The electrochemical nitrogen reduction reaction (NRR) offers an energy‐saving and environmentally friendly approach to produce ammonia under ambient conditions. However, traditional catalysts have ...extremely poor NRR performances because of their low activity and the competitive hydrogen evolution reaction. The high catalytic activity of nanoporous gold (NPG) and the hydrophobicity and molecular concentrating effect of the zeolitic imidazolate framework‐8 (ZIF‐8) were incorporated in the NPG@ZIF‐8 nanocomposite so that the ZIF‐8 shell could weaken hydrogen evolution and retard reactant diffusion. A highest Faradaic efficiency of 44 % and an excellent rate of ammonia production of (28.7±0.9) μg h−1 cm−2 were achieved, which are superior to traditional gold nanoparticles and NPG. Moreover, the composite catalyst shows high electrochemical stability and selectivity (98 %). The superior NRR performance makes NPG@ZIF‐8 one of the most promising water‐based NRR electrocatalysts for ammonia production.
Being efficient: A core–shell structure composite of nanoporous gold embedded in a ZIF‐8 shell has been developed. The high catalytic activity of the nanoporous gold and the hydrophobic porous shell of ZIF‐8 results in a superior enhancement of electrochemical nitrogen fixation compared to traditional electrocatalysts, as shown by a Faradaic efficiency of 44 % (see picture, scale bar: 300 nm).
Complex metal–organic frameworks used as precursors allow design and construction of various nanostructured functional materials which might not be accessible by other methods. Here, we develop a ...sequential chemical etching and sulfurization strategy to prepare well‐defined double‐shelled zinc–cobalt sulfide (Zn‐Co‐S) rhombic dodecahedral cages (RDCs). Yolk‐shelled zinc/cobalt‐based zeolitic imidazolate framework (Zn/Co‐ZIF) RDCs are first synthesized by a controlled chemical etching process, followed by a hydrothermal sulfurization reaction to prepare double‐shelled Zn‐Co‐S RDCs. Moreover, the strategy reported in this work enables easy control of the Zn/Co molar ratio in the obtained double‐shelled Zn‐Co‐S RDCs. Owing to the structural and compositional benefits, the obtained double‐shelled Zn‐Co‐S RDCs exhibit enhanced performance with high specific capacitance (1266 F g−1 at 1 A g−1), good rate capability and long‐term cycling stability (91 % retention over 10,000 cycles) as a battery‐type electrode material for hybrid supercapacitors.
Shell dressed: Double‐shelled zinc–cobalt sulfide rhombic dodecahedral cages are synthesized by a sequential chemical etching and sulfurization strategy. With the structural advantages, these well‐defined cages exhibit much enhanced electrochemical performance compared to the single‐shelled counterpart as electrode materials for hybrid supercapacitors.
The development of stable non-noble and cost-effective metal sulfide-based electrocatalyst materials for hydrogen evolution reaction (HER) is still a great challenge. Herein, we report the rationally ...designed electrocatalysts containing Co3S4/Co9S8 co-doped nitrogen-enriched porous carbon polyhedrons (Co3S4/Co9S8/NC PHs). The Co3S4/Co9S8/NC PHs were achieved from Zeolitic imidazolate framework-67 PHs by adding sulfur powder and then placing them in an inert atmosphere at 375 °C for 2 h. The prepared electrocatalyst materials were analyzed using X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, and X-ray photoelectron spectroscopy techniques. The HER catalytic activity of the Co3S4/Co9S8/NC PHs exhibited the superior overpotential performance of 134 mV at a current density of 10 mA cm−2 with the Tafel slope of −119 mV dec−1. Additionally, the results from chronopotentiometry maintained a strong kinetic response as well as the long cycling stability of 100 h for the Co3S4/Co9S8/NC PHs electrocatalyst at a constant current density of −10 mA cm−2 with 8.4% decay rate. This study demonstrates a new strategy for hydrogen generation synthesizing non-noble catalyst materials with excellent HER activities.
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•Co3S4/Co9S8/NC PHs were achieved by sulfur to ZIF-67 PHs, followed by N2 treatment.•Sulfurizing ZIF changed its morphology and improved electrochemical activity.•The Co3S4/Co9S8/NC PHs improved HER activity with η = 134 mV to reach j = 10 mA cm−2.•The Co3S4/Co9S8/NC PHs exhibited excellent cycling stability over 100 h.
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•A series of mixed matrix membranes (MMM) based on 6FDA-ODA and bimetallic Zn/Co-ZIF were successfully prepared and compared to homometallic ZIF-8 and ZIF-67 MMM.•Particle clustering ...in MMM was reduced upon using colloidal ZIF solution for membrane fabrication.•Zn/Co-ZIF showed better CO2/CH4 separation performances than parent frameworks ZIF-8 and ZIF-67.
Bimetallic metal–organic frameworks (MOF) have received growing attention in several fields for gas separation/adsorption, energy storage and catalysis because of their synergic effect and enhanced properties compared to their parent structures. Here, we first report on a facile and low cost direct synthesis of solid solution of bimetallic Zn/Co-ZIF and its monometallic counterparts, ZIF-8 and ZIF-67 at room temperature. Zn/Co-ZIF showed higher pore volume and BET surface area than their parents, homogeneous distribution of metals within the framework and a slightly higher Zn-rich external surface. Next, mixed matrix membranes (MMM) of Zn/Co-ZIF, ZIF-8 and ZIF-67 based 6FDA-ODA polyimide were fabricated with different content (3–10 %wt) via a wet approach using undried MOF for CO2/CH4 single and mixed gas (10:90 vol%) separation application to determine the effect of the metal center on the gas transport properties. While Zn/Co-ZIF (10 wt%)/6FDA-ODA had the highest CO2/CH4 selectivity (39.8) and CO2 permeability (45.8 Barrer) compared to the MMM of ZIF-8 (PCO2 = 41.6 Barrer, SCO2/CH4 = 36.1) and ZIF-67 (PCO2 = 26.2 Barrer, SCO2/CH4 = 26.3) at the same concentration, the best performance was observed for Zn/Co (7.5 wt%)/6FDA-ODA MMM with 104% and 41% increase in CO2 permeability up to 44.2 Barrer and CO2/CH4 ideal selectivity to 45.1, compared to the neat polymer, respectively.
•Bimetallic Zn/Co ZIFs were synthesized and used for the preparation of porous carbon.•Hierarchical porous carbon with magnetic properties was obtained.•Zn/Co ZIF-derived carbon showed a high ...Rhodamine B adsorption capacity of 116.2 mg/g.•Electrostatic interaction is important for high adsorptions over ZIF-derived carbon.
Using zeolitic imidazolate frameworks (ZIFs) as precursors to yield highly nanoporous carbon materials for clean energy applications have received great attention in recent years, because of its diverse structure and dual characteristics from carbon and metals. To further explore the property and application of ZIFs-derived carbons, herein, bimetallic Zn/Co ZIFs were synthesized and used as self-sacrificial templates and carbon sources for the preparation of porous carbons. By direct carbonization at 900 °C, hierarchical porous carbon with magnetic properties was obtained in which highly dispersed Co nanoparticles were found. The as-prepared carbons were further used as adsorbents for the removal of Rhodamine B (RhB) from water. For comparison, ZIF-8- and ZIF-67-derived carbons were also synthesized, characterized and tested for RhB adsorption. The results show that Zn/Co ZIF-derived carbon exhibited the highest RhB adsorption capacity compared to ZIF-8- and ZIF-67-derived carbons, and it could be easily separated from water by an external magnetic field. The adsorption isotherm data conform to the Langmuir model, and the adsorption kinetic data obey a pseudo-second-order model. Moreover, Zn/Co ZIF-derived carbons can be regenerated by ethanol washing and reused at least 6 times without a significant loss in capacity.
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•Fe and Co bi-metal single atoms were doped in 3D nitrogen-doped carbon nanosheets with synergetic coupling strategy.•Synergetic coupling effect between metals atoms increases their ...intrinsic activity.•A-FeCo@NCNs exhibits excellent ORR/OER activity and Zn-air battery performance.
Single atom catalysts (SACs) with unique structure gain much interest in the field of electrocatalysis and show a broad application prospect in long-life rechargeable Zn-air batteries. However, ingenious design and preparation of bi-metal SACs is still difficult to further enhance the bifunctional electrocatalytic activity. Herein, modified zeolitic imidazolate frameworks (SiO2@Fe-ZIF-8/67) was facilely designed to preparation atomically dispersed Fe and Co doping 3D nitrogen-doped carbon nanosheets (A-FeCo@NCNs). The Fe or Co single atoms are identified to be coordinated with N atoms and form FeN4, CoN4 or N3Fe-CoN3 anchored on 3D defect carbon, which act as reactive sites for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Through synergetic coupling effect, A-FeCo@NCNs exhibits excellent electrochemical performance with ORR/OER potential gap of 0.80 V. Density functional theory (DFT) calculations further indicate the synergistic effect between Fe and Co in A-FeCo@NCNs towards the enhancing ORR activity. The as-prepared catalyst assembled Zn-air battery shows a maximum power density, and superb cycling stability, surpassing that based on commercial Pt/C + IrO2. Results from this study may provide a facile method for precious control of dual-metal single sites doped carbon with highly activity and durability for bifunctional electrocatalysis.
In this study, zeolitic imidazolate frameworks (ZIF) were employed as effective porous supports for laccase enzyme attachment and further explored synergistic adsorption and biocatalytic degradation ...of carbamazepine (CBZ) in aqueous solutions. Characterization results from FTIR and NMR analysis confirmed successful incorporation of the laccase enzyme onto ZIF particles. Further analyses from SEM and TEM revealed rhombic dodecahedral morphologies of ZIF crystals with crusts of the enzyme observed on the particles' surface. The carbamazepine degradation results showed that immobilization of the laccase improved its stability and resistance at various pH's, in comparison to the free enzyme. The immobilized laccase also exhibited relatively higher activities across the studied temperature range compared to the free form. Kinetic studies revealed a negligible decline in velocity, Vmax after immobilization, evaluated to be 0.873 and 0.692 mg L−1 h−1 for the free and immobilized laccase, respectively. The immobilized laccase demonstrated improved stabilities towards organic solvents, which qualifies the composite's application in real wastewater samples. In which case, the laccase-ZIF composite proved effective in CBZ decontamination with an efficiency of ∼92%. Furthermore, the immobilized laccase exhibited appreciable storage stabilities (∼70% residual activity) for up to 15 days before any significant loss in activity.
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•Zeolitic imidazolate frameworks (ZIFs) form stable crystalline supports for enzyme immobilization.•Rhombic dodecahedral morphologies of ZIF crystals were observed.•Aspergillus-based laccase effectively degrade carbamazepine.•Immobilized laccase exhibits enhanced enzyme activity and stability (pH, temperature, and storage).•Efficient abatement of carbamazepine from real river water was achieved.
Abundant Co-Nx sites are obtained by using zinc as a sacrificial agent, which act as bifunctional electrocatalytic sites for the reversible deposition and dissolution of Li2S.
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...•Abundant Co-Nx sites were obtained by pyrolyzing Zn/Co bimetallic zeolitic imidazolate frameworks.•Zn as sacrificial agent to realize a homogenous distribution Co-Nx sites.•Co-Nx sites have a bifunctional catalytic effect towards Li2S deposition and dissolution.•Gibbs free energy of LiPSs conversion was reduced by Co-Nx sites.•The resultant LSB delivers an excellent capacity and stability at high rates.
Lithium sulfur battery (LSB) is promising next-generation energy storage system due to its high theoretical energy density and low cost. However, the poor reaction reversibility weakened its application. Here, a bifunctional electrocatalyst with highly active Co-Nx sites was synthesized by pyrolyzing Co/Zn bimetallic zeolitic imidazolate frameworks and used as separator coating layer to improve the reversibility of LSB. Using zinc as sacrificial template, the severe agglomeration of cobalt is effectively avoided, and abundant Co-Nx active sites are obtained. Investigations in reaction kinetic reveal that Co-Nx sites have a bifunctional electrocatalytic activity towards Li2S deposition and dissolution during cycling. Density functional theory calculations further confirm the strong electrocatalytic effect of Co-Nx sites, which results in a reduced Gibbs free energy for the liquid-solid reactions of lithium polysulfides to Li2S. Under the same experimental condition, the introduction of Co-Nx bitunctional electrocatalyst contributed to a 31% reversible capacity increase for LSB, with a capacity of 896 mAh g−1 at 1 C, and a slow capacity decay rate of 0.033% per cycle over 1000 cycles. Even for thick electrode with a sulfur loading of 6 mg cm−2, a reversible capacity of 4.2 mAh cm−2 can still be obtained at 0.2 C over 100 cycles.
•Novel bifunctional heterogeneous catalyst was synthesized for biodiesel production.•SA/ZIF-90 exhibited synergistic catalysis of Brønsted and Lewis acid sites.•The new bond formed between SA and ...ZIF-90 strengthened catalysts recyclability.•DFT calculation revealed reaction pathway of lipids catalyzed over Zn-Nx.•The conversion efficiency of microalgal lipids to FAME with SA/ZIF-90 was 98.3%
In order to enhance acidic sites in catalysts to improve conversion efficiency of microalgal lipids into biodiesel, an efficient bifunctional catalyst with synergetic Lewis and Brønsted acid sites was synthesized by modifying zeolitic imidazolate framework (ZIF-90) with sulfamic acid (SA). The sulfamic acid that combined with ZIF-90 through imine bond (CN) provided protons and destroyed coordinated Zn-N bonds in ZIF-90, thereby enhancing the number of Brønsted and Lewis acid sites. The total acidity of optimal catalyst increased from 0.478 to 0.848 mmol/g, while ratio of Brønsted acid to Lewis acid increased from 0.32 to 0.49. The Lewis acid sites in bifunctional catalysts exhibited higher activity towards transesterification reactions of triglycerides in microalgal lipids, while Brønsted acid sites exhibited higher activity towards esterification reactions of free fatty acids. Therefore, the optimal catalyst (weight ratio of SA to ZIF-90 was 0.05) promoted conversion efficiency of microalgal lipids into biodiesel from 80.6 % to 98.3 % at 200 °C, while conversion efficiency remained 91.7 % after 6 reusability cycles.
The Cover Feature shows the catalyst production process starting from a mixture of zeolitic imidazolate framework‐8 (ZIF‐8) and Ni2+ precursor, which is then pyrolyzed to yield the intermetallic ...Ni3ZnC catalyst. This intermetallic compound catalyzes the selective hydrogenation of CO2 into CO via the reverse water gas shift reaction pathway, while the most common methanation reaction pathway is suppressed, even at high pressure. The gain in selectivity is represented by the catalyst's being able to move the railway switch control towards CO. Image credit: Eliana R. de Almeida. More information can be found in the Full Paper by L. M. Rossi and co‐workers.
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