Crystalline versus Amorphous: High-Performance Hafnium Phosphonate Framework for the Separation of Uranium and Transuranium Elements.

Metal phosphonate frameworks (MPFs) consisting of tetravalent metal ions and aryl-phosphonate ligands feature a large affinity for actinides and excellent stabilities in harsh aqueous environments. However, it remains elusive how the crystallinity of MPFs influences their performance in actinide separation. To this end, we prepared a new category of porous, ultrastable MPF with different crystallinities for uranyl and transuranium separation. The results demonstrated that crystalline MPF was generally a better adsorbent for uranyl than the amorphous counterpart and ranked as the top-performing one for uranyl and plutonium in strong acidic solutions. A plausible uranyl sequestration mechanism was unveiled by using powder X-ray diffraction in tandem with vibrational spectroscopy, thermogravimetry, and elemental analysis.

Thermodynamics-Kinetics-Balanced Metal-Organic Framework for In-Depth Radon Removal under Ambient Conditions.

Radon (Rn), a ubiquitous radioactive noble gas, is the main source of natural radiation to human and one of the major culprits for lung cancer. Reducing ambient Rn concentration by porous materials is considered as the most feasible and energy-saving option to lower this risk, but the in-depth Rn removal under ambient conditions remains an unresolved challenge, mainly due to the weak van der Waals (vdW) interaction between inert Rn and adsorbents and the extremely low partial pressure (<1.8 × 10-14 bar, <106 Bq/m3) of Rn in air. Adsorbents having either favorable adsorption thermodynamics or feasible diffusion kinetics perform poorly in in-depth Rn removal. Herein, we report the discovery of a metal-organic framework (ZIF-7-Im) for efficient Rn capture guided by computational screening and modeling. The size-matched pores in ZIF-7-Im abide by the thermodynamically favorable principle and the exquisitely engineered quasi-open apertures allow for feasible kinetics with little sacrifice of sorption thermodynamics. The as-prepared material can reduce the Rn concentration from hazardous levels to that below the detection limit of the Rn detector under ambient conditions, with an improvement of at least two orders of amplitude on the removal depth compared to the currently best-performing and only commercialized material activated charcoal.

Tuning the Channel Size and Structure Flexibility of Metal-Organic Frameworks for the Selective Adsorption of Noble Gases.

Two ultramicroporous metal-organic frameworks, Zn(ox)0.5(trz) and Zn(ox)0.5(atrz) (ox = oxalate, trz = triazolate, and atrz = 3-aminotriazolate), have been synthesized and tested for the adsorptive separation of Xe and Kr. We demonstrate that the Xe/Kr adsorption selectivity relates to the pore size as well as the structure flexibility of the adsorbents.

A Designed ZnO@ZIF-8 Core-Shell Nanorod Film as a Gas Sensor with Excellent Selectivity for H2 over CO.

The development of H2 gas sensors is important for H2 production as a fuel. In this work, a ZnO@ZIF-8 core-shell nanorod film is designed and synthesized as a gas sensor through a facile solution deposition process. This film shows an excellent selective response for H2 over CO. By fine-tuning the reaction conditions, a ZnO@ZIF-8 core-shell structure with a thin, fine-grain, porous ZIF-8 shell is obtained. Owing to the facile H2 penetration through the ZIF-8 thin shell (≈110 nm) and the increased oxygen vacancies for the complex film, the ZnO@ZIF-8 nanorod film shows a higher H2 sensitivity than a raw ZnO nanorod film. More importantly, the ZnO@ZIF-8 nanorod film shows no response for CO at 200 °C. Because of the fine-grain confinement of the porous ZIF-8 shell (<140 nm), the molecular sieving effect is strengthened, which allows the effective separation of H2 over CO. This work provides a promising strategy for the design of high-performance H2 sensors.

Microporous Metal-Organic Framework Stabilized by Balanced Multiple Host-Couteranion Hydrogen-Bonding Interactions for High-Density CO2 Capture at Ambient Conditions.

Microporous metal organic frameworks (MOFs) show promising application in several fields, but they often suffer from the weak robustness and stability after the removal of guest molecules. Here, three isostructural cationic metal-organic frameworks {[(Cu4Cl)(cpt)4(H2O)4]·3X·4DMAc·CH3OH·5H2O} (FJU-14, X = NO3, ClO4, BF4; DMAc = N,N'-dimethylacetamide) containing two types of polyhedral nanocages, one octahedron, and another tetrahedron have been synthesized from bifunctional organic ligands 4-(4H-1,2,4-triazol-4-yl) benzoic acid (Hcpt) and various copper salts. The series of MOFs FJU-14 are demonstrated as the first examples of the isostructural MOFs whose robustness, thermal stability, and CO2 capacity can be greatly improved via rational modulation of counteranions in the tetrahedral cages. The activated FJU-14-BF4-a containing BF4(-) anion can take CO2 of 95.8 cm(3) cm(-3) at ambient conditions with an adsorption enthalpy only of 18.8 kJ mol(-1). The trapped CO2 density of 0.955 g cm(-3) is the highest value among the reported MOFs. Dynamic fixed bed breakthrough experiments indicate that the separation of CO2/N2 mixture gases through a column packed with FJU-14-BF4-a solid can be efficiently achieved. The improved robustness and thermal stability for FJU-14-BF4-a can be attributed to the balanced multiple hydrogen-bonding interactions (MHBIs) between the BF4(-) counteranion and the cationic skeleton, while the high-density and low-enthalpy CO2 capture on FJU-14-BF4-a can be assigned to the multiple-point interactions between the adsorbate molecules and the framework as well as with its counteranions, as proved by single-crystal structures of the guest-free and CO2-loaded FJU-14-BF4-a samples.

Monomer Symmetry-Regulated Defect Engineering: In Situ Preparation of Functionalized Covalent Organic Frameworks for Highly Efficient Capture and Separation of Carbon Dioxide.

Developing crystalline porous materials with highly efficient CO2 selective adsorption capacity is one of the key challenges to carbon capture and storage (CCS). In current studies, much more attention has been paid to the crystalline and porous properties of crystalline porous materials for CCS, while the defects, which are unavoidable and ubiquitous, are relatively neglected. Herein, for the first time, we propose a monomer-symmetry regulation strategy for directional defect release to achieve in situ functionalization of COFs while exposing uniformly distributed defect-aldehyde groups as functionalization sites for selective CO2 capture. The regulated defective COFs possess high crystallinity, good structural stability, and a large number of organized and functionalized aldehyde sites, which exhibit one of the highest selective separation values of all COF sorbing materials in CO2/N2 selective adsorption (128.9 cm3/g at 273 K and 1 bar, selectivity: 45.8 from IAST). This work not only provides a new strategy for defect regulation and in situ functionalization of COFs but also provides a valuable approach in the design and preparation of new adsorbents for CO2 adsorption and CO2/N2 selective separation.

Efficient Xe/Kr Separation Based on a Lanthanide-Organic Framework with One-Dimensional Local Positively Charged Rhomboid Channels.

Efficient xenon/krypton (Xe/Kr) separation has played an important role in industry due to the wide application of high-purity Xe and with regard to the safe disposal of radioactive noble gases (85Kr and 133Xe). A less energy-demanding separation technology, adsorptive separation using porous solid materials, has been proposed to replace the traditional cryogenic distillation with intensive energy consumption. As a cutting-edge class of porous materials, metal-organic frameworks (MOFs) featuring permanent porosity, designable chemical functionalities, and tunable pore sizes hold great promise for Xe/Kr separation. Here, we report a two-dimensional (2D) lanthanide-organic framework (termed LPC-MOF, [Eu(Ccbp)(NO3)(HCOO)]·DMF0.3(H2O)2.5) with one-dimensional (1D) local positively charged rhomboid channels whose size matches well with the kinetic diameter of Xe, leading to its superior Xe/Kr separation performance. Column breakthrough experiments demonstrate that LPC-MOF exhibits a high Xe/Kr selectivity of 12.4 and an Xe adsorption amount of 3.39 mmol kg-1 under simulated conditions for real used nuclear fuel (UNF)-reprocessing plants. Furthermore, density functional theory (DFT) calculations elucidate not only the intrinsic mechanisms of Xe/Kr separation at the molecular level but also the detailed influence of the local positive charge (N+) on the performance of Xe/Kr separation in the MOF system.

Rational design of zinc-organic coordination polymers directed by N-donor co-ligands.

A family of Zn(II) -based metal-organic coordination polymers (MOCPs) [Zn(L)(imid)(2)] (1), [Zn(L)(2,2'-bpy)] (2), [Zn(2)(L)(2)(Py)(3)] (3), [Zn(L)(DPP)]⋅DMF (4), [Zn(L)(DPEA)] (5), [Zn(2)(L)(2)(4,4'-bpy)] (6), [Zn(L)(3,4'-DPEE)]⋅DMF (7), and [Zn(3)(L)(3)(3,4'-DPEE)(2)]⋅DMF (8) (L=dithieno[3,2-b:2',3'-e]benzene-2,6-dicarboxylic acid, imid=imidazole, bpy=bipyridine, Py=pyridine, DPP=1,3-di(pyridin-4-yl)propane, DPEA=1,2-di(pyridin-4-yl)ethane, and DPEE=(E)-3,4'-(ethene-1,2-diyl)dipyridine) have been rationally designed and generated in the solvothermal reaction systems of the new conjugated thiophene derivative L, Zn(ClO(4))(2)⋅6H(2)O, and seven different aromatic N-donor co-ligands separately. These N-donor compounds were carefully selected and employed in the crystal preparation of the eight MOCPs as structure-directing co-ligands owing to their structural specialties and habitual coordination fashions. Among these MOCPs, compounds 1-3 are 1D polymers with different chain structures. Compounds 4, 7, and 8 are 2D structures, in which 4 has two sets of twofold interpenetrating layers, whereas 7 and 8 are both built from three independent sheets. Compounds 5 and 6 are 3D frameworks, in which 5 exhibits a fivefold interpenetrating diamondoid network, whereas 6 shows a typical twofold interpenetrating pillared layer structure with nanoscale channels. The photoluminescent properties of these MOCPs, including excitation, emission, and radiactive lifetime, have also been investigated to help us tentatively understand their structure-property relationships.

Porphyrinic Metal-Organic Framework Nanorod-Based Dual-Modal Nanoprobe for Sensing and Bioimaging of Phosphate.

Herein, a dual-modal fluorescent/colorimetric "Signal-On" nanoprobe based on PCN-222 nanorods (NRs) toward phosphate was proposed for the first time. Due to the high affinity of the zirconium node in PCN-222 NRs for phosphate, the structure collapse of PCN-222 NRs was triggered by phosphate, resulting in the release of the tetrakis(4-carboxyphenyl)porphyrin (TCPP) ligand from PCN-222 NRs as well as the enhancement of fluorescence and absorbance signals. The PCN-222 NR-based nanoprobe could be employed for phosphate detection over a wide concentration range with a detection limit down to 23 nM. The practical application of the PCN-222 NR-based nanoprobe in real samples was evaluated. Moreover, benefitting from the good biocompatibility and water dispersibility of PCN-222 NRs, this nanoprobe was successfully employed in the intracellular imaging of phosphate, revealing its promising application in the biological science. The present work would greatly extend the potential of nanostructured MOFs in the sensing and biological fields.

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.

Direct Evidence of CO2 Capture under Low Partial Pressure on a Pillared Metal-Organic Framework with Improved Stabilization through Intramolecular Hydrogen Bonding.

Direct structural observation of CO2 -loaded MOFs is helpful for revealing the specific binding interactions to allow the design of better CO2 sorbents, but such direct structural evidence is almost always observed for pure-component CO2 under a pressure of 1 atm or more, which does not really represent practical CO2 capture and separation under low partial pressure (≤1 atm) in the presence of other gases. Herein, a series of isoreticular MOFs [Zn(Trz)(R-BDC)1/2 ] (FJU-40-R, R=H, NH2 , Br, or OH) are synthesized. Among them, FJU-40-NH2 exhibits the highest robustness, and good heat and water resistance, attributed to its intramolecular hydrogen-bonding interactions. A CO2 /N2 (15:85, v/v) mixture can be separated efficiently through a column packed bed of FJU-40-NH2 solid. The structures of CO2 -loaded FJU-40-NH2 at 1 atm under various atmosphere conditions, including pure CO2 , CO2 /N2 (15:85, v/v), and air, are observed, and it is found that: 1) the mechanism for CO2 loading into the cages depends on the CO2 partial pressure; 2) FJU-40-NH2 can capture CO2 directly from air, and CO2 will have priority to occupy hydrophobic cage-I, whereas hydrophilic cage-II containing the amino group is occupied by H2 O molecules; 3) the triazolate C-H groups, rather than the amino groups in past observations in dry ice, act as predominant functional sites here under low CO2 partial pressure.

An aminopyrimidine-functionalized cage-based metal-organic framework exhibiting highly selective adsorption of C2H2 and CO2 over CH4.

There has been considerable interest in adsorptive separation of C2H2/CH4 and CO2/CH4 gas mixtures due to its industrial significance and scientific challenge. In this work, we have designed and synthesized a bent diisophthalate ligand functionalized with aminopyrimidine groups, and constructed via a solvothermal reaction, a porous copper-based framework. Single-crystal X-ray diffraction studies show that the framework is a three-dimensional network containing three different types of polyhedral nanocages, which are stacked together to form two distinct types of one-dimensional channels along the crystallographic c axis. The compound after activation shows exceptionally high C2H2 and CO2 uptakes of 211 and 120 cm(3) (STP) g(-1) at 295 K and 1 atm, as well as impressive adsorption selectivities towards C2H2 and CO2 over CH4. High C2H2 and CO2 uptake capacities as well as significant adsorption selectivities of C2H2 and CO2 over CH4 imply potential applications in the adsorptive separation and purification of C2H2/CH4 and CO2/CH4 gas mixtures, which have been verified by column breakthrough experiments. Several important binding sites for C2H2 and CO2 in ZJNU-54 were revealed by quantum chemical calculations, demonstrating that the organic linkers in ZJNU-54 form unique structures that facilitate the adsorption of C2H2, while the amine groups and the Lewis basic pyrimidine-ring nitrogen sites in the organic linker improve the adsorption energies for CO2, finally leading to the increase of adsorption capacities for these two gas molecules. This work provides an efficient strategy for incorporating specific functional groups into cage-based MOFs for generating new adsorbents for highly selective gas storage and separation.

A new tetrazolate zeolite-like framework for highly selective CO2/CH4 and CO2/N2 separation.

A new tetrazolate zeolite-like framework with a diamond topology, UTSA-49, was synthesized. UTSA-49 shows high selectivity for CO2/CH4 and CO2/N2 indicating a synergistic effect of the suitable pore size/shape and functional groups.

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.