Electrocatalytic Reduction of Carbon Dioxide in Acidic Electrolyte with Superior Performance of a Metal-Covalent Organic Framework over Metal-Organic Framework.

CO2 electroreduction (CO2RR) to generate valuable chemicals in acidic electrolytes can improve the carbon utilization rate in comparison to that under alkaline conditions. However, the thermodynamically more favorable hydrogen evolution reaction under an acidic electrolyte makes the CO2RR a big challenge. Herein, robust metal phthalocyanine(Pc)-based (M = Ni, Co) conductive metal-covalent organic frameworks (MCOFs) connected by strong metal tetraaza[14]annulene (TAA) linkage, named NiPc-NiTAA and NiPc-CoTAA, are designed and synthesized to apply in the CO2RR in acidic electrolytes for the first time. The optimal NiPc-NiTAA exhibited an excellent Faradaic efficiency (FECO) of 95.1% and a CO partial current density of 143.0 mA cm-2 at -1.5 V versus the reversible hydrogen electrode in an acidic electrolyte, which is 3.1 times that of the corresponding metal-organic framework NiPc-NiN4. The comparison tests and theoretical calculations reveal that in-plane full π-d conjugation MCOF with a good conductivity of 3.01 × 10-4 S m-1 accelerates migration of the electrons. The NiTAA linkage can tune the electron distribution in the d orbit of metal centers, making the d-band center close to the Fermi level and then activating CO2. Thus, the active sites of NiPc and NiTAA collaborate to reduce the *COOH formation energy barrier, favoring CO production in an acid electrolyte. It is a helpful route for designing outstanding conductive MCOF materials to enhance CO2 electrocatalysis under an acidic electrolyte.

Br, O-Modified Cu(111) Interface Promotes CO2 Reduction to Multicarbon Products.

Electrochemical reduction of CO2 to multicarbon (C2+) products with added value represents a promising strategy for achieving a carbon-neutral economy. Precise manipulation of the catalytic interface is imperative to control the catalytic selectivity, particularly toward C2+ products. In this study, a unique Cu/UIO-Br interface is designed, wherein the Cu(111) plane is co-modified simultaneously by Br and O from UIO-66-Br support. Such Cu/UIO-Br catalytic interface demonstrates a superior Faradaic efficiency of ≈53% for C2+ products (ethanol/ethylene) and the C2+ partial current density reached 24.3 mA cm-2 in an H-cell electrolyzer. The kinetic isotopic effect test, in situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory calculations have been conducted to elucidate the catalytic mechanism. The Br, O co-modification on the Cu(111) interface enhanced the adsorption of CO2 species. The hydrogen-bond effect from the doped Br atom regulated the kinetic processes of *H species in CO2RR and promoted the formation of *COH intermediate. The formed *COH facilitates the *CO-*COH coupling and promotes the C2+ selectivity finally. This comprehensive investigation not only provides an in-depth study and understanding of the catalytic process but also offers a promising strategy for designing efficient Cu-based catalysts with exceptional C2+ products.

Rational Design of Electron Transfer Kineties of CdS/Zn(impim) Dots-on-Rods for Efficient Visible-Light Reduced C-X Bond.

Halogenated organic compounds are a kind of common environmental pollutants. Photocatalytic dehalogenation of C-halogen (C-X) bonds to C-H bonds can not only control environmental pollution but also realize important organic conversion reactions. However, the electron transfer kinetics of photocatalytic reduction of the C-X bond for semiconductor/MOF composites has remained unexplored. Herein, we successfully synthesized CdS/Zn(impim) (MOF) dots-on-rods composite photocatalyst under mild conditions. Zn(impim) MOF consists of Zn(µ-N)4 clusters and imidazole derivative ligands. Zn(impim), as a carrier, is beneficial to the dispersion of CdS nanoparticles and avoiding the agglomeration of CdS nanoparticles. The photocatalytic performance of CdS/Zn(impim) composites for the reduction of the C-X bond is much higher than that of pure CdS or Zn(impim). This high activity is due to the high electron separation efficiency of CdS assisted by Zn(impim). Under visible light irradiation, Zn(impim) is not excited due to its wide band gap of 3.26 eV. Through metal-to-ligand charge transfer of Zn(µ-N)4 clusters, Zn(impim) accepts excited electrons from CdS because the Fermi energy level of CdS is more negative by Kelvin probe force microscopy. Moreover, fluorescence spectrum and femtosecond transient absorption spectroscopy reveal the related electron transfer kinetics in detail. In addition, the inherent porous structure of MOFs is beneficial to the adsorption of halogenated hydrocarbons, providing a suitable environment for the dehalogenation reaction, thus improving the activity. This work can further understand the electron transfer mechanism in semiconductor/MOF composites for photocatalytic halide dehalogenation.

Dual-Emitting UiO-66(Zr&Eu) Metal-Organic Framework Films for Ratiometric Temperature Sensing.

A novel dual-emitting metal-organic framework based on Zr and Eu, named as UiO-66(Zr&Eu), was built using a clever strategy based on secondary building units. With the use of polymers, the obtained UiO-66(Zr&Eu) was subsequently deposited as thin films that can be utilized as smart thermometers. The UiO-66(Zr&Eu) polymer films can be used for the detection of temperature changes in the range of 237-337 K due to the energy transfer between the lanthanide ions (Eu in clusters) and the luminescent ligands, and the relative sensitivity reaches 4.26% K-1 at 337 K. Moreover, the sensitivity can be improved to 19.67% K-1 by changing the film thickness. In addition, the temperature-sensing performance of the films is superior to that of the powders, and the sensor can be reused 3 times without loss of performance.

C-QDs@UiO-66-(COOH)2 Composite Film via Electrophoretic Deposition for Temperature Sensing.

Temperature plays a crucial role in both scientific research and industry. However, traditional temperature sensors, such as liquid-filled thermometers, thermocouples, and transistors, require contact to obtain heat equilibrium between the probe and the samples during the measurement. In addition, traditional temperature sensors have limitations when being used to detect the temperature change of fast-moving samples at smaller scales. Herein, the carbon quantum dots (C-QDs) functionalized metal-organic framework (MOF) composite film, a novel contactless solid optical thermometer, has been prepared via electrophoretic deposition (EPD). Instead of terephthalic acid (H2BDC), 1',2',4',5'-benzenetetracarboxylic (H4BTEC) acid was employed to construct a UiO-66 framework to present two uncoordinated carboxylic groups decorated on the pore surface. The uncoordinated carboxylic groups can generate negative charges, which facilitates the deposition of film on the positive electrode during the EPD process. Moreover, UiO-66-(COOH)2 MOFs can absorb C-QDs from the solution and prevent C-QDs from aggregating, and the well-dispersed C-QDs impart fluorescence characteristics to composites. As-synthesized composite film was successfully used to detect temperature change in the range of 97-297 K with a relative sensitivity up to 1.3% K-1 at 297 K.

Preparation of Dual-Emitting Ln@UiO-66-Hybrid Films via Electrophoretic Deposition for Ratiometric Temperature Sensing.

Engineering novel dual-emitting metal-organic frameworks (MOFs) with wide emission ranges for application as ratiometric temperature sensors is still a challenge. In this paper, two novel dual-emitting MOFs with intergrated lanthanide metals and luminescent ligand in a UiO-66-type structure, named Ln@UiO-66-Hybrid, were prepared via the combination of postsynthetic modification and postsynthetic exchange methods. Subsequently, the as-synthesized MOFs were deposited onto fluorine tin oxide substrates through electrophoretic deposition by taking advantage of the charges from the unmodified carboxylic groups of the MOFs. The as-prepared Tb@UiO-66-Hybrid and Eu@UiO-66-Hybrid films were applied to detect temperature changes. The resulting Tb@UiO-66-Hybrid film exhibited good temperature-sensing properties with a relative sensitivity of up to 2.76% K-1 in the temperature range of 303-353 K. In addition, the Eu@UiO-66-Hybrid film showed excellent temperature-sensing performance based on the energy transfer between the luminescent ligand (H2NDC) and europium ions with a relative sensitivity of up to 4.26% K-1 in the temperature range of 303-403 K.

Facile and Rapid Growth of Nanostructured Ln-BTC Metal-Organic Framework Films by Electrophoretic Deposition for Explosives sensing in Gas and Cr 3+ Detection in Solution.

Until now, it has been a challenge to prepare lanthanide metal-organic framework films on traditional substrates, like zinc plate, indium oxide (ITO), and fluorine-doped tin oxide (FTO) glasses in a rapid and facile method. In this paper, continuous and dense Ln-BTC MOFs films on unmodified low-cost substrates have been rapidly and easily fabricated though the newly developed electrophoretic deposition (EPD) method in 5 min. Moreover, the as-prepared luminescent films were successfully used for the detection of nitrobenzene (NB), trinitrotoluene (TNT) in gas phases, as well as NB, Cr3+ ions for detection in solution.

Integration of metal-organic frameworks into an electrochemical dielectric thin film for electronic applications.

The integration of porous metal-organic frameworks onto the surface of materials, for use as functional devices, is currently emerging as a promising approach for gas sensing and flexible displays. However, research focused on potential applications in electronic devices is in its infancy. Here we present a facile strategy by which interpenetrated, crystalline metal-organic framework films are deposited onto conductive metal-plate anodes via in situ temperature-controlled electrochemical assembly. The nanostructure of the surface as well as the thickness and uniformity of the film are well controlled. More importantly, the resulting films exhibit enhanced dielectric properties compared to traditional inorganic or organic gate dielectrics. This study demonstrates the successful implementation of the rational design of metal-organic framework thin films on conductive supports with high-performance dielectric properties.

Patterned growth of luminescent metal-organic framework films: a versatile electrochemically-assisted microwave deposition method.

Electrochemically-assisted microwave deposition technology, a facile method for the fabrication of luminescent metal-organic framework (LMOF) films, is presented herein. This method was further developed into a versatile method for preparing patterned LMOF films. The strategy based on this method can spatially locate microcrystals of MOFs on a surface, which provides great promise in anti-counterfeiting barcode applications.

An Anion Metal-Organic Framework with Lewis Basic Sites-Rich toward Charge-Exclusive Cationic Dyes Separation and Size-Selective Catalytic Reaction.

Organic dye pollutants become a big headache due to their toxic nature to the environment, and it should be one of the best solutions if we can separate and reuse them. Here, we report the synthesis and characterization of a microporous anion metal-organic framework (MOF) with Lewis basic sites-rich based on TDPAT (2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) ligand, FJI-C2, which shows high adsorption and separation of cationic dye based on the charge-exclusive effect. Compared to other MOF materials, FJI-C2 shows the largest adsorption amount of methylene blue (1323 mg/g) at room temperature due to the nature of the anion frameworks and high surface area/pore volume. Furthermore, motivated by the adsorption properties of large guest molecules, we proceeded to investigate the catalytic behaviors of FJI-C2, not only because the large pore facilitates the mass transfer of guest molecules but also because the high density of Lewis basic sites can act as effective catalytic sites. As expected, FJI-C2 exhibits excellent catalytic performance for size-selective Knoevenagel condensation under mild conditions and can be reused several times without a significant decrease of the activity.

In situ growth of metal-organic framework thin films with gas sensing and molecule storage properties.

New porous metal-organic framework (MOF) films based on the flexible ligand 1,3,5-tris[4-(carboxyphenyl)oxamethyl]-2,4,6-trimethylbenzene (H3TBTC) were fabricated on α-Al2O3 substrates under solvent thermal conditions. The factors affecting the fabrication of films, such as the temperature of pre-activation and the dosage of the reagents, were investigated. Tuning the subtle factors on film fabrications, a series of MOF thin films with different morphologies and grain sizes were prepared. The morphology and grain size of the films are monitored by scanning electron microscopy (SEM). X-ray diffraction (XRD) and attenuated total reflection infrared (ATR-IR) were also used to characterize the MOF films. The results indicate that the temperature of pre-activation and the dosage of the reagents are the key parameters during the process of film formation. The properties of the films, especially the sensing and sorption behavior, have been studied by an optical digital cameral and ultraviolet-visible (UV-vis) spectra. The evidence shows that the films are sensitive to small organic molecules, such as methanol and pyridine. Meanwhile, the films can adsorb small dye molecules. Thus, the films may have potential applications in either organic vapor sensing or storage of small dye molecules.

Preparation and characterization of lanthanide-azo-dye coordination polymers and polymer thin films via layer-by-layer depositions.

A series of tartrazine-lanthanide dye compounds has been synthesized and characterized. Structural studies reveal that the light rare-earth elements La, Ce, Pr and Nd form coordination compounds with tartrazine ligands in a 1:1 ratio and result in 1-D 'fish-bone' chain-like structures having uncoordinated organosulfonate groups on each side of the chain. However, reactions of tartrazine and heavy rare-earth elements Ho, Er, Tm and Yb, in the presence of auxiliary 1,10-phenanthroline, give new 1-D coordination polymers in which uncoordinated organosulfonate groups are located on the same side of the chains. The tartrazine ligands display similar but slightly different coordination modes in both types of structures and the 1,10-phenanthroline plays a vital role in the formation of heavy rare-earth dye compounds. Based on the knowledge of their structures, the light rare-earth dye compounds were utilized to assemble with positively-charged PEI into multilayer thin films by means of layer-by-layer depositions. The as-synthesized thin films showed enhanced stability and consistency on solid surfaces.

Systematic investigation on the coordination chemistry of a sulfonated monoazo dye: ligand-dominated d- and f-block derivatives.

Ten coordination compounds based on a sulfonated monoazo dye, formulated as M(H(2)O)(2)(4,4'-abs)(2) (M = Mn , Co , Cu , Zn , Cd and Pb ; 4,4'-abs = 4-aminoazobenzene-4'-sulfonic anion), Ag(4,4'-abs) (), [Ln(H(2)O)(phen)(2)(4,4'-abs)(3)].3H(2)O (Ln = Gd , Tb , and Ho ; phen = 1,10-phenanthroline), as well as the parent ligand L [(4,4'-Habs)(2).4H(2)O] and precursor NaL.HL [Na(4,4'-abs)(4,4'-Habs)] were successfully isolated. Structural analyses revealed that the structures of compounds, and vary according to the coordination geometries of the metal ions, and vary from double-strand chain structures () to a 3-D pillared-layer framework to mononuclear complexes. The double-strand chain structures of are isostructural, and are built on octahedral metal centers and double bridging 4,4'-abs ligands coordinating via terminal N- and O-donors. The silver-containing compound displays a pillared-layer structure constructed from 4.8(2) silver sulfonate nets pillared by the linear backbones of 4,4'-abs ligands. Compounds , which are also isostructural, possess mononuclear structures consisting of a metal cation, three 4,4'-abs anions, two auxiliary phen ligands, one aqua ligand and three non-coordinated water molecules. Evidence on two series of isostructural compounds indicates that structures of d- and f-block metal derivatives are dominated by the coordination mode of the ligands. The surface chemistry of compound has been investigated based on the LBL (layer-by-layer) technique. The as-synthesized multilayer films with different composite components exhibit different surface behaviours.