Preparation of N-doped porous carbon coated MnO nanospheres through solvent-free in-situ growth of ZIF-8 on ZnMn2O4 for high-performance lithium-ion battery anodes

MnO/TiO2/C/N-CNTs derived from Mn-doped Ti MOFs for simultaneous detection of catechol and hydroquinone

Mn-doped Ti-based MOFs (MnTi MOFs) were synthesized by a solvothermal method, and calcined at high temperature after being mixed with pre-prepared PPy nanotubes to give MnO/TiO2/C/N-CNTs composites. The composites were studied by SEM, XRD, XPS and FTIR. Based on these composites, a new electrochemical sensor was prepared, which has good electrocatalytic ability for the redox of catechol (CC) and hydroquinone (HQ), and can detect CC and HQ simultaneously. The results showed that the oxidation peak current of CC and HQ increased linearly in the concentration range of 0.50-120.00 μM. The detection limits were 0.033 μM and 0.019 μM, respectively. The constructed sensor has been successfully used for the simultaneous detection of CC and HQ in lake water and tap water, and has a good recovery rate.

Enhanced activity and water tolerance promoted by Ce on MnO/ZSM-5 for ozone decomposition

Catalytic decomposition is a promising way to eliminate ozone using manganese oxides. However, water-induced deactivation of the catalysts remains a challenge for further application. In this work, a series of Ce-promoted MnO supported on ZSM-5 (Mn-xCe/ZSM-5) were developed for ozone decomposition, which exhibited superior catalytic performance. The catalysts were characterized by multiple techniques. It is indicated that MnO was highly dispersed on ZSM-5 (Mn/ZSM-5), accounting for the high performance of ozone decomposition. Addition of Ce in Mn/ZSM-5 formed abundant redox pairs that promoted electron transfer, and thus exhibited superior ozone decomposition activity. Mn-3Ce/ZSM-5 with medium Ce loading showed the maximum activity by exposing the most active sites. Furthermore, Mn-3Ce/ZSM-5 was highly water-resistant in comparison with Mn/ZSM-5 by modulating the surface acidic property to be beneficial for the water desorption. This work provides an efficient and facile way to fabricate Ce-promoted Mn with low valence for effective and stable decomposition of ozone at room temperature.

Synergistic effects of flake-like ZnO/SnFe2O4/nitrogen-doped carbon composites on structural stability and electrochemical behavior for lithium-ion batteries

In order to improve the electrochemical performance and relieve volume expansion of pure SnFe₂O₄ anode for lithium-ion batteries (LIBs), we synthesized a novel ZnO/SnFe₂O₄/nitrogen-doped carbon composites (ZSFO/NC) with flake-like polyhedron morphology by using ZIF-8 as a sacrificial template. Remarkably, it exhibited an initial charge/discharge capacities of 1078.3/1507.5 mAh g^-1 with a high initial coulombic efficiency (ICE) of 71.2%, and maintained a steady charge/discharge capacities of 1495.7/1511.8 mAh g^-1 at 0.2 A g^-1 after 300 cycles. The excellent rate performance of 435.6 mAh g^-1 at a higher current density of 10.0 A g^-1 and superior reversible capacity of 532.3/536.2 mAh g^-1 after 500 cycles at 2.0 A g^-1 were obtained. It revealed that the nitrogen-doped carbon matrix and peculiar structure of ZSFO/NC not only effectively buffered large volume expansion upon (de)lithiation through the synergistic interface action between ZnO, SnFe₂O₄ and NC, but also improved capacity of the composite by large contribution of surface pseudo-capacitance. The excellent charge-discharge performance showed that ZSFO/NC composite has a great potential for LIBs due to the synergistic effect of the multi-components.

One-pot thermal decomposition of commercial organometallic salt to Fe2O3@C-N and MnO@C-N for lithium storage

Iron oxide (Fe2O3) nanoparticles encapsulated in the N-doped carbon framework (Fe2O3@C-N) were synthesized via a one-step thermal decomposition reaction of commercial C10H12FeN2NaO8 (ethylenediaminetetraacetic acid monosodium ferric salt), which can serve as the source of Fe, O, C, and N. As an anode material for lithium storage, the Fe2O3@C-N sample exhibits a reversible capacity of 1072 mA h g-1 after 200 cycles at 0.2 A g-1 and 553 mA h g-1 after 500 cycles at 0.5 A g-1. Furthermore, the synthetic strategy can be simply extended to prepare other similar products, e.g. MnO@C-N and ZnO@C-N. The MnO@C-N anode also shows good cycling performances (915 mA h g-1 after 200 cycles at 0.2 A g-1 and 768 mA h g-1 after 500 cycles at 0.5 A g-1).

Advances in metal-organic framework coatings: versatile synthesis and broad applications

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

A Nitrogen-Doped Manganese Oxide Nanoparticles/Porous Carbon Nanosheets Hybrid Material: A High-Performance Anode for Lithium Ion Batteries

A nitrogen-doped MnO nanoparticles/ porous carbon nanosheets (N-MnO/PCS) composite was synthesized by the room-temperature redox reaction between KMnO₄ and PCS followed by a facile carbothermal reduction, and a subsequent coating process of urea onto MnO/PCS and heat treatment. N-MnO nanoparticles with a grain size of about 30 nm are homogenously embedded on the surface of the N-PCS, corresponding to a high loading of 50.09 wt.% in the resulting composite. Benefiting from the enhanced reaction kinetics as well as electrical conductivity and continuous transport pathways of Li⁺ /electron resulting from the N-doping and hybridization of the cross-linked porous carbon substrate, the as-synthesized N-MnO/PCS-1 electrode delivers a large reversible specific capacity (1497.2 mA h g^-1 at 100 mA g^-1 after 160 cycles), outstanding rate capacities (710.6 mA h g^-1 at 1 A g^-1 and 640.1 mA h g^-1 at 2 A g^-1 ) and long-term cycling stability with specific capacity (976 mA h g^-1 at 0.5 A g^-1 after cycling 300 cycles). The simple and green synthesis and electronic properties of this composite mean that it has great potential as a high-capacity anode material for practical application in large-scale energy storage devices.

MOF-derived manganese monoxide nanosheet-assembled microflowers for enhanced lithium-ion storage

Achieving high energy density, power density and cycling performance is a great challenge for lithium-ion battery (LIB) anodes. To obtain favorable electrochemical properties, an effective approach for designing composite nanomaterials with good stability and large specific surface area has been reported here. In this work, metal-organic framework (MOF)-derived manganese monoxides with a stable macromolecular framework were synthesized by utilizing the template agent 1,2,3,4-butanetetracarboxylic acid (BTCA) and the organic salt manganese acetylacetone, which possess a compact microflower structure assembled by nanosheets. As a synergistic effect, not only the amorphous carbon derived from MOFs enhances the specific capacity and stability, but also the unique nanosheet exhibits a significant nano-effect and high areal capacity, which is in favour of an electrochemical reaction. For further enhancement of the electrochemical performance, reduced graphene oxide (rGO) was introduced. When tested as a LIB anode, the MnO@rGO composite displays superior reversible capacities (1716 mA h g-1 at 0.1 A g-1 and 930 mA h g-1 at 2 A g-1) and remarkable rate performances. The research results of the composite nanomaterials lay a foundation for the fabrication of high-capacity and stable anode materials in LIBs.

In situ growth of ZIF-8-derived ternary ZnO/ZnCo2O4/NiO for high performance asymmetric supercapacitors

In this paper, the rational design and synthesis of ZIF-8-derived ternary ZnO/ZnCo₂O₄/NiO wrapped by nanosheets is introduced. Polyhedral ternary ZnO/ZnCo₂O₄/NiO composites surrounded by nanosheets with different compositions are successfully fabricated through in situ growth on ZIF-8 templates and subsequent thermal annealing in air. Electrochemical investigation reveals that when the molar ratio of nickel nitrate to cobalt nitrate is 1, the composite material is more outstanding, which shows a high specific capacitance of 1136.4 F g^-1 at 1 A g^-1 and excellent cycling stability of 86.54% after 5000 cycles. Moreover, the excellent performance of this material is also confirmed by assembling an asymmetric supercapacitor. The assembled hybrid device can reach a large potential range of 0-1.6 V and deliver a high energy density of 46.04 W h kg^-1 as well as the maximum power density of 7987.5 W kg^-1.

A hollow mesoporous carbon from metal-organic framework for robust adsorbability of ibuprofen drug in water

Herein, we described a tunable method for synthesis of novel hollow mesoporous carbon (MPC) via direct pyrolysis (800^oC) of MIL-53 (Fe) as a self-sacrificed template. The structural characterization revealed a hollow, amorphous, defective and mesoporous MPC along with high surface area (approx. 200 m² g^-1). For the experiments of ibuprofen adsorption onto MPC, effects of contact time, MPC dosage, ionic strength, concentration and temperature were systematically investigated. The optimal conditions consisted of pH = 3, concentration 10 mg l^-1 and dose of 0.1 g l^-1 for the highest ibuprofen removal efficiency up to 88.3% after 4 h. Moreover, adsorption behaviour, whereby chemisorption and monolayer controlled the uptake of ibuprofen over MPC, were assumed. Adsorption mechanisms including H-bonding, π-π interaction, metal-oxygen, electrostatic attraction were rigorously proposed. In comparison to several studies, the MPC nanocomposite in this work obtained the outstanding maximum adsorption capacity (206.5 mg g^-1) and good reusability (5 cycles); thus, it can be used as a feasible alternative for decontamination of ibuprofen anti-inflammatory drug from water.

MnO/N-Doped Mesoporous Carbon as Advanced Oxygen Reduction Reaction Electrocatalyst for Zinc-Air Batteries

The development of alternative electrocatalysts exhibiting high activity in the oxygen reduction reaction (ORR) is vital for the deployment of large-scale clean energy devices, such as fuel cells and zinc-air batteries. N-doped carbon materials offer a promising platform for the design and synthesis of electrocatalysts due to their high ORR activity, high surface area, and tunable porosity. In this study, materials in which MnO nanoparticles are entrapped in N-doped mesoporous carbon (MnO/NC) were developed as electrocatalysts for the ORR, and their performances were evaluated in zinc-air batteries. The obtained carbon materials had large surface area and high electrocatalytic activity toward the ORR. The carbon compounds were fabricated by using NaCl as template in a one-pot process, which significantly simplifies the procedure for preparing mesoporous carbon materials and in turn reduces the total cost. A primary zinc-air battery based on this material exhibits an open-circuit voltage of 1.49 V, which is higher than that of conventional zinc-air batteries with Pt/C (Pt/C cell) as ORR catalyst (1.41 V). The assembled zinc-air battery delivered a peak power density of 168 mW cm^-2 at a current density of about 200 mA cm^-2 , which is higher than that of an equivalent Pt/C cell (151 mW cm^-2 at a current density of ca. 200 mA cm^-2 ). The electrocatalytic data revealed that MnO/NC is a promising nonprecious-metal ORR catalyst for practical applications in metal-air batteries.