Zhijuan Zhang

Enhanced Binding Affinity, Remarkable Selectivity, and High Capacity of CO2 by Dual Functionalization of a rht‐Type Metal–Organic Framework

This work was supported by the Foundation of the National Natural Science Foundation of China (grant numbers 20971054 and 90922034) and the Key Project of the Chinese Ministry of Education. The RU and UTD teams would like to acknowledge support from DOE (grant number DE-FG02-08ER46491). We thank Prof. Xianhe Bu and Dr. Ze Chang (Nankai University, China) and Dr. Ruiping Chen (Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences) for part of the gas adsorption measurements.

The first example of commensurate adsorption of atomic gas in a MOF and effective separation of xenon from other noble gases

In industry, cryogenic rectification for separating xenon from other noble gases such as krypton and argon is an energy and capital intensive process. Here we show that a microporous metal–organic framework, namely Co3(HCOO)6 is capable of effective capture and separation of xenon from other noble gases. Henrys constant, isosteric heat of adsorption (Qst), and IAST selectivity are calculated based on single component sorption isotherms. Having the highest Qst reported to date, Co3(HCOO)6 demonstrates high adsorption capacity for xenon and its IAST selectivity for Xe–Kr is the largest among all MOFs investigated to date. To mimic real world conditions, breakthrough experiments are conducted on Xe–Kr binary mixtures at room temperature and 1 atmosphere. The results are consistent with the calculated data. These findings show that Co3(HCOO)6 is a promising candidate for xenon capture and purification. Our gas adsorption measurements and molecular simulation study also reveal that the adsorption of xenon represents the first example of commensurate adsorption of atomic gases near ambient conditions.

An N-rich metal–organic framework with an rht topology: high CO2 and C2 hydrocarbons uptake and selective capture from CH4

We report the storage capacities and separation selectivity of an rht-type s-heptazine-based metal organic framework (MOF), [Cu3(TDPAH)(H2O)3]·13H2O·8DMA, 1, (where TDPAH is 2,5,8-tris(3,5-dicarboxylphenylamino)-s-heptazine and DMA is N,N-dimethylacetamide) for C2 hydrocarbons and CO2 over CH4. MOF 1 displays the highest C2H2/CH4 selectivity of 80.9 as well as record high C2H4 and C2H6 adsorption enthalpies. Theoretical calculations reveal that s-heptazine and NH groups within the framework have synergistic effects on CO2 binding.

Mechanism of Carbon Dioxide Adsorption in a Highly Selective Coordination Network Supported by Direct Structural Evidence

Understanding the interactions between adsorbed gas molecules and a pore surface at molecular level is vital to exploration and attempts at rational development of gasselective nanoporous solids. Much current work focuses on the design of functionalized metal–organic frameworks (MOFs) or coordination networks (CNs) that selectively adsorb CO2. [1–9] While interactions between CO2 molecules and the p clouds of aromatic linkers in MOFs under ambient conditions have been explored theoretically, no direct structure evidence of such interactions are reported to date. Here we provide the first structural insight of such interactions in a porous calcium based CN using single-crystal X-ray diffraction methods, supported by powder diffraction coupled with differential scanning calorimetry (DSC-XRD), in situ IR/Raman spectroscopy, and molecular simulation data. We further postulate that such interactions are responsible for the high CO2/N2 adsorption selectivity, even in the case of a high relative humidity (RH). Our data suggest that the key interaction responsible for such selectivity, the room-temperature stability and the relative insensitivity to the RH of the CO2-CN adduct, is between two phenyl rings of the linker in the CN and the molecular quadrupole of CO2. The specific geometry of the linker molecule results in a “pocket” where carbon from the CO2 molecule is placed between two centroids of the aromatic ring. Our experimental confirmation of this variation on theoretically postulated interactions between CO2 and a phenyl ring will promote the search for other CNs containing phenyl ring pockets. Selective adsorption and sequestration of CO2 from sources of anthropogenic emissions, such as untreated waste from flue gas and products of the water gas shift reaction, is important to mitigate the growing level of atmospheric CO2. [10] Current separation methods use absorption in alkanolamine solutions, which are toxic, corrosive, and require significant energy for their regeneration. Hence microporous solid-state adsorbents, such as zeolites, hybrid zeolite–polymer systems, porous organic materials, and MOFs are proposed as alternatives, especially in combination with pressure swing processes. Rather than relying solely on tuning the pore diameters of microporous materials to select between gases based on size (the kinetic diameters of CO2, CH4 and N2 are 3.30, 3.76 3.64 , respectively ) selective separation relies on differences in electronic properties, such as the quadrupole moment and polarizability. Attempts to produce MOFs or CNs with adsorption properties competitive with those of commercially established aluminosilicate zeolites, relies on strategies that include pore surface modification with strongly polarizing functional groups, such as amines 7, 9,15] and desolvating metals centers 8, 16] to produce low-coordinated sites suitable for CO2 adsorption. The amine-functionalized materials offer a high selectivity toward CO2 adsorption, but a low effective surface area and thus, a low total uptake capacity. Strong interactions with polarizing functional groups, as well as with open metal sites presents other drawbacks including an increase in the costs for material regeneration. Furthermore, water effectively competes with CO2 at low-coordinated cation sites, impeding the performance of frameworks in commercial flue gas. We recently described a porous framework, CaSDB (SDB: sulfonyldibenzoate, compound 1) with a high CO2/N2 selectivity. At 0.15 bar of CO2 and 0.85 bar of N2, a typical composition of flue gas mixture from power plants, the selectivity is in the range of 48 to 85 at 298 K. CaSDB shows a reversible uptake of CO2 of 5.75 wt% at 273 K and 1 bar pressure and 4.37 wt% at room temperature, with heats of adsorption for CO2 and N2 of 31 and 19 kJmol , respectively. The as-synthesized compound contains not coordinated water molecules and is easily activated for gas adsorption by heating to 563 K in vacuum; remarkably the activated framework does not readsorb water, even if exposed to a RH greater than [*] A. M. Plonka, W. R. Woerner, Prof. Dr. J. B. Parise Department of Geosciences, Stony Brook University Stony Brook, NY 11794-2100 (USA) E-mail: john.parise@stonybrook.edu

High storage capacity and separation selectivity for C2 hydrocarbons over methane in the metal–organic framework Cu–TDPAT

We report on the storage capacity and separation selectivity of an rht-type metal–organic framework, Cu–TDPAT [TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine], for C2 hydrocarbons over CH4. Henrys constant, the isosteric heat of adsorption and the ideal adsorbed solution theory selectivity were calculated based on single-component sorption isotherms. Theoretical calculations indicate that both the open metal sites and the Lewis basic sites have strong interactions with the C2 molecules. The combination of these two kinds of sites lead to the highest C2H2–CH4 selectivity of 127.1 as well as record high values for C2H4 adsorption enthalpies. To mimic real-world conditions, breakthrough experiments were conducted on an equimolar four-component mixture containing C2H2, C2H4, C2H6 and CH4 at room temperature and 1 atm pressure. Our results show that Cu–TDPAT is a promising candidate for CH4 capture and purification.

Effect of ligand geometry on selective gas-adsorption: the case of a microporous cadmium metal organic framework with a V-shaped linker.

A microporous cadmium metal organic framework is synthesized and structurally characterized. The material possesses a 3-D framework with a 1-D sinusoidal chain and shows high selectivity for CO2 over N2. The selectivity is attributed to CO2 interacting with two phenyl rings of a V-shaped linker as estimated by the in situ XRD-DSC study.

Two three-dimensional metal–organic frameworks constructed by thiazole-spaced pyridinecarboxylates exhibiting selective gas sorption or antiferromagnetic coupling

The ligand of 2-(4-pyridyl)-4-methylthiazole-5-carboxylic acid (HL) has been employed to react with Cd(NO3)2·6H2O or a 50% aqueous solution of Mn(NO3)2, to yield two isomorphous three-dimensional (3D) coordination compounds, [Cd(L)2](H2O)4(DMF) (1) and [Mn(L)2](H2O)3(DMF) (2). The structures and properties of the compounds have been characterized by several techniques. Both compounds are three-dimensional (3D) neutral frameworks possessing permanent pores that give rise to straight one-dimensional channels. Compound 1 displays adsorption selectivity for CO2, while the low pressure sorption of H2, N2, CH4, CO, O2 at 298 K are negligible; Compound 2 shows weak anti-ferromagnetic coupling between the magnetic centres.