Bimetal Metal-organic Frameworks Research Articles

Nitrogen-doped carbon wrapped Co-Mo2C dual Mott–Schottky nanosheets with large porosity for efficient water electrolysis

Efficient, inexpensive and stable electrocatalysts are challenging and desperately required in order to complement the water electrolysis of noble metal catalysts. Herein, a porous nitrogen-doped carbon wrapped Co-Mo2C dual Mott–Schottky heterostructure has been successfully fabricated by carbonization of Co-Zn bimetal metal-organic framework (MOF) for water electrolysis. The heterostructure is found to feature with Co and Mo2C nanoparticles uniformly encapsulated in the highly porous leaf-like N-doped carbon nanosheet matrix. Such a thin porous dual-Mott–Schottky configuration can afford abundant surface active sites and the boosted electron transfer to promote the water splitting. As for hydrogen/oxygen evolution reaction (HER/OER), it has demonstrated fast kinetics and low overpotentials of 92 mV (HER) and 338 mV (OER) at a current density of 10 mA cm−2 in 1 M KOH. Furthermore, the overall water splitting is stably delivered with a low cell voltage of 1.68 V at 10 mA cm-2 in 1 M KOH. Density function theory (DFT) calculations demonstrate that the interface correlation is favorable to water transfer by electron and speeds up adsorption and water dissociation. The work here opens up interesting possibilities for the rational design and innovation of MOF derived Mott–Schottky electrocatalysts for highly efficient water electrolysis.

Surface imprinted CoZn-bimetalic MOFs as selective colorimetric probe: Application for detection of dimethoate

Designing simple and selective sensors for on-site recognition of organophosphate toxins (OPs) is of great importance. Here, molecularly imprinted polymer (MIP)-capped CoZn bimetal imidazolate framework (CoZn ZIF) has been introduced as a specific probe for the quantification of dimethoate. The detection is based on its diminishing effect on the catalytic action of ZIF in 3,3′,5,5′-Tetramethylbenzidine (TMB)-hydrogen peroxide (H2O2) reaction. CoZn ZIF catalyzes the dissociation of H2O2 to hydroxyl radicals, which can then oxidize TMB and create a blue colored product. It was demonstrated that the catalytic performance of bimetal metal organic framework (MOF) is higher than that of single metal MOF of Co (ZIF-67) or Zn (ZIF-8). On the other hand, adsorbing dimethoate in the specific MIP sites on the surface of CoZn ZIF declines its catalytic action. This effect was exploited to design a selective colorimetric assay for dimethoate determination in fruit and wastewater samples. The decrease in the absorption intensity of final solution was proportional to the dimethoate concentration in the range of 0.02–1.2 μM, with a detection limit of 5.6 nM. The high specificity of MIP technique and great catalytic activity of CoZn ZIF, as well as the simplicity of colorimetric method led to a reliable screening assay.

Strategies for improving Co/Ni-based bimetal-organic framework to water splitting

The preparation of high-efficiency, stable, and low-cost oxygen evolution reactions (OER) and hydrogen evolution reactions (HER) electrocatalysts remains a challenge for new energy systems. In this study, three-dimensional (3D) cobalt-nickel bimetal MOFs were used as precursors to synthesize catalysts through thermal decomposition, carbonization, nitriding, oxidation, phosphating, sulfurizing, and selenization, respectively. In 1.0 M KOH electrolyte, the overpotential of Co/Ni-MOFs@Se for OER was 238 mV and the that of Co/Ni-MOFs@P for HER was 194 mV at a current density of 10 mA cm−2. Based on the excellent OER and HER performances of Co/Ni-MOFs@Se and Co/Ni-MOFs@P, these two materials were further assembled into electrodes for overall water splitting. Results showed that a potential of only 1.59 V was required to provide a current density of 10 mA cm−2. The electrodes also exhibited long-term durability in a 2000 min stability test without significant changes in the catalytic performances. According to the difference in the doped non-metal elements, an electrode pair with a suitable matching degree was constructed, thereby improving the overall water splitting performance. Thus, the controllable modification of the metal-organic frameworks (MOFs)-derived carbon materials (CMs) effectively improved the materials’ catalytic water splitting performance. It was possible to further develop an efficient, inexpensive, and low-cost assembled electrode pair.

Rational design of nickel-cobalt selenides derived from multivariate bimetal metal-organic frameworks for high-performance asymmetric supercapacitor

The transition metal selenides have aroused wide concern due to their potential characteristics in the energy storage and conversion. The formation of multivariate MOFs attracts much research attention and provides the essential guarantee for multivariate mixed-metal selenides. Herein, a series of isostructural MOF-74 materials with different divalent metals were prepared by changing the molar ratios of nickel to cobalt. After selenizing, CoSe2, NiSe2 and three kinds of mixed-metal selenides were easily obtained, prompting us to systematically research the effect of different metal species and molar ratios on the electrochemical performance of the mixed-metal selenides. It is found that mixed-metal selenides derived from MOF-74 display much better performance than single metal selenides, and NiCoSe-4 with a Ni/Co molar ratio of 4:1 demonstrates a high specific capacity of 211 mAh g−1 at a current density of 1 A g−1. What's more, the assembled asymmetric supercapacitor NiCoSe-4//AC shows a high energy density of 61.24 Wh kg−1 at power density of 800 W kg−1, which suggests that NiCoSe-4 as a promising electrode material possesses further research value and potential for practical applications in energy storage fields.

Solvent-Controlled Morphology of Amino-Functionalized Bimetal Metal-Organic Frameworks for Asymmetric Supercapacitors.

The composition-tuned, structure-modified, and morphology-controlled nanoscale metal-organic frameworks (MOFs) are quite important to improve the electrochemical performances for supercapacitors. In this work, a solvent-controlled method to prepare amino-functionalized bimetal MOFs with various morphologies is proposed. Three different morphologies of NiCo-MOFs, such as nanospheres, nanosheet-assembled hollow spheres (NSHSs), and rhombus sheets, have been successfully synthesized by using different solvents. The as-prepared three nanoscale NiCo-MOFs are comparatively characterized and are endowed a possible mechanism on nucleation and crystal growth controlling morphology. When used as electrode materials for supercapacitors, all NiCo-MOFs have excellent electrochemical properties. Specifically, the NiCo-MOF NSHS owns the best specific capacitance, which can achieve 1126.7 F g-1 at the current density of 0.5 A g-1 and maintain 93% of its original capacitance at the current density of 10 A g-1 after 3000 charge-discharge cycles. Moreover, an asymmetric supercapacitor device (NiCo-MOF NSHS//AC) assembled with NiCo-MOF NSHS as the positive electrode and activated carbon (AC) as the negative electrode achieves an energy density of 20.94 Wh kg-1 at a power density of 750.84 W kg-1. This work is facile and highly reproducible and can be extended to prepare other nano-MOFs in energy storage and conversion fields. In addition, it opens up an effective approach to synthesizing amino-functionalized MOFs by a solvent-controlled method without any other changes in the experimental conditions.

Transition Bimetal Based MOF Nanosheets for Robust Aqueous Zn Battery

High-performance, good stability, low-cost and environmentally friendly batteries are important for portable electronics and electric vehicles. Compared with the high-energy density lithium-ion batteries, aqueous rechargeable battery has been extensively researched due to high safety, low cost and much better rate performance. Here, we report a one-step approach to fabricate porous Ni-Cu metal–organic framework (MOF) nanosheet arrays structures for stable energy storage with a high-energy (71.2 mWh cm−3) and high-stability (capacity retention of ≈91% after 2500 cycles) performance. Furthermore, we synthesized various porous homogeneous Ni-Co, Ni-Zn, Ni-Fe and Ni-Mn bimetal MOF structures with high surface area and conductivity utilizing this rational design. This work provides a simple efficient strategy for constructing porous homogeneous bimetal MOF nanosheet arrays with high energy and stability performance, holding a great potential for future multifunctional electronic devices.

Low-temperature and highly sensitivity H2S gas sensor based on ZnO/CuO composite derived from bimetal metal-organic frameworks

The bimetallic metal-organic frameworks (MOF) Zn/Cu-BTC were prepared by a facile solvothermal method in one step and used as a self-sacrificed template to obtain the ZnO/CuO composites. The composites with different Cu/Zn molar ratios were characterized by XRD, FESEM, and XPS. The ZnO/CuO composite exhibited an octahedral structure, and a p-n heterojunction may be formed between p-type CuO and n-type ZnO. To prove its functional characteristics, the ZnO/CuO composite was used as a sensing material to test its gas sensitivity. The effect of Cu/Zn molar ratios was examined, and the results showed that the optimized ZnO/CuO (1: 0.33) composite based gas sensor exhibited reasonable selectivity to 10 ppm H2S, operated at 40 °C. The sensitivities were improved by 17.1 times and 327.8 times compared with the pristine CuO and ZnO based gas sensors, respectively. Moreover, the detection limit to H2S of such sensors could be reduced as low as 300 ppb. The sensing mechanism has been thoroughly studied and such ZnO/CuO composite is an ideal candidate for highly sensitive detection for H2S with low power consumption in the real application.

Application of surface molecular imprinted magnetic graphene oxide and high performance mimetic behavior of bi-metal ZnCo MOF for determination of atropine in human serum

Herein, high performance peroxidase-like activity of zinc and cobalt bi-metal metal-organic framework (ZnCo MOF) is reported and applied for the sensitive measurement of atropine. ZnCo MOF was synthesized by the reaction of 2-methylimidazole with Zn and Co (II) cations in aqueous media. The colorimetric and fluorometric experiments were applied to investigate the catalytic activity of obtained MOF, using o-phenylenediamine (OPD) and terephthalic acid (TA) peroxidase substrates, respectively. The results demonstrated the more efficient mimetic behavior of ZnCo MOF compared with common Zn or Co MOFs. Besides, it was found that atropine hindered the catalytic action of ZnCo MOF and this effect was intensified by increasing the atropine concentration. So, it was considered to design a sensitive analytical assay for atropine detection. To assure a high specific recognition, molecularly imprinted polymer (MIP)-based extraction using magnetic graphene oxide supports was applied to extract atropine before its determination. The combination between the high specific extraction and great catalytic activity of ZnCo MOF led to the ultrasensitive and reliable determination of atropine. The best linear range of calibration graph was achieved using fluorometric detection system for 0.1–45 ng mL−1 atropine concentrations, and detection limit (3Sb/m) was 27 pg mL−1. The relative standard deviations (RSD %) for the determination of 1, and 10 ng mL−1 atropine (n = 5) were 2.13% and 3.08%, respectively. The explained fluorometric assay was examined for the measurement of atropine in biological fluids (Recoveries were in the range of 95.90–103.57%), and the results were validated by an official method.

MOFs-derived NiFe2O4 fusiformis with highly selective response to xylene

NiFe2O4 fusiformis was derived from Ni/Fe bimetal metal-organic frameworks (MOFs) precursors prepared using a facile hydrothermal method, and the corresponding morphology, microstructure, and gas sensing properties were investigated. After thermal treatment at 350 °C in air, the Ni/Fe MOFs ellipsoid were completely converted into NiFe2O4 fusiformis, leading to a big volume shrink because of the removing of organic ligands. The NiFe2O4 fusiformis was used to fabricate gas sensor to detect xylene operating at 300 °C. The sensor exhibited a good response sensitivity of 31.52 with response/recovery time of 50.10 s/40.30 s, respectively, toward 500 ppm xylene. It also showed a remarkably high selectivity to xylene against other gases such as toluene, ethanol, methanol, acetone, isopropanol, ammonia, formaldehyde, and benzene. The excellent performance could be ascribed to the nature and the unique morphology of as-prepared NiFe2O4 with high specific surface area (60.50 m2/g) and porous microstructure. These findings may render a new opportunity to fabricate gas sensor for xylene detection based on p-type NiFe2O4.

Bimetal metal-organic frameworks derived Co0.4Fe0.28P and Co0.37Fe0.26S nanocubes for enhanced oxygen evolution reaction

In order to satisfy the desire of energy shortage for excellent OER catalyst, phosphide (Co0.4Fe0.28P), and sulfide (Co0.37Fe0.26S) nanocubes (NCs) were synthesized by heating CoFe-based Prussian blue analogues (CoFe-PBA) precursors under different atmosphere, respectively. The prepared Co0.4Fe0.28P and Co0.37Fe0.26S NCs have defined stoichiometry and larger surface area, which revealed excellent electrocatalytic activities toward OER in alkaline condition. Co0.4Fe0.28P and Co0.37Fe0.26S nanocubes show an excellent electrocatalytic performance for the OER in 1 M KOH, which are superior to the state-of-the-art commercialized IrOx catalyst and most of MOFs derived OER catalyst. Furthermore, we also briefly study the different electrochemical oxidation driving (EOD) influence of Co0.4Fe0.28P and Co0.37Fe0.26S NCs for exposed more active sites and further discovering that sulfides show a better driving effect. We expect to give some inspiration on the design of OER catalysts with enhanced performance, and catalysts applied in other designs of the new catalyst.

MO‐Co@N‐Doped Carbon (M = Zn or Co): Vital Roles of Inactive Zn and Highly Efficient Activity toward Oxygen Reduction/Evolution Reactions for Rechargeable Zn–Air Battery

A highly efficient bifunctional oxygen catalyst is required for practical applications of fuel cells and metal–air batteries, as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are their core electrode reactions. Here, the MO‐Co@N‐doped carbon (NC, M = Zn or Co) is developed as a highly active ORR/OER bifunctional catalyst via pyrolysis of a bimetal metal–organic framework containing Zn and Co, i.e., precursor (CoZn). The vital roles of inactive Zn in developing highly active bifunctional oxygen catalysts are unraveled. When the precursors include Zn, the surface contents of pyridinic N for ORR and the surface contents of Co–Nx and Co3+/Co2+ ratios for OER are enhanced, while the high specific surface areas, high porosity, and high electrochemical active surface areas are also achieved. Furthermore, the synergistic effects between Zn‐based and Co‐based species can promote the well growth of multiwalled carbon nanotubes (MWCNTs) at high pyrolysis temperatures (≥700 °C), which is favorable for charge transfer. The optimized CoZn‐NC‐700 shows the highly bifunctional ORR/OER activity and the excellent durability during the ORR/OER processes, even better than 20 wt% Pt/C (for ORR) and IrO2 (for OER). CoZn‐NC‐700 also exhibits the prominent Zn–air battery performance and even outperforms the mixture of 20 wt% Pt/C and IrO2.

Strongly Coupled FeNi Alloys/NiFe2O4@Carbonitride Layers-Assembled Microboxes for Enhanced Oxygen Evolution Reaction.

Hydrogen produced from electrocatalytic water splitting is a promising route due to the sustainable powers derived from the solar and wind energy. However, the sluggish kinetics at the anode for water splitting makes the highly effective and inexpensive electrocatalysts desirable in oxygen evolution reaction (OER) by structure and composition modulations. Metal-organic frameworks (MOFs) have been intensively used as the templates/precursors to synthesize complex hollow structures for various energy-related applications. Herein, an effective and facile template-engaged strategy originated from bimetal MOFs is developed to construct hollow microcubes assembled by interconnected nanopolyhedron, consisting of intimately dominant FeNi alloys coupled with a small NiFe2O4 oxide, which was confined within carbonitride outer shell (denoted as FeNi/NiFe2O4@NC) via one-step annealing treatment. The optimized FeNi/NiFe2O4@NC exhibits excellent electrocatalytic performances toward OER in alkaline media, showing 10 mA·cm-2 at η = 316 mV, lower Tafel slope (60 mV·dec-1), and excellent durability without decay after 5000 CV cycles, which also surpasses the IrO2 catalyst and most of non-noble catalysts in the OER, demonstrating a great perspective. The superior OER performance is ascribed to the hollow interior for fast mass transport, in situ formed strong coupling between FeNi alloys and NiFe2O4 for electron transfer, and the protection of carbonitride layers for long stability.