MOF-Derived Bimetallic CoFe-PBA Composites as Highly Selective and Sensitive Electrochemical Sensors for Hydrogen Peroxide and Nonenzymatic Glucose in Human Serum.

The fabrication of two-dimensional (2D) metal-organic frameworks (MOFs) and Prussian blue analogues (PBAs) combines the advantages of 2D materials, MOFs and PBAs, resolving the poor electronic conductivity and slow diffusion of MOF materials for electrochemical applications. In this work, 2D leaflike zeolitic imidazolate frameworks (Co-ZIF and Fe-ZIF) as sacrificial templates are in situ converted into PBAs, realizing the successful fabrication of PBA/ZIF nanocomposites on nickel foam (NF), namely, CoCo-PBA/Co-ZIF/NF, FeFe-PBA/Fe-ZIF/NF, CoFe-PBA/Co-ZIF/NF, and Fe/CoCo-PBA/Co-ZIF/NF. Such fabrication can effectively reduce transfer resistance and greatly enhance electron- and mass-transfer efficiency due to the electrochemically active PBA particles and NF substrate. These fabricated electrodes as multifunctional sensors achieve highly selective and sensitive glucose and H2O2 biosensing with a very wide detective linear range, extremely low limit of detection (LOD), and good stability. Among them, CoFe-PBA/Co-ZIF/NF exhibits the best sensing performance with a very wide linear range from 1.4 µM to 1.5 mM, a high sensitivity of 5270 µA mM-1 cm-2, a low LOD of 0.02 µM (S/N = 3), and remarkable stability and selectivity toward glucose. What is more, it can realize excellent detection of glucose in human serum, demonstrating its practical applications. Furthermore, this material as a multifunctional electrochemical sensor also manifests superior detection performance against hydrogen peroxide with a wide linear range of 0.2-6.0 mM, a high sensitivity of 196 µA mM-1 cm-2, and a low limit of detection of 1.08 nM (S/N = 3). The sensing mechanism for enhanced performance for glucose and H2O2 is discussed and proved by experiments in detail.

Iron-Based Metal-Organic Framework System as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Hydrogen Evolution Reactions.

The fabrication of highly efficient and sustainable electrocatalysts used for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is exceedingly challenging and warranted for overall water splitting. In this work, we successfully synthesized a series of metal-organic frameworks (MOFs), namely, as Fe2M-MOF (M = Fe, Co, Ni, Zn, Mn; H4L = 3,3,5,5'-azoxybenzenetetracarboxylic acid) under a simple and mild condition, in which the Fe3 cluster as a basic building unit was replaced by the second kind of metal center; at the same time, a redox-active organic linker was adopted. The Fe2M-MOF system as a multifunctional catalyst realizes great improvement of the OER and HER performances. Among of them, the Fe2Co-MOF catalyst exhibits an extremely low overpotential of 339 mV at a current density of 10 mA cm-2 and a very small Tafel slope of 36.2 mV dec-1 in an alkaline electrolyte for OER. This result has far exceeded the commercial catalyst IrO2. Meanwhile, Fe2Zn-MOF manifests excellent HER activity with a small overpotential of 221 mV at 10 mA cm-2 and a low Tafel slope of 174 mV dec-1. In addition, the good long-term stability for these catalysts can be evaluated under working conditions. Systematic investigations are used to explain the enhanced electrocatalytic mechanism. In conclusion, we provide a simple and effective strategy for the preparation of multifunctional catalysts for energy conversion applications based on a pristine MOF material with redox-active metal centers and organic linkers.

Rationally designed trimetallic Prussian blue analogues on LDH/Ni foam for high performance supercapacitors.

Rational design of a Prussian blue analogue (PBA)@Ni-Co layered double hydroxide (NiCo-LDH) nanocomposite electrode material is vitally important for synthesizing high-performance supercapacitor electrodes. In this work, such nanocomposite electrode materials were successfully fabricated by a facile hydrothermal method. Firstly, three-dimensional (3D) regulated NiCo-LDH nanosheets with high interlayer space were grown on nickel foam under mild synthetic conditions. Then these nanosheets as a precursor were in situ converted into the target PBA@NiCo-LDH/NF nanocomposite electrode by a facile thermal ion-exchange reaction with potassium ferricyanide (K3[Fe(CN)6]). A series of PBA@NiCo-LDH/NF nanocomposite electrodes were fabricated with different ratios of Ni and Co and reaction temperatures. Their structures and morphologies were characterized by X-ray diffraction (XRD), FT-IR and scanning electron microscopy (SEM). Electrochemical investigation reveals that the PBA@Ni0.4Co0.6-LDH electrode exhibits the best electrochemical performance with an area specific capacitance of 2004.26 mF cm-2 at 1 mA cm-2, which is much higher (about three times) than the properties of each single component. All results demonstrate that (1) high-performance composite electrodes can be effectively fabricated and (2) fabrication of such composites is highly necessary and important.

The interlocked in situ fabrication of graphene@prussian blue nanocomposite as high-performance supercapacitor.

High-quality graphene@prussian blue (G@PB) nanocomposite sheets have been successfully fabricated via a one-step in situ hydrothermal method, in which uniform PB nanoparticles completely covered both sides of graphene sheets through control of the etching of the raw material and growth of the target products. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) demonstrated effective combination. A series of G@PB nanocomposite sheets with different graphene contents as well as other PB/carbonaceous composites and mixed G@PB materials provided adequate proof for the synergetic effect of graphene and Prussian blue in G@PB nanocomposite sheets as well as the important effect of each composite on the electrochemical performance; graphene not only prevented the agglomeration of PB nanoparticles but also provided conductive network for fast electron transport, which was verified by the IR voltage drop and EIS test. In particular, the G@PB-5 hybrid composite showed the highest capacitance of 388.09 F g-1 at a current density of 1 A g-1 and enhanced rate capability and long-term stability with 97.2% retention over 5000 cycles as well as coulombic efficiency of nearly 100%. Asymmetric supercapacitor cells were assembled by pairing an optimized nanocomposite electrode with an activated carbon negative electrode, which displayed a reversible operating voltage of 2.0 V. These high electrochemical performances render the G@PB-5 nanocomposite sheets promising for energy-storage hybrid electrodes.

A heterobimetallic metal-organic framework as a "turn-on" sensor toward DMF.

A non-luminescent 3d-4f heterobimetallic CuEu organic framework (NBU-8) was designedly synthesized with Cu2+ ions as a fluorescence quencher. NBU-8 as a sensor realized selective light recovery with a "turn-on" luminescence response toward N,N'-dimethylformamide (DMF) even in the presence of other amide molecules.

Morphological control of lanthanide ferrocyanides and their highly efficient catalytic degradation performance toward organic dyes under dark ambient conditions.

KCe[FeII(CN)6]·4H2O (CePBA), a Prussian blue analogue, was successfully synthesized with various morphologies and different sizes. CePBA, when used as a heterogeneous catalyst, can rapidly and completely degrade a large number of methylene blue molecules in 30 seconds: 14.5 mg of MB (for each 5 mg of catalyst). The CePBA catalyst is reusable. These are very important parameters for practical applications.

A Dual-Functional Luminescent MOF Sensor for Phenylmethanol Molecule and Tb3+ Cation.

A highly luminescent porous metal-organic framework Cd3(L)2.5(4-PTZ)(DMF)3, labeled as NBU-9, has been designedly synthesized based on Cd(NO3)2·4H2O and mixed ligands of 4-(1 H-tetrazol-5-yl)pyridine (4-HPTZ) with N-coordinated sites and thiophene-2,5-dicarboxylic acid (H2L) with heteroatomic (S) ring and carboxylate groups in N, N-dimethylformamide (DMF) at 100 °C for 3 days. The interesting result is that this compound NBU-9 can be also obtained via the mixed raw materials of Cd(NO3)2·4H2O, 4-cyanopyridine, NaN3, and H2L under solvothermal condition at a higher temperature of 140 °C for 3 days, involving in situ ligand synthesis of 4-HPTZ. Its structure was indentified by single-crystal X-ray study, powder X-ray diffraction, element analysis, and TGA results. Structural analysis shows that the three-dimensional framework of NBU-9 contains cubic channels of 9.59 × 10.26 Å2 covered by a large number of open S- and O-coordinated sites and can be simplified into a 8-connected uninodal eca net with high potential solvent accessible volumes of 34.1%. Its luminescent properties demonstrate that NBU-9 as a multifunctional sensory material realizes the selective detection for the phenylmethanol molecule on the basis of fluorescence quenching mechanism and effectively sensitizing the visible emitting of the Tb3+ cation based on luminescence enhancement.