Electrochemical biosensor for rapid and sensitive monitoring of sulfadimethoxine based on nanoporous carbon and aptamer system

In this study, a straightforward electrochemical aptasensor was developed to detect sulfadimethoxine (SDM). It included a glassy carbon electrode decorated by boron nitride quantum dots (BNQDs) and aptamer-functionalized nanoporous carbon (APT/CZ). CZ was first synthesized by calcinating a zeolitic imidazolate framework (ZIF-8). Then, the electroactive dye methylene blue (MB) was entrapped inside its pores. By attaching aptamer to the CZ surface, APT/CZ acted as a bioguard, which prevented the MB release. Therefore, the electrochemical signal of the entrapped MB was high in the absence of SDM. Introducing SDM caused the conformation of aptamers to change, and a large number of MB was released, which was removed by washing. Therefore, the detection strategy was done based on the change in the electrochemical signal intensity of MB. The aptasensor was applied to detect SDM at a concentration range of 10-17 to 10-7 M with a detection limit of 3.6 × 10-18 M.

Removal of bisphenol A in a heterogeneous Fenton system via biochar synthesized using different Fe precursors: Properties, effects, and mechanisms

The reactivity and mechanism of the Fe-doped biochar (FeBC) Fenton reaction are typically influenced by the amount and type of Fe species in materials. This study investigated the effects of different Fe precursors (FeSO4, Fe(NO)3, FeCl2, and FeCl3) used to prepare Fenton catalyst FeBCs (FeSBC, FeNBC, FeC2BC, and FeC3BC) on the physicochemical characteristics, pH resistance, and reactivity for bisphenol A (BPA) removal. In addition to the FeSBC/H2O2 (0.007 min-1) system, FeNBC/H2O2 (1.143 min-1), FeC2BC/H2O2 (0.278 min-1), and FeC3BC/H2O2 (0.556 min-1) completely removed BPA within 20 min under the optimal conditions (FeBCs: 0.1 g/L; H2O2: 1 mM; BPA: 20 mg/L; pH 3). FeBCs/H2O2 systems demonstrated good stability and resistance to inorganic anions and natural organic matter under appropriate initial pH conditions. However, FeC2BC and FeC3BC exhibited better pH applicability than FeNBC. Characterization results indicated that the physicochemical properties of FeBCs were dependent on the Fe precursor, which correlated with the degree of Fe corrosion and the production of distinct reactive oxygen species (ROS). Quenching experiments and electron spin resonance detection results indicated that OH, 1O2, and O2- species were all engaged in BPA removal; the ROS concentrations were significantly influenced by the initial pH and Fe precursor. The results indicate that Fe precursors significantly impact the performance and characteristics of Fe-based biochar materials, which are tailorable to specific applications.

Hollow mesoporous carbon supported Co-modified Cu/Cu2O electrocatalyst for nitrate reduction reaction

The electroreduction of nitrate (NO3-) pollutants to ammonia (NH3) provides a sustainable approach for both wastewater treatment and NH3 synthesis. However, electroreduction of nitrate requires multi-step electron and proton transfer, resulting in a sluggish reaction rate. Herein, we synthesized a Co-modified Cu/Cu2O catalyst supported on hollow mesoporous carbon substrates (Co/Cu/Cu2O-MesoC) by a one-step microwave-assisted reduction method. At -0.25 V vs. reversible hydrogen electrode (RHE), Co/Cu/Cu2O-MesoC shows a Faradaic efficiency (FE) of 100 ± 1% in 0.1 M NO3-. Notably, the maximum NH3 yield rate (YieldNH3) reaches 6.416 ± 0.78 mmol mgcat-1h-1 at -0.45 V vs. RHE, which is much better than most of the previous reports. Electrochemical evaluation and in-situ Fourier transform infrared (FTIR) spectroscopy reveal that the addition of Co could promote water electrolysis, and the generated H* is involved in the following hydrogenation of intermediates, ultimately leading to faster kinetics and energetics during electrocatalytic conversion of NO3- to NH3. This synergetic electrocatalysis strategy opens a new avenue for the development of high-activity, selectivity, and stability catalysts.

Recent Advances in Hierarchical Porous Engineering of MOFs and Their Derived Materials for Catalytic and Battery: Methods and Application

Hierarchical porous materials have attracted the attention of researchers due to their enormous specific surface area, maximized active site utilization efficiency, and unique structure and properties. In this context, metal-organic frameworks (MOFs) offer a unique mix of properties that make them particularly appealing as tunable porous substrates containing highly active sites. This review focuses on recent advances in the types and synthetic strategies of hierarchical porous MOFs and their derived materials. Furthermore, it highlights the relationship between the mass diffusion and transport of hierarchical porous structures and the pore size with examples and simulations, while identifying their potential and limitations. On this basis, how the synthesis conditions affect the structure and electrochemical properties of MOFs based hierarchical porous materials with different structures is discussed, highlighting the prospects and challenges for the synthetization, as well as further scientific research and practical applications. Finally, some insights into current research and future design ideas for advanced MOFs based hierarchical porous materials are presented.

Leaching in Specific Facets of ZIF-67 and ZIF-L Zeolitic Imidazolate Frameworks During the CO2 Cycloaddition with Epichlorohydrin

Zeolitic imidazolate frameworks (ZIFs) have been profusely used as catalysts for inserting CO₂ into organic epoxides (i.e., epichlorohydrin) through cycloaddition. Here, we demonstrate that these materials suffer from irreversible degradation by leaching. To prove this, we performed the reactions and analyzed the final reaction mixtures by elemental analysis and the resulting materials by different microscopies. We found that the difference in catalytic activity between three ZIF-67 and one ZIF-L catalysts was related to the rate at which the materials degraded. Particularly, the {100} facet leaches faster than the others, regardless of the material used. The catalytic activity strongly depended on the amount of leached elements in the liquid phase since these species are extremely active. Our work points to the instability of these materials under relevant reaction conditions and the necessity of additional treatments to improve their stability.

Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO₂ and electrochemical synthesis of H₂ O₂ are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

MOF-derived nanoporous carbons with diverse tunable nanoarchitectures

Metal-organic frameworks (MOFs), or porous coordination polymers, are crystalline porous materials formed by coordination bonding between inorganic and organic species on the basis of the self-assembly of the reacting units. The typical characteristics of MOFs, including their large specific surface areas, ultrahigh porosities and excellent thermal and chemical stabilities, as well as their great potential for chemical and structural modifications, make them excellent candidates for versatile applications. Their poor electrical conductivity, however, has meant that they have not been useful for electrochemical applications. Fortuitously, the direct carbonization of MOFs results in a rearrangement of the carbon atoms of the organic units into a network of carbon atoms, which means that the products have useful levels of conductivity. The direct carbonization of zeolitic imidazolate framework (ZIF)-type MOFs, particularly ZIF-8, has successfully widened the scope of possible applications of MOFs to include electrochemical reactions that could be used in, for example, energy storage, energy conversion, electrochemical biosensors and capacitive deionization of saline water. Here, we present the first detailed protocols for synthesizing high-quality ZIF-8 and its modified forms of hollow ZIF-8, core-shell ZIF-8@ZIF-67 and ZIF-8@mesostuctured polydopamine. Typically, ZIF-8 synthesis takes 27 h to complete, and subsequent nanoarchitecturing procedures leading to hollow ZIF-8, ZIF-8@ZIF-67 and ZIF-8@mPDA take 6, 14 and 30 h, respectively. The direct-carbonization procedure takes 12 h. The resulting nanoporous carbons are suitable for electrochemical applications, in particular as materials for supercapacitors.

Biobased polyporphyrin derived porous carbon electrodes for highly efficient capacitive deionization

Recently, capacitive deionization (CDI) has attracted considerable interest as a potential desalination technique for seawater. It is thus desirable to develop low-cost, sustainable, and efficient electrode materials for desalination. In this study, the polyporphyrin was prepared by a one-pot reaction from biobased furan derivative, followed by activation to manufacture nitrogen-doped polyporphyrin derived porous carbons (NPPCs) for efficient capacitive deionization. In the presence of KOH as a pore activator, NPPCs exhibited cross-linked interconnected nanosphere chain-like structures inherited from the polyporphyrin backbone with coexisting mesopores and micropores, leading to extremely high specific surface area (2979.3 m² g^-1) and large pore volume (2.22 cm³ g^-1). The electrochemical measurements revealed good conductivity, outstanding stability, and extraordinary specific capacitance (328.7 F g^-1) of NPPCs, which can be ascribed to rich nitrogen content (8.0 at%) and high Pyrrolic nitrogen ratio. Due to their superior hierarchical porous structure and excellent electrochemical performance, the NPPC-800 electrodes presented a high salt adsorption capacity (SAC) of 35.7 mg g^-1 and outstanding cycling stability in 10 mM NaCl solution at 1.2 V during the desalination tests. This work demonstrates the utilization of biobased porous carbon material will pave a prospective way in sustainable and potential applications for CDI technique.

Highly efficient removal of quinolones by using the easily reusable MOF derived-carbon

As anthropogenic antibiotics, quinolones, e.g., ofloxacin have adverse impacts on ecological systems and human heaths. The removal of quinolones is of great importance, and adsorption techniques have been widely used to remove this hazardous contaminant. However, a robust and easy-operating adsorbent is still emergently required due to the complex chemical structure of quinolones. In this study, we successfully synthesized the promising metallic carbons (MCs) containing carbon nanotubes and cobalt nanoparticles by carbonizing Zn/Co-ZIF at 900 °C. Three different molar ratios of Co and Zn were applied to optimize the adsorption capacity on ofloxacin (OFL). Results showed MC with molar ratio of Co and Zn at 3:1 (Co-CNT/NPC_3/1) achieved the maximal adsorption capacity to 118.3 mg g^-1. Its adsorption performance was satisfied in the pH range from 5 to 9 and ionic strengths at 0.01 M. The main mechanisms for these adsorptions were identified as electrostatic attraction, metal coordination and π-π EDA. Removal efficiencies of quinolones higher than 68 mg g^-1 indicated the strong feasibility of this adsorbent for wastewater treatments. The regeneration of Co-CNT/NPC_3/1 at 600 °C allowed its at least 4-time reusability and its magnetic property enabled external magnets to recycle it from real environments.

Strategic design of Fe and N co-doped hierarchically porous carbon as superior ORR catalyst: from the perspective of nanoarchitectonics

In this study, we present microporous carbon (MPC), hollow microporous carbon (HMC) and hierarchically porous carbon (HPC) to demonstrate the importance of strategical designing of nanoarchitectures in achieving advanced catalyst (or electrode) materials, especially in the context of oxygen reduction reaction (ORR). Based on the electrochemical impedance spectroscopy and ORR studies, we identify a marked structural effect depending on the porosity. Specifically, mesopores are found to have the most profound influence by significantly improving electrochemical wettability and accessibility. We also identify that macropore contributes to the rate capability of the porous carbons. The results of the rotating ring disk electrode (RRDE) method also demonstrate the advantages of strategically designed double-shelled nanoarchitecture of HPC to increase the overall electron transfer number (n) closer to four by offering a higher chance of the double two-electron pathways. Next, selective doping of highly active Fe–N_x sites on HPC is obtained by increasing the nitrogen content in HPC. As a result, the optimized Fe and N co-doped HPC demonstrate high ORR catalytic activity comparable to the commercial 20 wt% Pt/C in alkaline electrolyte. Our findings, therefore, strongly advocate the importance of a strategic design of advanced catalyst (or electrode) materials, especially in light of both structural and doping effects, from the perspective of nanoarchitectonics.

This study elucidates the role of each class of nanopore by in-depth electrochemical analysis of three types of ZIF-8-derived carbons. Also, engineered co-doping of Fe and N is found essential to selectively form Fe–N_x sites in the carbon matrix.

KOH-Activated Hollow ZIF-8 Derived Porous Carbon: Nanoarchitectured Control for Upgraded Capacitive Deionization and Supercapacitor

Herein, the synergistic effects of hollow nanoarchitecture and high specific surface area of hollow activated carbons (HACs) are reported with the superior supercapacitor (SC) and capacitive deionization (CDI) performance. The center of zeolite imidazolate framework-8 (ZIF-8) is selectively etched to create a hollow cavity as a macropore, and the resulting hollow ZIF-8 (HZIF-8) is carbonized to obtain hollow carbon (HC). The distribution of nanopores is, subsequently, optimized by KOH activation to create more nanopores and significantly increase specific surface area. Indeed, as-prepared hollow activated carbons (HACs) show significant improvement not only in the maximum specific capacitance and desalination capacity but also capacitance retention and mean desalination rates in SC and CDI, respectively. As a result, it is confirmed that well-designed nanoarchitecture and porosity are required to allow efficient diffusion and maximum electrosorption of electrolyte ions.

The Central Role of Nitrogen Atoms in a Zeolitic Imidazolate Framework-Derived Catalyst for Cathodic Hydrogen Evolution

Platinum usually offers the most effective active center for hydrogen evolution reaction (HER), because of the optimal trade-off between the adsorption and desorption of hydrogeN atoms (H*) on Pt atoms. Herein, we report an unusual result regarding the active center of a HER catalyst, which was synthesized by electrodepositing traces of Pt nanoparticles (NPs) into a porous nitrogen-rich dodecahedron matrix derived from zeolitic imidazolate framework ZIF-8. With an ultra-low Pt loading of 2.76 μg cm^-2 , the N-Pt-bonded catalyst can produce a current density of 117 mA cm^-2 for the HER in 1.0 m H₂ SO₄ at an overpotential of 50 mV, whereas the commercial Pt/C (300 μg cm^-2 Pt) can only reach 50 mA cm^-2 under the same conditions. Cyclic voltammetry demonstrates that both the H* adsorption and the Pt oxidation are not allowed to occur on this catalyst, due to a full surface coverage of the trace Pt NPs by imidazole. The results from the specially designed experiments indicate that the imidazole N atoms may act as proton anchor-sites for the HER due to their electron donor nature. Density functional theory calculations also support a catalytic HER mechanism centered at the Pt-supported N active center, which needs a Gibbs free energy of H* absorption (ΔG_H* ) significantly smaller than the absolute value of ΔG_H* on the Pt(111) surface. We hope that the results of this study will encourage the research on novel N-centered catalysts for the HER.

Metal-Organic Framework-Derived CoOx/Carbon Composite Array for High-Performance Supercapacitors

Metal-organic frameworks (MOFs) and their derivatives are promising materials for energy conversion and storage. This study demonstrates a solvent-free method to fabricate a CoO_x/carbon composite array derived from ZIF-67 for asymmetric supercapacitors. Tree-like Co metal arrays are electrodeposited on a surface and then directly converted into composite ZIF-67/Co-based MOF arrays via a chemical vapor deposition method (MOF-CVD). Finally, the CoO_x/carbon composite array is obtained by regulated calcination of the ZIF-67/Co composite array. The as-prepared CoO_x/carbon composite arrays provide a less tortuous pathway for ion diffusion, high pseudocapacitance from transition-metal oxides, and good electrical conductivity from carbon. Moreover, the absence of adhesives in array electrodes is also beneficial to the promotion of the electrochemical performance. The as-fabricated CoO_x/carbon composite array electrode shows excellent electrochemical performance with high energy density, high power density, superior rate capability, and long cycle life in an asymmetric supercapacitor. These MOF-derived composite arrays are promising candidate materials for power sources because of their good electrochemical performance.

Nanoarchitecturing Carbon Nanodot Arrays on Zeolitic Imidazolate Framework-Derived Cobalt-Nitrogen-Doped Carbon Nanoflakes toward Oxygen Reduction Electrocatalysts

Two-dimensional (2D) nanoporous heterostructured composites formed by uniformly coating individual monolayers with porous layers introduce unparalleled opportunities to improve and optimize the electrochemical performances of 2D materials. Here, an all-porous carbon heterostructure composed of 2D microporous carbon nanoflakes uniformly decorated with carbon nanodots has been developed. Interestingly, resol-F127 micelles self-assemble on the surface of zeolitic imidazolate framework (ZIF) nanoflakes in the form of a nanodot array, yielding a heterostructure. Hydrothermal treatment followed by carbonization under a nitrogen atmosphere causes conversion of the nanodot-nanoflake assembly into a carbon-based material composed of hollow carbon nanodots (CNDs) and microporous carbon nanoflakes (CNFs), that is, a CND@CNF composite. The combination of 2D microporous carbon nanoflakes with carbon hollow nanodots enhances exposure of the active sites and improves mass transfer in all directions (including through the nanoflakes). The use of cobalt (Co)-containing ZIF leads to the synthesis of a Co-N_x-doped CND@CNF composite, which exhibits oxygen reduction reaction electrocatalytic activity and long-term stability superior even to commercial Pt/C catalysts. This architecture-engineering strategy has been used to design and synthesize 2D heterostructures possessing high electrocatalytic efficiency and will be useful for future developments in important electrochemical energy storage and conversion applications.

Porous carbon derived from ZIF-8 modified molecularly imprinted electrochemical sensor for the detection of tert-butyl hydroquinone (TBHQ) in edible oil

In this manuscript, ZIF-8 derived nanoporous carbon material (ZC) was prepared and used as modification material to construct a molecularly imprinted electrochemical sensor for the direct detection of tert-butyl hydroquinone (TBHQ) in edible oil. Electrochemical characterizations, scanning electron microscopy and X-ray diffraction show that ZC has excellent conductivity, high electrochemical active area and stable porous framework structure. Using TBHQ as template and o-phenylenediamine as functional monomer, the sensor was constructed. Experimental parameters such as the number of polymerization cycle, polymerization speed, and pH of the measured solution, removal and rebinding time were studied. Under optimized conditions, the prepared sensor showed a wider linear range from 1.0 μmol L^-1 to 75.0 μmol L^-1 with the detection limit of 0.42 μmol L^-1 (S/N = 3). Meanwhile, the sensor also expressed good selectivity, repeatability, reproducibility, stability and successfully applied for the determination of TBHQ in real edible oil, giving satisfactory results.

Metal-Organic Framework as a Functional Analyte Channel of Organic-Transistor-Based Air Pollution Sensors

Air pollution sensors based on organic transistors have attracted much interest recently; however, the devices suffer from low responsivity and slow response and recovery rates for gas analytes. These shortcomings are attributed to the low charge-carrier mobility of organic semiconductors and to a structural limitation resulting from the use of a thick and continuous active layer. In the present work, we investigated the material properties of a multiscale porous zeolitic imidazolate framework, [Zn(2-methylimidazole)₂]_n (ZIF-8), and examined its potential as an analyte channel material inserted at an organic-transistor active layer. A series of carbonized zeolitic imidazolate frameworks (ZIFs) were prepared by thermal conversion of ZIF-8 and also studied for comparison. The microstructures, morphologies, and optical/electrical characteristics of polythiophene/ZIF-8 hybrid films were systematically investigated. Organic-transistor-type nitrogen dioxide sensors based on the polythiophene/ZIF-8 hybrid films showed substantially improved sensing properties, including responsivity, response rate, and recovery rate. The electrical conductivity of the carbonized ZIF-8s enhanced the field-effect mobility of the organic transistors; however, the sensing performance was not improved, because of the closed pore structures resulting from the carbonization. These results provide invaluable information and useful insights into the design of transistor-type gas sensors based on organic semiconductor/metal-organic framework hybrid films.

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.

A facile template method to fabricate one-dimensional Fe3O4@SiO2@C/Ni microtubes with efficient catalytic and adsorption performance

The Fe3O4@SiO2@C/Ni microtubes were well constructed with MoO3 microrods as sacrificing template, which manifested excellent performance as both catalyst and adsorbent.

Insight into the Effect of ZIF-8 Particle Size on the Performance in Nanocarbon-Based Supercapacitors

Carbon materials derived from zeolitic imidazolate framework-8 (ZIF-8) and composites thereof have been intensively investigated in supercapacitors. The particle size of the used ZIF-8 ranges from dozens of nanometers to several microns. However, the influence of the particle size of ZIF-8 on the capacitive performances is still not clear. A series of ZIF-8 with different particle sizes (from 25 to 296 nm) has been synthesized and carbonized for supercapacitors. Based on TEM, EDX mapping, XRD, Raman, nitrogen adsorption-desorption, XPS, and the results of electrochemical tests, the optimal particle size (≈70 nm) for superior supercapacitor performances in both acidic and alkaline electrolytes has been obtained. This important result provides a significant reference to guide future ZIF-8 related research to achieve the best electrochemical performance.

Zeolitic imidazolate framework (ZIF)-derived porous carbon materials for supercapacitors: an overview

The present analysis focuses on the synthetic methods used for the application of supercapacitors with various mysterious architectures derived from zeolitic imidazolate frameworks (ZIFs). ZIFs represent an emerging and unique class of metal–organic frameworks with structures similar to conventional aluminosilicate zeolites, consisting of imidazolate linkers and metal ions. Their intrinsic porous properties, robust functionalities, and excellent thermal and chemical stabilities have resulted in a wide range of potential applications for various ZIF materials. In this rapidly expanding area, energetic research activities have emerged in the past few years, ranging from synthesis approaches to attractive applications of ZIFs. In this analysis, the development of high-performance supercapacitor electrodes and recent strategies to produce them, including the synthesis of various heterostructures and nanostructures, are analyzed and summarized. This analysis goes via the ingenuity of modern science when it comes to these nanoarchitecture electrodes. Despite these significant achievements, it is still difficult to accurately monitor the morphologies of materials derived from metal–organic frameworks (MOFs) because the induction force during structural transformations at elevated temperatures is in high demand. It is also desirable to achieve the direct synthesis of highly functionalized nanosized materials derived from zeolitic imidazolate frameworks (ZIFs) and the growth of nanoporous structures based on ZIFs encoded in specific substrates for the construction of active materials with a high surface area suitable for electrochemical applications. The latest improvements in this field of supercapacitors with materials formed from ZIFs as electrodes using ZIFs as templates or precursors are discussed in this review. Also, the possibility of usable materials derived from ZIFs for both existing and emerging energy storage technologies is discussed.

The present analysis focuses on the synthetic methods used for the application of supercapacitors with various mysterious architectures derived from zeolitic imidazolate frameworks (ZIFs).

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.

Structure-properties relationship for energy storage redox polymers: a review

Redox-active polymers among the energy storage materials (ESMs) are very attractive due to their exceptional advantages such as high stability and processability as well as their simple manufacturing. Their applications are found to useful in electric vehicle, ultraright computers, intelligent electric gadgets, mobile sensor systems, and portable intelligent clothing. They are found to be more efficient and advantageous in terms of superior processing capacity, quick loading unloading, stronger security, lengthy life cycle, versatility, adjustment to various scales, excellent fabrication process capabilities, light weight, flexible, most significantly cost efficiency, and non-toxicity in order to satisfy the requirement for the usage of these potential applications. The redox-active polymers are produced through organic synthesis, which allows the design and free modification of chemical constructions, which allow for the structure of organic compounds. The redox-active polymers can be finely tuned for the desired ESMs applications with their chemical structures and electrochemical properties. The redox-active polymers synthesis also offers the benefits of high-scale, relatively low reaction, and a low demand for energy. In this review we discussed the relationship between structural properties of different polymers for solar energy and their energy storage applications.

Metal-Organic Framework Nanoparticles Induce Pyroptosis in Cells Controlled by the Extracellular pH

Ion homeostasis is essential for cellular survival, and elevated concentrations of specific ions are used to start distinct forms of programmed cell death. However, investigating the influence of certain ions on cells in a controlled way has been hampered due to the tight regulation of ion import by cells. Here, it is shown that lipid-coated iron-based metal-organic framework nanoparticles are able to deliver and release high amounts of iron ions into cells. While high concentrations of iron often trigger ferroptosis, here, the released iron induces pyroptosis, a form of cell death involving the immune system. The iron release occurs only in slightly acidic extracellular environments restricting cell death to cells in acidic microenvironments and allowing for external control. The release mechanism is based on endocytosis facilitated by the lipid-coating followed by degradation of the nanoparticle in the lysosome via cysteine-mediated reduction, which is enhanced in slightly acidic extracellular environment. Thus, a new functionality of hybrid nanoparticles is demonstrated, which uses their nanoarchitecture to facilitate controlled ion delivery into cells. Based on the selectivity for acidic microenvironments, the described nanoparticles may also be used for immunotherapy: the nanoparticles may directly affect the primary tumor and the induced pyroptosis activates the immune system.

Physical Expansion of Layered Graphene Oxide Nanosheets by Chemical Vapor Deposition of Metal-Organic Frameworks and their Thermal Conversion into Nitrogen-Doped Porous Carbons for Supercapacitor Applications

Graphene oxide (GO) nanosheets show good electrical conductivity and corrosion resistance in electrochemical devices. However, strong van der Waals attraction between adjacent nanosheets causes GO materials to collapse, reducing the exposed surfaces and limiting electron/ion transport in porous electrodes. GO nanosheets mixed with Zn₅ (OH)₈ (NO₃ )₂ ⋅2 H₂ O (ZnON) nanoplates create a layered composite structure. Exposing the resultant GO/ZnON to 2-methylimidazole vapor leads to the conversion of ZnON into the zeolitic imidazolate framework ZIF-8. The transformation of ZnON into ZIF-8 leads to a huge physical expansion of the interlayer space between the GO sheets. Annealing the material at high temperature caused the ZIF-8 to be converted into highly porous nitrogen-doped carbon, but the GO nanosheets maintained a large separation and high surface area. The morphology and porous structure of the post-annealing carbon material was sensitive to the initial ratio of ZnON to GO. The optimized sample exhibited several favorable features, including a large surface area, high degree of graphitization, and a high amount of nitrogen doping. Using chemical vapor deposition of metal-organic frameworks to physically expand nanomaterials is a novel method to increase the surface area and porosity of materials. It enabled the synthesis of nanoporous carbon electrodes with high capacitance, good rate capability, and long cyclic stability in supercapacitor devices.

Boosting Supercapacitor Performance of Graphene by Coupling with Nitrogen-Doped Hollow Carbon Frameworks

Graphene as a suitable electrode has been extensively used for electrochemical double-layer capacitors based on its excellent properties, including high electrical conductivity and large specific surface area. However, one of the drawbacks is the unavoidable stacking tendency between the graphene nanosheets, resulting in limited electrochemically specific surface area. Herein, novel graphene nanosheets supported by hollow nitrogen-doped carbon frameworks derived from ZIF-8 (GPNC) were fabricated through a simple polyethyleneimine (PEI)-assisted pyrolysis strategy, to boost capacitance performance. Benefiting from the unique scaffold/support role of hollow nitrogen-doped carbon frameworks within the graphene interlayer, the GPNC with a large specific surface area, along with ample micropore/mesopore channels and high nitrogen content, is capable of facilitating electron and electrolyte ion migration kinetics and enhancing intrinsic electrochemical activity. Thus, the GPNC exhibits the highest charge storage of 218 F g^-1 and superior rate capability of 74 % when the current density increased from 0.5 to 20 Ag^-1 in comparison to pristine graphene and common ZIF-derived carbon/graphene electrodes. The assembled GPNC//GPNC two-electrode system further delivers a maximum power of 9080 Wkg^-1 with outstanding electrochemical retention of 84 % over 10 000 cycles.

Ordered Mesoporous Carbon Embedded with Cu Nanoparticle Materials for Electrocatalytic Synthesis of Benzyl Methyl Carbonate from Benzyl Alcohol and Carbon Dioxide

We prepared a series of ordered mesoporous carbons embedded with different contents of Cu nanoparticles (Cu/OMC-X) and applied them to electrocatalytic synthesis of benzyl methyl carbonate. The materials were characterized by many measurements, which showed that Cu/OMC-X materials maintain highly ordered mesoporous structures with high surface area and highly dispersed Cu nanoparticles. As expected, the materials exhibit good electrocatalytic performance. The optimal yield of benzyl methyl carbonate reaches 69.7% on Cu/OMC-3.

NiSe2/Ni(OH)2 Heterojunction Composite through Epitaxial-like Strategy as High-Rate Battery-Type Electrode Material

Constructing heterojunction is a promising way to improve the charge transfer efficiency and can thus promote the electrochemical properties. Herein, a facile and effective epitaxial-like growth strategy is applied to NiSe₂ nano-octahedra to fabricate the NiSe₂-(100)/Ni(OH)₂-(110) heterojunction. The heterojunction composite and Ni(OH)₂ (performing high electrochemical activity) is ideal high-rate battery-type supercapacitor electrode. The NiSe₂/Ni(OH)₂ electrode exhibits a high specific capacity of 909 C g^-1 at 1 A g^-1 and 597 C g^-1 at 20 A g^-1. The assembled asymmetric supercapacitor composed of the NiSe₂/Ni(OH)₂ cathode and p-phenylenediamine-functional reduced graphene oxide anode achieves an ultrahigh specific capacity of 303 C g^-1 at 1 A g^-1 and a superior energy density of 76.1 Wh kg^-1 at 906 W kg^-1, as well as an outstanding cycling stability of 82% retention for 8000 cycles at 10 A g^-1. To the best of our knowledge, this is the first example of NiSe₂/Ni(OH)₂ heterojunction exhibiting such remarkable supercapacitor performance. This work not only provides a promising candidate for next-generation energy storage device but also offers a possible universal strategy to fabricate metal selenides/metal hydroxides heterojunctions.

From metal-organic frameworks to porous carbon materials: recent progress and prospects from energy and environmental perspectives

Metal-organic frameworks (MOFs) have emerged as promising materials in the areas of gas storage, magnetism, luminescence, and catalysis owing to their superior property of having highly crystalline structures. However, MOF stability toward heat or humidity is considerably less as compared to carbons because they are constructed from the assembly of ligands with metal ions or clusters via coordination bonds. Transforming MOFs into carbons is bringing the novel potential for MOFs to achieve industrialization, and carbons with controlled pore sizes and surface doping are one of the most important porous materials. By selecting MOFs as a precursor or template, carbons with heteroatom doping and well-developed pores can be achieved. In this review, we discussed the state-of-art study progress made in the new development of MOF-derived metal-free porous carbons. In particular, the potential use of metal-free carbons from environmental and energy perspectives, such as adsorption, supercapacitors, and catalysts, were analyzed in detail. Moreover, an outlook for the sustainable development of MOF-derived porous carbons in the future was also presented.

Three Dimensionally Free-Formable Graphene Foam with Designed Structures for Energy and Environmental Applications

Three-dimensional assemblies of graphene have been considered as promising starting materials for many engineering, energy, and environmental applications due to its desirable mechanical properties, high specific area, and superior thermal and electrical transfer ability. However, little has been done to introduce designed shapes into scalable graphene assemblies. In this work, we show here a combination of conventional graphene growing technique-chemical vapor deposition with additive manufacturing. Such synthesis collaboration enables a hierarchically constructed porous 3D graphene foam with large surface area (994.2 m²/g), excellent conductivity (2.39 S/cm), reliable mechanical properties (E = 239.7 kPa), and tunable surface chemistry that can be used as a strain sensor, catalyst support, and solar steam generator.

Pt2+-Exchanged ZIF-8 nanocube as a solid-state precursor for L10-PtZn intermetallic nanoparticles embedded in a hollow carbon nanocage

Nanoparticles with an atomically ordered alloy phase have received enormous attention for application as catalysts in fuel cells because of their unique electronic properties resulting from unusually strong d-orbital interactions between two metal components. However, the synthesis of intermetallic nanoparticles requires a high reaction temperature, thus necessitating the protection of nanoparticles with inorganic layers to prevent aggregation of nanoparticles during synthesis. The protective layer needs to be removed later for application as a catalyst, which is a cumbersome process. Herein, a novel synthetic strategy is reported for the preparation of L1₀-PtZn intermetallic nanoparticles by utilizing Pt²⁺-exchanged ZIF-8 nanocubes as a solid-state precursor. The Pt²⁺-exchanged ZIF-8 phase plays a dual role as a metal ion source for L1₀-PtZn nanoparticles and as a carbonaceous matrix that restrains the aggregation of nanoparticles during thermal treatment. The L1₀-PtZn nanoparticles embedded in a hollow carbon nanocage obtained from one-step annealing of Pt²⁺-exchanged ZIF-8 showed better electrocatalytic activity and durability toward methanol oxidation under acidic electrolyte conditions than those obtained from commercial Pt/C catalysts.