Shunshun Xiong

A microporous lanthanide-tricarboxylate framework with the potential for purification of natural gas

A novel robust three-dimensional lanthanide organic framework with high thermal stability has been demonstrated to exhibit the potential for purification of natural gas in nearly pure form from an 8-component gas mixture at room temperature.

A flexible zinc tetrazolate framework exhibiting breathing behaviour on xenon adsorption and selective adsorption of xenon over other noble gases

Given the fact that traditional cryogenic rectification is highly energy and capital intensive for the purification of xenon, effective selective adsorption of xenon over other noble gases at room temperature using porous materials is a critical and urgent issue. Here, we present a flexible zinc tetrazolate framework ([Zn(mtz)2]), which exhibits a high capture capacity for xenon and selective adsorption of xenon over other noble gases at room temperature. Due to its high adsorption enthalpy for xenon, a suitable pore size that matches well with the xenon atom, as well as the high polarizability of Xe, [Zn(mtz)2] shows breathing behaviour on xenon adsorption, which is confirmed by the experimental adsorption isotherms of xenon and thermodynamic analysis of breathing transition. The isosteric heats of adsorption and S(DIH) calculations indicate that [Zn(mtz)2] has significantly higher adsorption affinity and capacity for Xe compared with Kr, Ar and N2. The high capture capacity of Xe (2.7 mmol g−1) in an idealized PSA process and high Xe/Kr selectivity (15.5) from breakthrough experiment promise the potential application of [Zn(mtz)2] in Xe capture and separation from Xe–Kr gas mixtures.

Four new metal–organic frameworks constructed from H2DBTDC-O2 (H2DBTDC-O2 = dibenzothiophene-5,5′-dioxide-3,7-dicarboxylic acid) ligand with guest-responsive photoluminescence

Four new metal–organic frameworks (MOFs): [Cd(L)(Py)2]n (1), [Zn2(L)2(4,4′-bipy)]n (2), [Zn(L)(DIB)]n (3), [Co(L)(2,2′-bipy)]n (4), (H2L = dibenzothiophene-5,5′-dioxide-3,7-dicarboxylic acid, Py = pyridine, 4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine, DIB = 1,4-di(1H-imidazol-1-yl)butane) were constructed from H2L, different metal ions in the presence of various N-donor co-ligands, under solvothermal conditions. 1 displays a 2D 4-connected layered structure and accumulates in ABAB type. 2 exhibits a 3D two-fold interpenetrated pcu uninodal network with a 6-connected (412·63) Schlafli symbol. 3 shows a parallel four-fold interpenetrated dia uninodal network with a 4-connected (66) Schlafli symbol. Compound 4 is a 1D double-strand catenarian polymer. Solid-state properties for these crystalline materials, such as thermal stability, luminescent emission and the radiative lifetime of their emissions have been investigated. In particular, compounds 2 and 3 present guest-responsive luminescent properties.

Multi-functional metal–organic frameworks based on H4mdip: Crystal structure, photoluminescence, selective ion-exchange and catalysis

Four new metal organic frameworks based on flexible V-type tetracaboxylate ligands [Me2NH][In(mdip)]·2.5DMF·4H2O (1), [Zn2(mdip)(bpe)2]·3H2O (2), [Co2(mdip)(4,4′-bipy)2]·2.5DMF·7H2O (3), [Co4(mdip)2(μ2-O)2(py)7]·3DMF·7.5H2O (4) (H4mdip = 5,5′-methylenediisophthalic acid, 4,4′-bipy = 4,4′-bipyridine, bpe = (E)-1,2-di(pyridin-4-yl)ethene, py = pyridine), have been synthesized by using solvothermal reactions. Compound 1 was a 3D anionic framework with a (42·63·8) Schlafli symbol and exhibits selective ion exchange (M = Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Cu2+, Fe3+). What is more, Compound 1 has a suitable Lewis acidity and good chemical stability, which makes it a good heterogeneous catalyst for the Friedel–Crafts alkylation of pyrrole with nitroolefins. Compound 2 has a 3D framework with a novel (62·84)(64·82)2 Schlafli symbol, which is first found for 4-connected binodal network. Compound 3 exhibits a 3D open porous framework and exhibits a (4,6)-connected binodal network with a (44·610·8)(44·62) Schlafli symbol. Compound 4 crystallizes in a chiral space groupP32 and has a 3D 4-connected uninodal network with a Schlafli symbol of (65·8). It possesses regular triangular (1D) homochiral channels with an edge of 14.7 A along the c axis. The crystal structures and coordination modes of H4midp, as well as regulatory effect of N-donor co-ligands in these compounds are discussed. Solid-state properties for these crystalline materials, such as thermal stability, powder X-ray diffraction have been investigated. Emissive wavelengths and the radiative lifetime of their luminescent emissions for compounds 1 and 2 have also been investigated.

Dynamic separation of Xe and Kr by metal-organic framework and covalent-organic materials: a comparison with activated charcoal

We systematically investigate dynamic separation of Xe and Kr at room temperature using four representative porous materials (Cu-BTC, ZIF-8, COP-4 and activated carbon (AC)). Results indicate that among the four materials, Cu-BTC not only shows the highest retention volume per gram (Vg=788 mL g-1, which is 1.8 times of activated carbon (436 mL g-1)) under flowing condition, but also can separate 350 ppm Xe from 35 ppm Kr mixture in air with a high Xe/Kr selectivity of 8.6 at room temperature and 200 kPa, due to its suitable pore morphology, open metal sites, small side pockets in the framework. Moreover, the Cu-BTC also performs well on individual separation of Xe, Kr, CO2 from five-component gas mixture (Xe:Kr:CO2:Ar:N2=1:1:1:1:0.5, V/V) and has the longest retention time for Xe (20 min) in gas chromatographic separation, suggesting that it is a good candidate for potential applications as polymeric sieves.

Enhanced xenon adsorption and separation with an anionic indium–organic framework by ion exchange with Co2+

The separation of xenon/krypton is industrially significant and an environmental concern. Adsorptive capture and separation xenon from krypton using porous MOFs provides an energy and capital efficient approach compared with the current cryogenic distillation process. Herein, we investigated the adsorptive Xe/Kr separation potential of three anion In-MOFs (CPM-5, CPM-6 and the Co2+-exchanged framework analogue Co2+-CPM-6). Anionic In-MOF Co2+-CPM-6 with Co2+ ions in pore spaces has been obtained using a simple cation-exchange process and exhibits much higher Xe adsorption capacity and Xe/Kr selectivity than organic cation-analogues CPM-5 ([(CH3)2NH2]+) and CPM-6 ([CH3NH3]+), verified by single-component gas isotherms, IAST calculations and breakthrough experiments. The enhanced adsorptive Xe/Kr separation performance for Co2+-CPM-6 could be due to the increased pore size or accessible micropore volume and enhanced electric field within the pore spaces, which could induce strong interaction with Xe and simultaneously reduce the affinity with Kr.

Influence of co-ligands and solvents on the packing and photoluminescence of three related MnII metal–organic frameworks

Upon the alteration of selected co-ligands or reaction solvents, the solvothermal reactions of 2,6-DTT-dicarboxylic acid (H2DTDC) and Mn(ClO4)2·6H2O afforded three related 3D metal–organic frameworks, in which 1D chains were interlinked by using DTDC ligands in various coordination modes, generating different photoluminescence.

Synthesis, crystal structure and luminescence of a 3-D coordination polymer based on 4-(1H-tetrazol-5-yl) benzoic acid

A cobalt(II) coordination polymer [Co(4-TZBA2−)(H2O)2] (1) was obtained by treatment of Co(ClO4)2 · 6H2O with 4-(1H-tetrazol-5-yl)benzoic acid [H2(4-TZBA)] under hydrothermal conditions. The X-ray single crystal diffraction analysis reveals that 1 crystallizes in monoclinic P21/c, with a = 10.503(2) Å, b = 9.0860(18) Å, c = 10.179(2) Å, β = 96.75(3)° and Z = 4. In 1, adjacent cobalt(II) atoms are bridged by two 4-TZBA2− ligands to form a dimer, which is linked with six dimers to result in a 3-D structure. 1 exhibits strong luminescence at room temperature in the solid state.

Exploring the Effect of Ligand-Originated MOF Isomerism and Methoxy Group Functionalization on Selective Acetylene/Methane and Carbon Dioxide/Methane Adsorption Properties in Two NbO-Type MOFs

Investigation of the impact of ligand-originated MOF (metal-organic framework) isomerism and ligand functionalization on gas adsorption is of vital importance because a study in this aspect provides valuable guidance for future fabrication of new MOFs exhibiting better performance. For the abovementioned purpose, two NbO-type ligand-originated MOF isomers based on methoxy-functionalized diisophthalate ligands were solvothermally constructed in this work. Their gas adsorption properties toward acetylene, carbon dioxide, and methane were systematically investigated, revealing their promising potential for the adsorptive separation of both acetylene/methane and carbon dioxide/methane gas mixtures, which are involved in the industrial processes of acetylene production and natural gas sweetening. In particular, compared to its isomer ZJNU-58, ZJNU-59 displays larger acetylene and carbon dioxide uptake capacities as well as higher acetylene/methane and carbon dioxide/methane adsorption selectivities despite its lower pore volume and surface area, demonstrating a very crucial role that the effect of pore size plays in acetylene and carbon dioxide adsorption. In addition, the impact of ligand modification with a methoxy group on gas adsorption was also evaluated. ZJNU-58 exhibits slightly lower acetylene and carbon dioxide uptake capacities but higher acetylene/methane and carbon dioxide/methane adsorption selectivities as compared to its parent compound NOTT-103. By contrast, enhanced adsorption selectivities and uptake capacities were observed for ZJNU-59 as compared to its parent compound ZJNU-73. The results demonstrated that the impact of ligand functionalization with a methoxy group on gas adsorption might vary from MOF to MOF, depending on the chosen parent compound. The results might shed some light on understanding the impact of both ligand-originated MOF isomerism and methoxy group functionalization on gas adsorption.

A microporous metal–organic framework with commensurate adsorption and highly selective separation of xenon

The separation of xenon (Xe) and krypton (Kr) becomes increasingly important due to the industrial significance of high-purity Xe gas and the concern with reprocessing radioactive isotopes of Xe and Kr at parts per million concentrations from the off-gas of used nuclear fuel. Current separation processes mainly rely on energy and capital intensive cryogenic distillation. Thus, more economical and energy-efficient alternatives, such as physisorptive separation, using porous materials are needed to be developed. Herein, we present a microporous metal–organic framework (MOF-Cu-H) in which the suitable pore/cage-like structure with a precise size matching with the xenon atom leads to its commensurate adsorption phenomenon of Xe under ambient conditions and superior performance for Xe capture and separation. MOF-Cu-H exhibits by far the highest Xe Henry coefficient, remarkable Xe/Kr selectivity and significantly high Xe adsorption capacity at very low partial pressures relevant to nuclear fuel reprocessing. Temperature dependent isotherms, adsorption kinetics experiments, single column breakthrough curves and molecular simulation studies collaboratively support the claim, underlining the potential of this material for energy and cost-effective removal of xenon from nuclear fuel reprocessing plants compared with cryogenic distillation.