an additive, affords high-quality MOFs in less than 1 h of milling, with minimal requirements for workup processing and eliminating the need for conventional hazardous solvents, such as dimethylformamide. Moreover, the use of a dodecanuclear zirconium acetate precursor circumvents the need for modulators resulting in acetic acid as the only byproduct of the reaction, which does not harm these acid-resistant materials. The porosity, thermal and chemical stability, as well as catalytic activity of mechanochemically prepared Zr-based MOFs are similar to those of solvothermally synthesized counterparts. Finally, the synthesis is readily applicable on a 10 g scale by using a planetary mill, and is also performed by solid-state flow synthesis using twin-screw extrusion (TSE), affording more than 100 g of catalytically active UiO-66-NH2 material in a continuous process at a rate of 1.4 kg/h

Green Synthesis of a Functionalized Zirconium-Based Metal–Organic Framework for Water and Ethanol Adsorption

Aqueous synthesis of metal−organic frameworks (MOFs) at room temperature offers many advantages such as reduction in the generation of toxic byproducts and operation costs, as well as increased safety in the material’s production. Functional group-bearing MOFs have received growing attention compared to nonfunctionalized analogues due to enhanced adsorption properties of the former in many cases. Here, we report an aqueous solution-based synthesis of a robust zirconium MOF, UiO-66-NO2, at room temperature. We evaluated the phase purity, porosity, thermal stability, particle morphology and size of the resulting material. High uptake, as well as near complete recyclability of water and ethanol vapor isotherms at room temperature supports the potential of UiO-66-NO2 as a solid adsorbent in adsorption-based cooling applications or water harvesting systems

Ammonia Capture within Isoreticular Metal-Organic Frameworks with Rod Secondary Building Units

The efficient removal, capture, and recycling of ammonia (NH3) constitutes a demanding process, thus the development of competent adsorbent materials is highly desirable. The implementation of metal-organic frameworks (MOFs), known for their tunability and high porosity, has attracted much attention for NH3 adsorption studies. Here, we report three isoreticular porphyrin-based MOFs containing aluminum (Al-PMOF), gallium (Ga-PMOF), and indium (In-PMOF) rod secondary building units with Brønsted acidic bridging hydroxyl groups. NH3 sorption isotherms in Al-PMOF demonstrated reversibility in isotherms. In contrast, the slopes of the adsorption isotherms in Ga-PMOF and In-PMOF were much steeper than Al-PMOF in lower pressure regions, with a decrease of NH3 adsorbed amounts observed between first cycle and second cycle measurements. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) suggested that the strength of the Brønsted acidic -OH sites was controlled by the identity of the metal, which resulted in stronger interactions between ammonia and the framework in Ga-PMOF and In-PMOF compared to Al-PMOF

Air Oxidation of Sulfur Mustard Gas Simulant Using a Pyrene-Based Metal-Organic Framework Photocatalyst

We demonstrate a microporous metal-organic framework NU-400 based on a 2,7-disubstituted pyrene linker as a highly efficient photosensitizer for generating singlet oxygen and subsequent oxidative degradation of chemical warfare agents (CWAs). The high activity of NU-400 permits photocatalytic conversion of the 2-chloroethyl ethyl sulfide (CEES) mustard gas simulant into a benign sulfoxide derivative, in air, with less than 15 minutes half-life. This is a considerable improvement to NU-1000 based on a 1,3,6,8-tetrasubstituted pyrene unit, demonstrating how variation of the substitution pattern of a metal-organic framework linker permits modification of its photoactive behavior

Tuning the Redox Activity of Metal−Organic Frameworks for Enhanced, Selective O₂ Binding: Design Rules and Ambient Temperature O₂ Chemisorption in a Cobalt−Triazolate Framework

Metal−organic frameworks (MOFs) with coordinatively unsaturated metal sites are appealing as adsorbent materials due to their tunable functionality and ability to selectively bind small molecules. Through the use of computational screening methods based on periodic density functional theory, we investigate O2 and N2 adsorption at the coordinatively unsaturated metal sites of several MOF families. A variety of design handles are identified that can be used to modify the redox activity of the metal centers, including changing the functionalization of the linkers (replacing oxido donors with sulfido donors), anion exchange of bridging ligands (considering μ-Br-, μ-Cl-, μ-F-, μ-SH-, or μ-OH- groups), and altering the formal oxidation state of the metal. As a result, we show that it is possible to tune the O2 affinity at the open metal sites of MOFs for applications involving the strong and/or selective binding of O2. In contrast with O2 adsorption, N2 adsorption at open metal sites is predicted to be relatively weak across the MOF dataset, with the exception of MOFs containing synthetically elusive V2+ open metal sites. As one example from the screening study, we predicted that exchanging the μ-Cl- ligands of M2Cl2(BBTA) (H2BBTA = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) with μ-OH- groups would significantly enhance the strength of O2 adsorption at the open metal sites without a corresponding increase in the N2 affinity. Experimental investigation of Co2Cl2(BBTA) and Co2(OH)2(BBTA) confirms that the former exhibits weak physisorption of both N2 and O2, whereas the latter is capable of chemisorbing O2 at room temperature in a highly selective manner. The O2 chemisorption behavior is attributed to the greater electron-donating character of the μ-OH- ligands and the presence of H-bonding interactions between the μ-OH- bridging ligands and the reduced O2 adsorbate.</p