Iodine Adsorption-Desorption-Induced Structural Transformation and Improved Ag+ Turn-On Luminescent Sensing Performance of a Nonporous Eu(III) Metal-Organic Framework.

Posttreatment of pristine metal-organic frameworks (MOFs) with suitable vapor may be an effective way to regulate their structures and properties but has been less explored. Herein, we report an interesting example in which a crystalline nonporous Eu(III)-MOF was transferred to a porous amorphous MOF (aMOF) via iodine vapor adsorption-desorption posttreatment, and the resulting aMOF showed improved turn-on sensing properties with respect to Ag+ ions. The crystalline Eu-MOF, namely, Eu-IPDA, was assembled from Eu(III) and 4,4'-{4-[4-(1H-imidazol-1-yl)phenyl]pyridine-2,6-diyl}dibenzoic acid (H2IPDA) and exhibited a two-dimensional (2D) coordination network based on one-dimensional secondary building blocks. The close packing of the 2D networks gives rise to a three-dimensional supramolecular framework without any significant pores. Interestingly, the nonporous Eu-IPDA could absorb iodine molecules when Eu-IPDA crystals were placed in iodine vapor at 85 °C, and the adsorption capacity was 1.90 g/g, which is comparable to those of many MOFs with large BET surfaces. The adsorption of iodine is attributed to the strong interactions among the iodine molecule, the carboxy group, and the N-containing group and leads to the amorphization of the framework. After immersion of the iodine-loaded Eu-IPDA in EtOH, approximately 89.7% of the iodine was removed, resulting in a porous amorphous MOF, denoted as a-Eu-IPDA. In addition, the remaining iodine in the a-Eu-IPDA framework causes strong luminescent quenching in the fluorescence emission region of the Eu(III) center when compared with that in Eu-IPDA. The luminescence intensity of a-Eu-IPDA in water suspensions was significantly enhanced when Ag+ ions were added, with a detection limit of 4.76 × 10-6 M, which is 1000 times that of pristine Eu-IPDA. It also showed strong anti-interference ability over many common competitive metal ions and has the potential to sense Ag+ in natural water bodies and traditional Chinese medicine preparations. A mechanistic study showed that the interactions between Ag+ and the absorbed iodine, the carboxylate group, and the N atoms all contribute to the sensing performance of a-Eu-IPDA.

Regulating the Porosity and Iodine Adsorption Properties of Metal-Organic Framework Glass via an Ammonia-Immersion Approach.

Metal-organic framework (MOF) glass is a new type of glass material, but it usually lacks sufficient porosity. Thus, regulating the pore structure of MOF glass to improve its adsorption performance is very important. Herein, we found that the porosity of MOF glasses agZIF-62 and agZIF-76 can be regulated via an ammonia-immersion approach. After ammonia immersion, the resulting agZIF-62-NH3 and agZIF-76-NH3 could be maintained in their glass states or converted to their amorphous states, respectively. Their porosity changed according to the gas adsorption experiments. Notably, compared with agZIF-62 and agZIF-76, the iodine uptake capacities for agZIF-62-NH3 and agZIF-76NH3 increased by 12 and 21 times, respectively. This work shows that the subsequent treatment of MOF glass can regulate their adsorption performance.

Assembly of a miRNA-modified QCM sensor for miRNA recognition through response patterns.

In this paper, a miRNA-based quartz crystal microbalance (QCM) biosensor was fabricated and used to the rapid and effective sensing of miRNA. The specific hybridization between probe miRNA and different selected miRNAs (miR-27a, miR-27b, and Let-7a) cause a different interaction mode, thus display different frequency change and response patterns in the QCM sensor, which were used to detect miR-27a and miR-27b. The selective sensing of miR-27a in mixed miRNA solution was also achieved. This miRNA-based QCM biosensor has the advantages of real-time, label-free, and short cycle detection.

Homochiral Cu(I) Coordination Polymers Based on a Double-Stranded Helical Building Block from Achiral Ligands: Symmetry-Breaking Crystallization, Photophysical and Photocatalytic Properties.

A pair of homochiral coordination polymers, [Cu(DPT)]n (1M and 1P, HDPT = 3,5-di-4-pyridinyl-2H-tetrazole), were assembled from achiral precursors. Crystal structure analysis showed that they are chiral three-dimensional (3D) coordination polymers based on a new double-stranded helical building block that is composed of two different 1D helices. Interestingly, rare symmetry-breaking crystallization was observed, in which the possibility of obtaining enantio-enriched bulk product with excessive M enantiomers (1-A) was obviously higher than that for P enantiomers (1-B) as demonstrated in multiple, repeated experiments with single-crystal diffraction and vibrational circular dichroism (VCD) spectra. Moreover, compound [Cu(DPT)]n shows good chemical stability in water, with pH values ranging from 3 to 13, as well as in many common organic solvents. Photophysical properties, including thermochromic properties and two-photon excited luminescence, were studied, and the potential for applications in temperature sensing was exhibited. In addition, the photocatalytic degradation of methylene blue in water indicated that compound [Cu(DPT)]n can be used as a photocatalyst.

Hydrolytically Stable Nanotubular Cationic Metal-Organic Framework for Rapid and Efficient Removal of Toxic Oxo-Anions and Dyes from Water.

Cationic framework materials capable of removing anionic pollutants from wastewater are highly desirable but relatively rarely reported. Herein, a cationic MOF (SCNU-Z1-Cl) possessing tubular channels with diameter of 1.5 nm based on Ni(II) and a nitrogen-containing ligand has been synthesized and applied to capture hazardous anionic contaminants from water. The SCNU-Z1-Cl exhibits high BET surface area of 1636 m2/g, and shows high hydrolytically stability in pH range from 4 to 10. Owing to the large tubular channels and the uncoordinated anions in the framework, the aqueous-phase anion-exchange applications of SCNU-Z1-Cl were explored with environmentally toxic oxo-anions including CrO42-, Cr2O72-, MnO4-, and ReO4-, and organic dyes. The adsorption of oxoanions exhibits high uptake kinetics and the adsorption capacities of CrO42-, Cr2O72-, MnO4-, and ReO4- are 126, 241, 292, and 318 mg/g, respectively, which were some of the highest values in the field of MOF/COF. In additional, the selectively is high when other concurrent anions are exist. The anionic dyes with different sizes including methyl orange, acid orange A, congo red, as well as methyl blue can be adsorbed by SCNU-Z1-Cl in few minutes to about 1 h. The adsorption capacities for them are 285, 180, 585, and 262 mg/g, respectively. In contrast, the adsorption kinetics for catinionic dyes with different sizes is obviously lower and exhibit a size-selectively adsorption that only cationic dye with suitable size (rhodamine B) can be adsorbed by SCNU-Z1-Cl. Consequently, SCNU-Z1-Cl can sepearate organic dyes in three different modes: size-dependent, charge-dependent, and kinetics-dependent selective adsorption. The excellent adsorption and separation properties of SCNU-Z1-Cl is attribute to the cationic framework, large tubular channel, as well as the high positive Zeta potential.

An Anionic Nanotubular Metal-Organic Framework for High-Capacity Dye Adsorption and Dye Degradation in Darkness.

A metal-organic framework (MOF), named SCNU-Z2, based on a new heterotopic tripodal nitrogen-containing ligand, has been constructed. Due to the replacement of one imidazole group in the reported ligand with one tetrazole group, the charge of the framework is changed from cationic to anionic but retains the same framework structure. The framework consists of tubular channels with a diameter of 1.5 nm and exhibits satisfactory stability in water with a pH range of 3-11. The anionic nature of the framework allows the effective adsorption of the cationic dyes MLB, CV, and RhB with capacities of 455.6, 847.4, and 751.8 mg/g, respectively. Among them, the adsorption capacities for SCNU-Z2 on CV and RhB rank as the highest when compared with other reported MOFs. In contrast, SCNU-Z2 exhibits an extremely low capacity for anionic dyes MO and AO, making it useful for the separation of anionic and cationic dyes based on a charge-dependent mode. Interestingly, SCNU-Z2 can be used to degrade an anionic dye, MB, within 30 min under darkness at room temperature. The apparent activation energy of the dye degradation reaction is calculated to be approximately 18.96 kJ·mol-1, implying that the catalytic reaction of MB can be considered as a low-temperature thermocatalytic reaction in the dark/SCNU-Z2 system.

Dimension Increase via Hierarchical Hydrogen Bonding from Simple Pincer-like Mononuclear complexes.

A tetradentate symmetric ligand bearing both coordination and hydrogen bonding sites, N(1),N(3)-bis(1-(1H-benzimidazol-2-yl)-ethylidene)propane-1,3-diamine (H2bbepd) was utilized to synthesize a series of transition metal complexes, namely [Co(H2bbepd)(H(2)O)2]·2ClO(4) (1), [Cu(H2bbepd)(OTs(-))]·OTs(-) (2),[Cu(bbepd)(CH(3)OH)] (3), [Cd(H(2)bbepd)(NO3)2]·CH(3)OH (4), [Cd(H(2)bbepd)(CH(3)OH)Cl]·Cl (5), and [Cd(bbepd)(CH(3)OH)2] (6). These complexes show similar discrete pincer-like coordination units, possessing different arrangements of hydrogen bonding donor and acceptor sites. With or without the aid of uncoordinated anions and solvent molecules, such mononuclear units have been effectively involved in the construction of hierarchical hydrogen bonding assemblies (successively via level I and level II), leading to discrete binuclear ring (complex 2), one-dimensional chain or ribbon (complexes 3, 4 and 6) and two-dimensional layer (complexes 1 and 5) aggregates.

Metal-organic framework derived heterostructured phosphide bifunctional electrocatalyst for efficient overall water splitting.

Developing high active and stable cost-effective bifunctional electrocatalysts for overall water splitting to produce hydrogen is of vital significance in clean and sustainable energy development. This work has prepared a novel porous unreported MOF (Ni-DPT) as a precursor to successfully synthesize a non-noble bifunctional NiCoP/Ni12P5@NF electrocatalyst through doping strategy and interface engineering. This catalyst is constructed by layered self-supporting arrays with heterojunction interface and rich nitrogen-phosphorus doping. Structural characterizations and the density function theory (DFT) calculations confirm that the interface effect of NiCoP/Ni12P5 heterojunction can regulate the electronic structure of the catalyst to optimize the Gibbs free energy of hydrogen (ΔGH*); simultaneously, the defect-rich layered nanoarrays can expose more active sites, shorten mass transfer distance, and generate a self-supporting structure for in-situ reinforcing the structural stability. As a result, this NiCoP/Ni12P5@NF catalyst exhibits favorable electrocatalytic performance, which simply needs overpotentials of 100 mV for HER and 310 mV for OER, respectively, at a current density of 10 mA·cm-2. The anion exchange membrane electrolyzer assembled with this NiCoP/Ni12P5@NF as both anode and cathode catalysts can operate stably for 200 h at a current density of 100 mA·cm-2 with an insignificant voltage decrease. This work may provide some inspiration for the further rational design of inexpensive non-noble multifunctional electrocatalysts and electrode materials for water splitting to generate hydrogen.

Hierarchical porous amorphous metal-organic frameworks constructed from ZnO/MOF glass composites.

For the first time, hierarchical porous amorphous metal-organic frameworks (HP-aMOFs) containing ultramicropores, micropores, and mesopores were synthesized by etching a composite of MOF glass (agZIF-76) and ZnO using ammonia. These materials show potential applications in the adsorption of C2 hydrocarbons.

Effect of chromatographic conditions on enantioseparation of bovine serum albumin chiral stationary phase in HPLC and thermodynamic studies.

Twelve chiral compounds were enantiomerically resolved on bovine serum albumin chiral stationary phase (BSA-CSP) by high-performance liquid chromatography (HPLC) in reversed-phase modes. Chromatographic conditions such as mobile phase pH, the percentage of organic modifier, and concentration of analyte were optimized for separation of enantiomers. For N-(2, 4-dinitrophenyl)-serine (DNP-ser), the retention factors (k) greatly increase from 0.81 to 6.23 as the pH decreasing from 7.21 to 5.14, and the resolution factor (R(s)) exhibited a similar increasing trend (from 0 to 1.34). More interestingly, the retention factors for N-(2, 4-dinitrophenyl)-proline (DNP-pro) decrease along with increasing 1-propanol in mobile phase (3%, 5%, 7% and 9% by volume), whereas the resolution factor shows an upward trend (from 0.96 to 2.04). Moreover, chiral recognition mechanisms for chiral analytes were further investigated through thermodynamic methods.

A mixed-ligand Co(II) MOF synthesized from a single organic ligand to capture iodine and methyl iodide vapour.

Mixed-ligand metal-organic frameworks (MOFs) are usually synthesized from two or more organic ligands as initial reactants, and MOFs synthesized from one organic ligand precursor through partial in situ reactions remain very limited. Herein, by introducing an imidazole-tetrazole bifunctional ligand, 5-(4-imidazol-1-yl-phenyl)-2H-tetrazole (HIPT), as a single ligand and performing in situ hydrolysis of the tetrazolium group, a mixed-ligand Co(II)-MOF based on HIPT and 4-imidazol-1-yl-benzoic acid (HIBA), [Co2(µ3-O)(IPT)(IBA)]·x solvent (Co-IPT-IBA), was constructed and applied to capture I2 and methyl iodide vapours. Single crystal structural analyses reveal that Co-IPT-IBA exhibits a 3D porous framework with 1D channels based on the relatively few reported ribbon-like rod SBUs. The nitrogen adsorption-desorption isotherms indicate that the BET surface area of Co-IPT-IBA is 168.5 m2 g-1 and it possesses both micropores and mesopores. Due to its porosity, nitrogen-rich conjugated aromatic rings, and Co(II) ions, Co-IPT-IBA was applied to capture iodine molecules in vapour and exhibited an adsorption capacity of 2.88 g g-1. By combining the IR, Raman, XPS and grand canonical Monte Carlo (GCMC) simulation results, it was deduced that the tetrazole ring, coordination water molecules, and the redox potential of Co3+/Co2+ facilitate iodine capture. The presence of mesopores was also responsible for the high iodine adsorption capacity. In addition, Co-IPT-IBA showed the ability to capture methyl iodide in vapours with a moderate capacity of 625 mg g-1. The transformation of crystalline Co-IPT-IBA to amorphous MOFs may be due to the methylation reaction. This work represents a relatively rare example of methyl iodide adsorption by MOFs.

Metal-organic framework derived FeNi alloy nanoparticles embedded in N-doped porous carbon as high-performance bifunctional air-cathode catalysts for rechargeable zinc-air battery.

Developing efficient and durable bifunctional air-cathode catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key efforts promoting the practical rechargeable zinc-air batteries (ZABs). In this paper, high-performance bifunctional air-cathode catalysts by a two-step strategy: atomically dispersed Ni on N-doped carbon is first derived from MOF to form uniformly dispersed NiNC, which are pyrolyzed together with Fe source at different high-temperatures to form FeNi@NC-T (T = 800, 900, and 1000 °C) catalysts. The as-synthesized non-noble metal FeNi@NC-900 catalyst exhibits a considerably small potential gap (ΔE) of 0.72 V between ORR and OER, which is as the same as commercial noble metal Pt/C + Ir black mixed catalyst. The performance of the ZABs using FeNi@NC-900 as the air-cathode catalyst displays a power density of 119 mW·cm-2 and a specific capacity of 830.1 mAh·g-1, which is superior to that of Pt/C + Ir black mixed catalyst. This work provides a guideline for designing alloy electrocatalysts with uniform size and nanoparticle distribution for metal-air batteries with bifunctional air-cathodes.

Porous amorphous metal-organic frameworks based on heterotopic triangular ligands for iodine and high-capacity dye adsorption.

The research on amorphous metal-organic frameworks (aMOFs) is still in its infancy, and designing and constructing aMOFs with functional pores remains a challenge. Two aMOFs based on Co(II) and heterotopic triangular ligands with large conjugated aromatic planes, namely aMOF-1 and aMOF-2, were constructed and characterized by IR, XPS, EA, ICP, XANS and so on. aMOF-1 possesses mesopores, whereas aMOF-2 possesses micropores. The porosity, conjugated aromatic plane and uncoordinated N atoms in the framework allow these aMOFs to adsorb iodine and dyes. The iodine adsorption capacity of aMOF-1 is 3.3 g per g, which is higher than that of aMOF-2 (0.56 g per g), mainly due to the expansion or swelling of aMOF-1 after iodine adsorption. The uptake of cationic dyes by aMOF-2 showed more rapid kinetics and a higher removal rate than that by aMOF-1, mainly due to the difference in the porosity and surface charge. Although the surface charges of aMOF-1 and aMOF-2 are negative, both of them showed significantly faster adsorption kinetics toward anionic dyes, among which methyl orange (MO) and Congo red (CR) can be removed in 5 min. This occurs possibly because the quick adsorption of Na+ ions alters the surface charge of the framework and promotes dye uptake. The adsorption capacities of aMOF-1 for MO and CR reached 921 and 2417 mg g-1, respectively. The correlation data for aMOF-2 are 1042 and 1625 mg g-1, respectively. All adsorption capacities are among the highest compared to many cMOFs. Adsorption in mixed dye solution is found to be charge-dependent, kinetic-dependent, and synergetic in these systems. The porosity, surface charge regulation during adsorption, weak interactions and multiple adsorption processes contribute to the dye adsorption performance.

Encapsulation of a metal-organic cage-based porous salt in silica nanopores.

A metal-organic cage (MOC)-based porous salt composed of cationic Zr-MOC and anionic Cu-MOC was incorporated into SBA-15 nanopores via a two-step impregnation method for the first time. The encapsulated MOC-based porous salt showed improved iodine adsorption capacity when compared with the bulk sample.

A new biosensor for chiral recognition using goat and rabbit serum albumin self-assembled quartz crystal microbalance.

Quartz crystal microbalance (QCM) biosensor was used for the chiral recognition of five pairs of enantiomers by using goat serum albumin (GSA) and rabbit serum albumin (RbSA) as chiral selectors. Serum albumin (SA) was immobilized on the QCM through the self-assembled monolayer technique, and the surface concentration of GSA and RbSA were 8.8 × 10(-12) mol cm(-2) and 1.2 × 10(-11) mol cm(-2) , respectively. The QCM biosensors showed excellent sensitivity and selectivity. Meanwhile, the chiral recognition of SA sensors was quite species dependent. There were differences between GSA and RbSA sensors in the ability and the preference of chiral recognition. To R,S-1,2,3,4-tetrahydro-1-naphthylamine (R,S-1-TNA), R,S-1-(4-methoxyphenyl)ethylamine (R,S-4-MPEA), and R,S-1-(3-methoxyphenyl)ethylamine (R,S-3-MPEA), the preference of the stereoselective SA-drug binding of the two kinds of SA sensors were consistent. However, to R,S-2-octanol (R, S-2-OT) and R,S-methyl lactate (R,S-MEL), the two kinds of SA sensors had opposite chiral recognition preference. Moreover, the interactions of SA and the five pairs of enantiomers have been further investigated through ultraviolet (UV) and fluorescent (FL) spectra. The UV/FL results were in accordance with the consequence of QCM.

A new two-dimensional cadmium coordination polymer with 1H-imidazole-4-carboxylate and oxalate.

The title compound, poly[aqua(µ(2)-1H-imidazole-4-carboxylato-κ(3)N(3),O:O')hemi(µ(2)-oxalato-κ(4)O(1),O(2):O(1'),O(2'))cadmium(II)], [Cd(C(4)H(3)N(2)O(2))(C(2)O(4))(0.5)(H(2)O)](n), exhibits a two-dimensional network. The Cd(II) cation is coordinated to one N atom and two carboxylate O atoms from two 1H-imidazole-4-carboxylate (Himc) ligands, two carboxylate O atoms from the bridging oxalate anion and one ligated water molecule; these six donor atoms form a distorted octahedral configuration. The oxalate anion lies on a centre of inversion. The Himc ligands connect the Cd(II) cations to form -Cd-Himc-Cd-Himc-Cd- zigzag chains, with a Cd···Cd separation of 5.8206 (6) Å along the b direction, which are further linked by tetradentate oxalate anions to generate a two-dimensional herringbone architecture in the ab plane. These layers are extended to form a three-dimensional supramolecular framework via O-H···O and N-H···O hydrogen bonds and π-π stacking interactions. The solid-state photoluminscent behaviour of the title compound has been investigated at room temperature.

Poly[aqua(µ(3)-5-aza-niumylisophthalato)-(µ-oxalato)neodymium(III)].

The title compound, [Nd(C(8)H(6)NO(4))(C(2)O(4))(H(2)O)](n), is a layer-like coordination polymer. The Nd(III) ion is coordinated by four carboxyl-ate O atoms from three bridging 5-aza-nium-yl-isophthalate (Haip) ligands, four carboxyl-ate O atoms from two oxalate (ox) anions and one ligated water mol-ecule in a tricapped trigonal-prismatic geometry. The Haip anion acts as a µ(3)-bridge, connecting three Nd(III) ions through two carboxyl-ate groups; the ox anion adopts a bis-bidentate-bridging mode, linking two Nd(III) ions. The layer framework is further extended to a three-dimensional supra-molecular structure through N-H⋯O and O-H⋯O hydrogen bonds.

Strategies for the Construction of Functional Materials Utilizing Presynthesized Metal-Organic Cages (MOCs).

Metal-organic cages (MOCs) that assemble from metal ions or metal clusters and organic ligands have attracted the interest of the scientific community because of their various functional coordination cavities. Unlike metal-organic frameworks (MOFs) with infinite frameworks, MOCs have discrete structures, making them soluble and stable in certain solvents and facilitating their application as starting reagents in the further construction of single components or composite materials. In recent years, increasing progress has been made in this field. In this review, we introduce these works from the perspective of design strategies, and focus on how presynthesized MOCs can be used to construct functional materials. Finally, we discuss the challenges and development prospects in this field.

Amorphous metal-organic frameworks obtained from a crystalline precursor for the capture of iodine with high capacities.

Two amorphous metal-organic frameworks (aMOFs) were obtained from crystalline Co-MOF (SCNU-Z6) via temperature-induced (aT-SCNU-Z6) and water-immersed (aW-SCNU-Z6) approaches. They exhibited high iodine uptake, with the adsorption capacities of aT-SCNU-Z6 and aW-SCNU-Z6 reaching 2.05 and 5.04 g g-1, respectively. This work is the first report of iodine uptake by aMOFs.

Fabrication of cellulose derivative coated spherical covalent organic frameworks as chiral stationary phases for high-performance liquid chromatographic enantioseparation.

Porous spherical silica-based chiral stationary phases (CSPs) have been commercially used in the field of chiral separation, however, the scope of their application is, to some extent, limited by the instability of silica towards mobile phase containing strong base or acid. As such, developing new matrix-based CSPs is one of the effective strategies to overcome this bottleneck in studies of chiral separation materials. In this work, we have demonstrated that stable spherical covalent organic frameworks (SCOFs) can be utilized as matrixes for the fabrication of new CSPs for the first time. Specifically, a porous imine-linked SCOF with good crystallinity, large surface area, and high chemical stability is synthesized at room temperature. Then, cellulose-tris (3,5-dimethylphenylcarbamate) (CDMPC), a typical cellulose derivative, is selected as a potential chiral selector and coated onto the robust SCOFs, giving rise to the fabrication of new CDMPC@SCOF CSPs. The as-synthesized stable SCOF-based CSPs are exploited for high-performance liquid chromatographic (HPLC) enantioseparation, showing high resolution abilities for the separation of racemic compounds such as metalaxyl, 1-(1-naphthalenyl)ethanol, epoxiconazol, trans-stilbene oxide, and so on. Moreover, the prepared SCOF-based CSPs exhibit more superior acid and base stability than those of the silica-based CSPs. Our work not only uncovers the great potential of SCOFs as matrixes for constructing novel CSPs, but also expands the application of COFs in the field of enantiomeric separation under harsh base and acid conditions.