Dingxuan Ma

Introduction of π-Complexation into Porous Aromatic Framework for Highly Selective Adsorption of Ethylene over Ethane

In this work, we demonstrate for the first time the introduction of π-complexation into a porous aromatic framework (PAF), affording significant increase in ethylene uptake capacity, as illustrated in the context of Ag(I) ion functionalized PAF-1, PAF-1-SO3Ag. IAST calculations using single-component-isotherm data and an equimolar ethylene/ethane ratio at 296 K reveal that PAF-1-SO3Ag shows exceptionally high ethylene/ethane adsorption selectivity (Sads: 27 to 125), far surpassing benchmark zeolite and any other MOF reported in literature. The formation of π-complexation between ethylene molecules and Ag(I) ions in PAF-1-SO3Ag has been evidenced by the high isosteric heats of adsorption of C2H4 and also proved by in situ IR spectroscopy studies. Transient breakthrough experiments, supported by simulations, indicate the feasibility of PAF-1-SO3Ag for producing 99.95%+ pure C2H4 in a Pressure Swing Adsorption operation. Our work herein thus suggests a new perspective to functionalizing PAFs and other types of advanced porous materials for highly selective adsorption of ethylene over ethane.

Metal–Organic Framework Based upon the Synergy of a Brønsted Acid Framework and Lewis Acid Centers as a Highly Efficient Heterogeneous Catalyst for Fixed-Bed Reactions

We report a strategy of combining a Brønsted acid metal-organic framework (MOF) with Lewis acid centers to afford a Lewis acid@Brønsted acid MOF with high catalytic activity, as exemplified in the context of MIL-101-Cr-SO3H·Al(III). Because of the synergy between the Brønsted acid framework and the Al(III) Lewis acid centers, MIL-101-Cr-SO3H·Al(III) demonstrates excellent catalytic performance in a series of fixed-bed reactions, outperforming two benchmark zeolite catalysts (H-Beta and HMOR). Our work therefore not only provides a new approach to achieve high catalytic activity in MOFs but also paves a way to develop MOFs as a new type of highly efficient heterogeneous catalysts for fixed-bed reactions.

Metal-Cation-Directed de Novo Assembly of a Functionalized Guest Molecule in the Nanospace of a Metal–Organic Framework

In this work, a new strategy is developed to encapsulate a metal-functionalized guest molecule into a metal-organic framework (MOF) via metal-cation-directed de novo assembly from the component fragments of the guest molecule. This strategy, as illustrated in proof-of-principle studies on the de novo assembly of metal(II) phthalocyanine molecules into bio-MOF-1, can circumvent some drawbacks of existing approaches for encapsulating guest molecules into MOFs, such as inaccessibility for larger guest molecules due to limitations of the MOF window size and disruption of the MOF framework structure by functionalized guest molecules. Overall, this work provides a general yet versatile approach for encapsulating a broader range of metal-functionalized guest molecules into MOFs for various applications.

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.

3d–4f Metal–Organic Framework with Dual Luminescent Centers That Efficiently Discriminates the Isomer and Homologues of Small Organic Molecules

A 3d-4f luminescent metal-organic framework (MOF), [Tb2(Cu8I8)(C12H8NO2)6(H2O)4]·5C4H8O2 (4), and three analogues {[La2(Cu8I8)(C12H8NO2)6(C4H8O2)2(H2O)2]·3C4H8O2·2H2O (1), [Ce2(Cu8I8)(C12H8NO2)6(H2O)4]·5C4H8O2 (2), and [Eu2(Cu8I8)(C12H8NO2)6(H2O)4]·5C4H8O2 (3)}, were self-assembled from copper(I) halide clusters and lanthanide metal ions with an organic linker [3-(pyridin-4-yl)benzoic acid] under solvothermal conditions. Compound 4 with high quantum yield (Φ = 68%) exhibits reversible luminescence behavior, accompanying the removal and recovery of guest molecules (1,4-dioxane). Because of the unique porous structure and dual luminescent centers of compound 4, it can efficiently differentiate benzene series with different sizes and provide readouts in corresponding optical signals. Furthermore, it also can unambiguously discriminate the isomers, homologues, and other small molecules with similar structural motifs from one another. The luminescent color of the MOF sensor in different guest solvents has obvious changes that can be clearly distinguished by the naked eye. This multicolor luminescence originates from emissions of the dual luminescent centers, and the emissions have shifted, enhanced, weakened, or quenched to different degrees.

Bifunctional MOF heterogeneous catalysts based on the synergy of dual functional sites for efficient conversion of CO2 under mild and co-catalyst free conditions

We reported herein a strategy for combining CUS-based MOF (CUS = coordinatively unsaturated metal sites) with ionic liquid (IL) functional sites to form bifunctional heterogeneous catalysts with extra high activity for CO2 fixation. Based on this strategy, two quaternary ammonium salt and quaternary phosphorus salt ionic liquid functionalized CUS-containing MOF heterogeneous catalysts, MIL-101-N(n-Bu)3Br and MIL-101-P(n-Bu)3Br, have been prepared for the first time by a post-synthesis modification method. Due to the synergetic role of dual functional sites including Lewis acid sites in the MOF framwork and Br− ions in the IL functional sites, MIL-101-N(n-Bu)3Br and MIL-101-P(n-Bu)3Br exhibit high catalytic activity for the cycloaddition of CO2 and epoxide under mild and co-catalyst free conditions, which significantly outperforms other benchmark MOF catalysts. Moreover, such bifunctional catalysts can be easily recovered and recycled several times without leaching and loss of activity. Our work thus paves a way for the development of IL functionalized MOFs as heterogeneous catalysts for CO2 fixation.

Multifunctional Luminescent Porous Organic Polymer for Selectively Detecting Iron Ions and 1,4-Dioxane via Luminescent Turn-off and Turn-on Sensing

The first case of selective Fe(3+) ions and 1,4-dioxane luminescent sensor based on a porous organic polymer, POP-HT, was synthesized by reaction of tetra(p-aminophenyl)methane and chromophoric 2,5,8-trichloro-s-heptazine. POP-HT displayed prominent fluorescence quenching or enhancement in the presence of Fe(3+) ion or 1,4-dioxane. Moreover, an excellent linear relationship was established between luminescent intensity and the corresponding Fe(3+) ion or 1,4-dioxane concentration. The mechanisms of luminescence quenching and enhancement were also studied by both experiment and theoretical calculation. The results of this study suggest that POP-HT can work as an effective luminescent indicator for qualitative and quantitative detection of Fe(3+) ions and 1,4-dioxane in aqueous solution over other metal ions and organic solvents.

Three metal–organic frameworks based on the semirigid V-shaped 5-(3-amino-tetrazole-5-phenoxy)-isophthalic acid ligand: syntheses, topological structures and properties

The designed organic ligand 5-(3-amino-tetrazole-5-phenoxy)-isophthalic acid (H2atpia) has been successfully prepared and its coordination features have been explored. By the reaction of H2atpia with transition metals, three metal–organic frameworks (MOFs), namely [Cd(atpia)]2 (1), [Cu3O2(atpia)2] (2) and [Mn3(OH)2(atpia)3]·1.25H2O (3) have been synthesized under hydrothermal conditions. All the compounds were fully characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, power X-ray diffraction and single-crystal X-ray diffraction. These three compounds all display new topologies. Compound 1 exhibits a 3D (2,3,10)-connected framework with (4·62)2(412·618·811·104)(4)2 topology. Compound 2 possesses a 2D 3-nodal layer with (416·614·811·104)(43)2(4)2 topology. Compound 3 features a 2D (3,3,8,8)-connected structure with unprecedented (3·42)2(34·46·56·68·73·8) topology. The diverse structures of these three compounds demonstrate that the distinctive coordination modes of different metals have a significant impact on the construction of MOFs. Moreover, the photoluminescence properties of 1 and the magnetic properties of 2 and 3 have been studied and discussed.

Syntheses, structures, luminescence and magnetic properties of eleven coordination polymers constructed by a N,N′-sulfuryldiimidazole ligand

Reactions of divalent transition metal ions with the N,N′-sulfuryldiimidazole ligand (sdi) gave rise to eleven coordination polymers, namely, [Zn(sdi)(NO3)2(H2O)] (1), [Zn(sdi)2(NO3)2] (2), [Co(sdi)2(NO3)2] (3), [Cu(sdi)2(NO3)2]·2CO(CH3)2 (4), [Mn(sdi)2(H2O)2]·2NO3 (5), [Co(sdi)2(H2O)2]·2ClO4 (6), [Zn(sdi)(bdc)0.5(OCH3)(H2O)]·ClO4·H2O (7), [Cd(sdi)(N3)2] (8), [Mn(sdi)(N3)2] (9), [Ni(sdi)2(SO4)] (10) and [Cd(sdi)0.5(Hbtc)(OCH3)] (11) (H2bdc = 1,4-benzenedicarboxylic acid, H3btc = 1,3,5-benzenetricarboxylic acid). X-ray single-crystal analyses reveal that they have rich structural chemistry ranging from zero-dimensional (0D) (1), one-dimensional (1D) (2–7), two-dimensional (2D) (8) to three-dimensional (3D) (9–11) networks. Compound 1 displays a 0D structure which consists of [Zn(sdi)]2 dimers. Compounds 2–7 possess 1D chains with closed loops. Compound 8 shows a 2D (63) network. Compounds 9 and 10 exhibit 3D uninodal 6-connected pcu frameworks with (412·63) topology. Compound 11 displays a 3D uninodal 4-connected framework with a CdSO4-like net (65·8). The effects of metal ions and anions on the final motifs of the compounds have been discussed in detail. All the compounds are characterized using powder X-ray diffraction (PXRD), IR spectroscopy, thermal stability analysis and elemental analyses. Moreover, the photoluminescence properties of 1, 2, 7, 8 and 11 have been investigated. Magnetic investigation of 9 reveals spin canting antiferromagnetic interactions.

Capture of organic iodides from nuclear waste by metal-organic framework-based molecular traps

Effective capture of radioactive organic iodides from nuclear waste remains a significant challenge due to the drawbacks of current adsorbents such as low uptake capacity, high cost, and non-recyclability. We report here a general approach to overcome this challenge by creating radioactive organic iodide molecular traps through functionalization of metal-organic framework materials with tertiary amine-binding sites. The molecular trap exhibits a high CH3I saturation uptake capacity of 71 wt% at 150 °C, which is more than 340% higher than the industrial adsorbent Ag0@MOR under identical conditions. These functionalized metal-organic frameworks also serve as good adsorbents at low temperatures. Furthermore, the resulting adsorbent can be recycled multiple times without loss of capacity, making recyclability a reality. In combination with its chemical and thermal stability, high capture efficiency and low cost, the adsorbent demonstrates promise for industrial radioactive organic iodides capture from nuclear waste. The capture mechanism was investigated by experimental and theoretical methods.Capturing radioactive organic iodides from nuclear waste is important for safe nuclear energy usage, but remains a significant challenge. Here, Li and co-workers fabricate a stable metal–organic framework functionalized with tertiary amine groups that exhibits high capacities for radioactive organic iodides uptake.