Fabrication of carbon nanorods and graphene nanoribbons from a metal–organic framework

Amine-Tagged Fragmented Ligand Installation for Covalent Modification of MOF-74

MOF-74 is one of the most explored metal-organic frameworks (MOFs), but its functionalization is limited to the dative post-synthetic modification (PSM) of the monodentate solvent site. Owing to the nature of the organic ligand and framework structure of MOF-74, the covalent PSM of MOF-74 is very demanding. Herein, we report, for the first time, the covalent PSM of amine-tagged defective Ni-MOF-74, which is prepared by de novo solvothermal synthesis by using aminosalicylic acid as a functionalized fragmented organic ligand. The covalent PSM of the amino group generates metal binding sites, and subsequent post-synthetic metalation with Pd^II ions affords the Pd^II -incorporated Ni-MOF-74 catalyst. This catalyst exhibits highly efficient, size-selective, and recyclable catalytic activity for the Suzuki-Miyaura cross-coupling reaction. This strategy is also useful for the covalent modification of amine-tagged defective Ni₂ (DOBPDC), an expanded analogue of MOF-74.

Rh particles in N-doped porous carbon materials derived from ZIF-8 as an efficient bifunctional electrocatalyst for the ORR and HER

Durable and efficient electrocatalysts toward the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are crucial to the development of sustainable energy conversion. In this article, we report a highly active bifunctional electrocatalyst derived from ZIF-8 through simple heat-treatment activation. The resultant catalyst is enriched with Rh nanoparticles in the carbon matrix, showing excellent ORR performance with a half-wave potential (E 1/2) of 0.803 V in alkaline electrolytes; it is simultaneously active for catalyzing the HER with an overpotential of 89 mV to reach a current density of 10 mA cm2 in acidic electrolytes. The prepared RhNC-900 catalyst (1.47 wt% Rh) is comparable to the commercial Pt/C catalyst (20 wt% Pt) in terms of the ORR in alkaline media and might inspire new ideas for the development of fuel cells and water splitting.

Buffered Coordination Modulation as a Means of Controlling Crystal Morphology and Molecular Diffusion in an Anisotropic Metal-Organic Framework

Significant advances have been made in the synthesis of chemically selective environments within metal-organic frameworks, yet materials development and industrial implementation have been hindered by the inability to predictively control crystallite size and shape. One common strategy to control crystal growth is the inclusion of coordination modulators, which are molecular species designed to compete with the linker for metal coordination during synthesis. However, these modulators can simultaneously alter the pH of the reaction solution, an effect that can also significantly influence crystal morphology. Herein, noncoordinating buffers are used to independently control reaction pH during metal-organic framework synthesis, enabling direct interrogation of the role of the coordinating species on crystal growth. We demonstrate the efficacy of this strategy in the synthesis of low-dispersity single-crystals of the framework Co₂(dobdc) (dobdc^4-= 2,5-dioxido-1,4-benzenedicarboxylate) in a pH 7-buffered solution using cobalt(II) acetate as the metal source. Density functional theory calculations reveal that acetate competitively binds to Co during crystallization, and by using a series of cobalt(II) salts with carboxylate anions of varying coordination strength, it is possible to control crystal growth along the c-direction. Finally, we use zero length column chromatography to show that crystal morphology has a direct impact on guest diffusional path length for the industrially important hydrocarbon m-xylene. Together, these results provide molecular-level insight into the use of modulators in governing crystallite morphology and a powerful strategy for the control of molecular diffusion rates within metal-organic frameworks.

Metal organic framework derived porous carbon materials excel as an excellent platform for high-performance packaged supercapacitors

Designing and synthesizing new materials with special physical and chemical properties are the key steps to assembling high performance supercapacitors. Metal organic framework (MOF) derived porous carbon materials have drawn great attention in supercapacitors because of their large specific surface area, high chemical/thermal stability and tunable pore structure. Thus, the recent development of porous carbon as an electrode material for supercapacitors is reviewed. The types, design and synthesis strategies of porous carbon are systematically summarized. This review will be divided into three main parts: (1) the design and synthesis of MOF precursors and templates for MOF-derived porous carbon materials; (2) the application of different types of MOF-derived carbon in supercapacitors; and (3) the design of typical structures of porous carbon composites for supercapacitors. Finally, the problems and challenges confronted when using porous carbon are assessed and elaborated, and some suggestions on future research directions are proposed.

Recent advances on preparation and environmental applications of MOF-derived carbons in catalysis

Carbon materials derived from metal organic frameworks (MOFs) have excellent properties of high surface area, high porosity, adjustable pore size, high conductivity and stability, and their applications in catalysis have become a rapidly expanding research field. In this review, we have summarized the synthesis strategies of MOF-derived carbons with different physical and chemical properties, obtained through direct carbonization, co-pyrolysis and post-treatment. The potential applications of derived carbons, especially monometal-, bimetal-, nonmetal-doped and metal-free carbons in organo-catalysis, photocatalysis and electrocatalysis are analyzed in detail from the environmental perspective. In addition, the improvement of catalytic efficiency is also considered from the aspects of increasing active sites, enhancing the activity of reactants and promoting free electron transfer. The function and synergy of various species of the composites in the catalytic reaction are summarized. The reaction paths and mechanisms are analyzed, and research ideas or trends are proposed for further development.

Electrochemical/Peroxymonosulfate/NrGO-MnFe2O4 for Advanced Treatment of Landfill Leachate Nanofiltration Concentrate

A simple one-pot method was used to successfully embed manganese ferrite (MnFe2O4) nanoparticles on the nitrogen-doped reduced graphene oxide matrix (NrGO), which was used to activate peroxymonosulfate to treat the landfill leachate nanofiltration concentration (LLNC) with electrochemical enhancement. NrGO-MnFe2O4 and rGO-MnFe2O4 were characterized by various means. This indicates that nitrogen-doped could induce more graphene oxide (GO) spall and reduction to produce more active centers, and was favorable for uniformly loading MnFe2O4 particles. The comparison between electrochemical/peroxymonosulfate/NrGO-MnFe2O4 (EC/PMS/NrGO-MnFe2O4) system and different catalytic systems shows that electrochemical reaction, NrGO and MnFe2O4 can produce synergies, and the chemical oxygen demand (COD) removal rate of LLNC can reach 72.89% under the optimal conditions. The three-dimensional (3D-EEM) fluorescence spectrum shows that the system has a strong treatment effect on the macromolecules with intense fluorescence emission in LLNC, such as humic acid, and degrades into substances with weak or no fluorescence characteristics. Gas chromatography-mass spectrometry (GC-MS) indicates that the complex structure of refractory organic compounds can be simplified, while the simple small molecular organic compounds can be directly mineralized. The mechanism of catalytic degradation of the system was preliminarily discussed by the free radical quenching experiment. Therefore, the EC/PMS/NrGO-MnFe2O4 system has significant application potential in the treatment of refractory wastewater.

Direct Pyrolysis of a Manganese-Triazolate Metal-Organic Framework into Air-Stable Manganese Nitride Nanoparticles

Although metal-organic frameworks (MOFs) are being widely used to derive functional nanomaterials through pyrolysis, the actual mechanisms involved remain unclear. In the limited studies to date, elemental metallic species are found to be the initial products, which limits the variety of MOF-derived nanomaterials. Here, the pyrolysis of a manganese triazolate MOF is examined carefully in terms of phase transformation, reaction pathways, and morphology evolution in different conditions. Surprisingly, the formation of metal is not detected when manganese triazolate is pyrolyzed in an oxygen-free environment. Instead, a direct transformation into nanoparticles of manganese nitride, Mn2N x embedded in N-doped graphitic carbon took place. The electrically conductive Mn2N x nanoparticles show much better air stability than bulk samples and exhibit promising electrocatalytic performance for the oxygen reduction reaction. The findings on pyrolysis mechanisms expand the potential of MOF as a precursor to derive more functional nanomaterials.

Uniformly bimetal-decorated holey carbon nanorods derived from metal-organic framework for efficient hydrogen evolution

The hydrogen evolution reaction (HER) as a fundamental process in electrocatalysis plays a significant role in clean energy technologies. For an energy-efficient HER, it demands an effective, durable, and low-cost catalyst to trigger proton reduction with minimal overpotential and fast kinetics. Here, we successfully fabricate a highly efficient HER catalyst of N-C/Co/Mo₂C holey nanorods with Co/β-Mo₂C nanoparticles uniformly embedded in nitrogen-doped carbon (N-C/Co/Mo₂C) by pyrolyzing the molybdate-coordinated zeolitic imidazolate framework (ZIF-67/MoO₄^2-) holey nanorods, which result from the reaction between CoMoO₄ and MeIM in a methanol/water/triethylamine mixed solution. The uniform distribution of MoO₄^2- in the ZIF-67/MoO₄^2- enables Co/β-Mo₂C nanoparticles to be well-distributed within nitrogen-doped carbon holey nanorods. This synthetic strategy endows the N-C/Co/Mo₂C catalyst with uniformly decorated bimetal, thus attaining excellent HER electrocatalytic activities with a small overpotential of 142.0 mV at 10 mA cm^-2 and superior stability in 1.0 mol L^-1 KOH aqueous solution.

Amperometric sensor based on ZIF/g-C3N4/RGO heterojunction nanocomposite for hydrazine detection

A dense  zeolitic imidazolate framework (ZIF) nanosheet is for the first time molded by reduced graphite oxide (RGO) and graphitic carbon nitride (g-C₃N₄) to fabricate an original 2D/2D/2D heterojunction (ZIF/g-C₃N₄/RGO nanohybrid), which is pipetted onto carbon cloth electrode (CCE) (ZIF/g-C₃N₄/RGO/CCE) as an electrochemical sensor. Profiting from the renowned synergistic and coupling effects, the resulting nanohybrid endows excellent electrocatalytic activity towards hydrazine. Amperometric detection reveals that the hybrid sensor possesses a low detection limit of 32 nM (S/N = 3) in a monitoring range of 0.0001 to 1.0386 mM, along with a high sensitivity 93.71 μA mM^-1 cm^-2. Importantly, the minimum detection concentration of hydrazine in the actual sample is lower than the maximum allowable limit of the World Health Organization (WHO) and has high reproducibility (RSD = 4.82%). As expected, the high sensing capability  of ZIF/g-C₃N₄/RGO combines the advantages of abundant surface-active sites and high conductivity along with 2D interfaces between ZIF, g-C₃N₄, and RGO nanosheets. This study provides a promising to expand 2D-based ternary nanojunction as a bridge for promoting sensing performance.Graphical abstract.

Ni@onion-like carbon and Co@amorphous carbon: control of carbon structures by metal ion species in MOFs

We first report the facile synthesis of metal-carbon composites consisting of metal nanoparticles (NPs) and different types of carbon species: onion-like and amorphous carbon, Ni@onion-like carbon and Co@amorphous carbon. By simply changing the metal species in an isostructural metal-organic framework, thermal decompositions of MOF-74 directly afforded different types of metal NPs and carbon composites, which exhibited good electrical conductivity. In particular, the Ni@onion-like carbon, having a well-ordered carbon structure, had high electrical conductivity (σ = 5.3 Ω-1 cm-1 at 295 K), explained by a modified model of the Efros-Shklovskii variable range hopping.

Tuning CuZn interfaces in metal–organic framework-derived electrocatalysts for enhancement of CO2 conversion to C2 products

CuZn alloy derived from a metal–organic framework shows a 5-fold enhancement in faradaic efficiency for CO2 reduction to C2 products compared to Cu alone. Density functional theory calculation provides important mechanistic insights.

Preferred zinc-modified melamine phytate for the flame retardant polylactide with limited smoke release

The higher flame retardancy and smoke suppression effects for PLA/MPAZn₂₀ were mainly ascribed to the condensed phase during combustion.

Covalent organic frameworks (COFs) for electrochemical applications

Covalent organic frameworks are a class of extended crystalline organic materials that possess unique architectures with high surface areas and tuneable pore sizes. Since the first discovery of the topological frameworks in 2005, COFs have been applied as promising materials in diverse areas such as separation and purification, sensing or catalysis. Considering the need for renewable and clean energy production, many research efforts have recently focused on the application of porous materials for electrochemical energy storage and conversion. In this respect, considerable efforts have been devoted to the design and synthesis of COF-based materials for electrochemical applications, including electrodes and membranes for fuel cells, supercapacitors and batteries. This review article highlights the design principles and strategies for the synthesis of COFs with a special focus on their potential for electrochemical applications. Recently suggested hybrid COF materials or COFs with hierarchical porosity will be discussed, which can alleviate the most challenging drawback of COFs for these applications. Finally, the major challenges and future trends of COF materials in electrochemical applications are outlined.

Ordered-Mesoporous-Carbon-Confined Pb/PbO Composites: Superior Electrocatalysts for CO2 Reduction

CO₂ electroreduction has gained significant interest. However, fabricating cost-effective nonprecious-metal electrocatalysts that can selectively convert CO₂ to a specific product remains highly challenging. Herein, Pb-based materials consisting of Pb⁰ and PbO confined in ordered mesoporous carbon (OMC) (Pb/PbO@OMC) were constructed for CO₂ electroreduction to CO. Interestingly, the activity and selectivity of the Pb/PbO@OMC varied with the molar ratio of Pb⁰ /PbO. The material calcined at 800 °C (Pb/PbO@OMC-800) with a Pb⁰ /PbO ratio of 0.58 provided the best result with CO as the only carbon-based product, and the Faradaic efficiency of CO reached 98.3 % at a high current density of 41.3 mA cm^-2 . Detailed studies indicated that Pb⁰ , PbO, and OMC co-operated well to enhance the performance of Pb/PbO@OMC-800, which mainly originated from the good interface between Pb⁰ and PbO, higher electrochemical active surface area, and faster electron transfer to form the CO₂ ^⋅- intermediate.

Multifunctional metal-organic frameworks in oil spills and associated organic pollutant remediation

The release of toxic organic compounds into the environment in an event of oil spillage is a global menace due to the potential impacts on the ecosystem. Several approaches have been employed for oil spills clean-up, with adsorption technique proven to be more promising for the total reclamation of a polluted site. Of the several adsorbents so far reported, adsorbent-based porous materials have gained attention for the reduction/total removal of different compounds in environmental remediation applications. The superior potential of mesoporous materials based on metal-organic frameworks (MOFs) against conventional adsorbents is due to their intriguing and enhanced properties. Therefore, this review presents recent development in MOF composites; methods of preparation; and their practical applications towards remediating oil spill, organic pollutants, and toxic gases in different environmental media, as well as potential materials in the possible deployment in reclaiming the polluted Niger Delta due to unabated oil spillage and gas flaring.

Ink-Assisted Synthetic Strategy for Stable and Advanced Composite Electrocatalysts with Single Fe Sites

The oxygen evolution reaction is critical to the efficiency of many energy technologies that store renewable electricity in chemical form. However, the rational design of high-performance and stable catalysts to drive this reaction remains a formidable challenge. Here, a facile ink-assisted strategy to construct a series of stable and advanced composite electrocatalysts with single Fe sites for permitting seriously improved performance characteristics is reported. As revealed by a suit of characterization techniques and theoretical methods, the improved electrocatalytic performance and stability can be attributed to the unique coordination states of Fe in the form of distorted FeO₄ C and the interfacial effect in the composite system that optimize and stabilize single Fe sites in changing to better configurations for intermediates adsorption. The findings provide a novel strategy to in-depth understanding of practical guidelines for the electrocatalyst design for energy conversion devices.

Nanoribbon Superstructures of Graphene Nanocages for Efficient Electrocatalytic Hydrogen Evolution

Two-dimensional carbon architectures are attracting tremendous interests for various promising applications due to their outstanding electronic and mechanical properties, although it is a great challenge to rationally devise facile and operative methodologies to engineer their structural traits owing to complex synthetic processes. Herein, for the first time, we fabricate two-dimensional carbon nanoribbons via direct thermal exfoliation of one-dimensional Ni-based metal-organic framework (MOF) nanorods, in which interconnected graphitic carbon nanocages are self-assembled into a belt-like superstructure with carbon-encapsulated Ni nanoparticles immobilized on the surface. Due to the unparalleled structural superiority, the MOF-derived carbon nanobelts exhibit excellent catalytic performances in electrocatalytic hydrogen evolution. Importantly, the practical synthetic strategy may trigger the rapid development of carbon-based superstructures in many frontier fields.

Multi-functional flexible 2D carbon nanostructured networks

Two-dimensional network-structured carbon nanoscale building blocks, going beyond graphene, are of fundamental importance, and creating such structures and developing their applications have broad implications in environment, electronics and energy. Here, we report a facile route, based on electro-spraying/netting, to self-assemble two-dimensional carbon nanostructured networks on a large scale. Manipulation of the dynamic ejection, deformation and assembly of charged droplets by control of Taylor cone instability and micro-electric field, enables the creation of networks with characteristics combining nanoscale diameters of one-dimensional carbon nanotube and lateral infinity of two-dimensional graphene. The macro-sized (meter-level) carbon nanostructured networks show extraordinary nanostructural properties, remarkable flexibility (soft polymeric mechanics having hard inorganic matrix), nanoscale-level conductivity, and outstanding performances in distinctly different areas like filters, separators, absorbents, and wearable electrodes, supercapacitors and cells. This work should make possible the innovative design of high-performance, multi-functional carbon nanomaterials for various applications.

Bottom-Up, On-Surface-Synthesized Armchair Graphene Nanoribbons for Ultra-High-Power Micro-Supercapacitors

Bottom-up-synthesized graphene nanoribbons (GNRs) with excellent electronic properties are promising materials for energy storage systems. Herein, we report bottom-up-synthesized GNR films employed as electrode materials for micro-supercapacitors (MSCs). The micro-device delivers an excellent volumetric capacitance and an ultra-high power density. The electrochemical performance of MSCs could be correlated with the charge carrier mobility within the differently employed GNRs, as determined by pump-probe terahertz spectroscopy studies.

Heterogeneous Interface Induced the Formation of Hierarchically Hollow Carbon Microcubes against Electromagnetic Pollution

Carbon materials with multilevel structural features are showing great potentials in electromagnetic (EM) pollution precaution. With ZIF-67 microcubes as a self-sacrificing precursor, hierarchical carbon microcubes with micro/mesoporous shells and hollow cavities have been successfully fabricated with the assistance of rigid SiO₂ coating layers. It is found that the SiO₂ layer can effectively counteract the inward shrinkage of organic frameworks during high-temperature pyrolysis due to intensive interfacial interaction. The obtained hollow porous carbon microcubes (HPCMCs) exhibit larger Brunauer-Emmett-Teller surface area and pore volume than porous carbon microcubes (PCMCs) directly derived from ZIF-67 microcubes. The unique microstructure is confirmed to be favorable for conductive loss and interfacial polarization, thus boosting the overall dielectric loss capability of carbon materials. Besides, hollow cavity will also promote multiple reflection of incident EM waves and intensify the dissipation of EM energy. As expected, HPCMCs harvest better microwave absorption performance, including strong reflection loss intensity and broad response bandwidth, than many traditional microporous/mesoporous carbon materials. This study provides a new strategy for the construction of hierarchical carbon materials and may inspire the design of carbon-based composites with excellent EM functions.

Porous Carbon-Based Supercapacitors Directly Derived from Metal-Organic Frameworks

Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to other porous materials. Not only the electrical double-layer capacitance (EDLC)-based charge storage but also the pseudocapacitance driven by various dopants in the carbon matrix plays a significant role in enhancing the electrochemical supercapacitive performance of porous carbons. Since the electrochemical capacitive activities are primarily based on EDLC and further enhanced by pseudocapacitance, high-surface carbons are desirable for these applications. The porosity of carbons plays a crucial role in enhancing the performance as well. We have recently witnessed that metal-organic frameworks (MOFs) could be very effective self-sacrificing templates, or precursors, for new high-surface carbons for supercapacitors, or ultracapacitors. Many MOFs can be self-sacrificing precursors for carbonaceous porous materials in a simple yet effective direct carbonization to produce porous carbons. The constituent metal ions can be either completely removed during the carbonization or transformed into valuable redox-active centers for additional faradaic reactions to enhance the electrochemical performance of carbon electrodes. Some heteroatoms of the bridging ligands and solvate molecules can be easily incorporated into carbon matrices to generate heteroatom-doped carbons with pseudocapacitive behavior and good surface wettability. We categorized these MOF-derived porous carbons into three main types: (i) pure and heteroatom-doped carbons, (ii) metallic nanoparticle-containing carbons, and (iii) carbon-based composites with other carbon-based materials or redox-active metal species. Based on these cases summarized in this review, new MOF-derived porous carbons with much enhanced capacitive performance and stability will be envisioned.

Flexible supercapacitor electrodes using metal-organic frameworks

Advancements in the field of flexible and wearable devices require flexible energy storage devices to cater their power demands. Metal-ion batteries (such as lithium-ion batteries, sodium-ion batteries, etc.) and electrochemical capacitors (also called supercapacitors or ultracapacitors) have achieved great interest in the recent past due to their superior energy storage characteristics like high power density and long cycle life. A major bottleneck of using metal-ion batteries in wearable devices is their lack of flexibility. Low power density, toxicity and flammability due to organic electrolytes inhibit them from safe on-body device applications. On the other hand, supercapacitors can be made with aqueous electrolytes, making them a safer alternative for wearable applications. Metal-organic frameworks (MOFs) are novel candidates as electrode materials due to their salient features such as large surface area, three-dimensional porous architecture, permeability to foreign entities, structural tailorability, etc. Though pristine MOFs suffer from poor intrinsic conductivity, this can be rectified by preparing composites with other electronically conducting materials. MOF-based electrodes are highly promising for flexible and wearable supercapacitors since they exhibit good energy and power densities. This review focuses on the new developments in the field of MOF-based composite electrodes for developing flexible supercapacitors.

Synthesis of a Magnetic 2D Co@NC-600 Material by Designing a MOF Precursor for Efficient Catalytic Reduction of Water Pollutants

2D metal-organic framework (MOFs) can be ideal sacrificial templates for fabricating nanomaterials because of active sites exposed on the surface rather than in pores and channels, often exhibiting improved performance in catalysis applications. In this study, the novel 2D layered cobalt-based MOF [Co(TPT)(fma)(H₂O)₂]·3H₂O (Co-MOF) has been constructed by the selection of high N atom content ligands. On this basis, a 2D nitrogen-doped carbon-coated cobalt nanoparticle composite (Co@NC) was prepared by using this MOF as a precursor. Magnetic Co@NC has excellent catalytic activity and recycling features regarding the reaction of 4-nitrophenol (4-NP) reducing to 4-aminophenol (4-AP) in the presence of NaBH₄ at ambient temperature. 2D Co@NC-600 can reach nearly 100% conversion within 120 s and its stability remains almost unchanged after five reaction cycles. Moreover, this Co@NC catalyst also is highly active for catalytic reduction of dyes such as Rhodamine B (RhB) and Methylene blue (MB).

Simple homogeneous electrochemical target-responsive aptasensor based on aptamer bio-gated and porous carbon nanocontainer derived from ZIF-8

A simple homogeneous electrochemical aptasensor was designed by using target-responsive substrate releasing from aptamer-gated zeolitic imidazolate framework-8 (ZIF-8)-derived porous carbon nanocontainer. The nanocontainer (Z-700) was prepared by calcination of ZIF-8 at 700 °C. Z-700 had great biocompatibility, high surface areas and pore volume, especially the graphene-like π-rich structure, which was beneficial for adsorbing aptamer easily. The electroactive dyes methylene blue (MB) was then trapped in the pores of Z-700 and easily capped with aptamer as gatekeeper based on π-stacking interaction. Upon addition of target protein thrombin (Thb), the Thb could specifically recognize and combine with its aptamer to form complex. Thereafter, the aptamer bio-gate opened and the MB released from the pores, which could be detected on the screen-printed electrode. Under the optimized conditions, the proposed Thb aptasensor showed a wide detection range from 1 fM to 1 nM with a low detection limit of 0.57 fM. The strategy by using ZIF-8-derived porous carbon and aptamer bio-gate provides a promising scheme for developing simple, rapid, reliable and ultrasensitive bioassays, which has a great potential as a powerful tool in disease diagnosis and biomedicine.

Improving the Antioxidation Capability of the Ni Catalyst by Carbon Shell Coating for Alkaline Hydrogen Oxidation Reaction

Increasing the antioxidation capability of Ni for the hydrogen oxidation reaction (HOR) is considered important and challenging for alkaline polymer electrolyte fuel cells (APEFCs). Herein, we report a series of Ni-core carbon-shell (Ni@C) catalysts obtained by a vacuum pyrolysis method treated at different temperatures. According to the cyclic voltammetry tests and the HOR tests, Ni@C treated at 500 °C exhibits a much higher Ni core utilization and better catalytic activity toward HOR than the commonly used Ni/C catalyst. Furthermore, X-ray photoelectron spectroscopy characterization shows that a higher percentage of Ni⁰ appears at the surface of the Ni core of Ni@C than the Ni/C catalyst. The accelerated durability tests, as well as the chronoamperometry tests, suggest that the antioxidation capability of Ni has been obviously improved by the carbon shells. The Raman spectra show that the graphitization degree of the carbon shells might be the key factor affecting the Ni utilization and the HOR catalytic activity of the Ni@C catalysts. The APEFC achieves a peak power density of 160 mW/cm² using Ni@C-500 °C as the anode, which could also stably discharge for 120 h at 0.7 V.

Co-etching effect to convert waste polyethylene terephthalate into hierarchical porous carbon toward excellent capacitive energy storage

With the ever-increasing consumption of polyethylene terephthalate (PET) related products, how to recycle the waste PET still remains as a great challenge for the sustainable development. Converting waste PET into porous carbon material has been emerged as a promising way to address this issue. Recently, the microporous carbon derived from waste PET has drawn considerable attention in adsorption field, but its electrochemical application is still impeded by low specific surface area (SSA <1500 m² g^-1) and small meso-/macropores volume (<0.2 cm³ g^-1). Herein, hierarchical porous carbon (HPC) is successfully prepared from waste PET. The obtained HPC possesses a high SSA (2238 m² g^-1) and a large meso-/macropores volume (0.51 cm³ g^-1). The formation mechanism of hierarchical porous structure is proposed: co-etching effect of sp²/sp³ hybridized carbon produces micropores and meso-/macropores, respectively. In a three-electrode configuration, HPC based electrode achieves an outstanding capacitance of 413 F g^-1, while the traditional microporous carbon exhibits a low capacitance of 142 F g^-1. The fabricated symmetric supercapacitor shows a high energy density of 25 Wh kg^-1. This work provides a good reference to convert waste plastics into hierarchical porous carbon.

Bimetallic organic framework derivation of three-dimensional and heterogeneous metal selenides/carbon composites as advanced anodes for lithium-ion batteries

Heterogeneous structures have been attracting increasing attention in energy storage and conversion applications due to the phase interface and synergistic effect of multiple components. Herein, bimetal organic framework analogues were introduced to construct a Zn/Co bimetallic selenide heterostructure within a 3D-porous N-doped carbon matrix by a NaCl template-assisted lyophilization and annealing process. The cross-linked 3D network can enhance the transport kinetics for both lithium ions and electrons. The stress resulting from the cycling process can be released by interconnected channels in the composite. ZnSe and CoSe₂ experience electrochemical reactions at different potentials, which can buffer volume changes mutually to effectively increase structural stability. Meanwhile, abundant active sites due to the heterostructure enhance pseudocapacitive performance and reaction kinetics, resulting in high specific capacity and good rate performance. As anode materials for lithium-ion batteries, the three-dimensional ZnSe/CoSe₂-C composite exhibits a high reversible capacity of 700 mA h g^-1 after 500 cycles at 1 A g^-1.

Magnetic Fe3O4-encapsulated VAN@MIL-101(Fe) with mixed-valence sites and mesoporous structures as efficient bifunctional water splitting photocatalysts

Fe3O4/VAN@MIL-101(Fe) with both mesoporous and mixed-valence Fe3+/Fe2+ structures was controllably synthesized in the synthesis of MIL-101(Fe), and it was used as a bifunctional photocatalyst in both oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs) of photocatalytic water splitting. By the reduction of auxiliary ligand vanillin (VAN) and the introduction of Fe3O4, the mixed-valence Fe3+/Fe2+ structure in Fe3O4/VAN@MIL-101(Fe) was obtained, which improves the band gap of the Fe3+ reactive active center and increases the separation efficiency of photogenerated carriers. Owing to the partial difference in the structure between VAN and ligand terephthalic acid (H2BDC), hierarchical porous and vacant structures were effectively improved in Fe3O4/VAN@MIL-101(Fe), which can induce more active sites to adsorb more water molecules and shorten the electron-hole migration distance to improve the transfer efficiency of photogenerated carriers. Therefore, Fe3O4/VAN@MIL-101(Fe) presents excellent photocatalytic activities for improving the O2 and H2 production rate up to 360 000 μmol g-1 h-1 and 584 μmol g-1 h-1, respectively. Meanwhile, Fe3O4/VAN@MIL-101(Fe) maintains the excellent catalytic activity in OERs and HERs after recycling for 5 times. Moreover, the introduction of magnetic Fe3O4 nanoplates into Fe3O4/VAN@MIL-101(Fe) can make it easily recyclable by magnetic separation, which can maximize its performance.

Hierarchically Porous Carbons Derived from Nonporous Coordination Polymers

Hierarchically porous carbons (HPCs) with multimodal pore systems exhibit great technological potentials, especially in the fields of heterogeneous catalysis, energy storage, and conversion. Here, we establish a simple and general approach to HPCs by carbonization of nonporous coordination polymers that are produced by mixing metal salts with polytopic ligands in alkaline aqueous solutions at room temperature. The proposed approach is applicable to a wide scope of ligand molecules (18 examples), thus affording the synthesized HPCs with high diversity in porosity, morphology, and composition. In particular, the prepared HPCs exhibit high specific surface areas (up to 2647 m² g^-1) and large pore volumes (up to 2.39 cm³ g^-1). The HPCs-supported atomically dispersed Fe-N_x catalysts show much-improved fuel cell cathode performance over the micropore-dominated carbon black-supported catalysts, demonstrating the structural superiority of the HPCs for enhancing the mass transport properties.

Direct carbonization of organic solvents toward graphene quantum dots

The bottom-up synthesis of graphene quantum dots (GQDs) using solvothermal methods has attracted considerable attention because of their fewer defects and controllable size/morphology. However, the influence of organic solvents on the preparation of GQDs is still unknown. Herein, a systematic study on the carbonization of organic solvents toward GQDs is reported. The results show that organic solvents with the double bond or benzene ring or double hydrophilic groups could be directly decomposed into GQDs without the addition of catalysts or molecular precursors. The as-synthesized GQDs demonstrate ultra-small size distribution, high stability, tunable excitation wavelength and upconverted fluorescence. Both hematological and histopathological analyses show that the as-synthesized GQDs demonstrate a very good safety profile and excellent biocompatibility. The versatility of this synthesis strategy offers easy control of the surface group, composition, and optical properties of GQDs at the molecular level.