Large-Area Conductive MOF Ultrathin Film Controllably Integrating Dinuclear-Metal Sites and Photosensitizers to Boost Photocatalytic CO2 Reduction with H2O as an Electron Donor.

Owing to the electrical conductivity and periodic porosity, conductive metal-organic framework (cMOF) ultrathin films open new perspectives to photocatalysis. The space-selective assembly of catalytic sites and photosensitizers in/on cMOF is favorable for promoting the separation of photogenerated carriers and mass transfer. However, the controllable integration of functional units into the cMOF film is rarely reported. Herein, via the synergistic effect of steric hindrance and an electrostatic-driven strategy, the dinuclear-metal molecular catalysts (DMC) and perovskite (PVK) quantum dot photosensitizers were immobilized into channels and onto the surface of cMOF ultrathin films, respectively, affording [DMC@cMOF]-PVK film photocatalysts. In this unique heterostructure, cMOF not only facilitated the charge transfer from PVK to DMC but also guaranteed mass transfer. Using H2O as an electron donor, [DMC@cMOF]-PVK realized a 133.36 µmol·g-1·h-1 CO yield in photocatalytic CO2 reduction, much higher than PVK and DMC-PVK. Owing to the excellent light transmission of films, multilayers of [DMC@cMOF]-PVK were integrated to increase the CO yield per unit area, and the 10-layer device realized a 1115.92 µmol·m-2 CO yield in 4 h, which was 8-fold higher than that of powder counterpart. This work not only lightens the development of cMOF-based composite films but also paves a novel avenue for an ultrathin film photocatalyst.

Metal-Organic Framework-Based Hetero-Phase Nanostructure Photocatalysts with Molecular-Scale Tunable Energy Levels.

As an effective method to modulate the physicochemical properties of materials, crystal phase engineering, especially hetero-phase, plays an important role in developing high-performance photocatalysts. However, it is still a huge challenge but significant to construct porous hetero-phase nanostructures with adjustable band structures. As a kind of unique porous crystalline materials, metal-organic frameworks (MOFs) might be the appropriate candidate, but the MOF-based hetero-phase is rarely reported. Herein, we developed a secondary building unit (SBU) regulating strategy to prepare two crystal phases of Ti-MOFs constructed by titanium and 1,4-dicarboxybenzene, i.e., COK and MIL-125. Besides, COK/MIL-125 hetero-phase was further constructed. In the photocatalytic hydrogen evolution reaction, COK/MIL-125 possessed the highest H2 yield compared to COK and MIL-125, ascribing to the Z-Scheme homojunction at hetero-phase interface. Furthermore, by decorating with amino groups (i.e., NH2-COK/NH2-MIL-125), the light absorbing capacity was broadened to visible-light region, and the visible-light-driven H2 yield was greatly improved. Briefly, the MOF-based hetero-phase possesses periodic channel structures and molecularly adjustable band structures, which is scarce in traditional organic or inorganic materials. As a proof of concept, our work not only highlights the development of MOF-based hetero-phase nanostructures, but also paves a novel avenue for designing high-performance photocatalysts.

Construction of UiO-66-NH2 decorated by MoS2 QDs as photocatalyst for rapid and effective visible-light driven Cr(VI) reduction.

The photoactive metal-organic frameworks (MOFs) are good candidates for photocatalysts, but the quick electron-hole pairs recombination has greatly restricted the photocatalytic ability of MOFs. To improve the photoactivity of MOFs, MOFs-based composite materials have been extensively studied. Here, we successfully integrated MoS2 quantum dots (QDs) with UiO-66-NH2 for the first time under hydrothermal conditions. The as-prepared MoS2 QDs/UiO-66-NH2 (MS-U) had good visible light response ability (absorption edge at 445 nm), and charge separation and transfer ability, which lays the foundation for the photocatalytic Cr(VI) reduction. Photocatalytic studies revealed that MoS2 QDs-5/UiO-66-NH2 (MS-U-5) had superior Cr(VI) reduction activity than pure MoS2 QDs and UiO-66-NH2. MS-U-5 could remove 98% Cr(VI) at pH= 2 with visible light irradiation for 20 min, which is the fastest visible light driven Cr(VI) reduction rate among the reported MOFs-based composite photocatalysts without the presence of any cocatalysts or scavengers as far as we know. Importantly, MS-U-5 could be reused at least three times. In the end, the possible electron transfer path and mechanism of Cr(VI) reduction was also investigated.

One-step hydrothermal synthesis of WS2 quantum dots as fluorescent sensor for sensitive and selective recognition of hemoglobin and cardiac biomarker myoglobin.

Transition metal dichalcogenide (TMD) dots exhibit excellent photoluminescence performance due to the quantum confinement effect and edge effect, and are extensively applied in electronic and optical devices, sensors, catalysis, and bioimaging. In this work, WS2 quantum dots (WS2 QDs) were prepared under a simple one-step hydrothermal method by optimizing the reaction conditions, and a quantum yield of 11.23% was achieved. The as-prepared WS2 QDs possess good photo-bleaching resistance, salt tolerance, and pH stability. The fluorescence investigations showed that the WS2 QDs acted as a highly efficient fluorescent sensor to detect hemoglobin (Hb) and cardiac biomarker myoglobin (Myo). The linear range was 1-600 µg/mL for Hb and 0.01-120 µg/mL for Myo, with detection limits as low as 260 and 7.6 ng/mL, respectively. Importantly, the WS2 QDs were used to determine the Hb/Myo content in human blood/serum samples, with satisfactory results, indicating that this technique holds promise for application in clinical diagnosis associated with Hb/Myo levels. To the best of our knowledge, this is the first example of TMD QDs without any modification as a fluorescent sensor for detecting Hb and Myo simultaneously.

Polymer-Assisted Space-Confined Strategy for the Foot-Scale Synthesis of Flexible Metal-Organic Framework-Based Composite Films.

At the gas-liquid interface, the confined synthesis of metal-organic framework (MOF) films has been extensively developed by spreading an ultrathin oil layer on the aqueous surface as a reactor. However, this interface is susceptible to various disturbances and incapable of synthesizing large-area crystalline MOF films. Herein, we developed a polymer-assisted space-confined strategy to synthesize large-area films by blending poly(methyl methacrylate) (PMMA) into the oil layer, which improved the stability of the gas-liquid interface and the self-shrinkage of the oil layer on the water surface. Meanwhile, the as-synthesized MOFs as a quasi-solid substrate immobilized the edge of the oil layer, which maintained a large spreading area. Thanks to this synergistic effect, we synthesized the freestanding MOF-based film with a foot-level (0.66 ft) lateral dimension, which is the largest size reported so far. Besides, due to the phase separation of the two components, the MOF-PMMA composite film combined the conductivity of MOFs (1.13 S/m) with the flexibility of PMMA and exhibited excellent mechanical properties. More importantly, this strategy could be extended to the preparation of other MOFs, coordination polymers (CPs), and even inorganic material composite films, bringing light to the design and large-scale synthesis of various composite films for practical applications.

Water Stable [Tb4] Cluster-Based Metal-Organic Framework as Sensitive and Recyclable Luminescence Sensor of Quercetin.

A novel 3D metal-organic framework (MOF){[Tb3(CBA)2(HCOO)(µ3-OH)4(H2O)]·2H2O·0.5DMF} n (S-1) was synthesized by the solvothermal method. The crystal structure indicates that [Tb4O4] cubane clusters self-assemble into an infinite chain by sharing vertex, which is further linked to adjacent chains through 1,1-cyclobutanedicarboxylic acid ligand (H2CBA), resulting in a honeycomb arrayed framework. S-1 possesses excellent water stability and still retains intact structure after exposure to water for 10 weeks or boiling water for 10 weeks. Interestingly, S-1 acts as a luminescence sensor to selectively and sensitively detect quercetin with the limit of detection (LOD) as low as 0.23 ppm (7.6 × 10-7 M). The relationship between relative luminescence intensity and concentration obeys linear in the range of 0-300 ppm (0-993 µM), which allows quantitative detection of quercetin. Importantly, S-1 can be reused at least six times with almost no change in luminescent intensity. Compared with the high performance liquid chromatography-mass spectrometry (HPLC-MS) method, S-1 was used to determine the content of quercetin in onionskin and apple peel samples with satisfactory results. Furthermore, a portable S-1 test paper is also developed and expected to be applied in practice. To our knowledge, S-1 is the first example of MOFs as luminescent sensor for quercetin.

Construction of Large-Area Ultrathin Conductive Metal-Organic Framework Films through Vapor-Induced Conversion.

On account of unique characteristics, the integration of metal-organic frameworks as active materials in electronic devices attracts more and more attention. The film thickness, uniformity, area, and roughness are all fatal factors limiting the development of electrical and optoelectronic applications. However, research focused on ultrathin free-standing films is in its infancy. Herein, a new method, vapor-induced method, is designed to construct centimeter-sized Ni3 (HITP)2 films with well-controlled thickness (7, 40, and 92 nm) and conductivity (0.85, 2.23, and 22.83 S m-1 ). Further, traditional transfer methods are tactfully applied to metal-organic graphene analogue (MOGA) films. In order to maintain the integrity of films, substrates are raised up from bottom of water to hold up films. The stripping method greatly improves the surface roughness Rq (root mean square roughness) without loss of conductivity and endows the film with excellent elasticity and flexibility. After 1000 buckling cycles, the conductance shows no obvious decrease. Therefore, the work may open up a new avenue for flexible electronic and magnetic devices based on MOGA.

Highly Selective Enamination of ß-ketoesters Catalyzed by Interlocked [Cu8 ] and [Cu18 ] Nanocages.

Interlocking cages are of great interest due to their fascinating structures and potential applications. However, the interlocking of different cages has not been previously reported. Herein, quadruply interlocked [Cu8 ] and [Cu18 ] nanocages have been constructed and structurally characterized in cationic metal-organic framework {[CuI Cu4 II (XN)4 (PTA)4 (H2 O)4 ]0.5 SO4 ⋅5 H2 O⋅EtOH}n (1). 1 can trap the anionic pollutant CrO4 2- and the radioactive-contaminant simulant ReO4 - with an uptake capacity of 83.2 and 218 mg g-1 , respectively. Catalytic investigations reveal 1 is an efficient heterogeneous catalyst for the enamination of ethyl acetoacetate with aniline and the turnover frequency (TOF) can reach a record value of 4000 h-1 . More importantly, 1 represents the first of a catalyst of enamination to exhibit excellent size selectivity on different substrates. The robust catalyst can be reused at least ten times without obvious loss in catalytic activity.

Wheel-like Ln18 Cluster Organic Frameworks for Magnetic Refrigeration and Conversion of CO2.

Two isostructural 2D MOFs ([Ln7(CDA)6(HCOO)3(µ3-OH)6(H2O)8] n, abbreviated as 1-Gd and 2-Dy) were successfully synthesized under solvothermal conditions. The self-assembly of lanthanide(III) nitrate and 1,1'-cyclopropane-dicarboxylic acid (H2CDA) resulted in wheel-like Ln18 cluster second building units (SBU), which are further linked to six neighboring wheels to generate a 2D ordered honeycomb array. Both 1-Gd and 2-Dy exhibit high thermal stability and decompose above 330 °C. Moreover, they have good solvent stability in ten common solvents and pH stability with pH values from 1 to 13. Magnetic studies reveal that 1-Gd exhibits weak antiferromagnetic coupling between adjacent Gd3+ ions and has a large magnetocaloric effect of 47.30 J kg-1 K-1 (Δ H = 7.0 T at 2 K), while 2-Dy shows ferromagnetic interaction between adjacent Dy3+ ions. Interestingly, 1-Gd and 2-Dy can catalyze the cycloaddition of CO2 to epoxides under mild conditions and can be reused at least five rounds with negligible loss of catalytic performance.

Effective and Selective Catalysts for Cinnamaldehyde Hydrogenation: Hydrophobic Hybrids of Metal-Organic Frameworks, Metal Nanoparticles, and Micro- and Mesoporous Polymers.

Metal-organic frameworks (MOFs) as selectivity regulators for catalytic reactions have attracted much attention, especially MOFs and metal nanoparticle (NP) shelled structures, e.g., MOFs@NPs@MOFs. Nevertheless, making hydrophilic MOF shells for gathering hydrophobic reactants is challenging. Described here is a new and viable approach employing conjugated micro- and mesoporous polymers with iron(III) porphyrin (FeP-CMPs) as a new shell to fabricate MIL-101@Pt@FeP-CMP. It is not only hydrophobic and porous for enriching reactants, but also possesses iron sites to activate C=O bonds, thereby regulating the selectivity for cinnamyl alcohol in the hydrogenation of cinnamaldehyde. Interestingly, MIL-101@Pt@FeP-CMPsponge can achieve a high turnover frequency ( 1516.1 h-1 ), with 97.3 % selectivity for cinnamyl alcohol at 97.6 % conversion.

Bimetal-organic frameworks for functionality optimization: MnFe-MOF-74 as a stable and efficient catalyst for the epoxidation of alkenes with H2O2.

In this work, we synthesized a series of microcrystalline MnxN100-x-MOF-74 (N = Fe, Co and Ni) materials by a one-pot reaction. Powder X-ray diffraction (PXRD) patterns of MnxN100-x-MOF-74 matched well with those of single-metal MOF-74, and the scanning electron microscopy (SEM) images exhibited homogeneous nanocrystallites aggregated together. The amounts and dispersion of metals were analyzed by using inductively coupled plasma (ICP) and energy-dispersive X-ray spectroscopy (EDS), separately. MnxN100-x-MOF-74 could remain crystalline and efficiently catalyze the epoxidation of alkenes in DMF with NaHCO3 and 30% H2O2. In particular, Mn29.39Fe70.61-MOF-74 can achieve almost 100% conversion for styrene with 95.0% selectivity towards styrene oxide and be reused at least five times without loss of activity.

A unique zinc-organic framework constructed through in situ ligand synthesis for conversion of CO2 under mild conditions and as a luminescence sensor for Cr2O72-/CrO42.

A novel zinc-organic framework, {[Zn3(tza)2(µ2-OH)2(H2O)2]·H2O}n (1) (H2tza = 1H-tetrazolate-5-acetic acid), was synthesized through an in situ generated tetrazole ligand under hydrothermal conditions. In compound 1, tza2- ligands and Zn2+ are interlinked to form 2D layers, which are further pillared through µ2-OH groups to generate a 3D framework. Thermogravimetric analysis and powder X-ray diffraction confirm that 1 has high thermal stability, pH stability and solvent stability. Catalytic studies show that 1 exhibits excellent catalytic ability for the cycloaddition of CO2 with epoxides under 50 °C and 0.1 MPa. Importantly, 1 can be reused at least six times. Furthermore, luminescence investigations indicate that 1 can serve as a recyclable luminescence sensor to efficiently detect Cr2O72-/CrO42-, and the detection limit can reach 10-6 mol L-1 and 4 × 10-6 mol L-1, respectively.