Optimizing Trace Acetylene Removal from Acetylene/Ethylene Mixture in a Flexible Metal-Organic Framework by Crystal Downsizing.

Improving the gas separation performance of metal-organic frameworks (MOFs) by crystal downsizing is an important but often overlooked issue. Here, we report three different-sized flexible ZUL-520 MOFs (according to the crystal size from large to small, the three samples are, respectively, named ZUL-520-0, ZUL-520-1, and ZUL-520-2) with the same chemical structure for optimizing trace acetylene (C2H2) removal from acetylene/ethylene (C2H2/C2H4) mixture. The three differently sized activated ZUL-520 (denoted as ZUL-520a) exhibited almost identical C2H2 uptake of 4.8 mmol/g at 100 kPa, while the C2H2 uptake at 1 kPa increased with a downsizing crystal. The C2H2 uptake of activated ZUL-520-2 (denoted as ZUL-520-2a) at 1 kPa was ∼55% higher than that of activated ZUL-520-0 (denoted as ZUL-520-0a). The adsorption isotherms and adsorption kinetics validated that gas adsorptive separation is governed not only by adsorption thermodynamics but also by adsorption kinetics. In addition, all three different-sized ZUL-520a MOFs showed high C2H2/C2H4 selectivity. Grand canonical Monte Carlo (GCMC) simulations and dispersion-corrected density functional theory (DFT-D) computations illustrated a plausible mechanism of C2H2 adsorption in MOFs. Importantly, breakthrough experiments demonstrated that ZUL-520a can effectively separate the C2H2/C2H4 (1/99, v/v) mixture and the C2H4 productivity obtained by ZUL-520-2a was much higher than that by ZUL-520-0a. Our work may provide an easy but powerful strategy for upgrading the performance of gas adsorptive separation in MOFs.

Spatial Distribution of Nitrogen Binding Sites in Metal-Organic Frameworks for Selective Ethane Adsorption and One-Step Ethylene Purification.

The one-step purification of ethylene (C2 H4 ) from mixtures containing ethane (C2 H6 ) and acetylene (C2 H2 ) is an industrially important yet challenging process. In this work, we present a site-engineering strategy aimed at manipulating the spatial distribution of binding sites within a confined pore space. We realized successfully by incorporating nitrogen-containing heterocycles, such as indole-5-carboxylic acid (Ind), benzimidazole-5-carboxylic acid (Bzz), and indazole-5-carboxylic acid (Izo), into the robust MOF-808 platform via post-synthetic modification. The resulting functionalized materials, namely MOF-808-Ind, MOF-808-Bzz, and MOF-808-Izo, demonstrated significantly improved selectivity for C2 H2 and C2 H6 over C2 H4 . MOF-808-Bzz with two uniformly distributed nitrogen binding sites gave the optimal geometry for selective ethane trapping through multiple strong C-H⋅⋅⋅N hydrogen bonds, leading to the highest C2 H2 /C2 H4 and C2 H6 /C2 H4 combined selectivities among known MOFs. Column breakthrough experiments validated its ability to purify C2 H4 from ternary C2 H2 /C2 H4 /C2 H6 mixtures in a single step.

Customizing Metal-Organic Frameworks by Lego-Brick Strategy for One-Step Purification of Ethylene from a Quaternary Gas Mixture.

One-step purification of ethylene (C2 H4 ) from a quaternary gas mixture of C2 H6 /C2 H4 /C2 H2 /CO2 by adsorption is a promising separation process, yet developing adsorbents that synergistically capture various gas impurities remains challenging. Herein, a Lego-brick strategy is proposed to customize pore chemistry in a unified framework material. The ethane-selective MOF platform is further modified with customized binding sites to specifically adsorb acetylene and carbon dioxide, thus one-step purification of C2 H4 with high productivity of polymer-grade product (134 mol kg-1 ) is achieved on the assembly of porous coordination polymer-2,5-furandicarboxylic acid (PCP-FDCA) and PCP-5-aminoisophthalic acid (IPA-NH2 ). Computational studies verify that the low-polarity surface of this MOFs-based platform provides a delicate environment for C2 H6 recognition, and the specific binding sites (FDCA and IPA-NH2 ) exhibit favorable trapping of C2 H2 and CO2 via CHδ+ ···Oδ- and Cδ+ ···Nδ- electrostatic interactions, respectively. The proposed Lego-brick strategy to customize binding sites within the MOFs structure provides new ideas for the design of adsorbents for compounded separation tasks.

Strengthening Intraframework Interaction within Flexible MOFs Demonstrates Simultaneous Sieving Acetylene from Ethylene and Carbon Dioxide.

Efficient separation of acetylene (C2 H2 )/ethylene (C2 H4 ) and acetylene/carbon dioxide (CO2 ) by adsorption is an industrially promising process, but adsorbents capable of simultaneously capturing trace acetylene from ethylene and carbon dioxide are scarce. Herein, a gate-opening effect on three isomorphous flexible metal-organic frameworks (MOFs) named Co(4-DPDS)2 MO4 (M = Cr, Mo, W; 4-DPDS = 4,4-dipyridyldisulfide) is modulated by anion pillars substitution. The shortest CrO4 2- strengthens intraframework hydrogen bonding and thus blocks structural transformation after activation, striking a good balance among working capacity, separation selectivity, and trace impurity removal of flexible MOFs out of nearly C2 H2 /C2 H4 and C2 H2 /CO2 molecular sieving. The exceptional separation performance of Co(4-DPDS)2 CrO4 is confirmed by dynamic breakthrough experiments. It reveals the specific threshold pressures control in anion-pillared flexible materials enabled elimination of the impurity leakage to realize high purity products through precise control of the intraframework interaction. The adsorption mechanism and multimode structural transformation property are revealed by both calculations and crystallography studies. This work demonstrates the feasibility of modulating flexibility for controlling gate-opening effect, especially for some cases of significant aperture shrinkage after activation.

Shaping of gallate-based metal-organic frameworks for adsorption separation of ethylene from acetylene and ethane.

Shaping metal-organic frameworks (MOFs) powders into formed bodies plays a crucial role in opening up the excellent properties of MOFs to a broad range of applications. Gallate-based MOFs, termed as M-gallate (M = Co, Mg, Ni), have shown excellent performance for adsorption separation of C2 hydrocarbons. However, the industrial applications of MOF powders will inevitably confront problems of high pressure drop, pipe blockage, and dust pollution. Herein, we use hydroxypropyl cellulose (HPC) as a binder to produce gallate-based MOFs pellets. The crystal structure of the well-shaped materials after molding remained intact, and the surface area of the materials hardly decreases after shaping. Adsorption isotherms of C2 hydrocarbons including ethylene, ethane and acetylene on the activated powders and pellets of M-gallate were recorded and compared with the outperformers. The shaped pellets were also examined by breakthrough experiments on the fixed-bed separation of C2H2/C2H4 (1:99, v/v) and C2H4/C2H6 (50:50, v/v) gas mixtures. These results proved that M-gallate pellets was promising candidates for the practical industrial realization of C2 hydrocarbons separation.

Simultaneous interlayer and intralayer space control in two-dimensional metal-organic frameworks for acetylene/ethylene separation.

Three-dimensional metal-organic frameworks (MOFs) are cutting-edge materials in the adsorptive removal of trace gases due to the availability of abundant pores with specific chemistry. However, the development of ideal adsorbents combining high adsorption capacity with high selectivity and stability remains challenging. Here we demonstrate a strategy to design adsorbents that utilizes the tunability of interlayer and intralayer space of two-dimensional fluorinated MOFs for capturing acetylene from ethylene. Validated by X-ray diffraction and modeling, a systematic variation of linker atom oxidation state enables fine regulation of layer stacking pattern and linker conformation, which affords a strong interlayer trapping of molecules along with cooperative intralayer binding. The resultant robust materials (ZUL-100 and ZUL-200) exhibit benchmark capacity in the pressure range of 0.001-0.05 bar with high selectivity. Their efficiency in acetylene/ethylene separation is confirmed by breakthrough experiments, giving excellent ethylene productivities (121 mmol/g from 1/99 mixture, 99.9999%), even when cycled under moist conditions.

Microgeometry-independent equation for measuring infinite dilution activity coefficients using gas-liquid chromatography with static-wall-coated open-tubular columns.

Gas-liquid chromatography is an effective method to determine infinite dilution activity coefficients (γ∞). Wall-coated open-tubular (WCOT) column which offers more advantages over packed column should be a preferable column type; however, the small carrier gas flow rate and stationary phase amount in WCOT columns limit its application in the determination of γ∞. Mathematical strategy made some progress to avoid the quantification problem in the determination of γ∞ by static-wall-coated open-tubular (SWCOT) columns. However, the previously reported strategy was based on the assumption that SWCOT column was geometrically an ideal hollow cylinder, which indeed deviates from the reality. In this study, without that assumption, we derived a new microgeometry-independent equation by using the relationship between the hold-up volume (VM) and the volume of stationary phase (VL), and used it to measure the γ∞ of various organic solutes in two ionic liquids (ILs) 1­butyl­3-methylimidazolium dicyanamide and 1,3-dibutyronitrile-imidazolium bis((trifluoromethyl)sulfonyl)imide, both of which contain double cyano groups in the anion or cation. Phase loading study was adopted to eliminate the influence of interfacial adsorption to partition. The infinite dilution partial molar excess enthalpy, selectivity and capacity were directly calculated from the experimental γ∞ values, and the linear solvation energy relationship (LSER) model was used to characterize the specific properties of both ILs. This new established equation will promote the application of SWCOT columns in thermodynamic measurement and benefit the fast screening of novel solvents for chemical separation processes.

Facile Fabrication of Hierarchical MOF-Metal Nanoparticle Tandem Catalysts for the Synthesis of Bioactive Molecules.

Multifunctional metal-organic frameworks (MOFs) that possess permanent porosity are promising catalysts in organic transformation. Herein, we report the construction of a hierarchical MOF functionalized with basic aliphatic amine groups and polyvinylpyrrolidone-capped platinum nanoparticles (Pt NPs). The postsynthetic covalent modification of organic ligands increases basic site density in the MOF and simultaneously introduces mesopores to create a hierarchically porous structure. The multifunctional MOF is capable of catalyzing a sequential Knoevenagel condensation-hydrogenation-intramolecular cyclization reaction. The unique selective reduction of the nitro group to intermediate hydroxylamine by Pt NPs supported on MOF followed by intramolecular cyclization with a cyano group affords an excellent yield (up to 92%) to the uncommon quinoline N-oxides over quinolines. The hierarchical MOF and polyvinylpyrrolidone capping agent on Pt NPs synergistically facilitate the enrichment of substrates and thus lead to high activity in the reduction-intramolecular cyclization reaction. The bioactivity assay indicates that the synthesized quinoline N-oxides evidently inhibit the proliferation of lung cancer cells. Our findings demonstrate the feasibility of MOF-catalyzed direct synthesis of bioactive molecules from readily available compounds under mild conditions.

Copper chalcogenide materials as photothermal agents for cancer treatment.

Copper-based chalcogenide nanomaterials have made tremendous progress for cancer theranostics due to their simple preparation, low cost, stable performance, and easy functionalization. But a systematic review and analysis about them does not exist. Therefore, we offer an account, mainly focusing on the design and functionalization of the copper-based chalcogenide nanomaterials for cancer theranostics, aiming to briefly demonstrate the design and concepts, summarize some of the past studies and analyze the development trends in the copper-based chalcogenide nanomaterials for clinical application.

Biodegradable hollow manganese/cobalt oxide nanoparticles for tumor theranostics.

This article describes the fabrication of hollow manganese/cobalt oxide nanoparticles (MCO NPs) with a tunable size through a redox reaction and the Kirkendall effect for cancer imaging and drug delivery. MCO-70 NPs (with an average size of 70 nm) can act as glutathione (GSH)-responsive contrast agents for dual T1/T2-weighted magnetic resonance imaging (MRI). The degradation of MCO NPs by GSH led to the enhancement of their T1 and T2 signals by 2.24- and 3.43-fold compared with those of MCO NPs before degradation, respectively. Antitumor agents such as doxorubicin (Dox) could be encapsulated inside the cavity of the hollow MCO NPs (MCO-70-Dox) and be released in the presence of GSH. The MCO-70-Dox NPs showed good tumor growth inhibition effects in vitro and in vivo, and can be promising drug delivery vehicles and MRI contrast agents for tumor diagnosis and reporting drug release.

Enzyme-induced in vivo assembly of gold nanoparticles for imaging-guided synergistic chemo-photothermal therapy of tumor.

This article describes a nanoplatform based on matrix metalloproteinase (MMP)-responsive gold nanoparticles (AuNPs) for tumor-targeted photoacoustic (PA) imaging-guided photothermal therapy and drug delivery. AuNPs were grafted with complementary DNA strands, tethered with doxorubicin and coated with poly(ethylene glycol) via a thermal-labile linker and a MMP-cleavable peptide, respectively. The nanoprobes remained well-isolated in healthy tissues, but formed aggregates rapidly under MMP-abundant conditions. The DNA hybridization-induced assembly of the nanoprobes led to prolonged tumor retention and strong near-infrared (NIR) absorption, which is beneficial to deep-tissue imaging and therapy. Compared with MMP-inert nanoprobes, our platform demonstrated significantly enhanced efficiency in PA imaging and photothermal conversion upon NIR irradiation. Meanwhile, doxorubicin could be released rapidly in response to the localized elevation of temperature, leading to synergistic chemo-photothermal therapy. The unique nanoplatform may find applications in effective disease control by delivering imaging and therapy to tumors with high specificity, safety, and universality.

Adsorptive Separation of Acetylene from Ethylene in Isostructural Gallate-Based Metal-Organic Frameworks.

The separation of acetylene from ethylene is of paramount importance in the purification of chemical feedstocks for industrial manufacturing. Herein, an isostructural series of gallate-based metal-organic frameworks (MOFs), M-gallate (M=Ni, Mg, Co), featuring three-dimensionally interconnected zigzag channels, the aperture size of which can be finely tuned within 0.3 Šby metal replacement. Controlling the aperture size of M-gallate materials slightly from 3.69 down to 3.47 Šcould result in a dramatic enhancement of C2 H2 /C2 H4 separation performance. As the smallest radius among the studied metal ions, Ni-gallate exhibits the best C2 H2 /C2 H4 adsorption separation performance owing to the strongest confinement effect, ranking after the state-of-the-art UTSA-200a with a C2 H4 productivity of 85.6 mol L-1 from 1:99 C2 H2 /C2 H4 mixture. The isostructural gallate-based MOFs, readily synthesized from inexpensive gallic acid, are demonstrated to be a new top-performing porous material for highly efficient adsorption of C2 H2 from C2 H4 .

Engineering the Pore Size of Pillared-Layer Coordination Polymers Enables Highly Efficient Adsorption Separation of Acetylene from Ethylene.

The pore size of adsorbents plays a vital role in determining the overall separation performance of gas separation and purification by adsorption. In this work, the pore apertures of the coordination pillared layer (CPL) was systematically controlled by adjusting the length of pillared ligands. We used pyrazine, 4,4'-bipyridine, and 1,2-di(4-pyridyl)-ethylene with increased length to synthesize CPL-1 (L = pyrazine), CPL-2 (L = 4,4'-bipyridine), and CPL-5 [L = 1,2-di(4-pyridyl)-ethylene], respectively. The aperture size of these CPLs varies from 4 to 11 Å: CPL-1 (4 × 6 Å2), CPL-2 (9 × 6 Å2), and CPL-5 (11 × 6 Å2). Among the three frameworks, CPL-2 exhibits the highest C2H2 uptake at ambient conditions as it has moderate pore size and porosity. However, CPL-1 has the best separation performance in the breakthrough experiments with binary gas mixture of C2H2/C2H4, thanks to the optimal pore size nearly excluding C2H4, which is only observed in the state-of-the-art UTSA-300a so far. The DFT calculations were carried out to elucidate the specific adsorption sites for both acetylene and ethylene among these frameworks. The modeling results suggest that binding strength is highly related to aperture size and that CPL-1 shows the highest adsorption selectivity owing to the optimal pore size. This work demonstrates that engineering pore size enables us to fabricate the highly efficient metal-organic framework (MOF)-based adsorbents for specific gas separation on the basis of the isoreticular chemistry.

Molecular Sieving of Ethane from Ethylene through the Molecular Cross-Section Size Differentiation in Gallate-based Metal-Organic Frameworks.

Purification of C2 H4 from an C2 H4 /C2 H6 mixture, one of the most important while challenging industrial separation processes, is mainly through energy-intensive cryogenic distillation. Now a family of gallate-based metal-organic framework (MOF) materials is presented, M-gallate (M=Ni, Mg, Co), featuring 3D interconnected zigzag channels, the aperture sizes of which (3.47-3.69 Å) are ideally suitable for molecular sieving of ethylene (3.28×4.18×4.84 Å3 ) and ethane (3.81×4.08×4.82 Å3 ) through molecular cross-section size differentiation. Co-gallate shows an unprecedented IAST selectivity of 52 for C2 H4 over C2 H6 with a C2 H4 uptake of 3.37 mmol g-1 at 298 K and 1 bar, outperforming the state-of-the-art MOF material NOTT-300. Direct breakthrough experiments with equimolar C2 H4 /C2 H6 mixtures confirmed that M-gallate is highly selective for ethylene. The adsorption structure and mechanism of ethylene in the M-gallate was further studied through neutron diffraction experiments.

Fine Tuning and Specific Binding Sites with a Porous Hydrogen-Bonded Metal-Complex Framework for Gas Selective Separations.

Research on hydrogen-bonded organic frameworks (HOFs) has been developed for quite a long time; however, those with both established permanent porosities and functional properties are extremely rare due to weak hydrogen-bonding interactions among molecular organic linkers, which are much more fragile and difficult to stabilize. Herein, through judiciously combining the superiority of both the moderately stable coordination bonds in metal-organic frameworks and hydrogen bonds, we have realized a microporous hydrogen-bonded metal-complex or metallotecton framework HOF-21, which not only shows permanent porosity, but also exhibits highly selective separation performance of C2H2/C2H4 at room temperature. The outstanding separation performance can be ascribed to sieving effect confined by the fine-tuning pores and the superimposed hydrogen-bonding interaction between C2H2 and SiF62- on both ends as validated by both modeling and neutron powder diffraction experiments. More importantly, the collapsed HOF-21 can be restored by simply immersing it into water or salt solution. To the best of our knowledge, such extraordinary water stability and restorability of HOF-21 were observed for the first time in HOFs, underlying the bright perspective of such new HOF materials for their industrial usage.

An Ideal Molecular Sieve for Acetylene Removal from Ethylene with Record Selectivity and Productivity.

Realization of ideal molecular sieves, in which the larger gas molecules are completely blocked without sacrificing high adsorption capacities of the preferred smaller gas molecules, can significantly reduce energy costs for gas separation and purification and thus facilitate a possible technological transformation from the traditional energy-intensive cryogenic distillation to the energy-efficient, adsorbent-based separation and purification in the future. Although extensive research endeavors are pursued to target ideal molecular sieves among diverse porous materials, over the past several decades, ideal molecular sieves for the separation and purification of light hydrocarbons are rarely realized. Herein, an ideal porous material, SIFSIX-14-Cu-i (also termed as UTSA-200), is reported with ultrafine tuning of pore size (3.4 Å) to effectively block ethylene (C2 H4 ) molecules but to take up a record-high amount of acetylene (C2 H2 , 58 cm3 cm-3 under 0.01 bar and 298 K). The material therefore sets up new benchmarks for both the adsorption capacity and selectivity, and thus provides a record purification capacity for the removal of trace C2 H2 from C2 H4 with 1.18 mmol g-1 C2 H2 uptake capacity from a 1/99 C2 H2 /C2 H4 mixture to produce 99.9999% pure C2 H4 (much higher than the acceptable purity of 99.996% for polymer-grade C2 H4 ), as demonstrated by experimental breakthrough curves.

Pore chemistry and size control in hybrid porous materials for acetylene capture from ethylene.

The trade-off between physical adsorption capacity and selectivity of porous materials is a major barrier for efficient gas separation and purification through physisorption. We report control over pore chemistry and size in metal coordination networks with hexafluorosilicate and organic linkers for the purpose of preferential binding and orderly assembly of acetylene molecules through cooperative host-guest and/or guest-guest interactions. The specific binding sites for acetylene are validated by modeling and neutron powder diffraction studies. The energies associated with these binding interactions afford high adsorption capacity (2.1 millimoles per gram at 0.025 bar) and selectivity (39.7 to 44.8) for acetylene at ambient conditions. Their efficiency for the separation of acetylene/ethylene mixtures is demonstrated by experimental breakthrough curves (0.73 millimoles per gram from a 1/99 mixture).

Hydrous RuO2 nanoparticles as an efficient NIR-light induced photothermal agent for ablation of cancer cells in vitro and in vivo.

Metal oxides are receiving an incremental attention in recent years for their potential applications in ablation of cancer cells due to their efficient photothermal conversion and good biocompatibility, but the large sizes and poor photo-stability will seriously limit their practical application. Herein, hydrous RuO2 nanoparticles were synthesized by a facile hydrothermal treatment and surface-modified with polyvinylpyrrolidone (PVP) coating. PVP-coated RuO2 nanoparticles exhibit a well dispertion in saline solution, strong characteristic plasmonic absorption in NIR region, enhanced photothermal conversion efficiency of 54.8% and remarkable photo-stability under the irridation of an 808 nm laser. The nanoparticles were further employed as a new photothermal ablation agent for cancer cells which led rapidly to cellular deaths both in vitro and in vivo.

CuS@mSiO2-PEG core-shell nanoparticles as a NIR light responsive drug delivery nanoplatform for efficient chemo-photothermal therapy.

We report a facile and low-cost approach to design a difunctional nanoplatform (CuS@mSiO2-PEG) as a near-infrared (NIR) light responsive drug delivery system for efficient chemo-photothermal therapy. The nanoplatform demonstrated good biocompatibility and colloidal stability, as well as high loading capacity for the anticancer drug (26.5 wt% for doxorubicin (DOX)). The CuS nanocrystals (core) within these CuS@mSiO2-PEG core-shell nanoparticles can effectively absorb and convert NIR light to fatal heat under NIR light irradiation for photothermal therapy, and the release of DOX from the mesoporous silica (shell) can be triggered by pH and NIR light for chemotherapy. When the CuS@mSiO2-PEG/DOX nanocomposites were irradiated by 980 nm light, both chemotherapy and photothermal therapy were simultaneously driven, resulting in a synergistic effect for killing cancer cells. Importantly, compared with chemotherapy or photothermal treatment alone, the combined therapy significantly improved the therapeutic efficacy.

Accurate measurements of infinite dilution activity coefficients using gas chromatography with static-wall-coated open-tubular columns.

Wall-coated open-tubular (WCOT) columns provide higher column efficiency and lower solute interfacial adsorption effect than packed columns. However, previous efforts used to measure the infinite dilution activity coefficient (γ(∞)) via a chromatographic technique have used packed columns, because the low carrier gas flow rate (U) and the small stationary phase amount (n(2)) in WCOT columns raise large errors. By rationally revising the γ(∞)-calculation equation for static-wall-coated open-tubular column, we observed that U and n(2) are not necessarily needed and the resulting error could be reduced, and WCOT column gas chromatography subsequently became a superior method for the accurate γ(∞) determination. In this study, we validate our revised γ(∞)-calculation equation by measuring γ(∞) in an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate system, in which 55 organic compounds covering a wide range of functional groups were used as probe solutes and their γ(∞) values in the ionic liquid were determined at 40.0, 50.0, and 60.0 °C. Experimental error analysis shows that our revised equation remarkably reduces the error compared to the common γ(∞)-calculation equation. Our data is consistent with previously reported values obtained via other techniques, which further proves the credibility of our revised equation. The accurately determined γ(∞) values can be directly used to calculate the partial molar excess enthalpy, selectivity, and capacity, which will benefit for the rapid screening of solvents (especially ionic liquids) in separation approaches.