Thermal Conversion of Core–Shell Metal–Organic Frameworks: A New Method for Selectively Functionalized Nanoporous Hybrid Carbon

Ordered carbonaceous frameworks: a new class of carbon materials with molecular-level design

Ordered carbonaceous frameworks (OCFs) are a new class of carbon materials with a three-dimensional ordered structure synthesized by simple carbonization of metalloporphyrin crystals with polymerizable moieties. Carbonization via solid-state polymerization results in the formation of graphene-based ordered frameworks in which regularly aligned single-atomic metals are embedded. These unique structural features afford molecular-level designability like organic-based frameworks together with high electrical conductivity, thermal/chemical stability, and mechanical flexibility, towards a variety of applications including electrocatalysis and force-driven phase transition. This feature article summarizes the synthetic strategies and characteristics of OCFs in comparison with conventional organic-based frameworks and porous carbons, to discuss the potential applications and further development of the OCF family.

Ultrastable Covalent Triazine Organic Framework Based on Anthracene Moiety as Platform for High-Performance Carbon Dioxide Adsorption and Supercapacitors

Conductive and porous nitrogen-rich materials have great potential as supercapacitor electrode materials. The exceptional efficiency of such compounds, however, is dependent on their larger surface area and the level of nitrogen doping. To address these issues, we synthesized a porous covalent triazine framework (An-CTFs) based on 9,10-dicyanoanthracene (An-CN) units through an ionothermal reaction in the presence of different molar ratios of molten zinc chloride (ZnCl₂) at 400 and 500 °C, yielding An-CTF-10-400, An-CTF-20-400, An-CTF-10-500, and An-CTF-20-500 microporous materials. According to N₂ adsorption–desorption analyses (BET), these An-CTFs produced exceptionally high specific surface areas ranging from 406–751 m²·g⁻¹. Furthermore, An-CTF-10-500 had a capacitance of 589 F·g⁻¹, remarkable cycle stability up to 5000 cycles, up to 95% capacity retention, and strong CO₂ adsorption capacity up to 5.65 mmol·g⁻¹ at 273 K. As a result, our An-CTFs are a good alternative for both electrochemical energy storage and CO₂ uptake.

MOF-derived N-doped ZnO carbon skeleton@hierarchical Bi2MoO6 S-scheme heterojunction for photodegradation of SMX: Mechanism, pathways and DFT calculation

Semiconductor photocatalytic degradation of pollutants is considered to be one of the promising sustainable energy routes. Nevertheless, it is challenging for photocatalysts to have excellent visible light absorption and suppress photo-generated electron-hole recombination at the same time. Here, we prepared nitrogen-doped ZnO carbon skeleton by directly calcining the metal-organic framework. Then hierarchical Bi₂MoO₆ nanosheets are grown in situ on its surface to synthesize S-scheme heterojunction. This special 3D layered and oxygen vacancies work together to make photo-generated electrons and holes easier to separate and migrate. Therefore, the pseudo-first-order kinetic constant of N-doped ZnO carbon skeleton@Bi₂MoO₆ degradation of sulfamethoxazole reaches 0.022 min^-1, which is almost 10 times that of ZIF-8 derived ZnO and 27.5 times Bi₂MoO₆ under visible light irradiation. Meanwhile, the mechanism of driving charge transfer of S-scheme heterojunction, and the photocatalytic degradation pathway of sulfamethoxazole are also analyzed. This work will provide a new way to construct S-scheme heterojunction photocatalyst to degrade antibiotic pollutants.

Engineering Dual Single-Atom Sites on 2D Ultrathin N-doped Carbon Nanosheets Attaining Ultra-Low-Temperature Zinc-Air Battery

Herein, a novel dual single-atom catalyst comprising adjacent Fe-N₄ and Mn-N₄ sites on 2D ultrathin N-doped carbon nanosheets with porous structure (FeMn-DSAC) was constructed as the cathode for a flexible low-temperature Zn-air battery (ZAB). FeMn-DSAC exhibits remarkable bifunctional activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Control experiments and density functional theory calculations reveal that the catalytic activity arises from the cooperative effect of the Fe/Mn dual-sites aiding *OOH dissociation as well as the porous 2D nanosheet structure promoting active sits exposure and mass transfer during the reaction process. The excellent bifunctional activity of FeMn-DSAC enables the ZAB to operate efficiently at ultra-low temperature of -40 °C, delivering 30 mW cm^-2 peak power density and retaining up to 86 % specific capacity from the room temperature counterpart.

Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies

Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst-support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free high-performance and durable alkaline fuel cells and related technologies.

Process of metal-organic framework (MOF)/covalent-organic framework (COF) hybrids-based derivatives and their applications on energy transfer and storage

The fossil-fuel shortage and severe environmental issues have posed ever-increasing demands on clean and renewable energy sources, for which the exploration of electrocatalysts has been a big challenge toward energy transfer and storage. Some indispensable features of electrocatalysts, such as large surface area, controlled structure, high porosity, and effective functionalization, have been proved to be critical for the improvement of electrocatalytic activities. Recently, the rapid expansion of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous-organic polymers has provided extensive opportunities for the development of various electrocatalysts. Moreover, combining diverse descriptions of porous-organic frameworks (such as MOFs and COFs) can generate amazing and fantastic properties, affording the formed MOF/COF (including core-shell MOF@MOF and MOF@COF and layer-on-layer MOF-on-MOF or COF-on-MOF) heterostructures wide applications in diverse fields, especially in clean energy and energy transfer. To further boosts electronic conductivity, catalytic performances, and energy storage abilities, these MOF/COF hybrid materials have been widely utilized as versatile precursors for the manufacture of transition metal catalysts embedded within mesoporous carbon nitrides (M@CN_x) and porous carbon nitride frameworks (CN_x) via a facile pyrolysis process. Given that these M@CN_x and CN_x hybrids are composed of abundant catalytic centers, rich functionalities, and large specific surface areas, vast applications in energy transfer and energy storage fields can be realized. In this mini-review, we summarize the preparation strategies of MOF/COF-based hybrids, as well as their derivatives, nanostructure formation mechanism of M@CN_x and CN_x hybrids from MOF/COF-based hybrid materials, and their applications as catalysts for driving diverse reactions and electrode materials for energy storage. Further, current challenges and future prospects of applying these derivatives into energy conversion and storage devices are also discussed.

Material Evolution with Nanotechnology, Nanoarchitectonics, and Materials Informatics: What will be the Next Paradigm Shift in Nanoporous Materials?

Materials science and chemistry have played a central and significant role in advancing society. With the shift toward sustainable living, it is anticipated that the development of functional materials will continue to be vital for sustaining life on our planet. In the recent decades, rapid progress has been made in materials science and chemistry owing to the advances in experimental, analytical, and computational methods, thereby producing several novel and useful materials. However, most problems in material development are highly complex. Here, the best strategy for the development of functional materials via the implementation of three key concepts is discussed: nanotechnology as a game changer, nanoarchitectonics as an integrator, and materials informatics as a super-accelerator. Discussions from conceptual viewpoints and example recent developments, chiefly focused on nanoporous materials, are presented. It is anticipated that coupling these three strategies together will open advanced routes for the swift design and exploratory search of functional materials truly useful for solving real-world problems. These novel strategies will result in the evolution of nanoporous functional materials.

Target-Responsive Smart Nanomaterials via a Au-S Binding Encapsulation Strategy for Electrochemical/Colorimetric Dual-Mode Paper-Based Analytical Devices

Target-responsive nanomaterials attract growing interest in the application of drug delivery, bioimaging, and sensing due to the responsive releasing of guest molecules by the smart molecule gate. However, it remains a challenge to develop smart nanomaterials with simple assembly and low nonspecific leakage starting from encapsulation strategies, especially in the sensing field. Herein, Au nanoclusters (Au NCs) were first grown on porous carbon derived from ZIF-8 (PCZIF) to be employed as nanocarriers. By employing the Au NCs as linkers and aptamer (Apta) double-strand hybrids (target Apta and SH-complementary DNA) as capping units, we reported the novel target-responsive nanomaterials of Apta/Au NCs-PCZIF/hemin through Au-S binding encapsulation for sensing assays. The Au-S binding encapsulation strategy simplified the packaging procedure and reduced non-target responsive leakage. As a proof, ochratoxin A (OTA) as a model target participates in the double-strand hybrid competitive displacement reaction and triggered Apta conformation switches from a coil to a G-quadruplex structure accompanied by the dissociation of the gatekeeper. Simultaneously, the released hemin can initiate a self-assembly to form G-quadruplex/hemin DNAzyme. Interestingly, owing to DNAzyme providing electron transfer mediators and peroxidase-like activity, we proposed an electrochemical/colorimetric dual-mode paper-based analytical device (PAD) that provided self-verification to enhance reliability and accuracy, benefiting from independent signal conversion and transmission mechanism. As a consequence, the proposed dual-mode PAD could achieve sensitive electrochemical detection and visual prediction of OTA in the range of 1 pg/mL to 500 ng/mL and 50 pg/mL to 500 ng/mL, respectively. The electrochemical detection limit for OTA was as low as 0.347 pg/mL (S/N = 3). We believe that this work provides point-of-care testing (POCT) tools for a broad spectrum of applications.

Toward an Understanding of the Reversible Li-CO2 Batteries over Metal-N4-Functionalized Graphene Electrocatalysts

The lack of low-cost catalysts with high activity leads to the unsatisfactory electrochemical performance of Li-CO₂ batteries. Single-atom catalysts (SACs) with metal-N_x moieties have great potential to improve battery reaction kinetics and cycling ability. However, how to rationally select and develop highly efficient electrocatalysts remains unclear. Herein, we used density functional theory (DFT) calculations to screen SACs on N-doped graphene (SAMe@NG, Me = Cr, Mn, Fe, Co, Ni, Cu) for CO₂ reduction and evolution reaction. Among them, SACr@NG shows the promising potential as an effective electrocatalyst for the reversible Li-CO₂ batteries. To verify the validity of the DFT calculations, a two-step method has been developed to fabricate SAMe@NG on a porous carbon foam (SAMe@NG/PCF) with similar loading of ∼8 wt %. Consistent with the theoretical calculations, batteries with the SACr@NG/PCF cathodes exhibit a superior rate performance and cycling ability, with a long cycle life and a narrow voltage gap of 1.39 V over 350 cycles at a rate of 100 μA cm^-2. This work not only demonstrates a principle for catalysts selection for the reversible Li-CO₂ batteries but also a controllable synthesis method for single atom catalysts.

PtNi Alloy Coated in Porous Nitrogen-Doped Carbon as Highly Efficient Catalysts for Hydrogen Evolution Reactions

The development of low platinum loading hydrogen evolution reaction (HER) catalysts with high activity and stability is of great significance to the practical application of hydrogen energy. This paper reports a simple method to synthesize a highly efficient HER catalyst through coating a highly dispersed PtNi alloy on porous nitrogen-doped carbon (MNC) derived from the zeolite imidazolate skeleton. The catalyst is characterized and analyzed by physical characterization methods, such as XRD, SEM, TEM, BET, XPS, and LSV, EIS, it, v-t, etc. The optimized sample exhibits an overpotential of only 26 mV at a current density of 10 mA cm⁻², outperforming commercial 20 wt% Pt/C (33 mV). The synthesized catalyst shows a relatively fast HER kinetics as evidenced by the small Tafel slope of 21.5 mV dec⁻¹ due to the small charge transfer resistance, the alloying effect between Pt and Ni, and the interaction between PtNi alloy and carrier.

Porous carbon-confined CoxSy nanoparticles derived from ZIF-67 for boosting lithium-ion storage

Reasonable regulation and synthesis of hollow nanostructure materials can provide a promising electrode material for lithium-ion batteries (LIBs). In this work, utilizing a metal–organic framework (MOF, ZIF-67) as the raw material and template, a composite of Co_xS_y with a carbon shell is successfully formed through a hydrothermal vulcanization and a subsequent high temperature sintering process. The as-obtained Co_xS_y(700) material sintered at 700 °C has a large specific surface area, and at the same time possesses a hollow carbon shell structure. Benefiting from unique structural advantages, the volume change during the electrochemical reaction can be well alleviated, and thus the structural stability is greatly improved. The presence of the carbon matrix can also offer sufficient ion/electron transfer channels, contributing to the enhanced electrochemical performance. As a result, the Co_xS_y(700) electrode can deliver an excellent capacity of 875.6 mA h g⁻¹ at a current density of 100 mA g⁻¹. Additionally, a high-capacity retention of 88% is achieved after 1000 cycles when the current density is increased to 500 mA g⁻¹, and exhibiting a prominent rate capability of 526.5 mA h g⁻¹, simultaneously. The novel synthesis route and considerable electrochemical properties presented by this study can afford guidance for the exploration of high-performance cobalt sulfide anodes in LIBs.

A composite of Co_xS_y and carbon shell is successfully formed, and as a result it can well alleviate volume change as well as offer sufficient ions/electrons transfer channels, contributing to enhance electrochemical performance.

Fast catalytic transfer hydrogenation of phenol to cyclohexanol over urea modified Ni@CN nanoparticles

The Ni@CN-450 catalyst prepared via direct pyrolysis of Ni-MOF-74(N) exhibited superior catalytic activity in catalytic transfer hydrogenation.

Exploring novel heterojunctions based on the cerium metal–organic framework family and CAU-1, as dissimilar structures, for the sake of photocatalytic activity enhancement

Ce-based metal–organic frameworks (Ce-MOFs) are excellent photocatalysts due to their high efficiency in charge transportation.

Deep-Breathing Fe-Doped Superstructure Modified by Polyethyleneimine as Oxygen Reduction Electrocatalysts for Zn-Air Batteries

The development of economical, robust and high active non-precious metal oxygen reduction reaction (ORR) electrocatalysts to replace the precious metal is extremely crucial for the widespread applications of metal-air batteries....

CoZn-ZIF-derived carbon-supported Cu catalyst for methanol oxidative carbonylation to dimethyl carbonate

Carbon materials derived from CoZn-ZIFs were used to load Cu catalysts and were applied for DMC synthesis, and the effects of the graphitization degree and the (N1 + N3)/N2 ratio were studied.

Connectivity Replication of Neutral Eu3+- and Tb3+-Based Metal-Organic Frameworks (MOFs) from Anionic Cd2+-Based MOF Crystallites

Neutral three-dimensional Eu³⁺- and Tb³⁺-based metal-organic frameworks (MOFs) with 4-fold interpenetration can be produced by seeding with anionic Cd²⁺-based MOF crystallites of identical connectivity. In the absence of these crystallites, two-dimensional networks are formed.

State of the art developments and prospects of metal-organic frameworks for energy applications

The progress on technologies for the cleaner and ecological transformation and storage of energy to combat effluence or pollution and the impending energy dilemma has recently attracted interest from energy research groups, particularly in the field of coordination chemistry, among inorganic chemists. Carriers for storing energy or facilitating mass and e^- transport are considered significant for energy conversion. Accordingly, considering their properties such as large surface area, low cost, customizable pore diameter, tunable topologies, low densities, and variable frameworks, MOFs (metal-organic frameworks) and their derivatives are well-suited for this purpose. MOFs are an innovative category of porous and crystalline materials, which have gained significant interest in recent years. Thus, herein, we highlight the state of the art progress on MOFs for energy-based applications, as perfect compounds and elements in compound assemblies for converting solar energy, lithium-ion arrays, fuel devices, hydrogen production, photocatalytic CO₂ reduction, proton conduction, etc. In addition, the substantial progress achieved in the production of various composites and derivatives containing MOFs with particular focus on supercapacitors and gas adsorption and storage is summarized, concentrating on the correlation between their coordination structural frameworks and applications in the field of energy. The current improved strategies, challenges, and future prospects are also presented in view of the coordination chemistry governing the structural modification of MOFs for energy applications.

Templating Synthesis of Metal-Organic Framework Nanofiber Aerogels and Their Derived Hollow Porous Carbon Nanofibers for Energy Storage and Conversion

A kind of metal-organic framework (MOF) aerogels are synthesized by the self-assembly of uniform and monodisperse MOF nanofibers. Such MOF nanofiber aerogels as carbon precursors can effectively avoid the aggregation of nanofibers during calcination, resulting in the formation of well-dispersed hollow porous carbon nanofibers (HPCNs). Moreover, HPCNs with well-dispersion are investigated as sulfur host materials for Li-S batteries and electrocatalysts for cathode oxygen reduction reaction (ORR). On the one hand, HPCNs act as hosts for the encapsulation of sulfur into their hierarchical micro- and mesopores as well as hollow nanostructures. The obtained sulfur cathode exhibits excellent electrochemical features, good cycling stability and high coulombic efficiency. On the other hand, HPCNs exhibit better electrocatalytic activity than aggregated counterparts for ORR. Furthermore, a highly active single atom electrocatalyst can be prepared by the carbonization of bimetallic MOF nanofiber aerogels. The results indicate that well-dispersed HPCNs show enhanced electrochemical properties in contrast to their aggregated counterparts, suggesting that the dispersion situation of nanomaterials significantly influence their final performance. The present concept of employing MOF nanofiber aerogels as precursors will provide a new strategy to the design of MOF-derived nanomaterials with well-dispersion for their applications in energy storage and conversion.

High-Performance Capacitive Deionization and Killing Microorganism in Surface-Water by ZIF-9 Derived Carbon Composites

The protection and regeneration of the water environment is currently one of the most critical concerns for the sustainable development of human society. To solve the water crisis, the use of capacitive deionization (CDI) technology to extract fresh-water that is suitable for human consumption from abundant surface-water is a feasible solution. In this work, a cobalt benzimidazole frameworks (ZIF-9) derived carbon composites with a unique quasi-microcubic morphology is synthesized and used the as-prepared materials as an electrode material for the CDI. Interestingly, the ZIF-9 derived carbon composites exhibit an impressive desalination capacity of 55.4 mg g^-1 and can be reused. Measurements in surface-water (Beijing-Hangzhou Grand Canal, Slender West Lake, Initial rainwater, Rain water) show that this CDI technology based on ZIF-9 derived carbon composites not only has a strong adsorption effect on metal ions but also can remarkably kill microorganisms. The results show that the technology can effectively kill bacteria (Escherichia coli and Bacillus) and algae with 95% and 91.7% inhibition rates, respectively. This work provides a valuable example for the use of metal-organic framework-derived carbon composites as high-performance electrode materials of CDI and opens a new direction for promoting the application of CDI in surface-water.

Solution combustion synthesis of ternary Ni/WC/C composites with efficient electrocatalytic oxygen reduction performance

In this paper, a fast processing route involving a wet-chemical method (solution combustion synthesis, SCS) and carbonization in a CH₄ environment was demonstrated, through which nanosized Ni/WC/C powder with an average size of 80 nm was obtained. In the catalyst powder, Ni was evenly distributed and it could form NiOOH to promote catalysis, and an amorphous carbon (C) layer with a thickness of <10 nm was formed on the surface of the composite particles, improving the stability of the Ni/WC powder and promoting electron transport. Due to the characteristics of uniformity and a large specific surface area and the synergistic effect of Ni, WC, and C, this powder showed significantly improved ORR catalytic activity in alkaline solution. When the amount of Ni doping was 15 wt%, the composite powder showed the smallest particle size and the best ORR catalytic performance. Its cathode peak potential was -0.31 V and the half wave potential was -0.34 V. The number of electrons transferred in the ORR reaction was 3.6. This work provided a fast and cheap method for the preparation of multicomponent composite catalyst materials.

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.

Base-free catalytic aerobic oxidation of mercaptans over MOF-derived Co/CN catalyst with controllable composition and structure

The oxidation of mercaptans under mild and base-free conditions is of vital importance in terms of economy and environment for petroleum processing industry. Here, we developed a series of MOF-derived cobalt-based nitrogen-doped (N-doped) carbon (Co/CN-x) catalysts for the base-free catalytic oxidation of mercaptans. The optimal Co/CN-900 showed excellent catalytic activity for the oxidation of mercaptans under base-free conditions, yielding complete conversion of various mercaptans and > 99.0% selectivity of disulfides. The high performance can be contributed to the advantages of hierarchical pore structure for the diffusion and migration of substrates, self-carrying alkalinity for the formation of mercaptide anion, abundant active Co sites for catalytic oxidation of mercaptans as well as the synergistic effects between the Co nanoparticles (NPs) and N-doped carbon supports. Furthermore, a possible mechanism for base-free catalytic oxidation of mercaptans over Co/CN-x catalysts is proposed based on a set of control experiments and density functional theory (DFT) calculations.

Nitrogen-Doped Carbon Composites with Ordered Macropores and Hollow Walls

Metal-organic frameworks provide versatile templates for the fabrication of various metal/carbon materials, but most of the derived composites possess only microspores, limiting the accessibility of embedded active sites. Herein, we report the construction of cobalt/nitrogen-doped carbon composites with a three-dimensional (3D) ordered macroporous and hollow-wall structure (H-3DOM-Co/NC) using a single-crystal ordered macropore (SOM)-ZIF-8@ZIF-67 as precursor. During the pyrolysis, the interconnected macroporous structure of SOM-ZIF-8@ZIF-67 is mostly preserved, whereas the pore wall achieves a solid-to-hollow transformation with Co nanoparticles formed in the hollow walls. The 3D-ordered macroporous carbon skeleton may effectively promote long-range mass transfer and the hollow wall can facilitate local accessibility of active sites. This unique structure can greatly boost its catalytic activity in the selective hydrogenation of biomass-derived furfural to cyclopentanol, much superior to its counterparts without this well-designed hierarchically porous structure.

A Hydrolytically Stable Cu(II)-Based Metal-Organic Framework with Easily Accessible Ligands for Water Harvesting

Water scarcity is a critical issue in desert and arid regions, and atmospheric water harvesting is a potential solution. The challenge is lacking ideal adsorbents that can efficiently capture water from low-humidity air and be regenerated readily. Herein, we report a hydrolytically stable metal-organic framework (MOF), [Cu₂(AD)₂(SA)] (Cu-AD-SA), with excellent performance in water harvesting. More importantly, this material can be facilely prepared from two easily accessible ligands adenine (HAD) and succinic acid (H₂SA). Cu-AD-SA has a three-dimensional (3D) framework structure with the crs topology and intersecting channels of ∼5 Å in diameter. The channel surface is decorated by uncoordinated aromatic N atoms, amine groups, and alkyl moieties. Interestingly, Cu-AD-SA shows a high water adsorption capacity of 0.16 g g^-1 at low pressure of 0.2 P/P₀ and 25 °C. Furthermore, dynamic water adsorption-desorption cycling experiments demonstrated a stable working capacity of 0.13 g g^-1 for uptaking water from a low-humidity air (water partial pressure: 0.85 kPa, 20% RH at 30 °C, 5.3% RH at 55 °C) at 30 °C and desorption at 55 °C. The water adsorption mechanism was also studied by analyzing its single-crystal structure after water loading. The results indicated the existence of strong H-bonding interactions between water molecules and uncoordinated N atoms and amine groups on the framework, which should play an important role in the high adsorption at low pressure. All the above features suggest great potential of Cu-AD-SA for water harvesting in arid regions.

Dual confinement of high-loading enzymes within metal-organic frameworks for glucose sensor with enhanced cascade biocatalysis

The intrinsically fragile nature and leakage of the enzymes is a major obstacle for the commercial sensor of a continuous glucose monitoring system. Herein, a dual confinement effect is developed in a three dimensional (3D) nanocage-based zeolite imidazole framework (NC-ZIF), during which the high-loading enzymes can be well encapsulated with unusual bioactivity and stability. The shell of NC-ZIF sets the first confinement to prevent enzymes leakage, and the interior nanocage of NC-ZIF provides second confinement to immobilize enzymes and offers a spacious environment to maintain their conformational freedom. Moreover, the mesoporosity of the formed NC-ZIF can be precisely controlled, which can effectively enhance the mass transport. The resulted GOx/Hemin@NC-ZIF multi-enzymes system could not only realize rapid detection of glucose by colorimetric and electrochemical sensors with high catalytic cascade activity (with an 8.3-fold and 16-fold enhancements in comparison with free enzymes in solution, respectively), but also exhibit long-term stability, excellent selectivity and reusability. More importantly, the based wearable sweatband sensor measurement results showed a high correlation (>0.84, P < 0.001) with the levels measured by commercial glucometer. The reported dual confinement strategy opens up a window to immobilize enzymes with enhanced catalytic efficiency and stability for clinical-grade noninvasive continuous glucose sensor.

Zeolite Imidazolate Frameworks-67 Precursor to Fabricate a Highly Active Cobalt-Embedded N-Doped Porous Graphitized Carbon Catalyst for the Thermal Decomposition of Ammonium Perchlorate

The more apparent specific heat release at a lower high-temperature decomposition (HTD) temperature of ammonium perchlorate (AP) poses a challenge for the development of highly active catalysts. In this work, a well-designed cobalt-embedded N-doped porous graphitized carbon (Co@NC) catalyst is obtained by high-temperature calcination of a zeolite imidazolate frameworks-67 precursor, in which the cobalt catalytic active center realizes effective nanoscale dispersion; meanwhile, the cobalt and N-doped porous graphitized carbon can release considerable heat after oxidation, and the cobalt oxides have an excellent catalytic effect on reducing the HTD temperature of AP. The catalytic activity of Co@NC was tested by a differential thermal analytical method. The results indicated that the HTD peak of AP was significantly decreased by 100.5 °C, the apparent activation energy of the HTD reaction of AP was reduced by 82.0 kJ mol-1, and the heat release compared with pure AP increased 2.9 times. On teh basis of these findings, Co@NC is expected to be one of the best candidate materials for AP thermal decomposition.

Space-confined construction of two-dimensional nitrogen-doped carbon with encapsulated bimetallic nanoparticles as oxygen electrocatalysts

A space-confined strategy has been used to control the pyrolysis of two-dimensional (2D) NiCo-MOF@ZIF-L(Zn). A thin SiO₂ layer as a confined space could avoid the destruction of the 2D morphology during pyrolysis and expose more active sites. The obtained NiCo-NC material exhibits high ORR and Zn-air battery performance.

Cubic-like Co/NC composites derived from ZIF-67 with a dual control strategy of size and graphitization degree for microwave absorption

MOFs with high tunability are considered ideal candidates as microwave-absorbing materials. Strict experimental conditions can ensure the repeatability and maximize the potential of such materials. In this study, cubic ZIF-67 carbides synthesized at different solution temperatures showed an adjustable average size, and then by adjusting the calcination temperature we could control the degree of graphitization, so as to explore the synergistic effect of these two aspects to achieve an in-depth understanding of the electromagnetic properties and microwave absorption properties. The results showed that sample 30-600 (with the former number referring to the synthesis temperature and the latter to the calcination temperature) showed the widest effective absorption bandwidth (5.75 GHz, 1.8 mm) and the optimal reflection loss (-56.92 dB, 2.1 mm). The best matching electromagnetic parameters were obtained under the synergistic action of a smaller particle size and appropriate degree of graphitization, so as to achieve strong attenuation characteristics under low electromagnetic wave reflection. The microwave loss mechanism of the sample mainly involved dielectric losses, such as from conductance loss, dipole polarization, and interface polarization. Starting from the experimental details, this work proposes a dual control strategy for developing microwave-absorbing materials with both simplicity and practicability, which provides a useful reference for other microwave absorbents synthesized at room temperature.

Recent advances in metal-organic framework-based electrode materials for supercapacitors

Exploring porous electrode materials with designed micro/nano-structures is an effective way to realize high-performance supercapacitors (SCs). A metal-organic framework (MOF) is a porous crystalline material with a periodic structure formed by coordination of metal ions/clusters and organic ligands. Due to the excellent properties (e.g., large specific surface area, high porosity and tailorable structure), MOFs have been widely used in diverse applications. This Frontier article highlights the recent progress in the synthesis of MOF-based micro/nano-structured electrode materials including pristine MOFs, MOF composites and MOF derivatives, and their application in SCs. Furthermore, the challenges of MOF-based electrode materials and possible solutions are also discussed.

Zeolitic imidazolate framework-derived porous carbon enhances methanogenesis by facilitating interspecies electron transfer: Understanding fluorimetric and electrochemical responses of multi-layered extracellular polymeric substances

Modulating microbial electron transfer during anaerobic digestion can significantly improve syntrophic interactions for enhanced biogas production. As a carbonaceous conductive material, zeolite imidazolate framework-67 (ZIF-67)-derived porous carbon (PC) was hypothesized to act as a microbial electron transfer highway and assessed with respect to understanding the fluorimetric and electrochemical responses of multilayered extracellular polymeric substances (EPS). The highest biomethane yield (614.0 mL/g) from ethanol was achieved in the presence of 100 mg/L PC prepared at a carbonization temperature of 800 °C (PC-800), which was 28.2% higher than that without PC addition. Electrochemical analysis revealed that both the redox peak currents and conductivity of the methanogenic sludge increased, while the free charge transfer resistance decreased with PC-800 addition. The conductive PC-800 potentially functioned as an abiotic electron conduit to promote direct interspecies electron transfer, thereby resulting in decreased expression of functional genes associated with electrically conductive pili (e-pili) and hemeproteins. Additionally, PC-800 stimulated the secretion of redox-active humic substances (HSs), and excitation emission matrix spectra analysis indicated that the largest increase in percent fluorescence response of HSs occurred in the tightly bound EPS (TB-EPS) with addition of PC-800. This was attributed to the strong complexation ability of PC-800 particles to hydroxyl/carboxylic/phenolic moieties of HSs contained in the TB-EPS. Microbial analysis revealed that syntrophic/exoelectrogenic bacteria such as Pelotomaculum and Syntrophomonas, as well as hydrogenotrophic/electrotrophic methanogens such as Methanoculleus and Methanobacterium, were enriched in methanogenic sludge with adding PC-800. This study provided comprehensive insights for understanding the interactions among ZIF-derived PC, methanogenic microorganisms and their multilayered EPS.

Lightweight, Fire-Retardant, and Anti-Compressed Honeycombed-Like Carbon Aerogels for Thermal Management and High-Efficiency Electromagnetic Absorbing Properties

Ordered porous carbon materials (PCMs) have potential applications in various fields due to their low mass densities and porous features. However, it yet remains extremely challenging to construct PCMs with multifunctionalization for electromagnetic wave absorption. Herein, the honeycombed-like carbon aerogels with embedded Co@C nanoparticles are fabricated by a directionally freeze-casting and carbonization method. The optimized aerogel possesses low density (0.017 g cm^-3 ), fire-retardant, robust mechanical performance (compression moduli reach 1411 and 420 kPa in the longitudinal and transverse directions at 80% strain, respectively), and high thermal management (high thermal insulation capability and high-efficiency electrothermal conversion ability). Notably, the optimized aerogel exhibits the excellent electromagnetic wave absorption properties with broad effective absorption bandwidth (13.12-17.14 GHz) and strong absorption (-45.02 dB) at a thickness of only 1.5 mm. Density functional theory calculations and the experimental results demonstrate that the excellent electromagnetic wave absorption properties stem from the synergetic effects among high electrical conductivity, numerous interfaces and dipoles and unique ordered porous structure. Meanwhile, the computer simulation technology (CST) simulation confirms that the multifunctional aerogel can attenuate more electromagnetic energy in a practical environment. This work paves the way for rational design and fabrication of the next-generation electromagnetic wave absorbing materials.

Core-Shell MOF-in-MOF Nanopore Bifunctional Host of Electrolyte for High-Performance Solid-State Lithium Batteries

Solid-state lithium-ion batteries with high safety are the encouraging next-generation rechargeable electrochemical energy storage devices. Yet, low Li⁺ conductivity of solid electrolyte and instability of solid-solid interface are the key issues hampering the practicability of the solid electrolyte. In this research, core-shell MOF-in-MOF nanopores UIO-66@67 are proposed as a unique bifunctional host of ionic liquid (IL) to fabricate core-shell ionic liquid-solid electrolyte (CSIL). In the current design of CSIL, the shell structure (UIO-67) has a large pore size and a high specific surface area, boosting the absorption amount of ionic liquid electrolyte, thus increasing the ionic conductivity. Nevertheless, the core structure (UIO-66) has a small pore size compared to the ionic liquid, which can confine the large ions, decreasing their mobility, and selectively boost the transport of Li⁺ . The CSIL solid electrolyte exhibits considerable enhancement in the lithium transference number (t_Li ⁺ ) and ionic conductivity compared to the homogenous porous host (pure UIO-66 and UIO-67). Additionally, the Li|CSIL|Li symmetric batteries maintain a stable polarization of less than 28 mV for more than 1000 h at 1000 µA cm^-2 . Overall, the results demonstrate the concept of core-shell MOF-in-MOF nanopores as a promising bifunctional host of electrolytes for solid-state or quasi-solid-state rechargeable batteries.

A Gas-Steamed MOF Route to P-Doped Open Carbon Cages with Enhanced Zn-Ion Energy Storage Capability and Ultrastability

Carbon micro/nanocages have received great attention, especially in electrochemical energy-storage systems. Herein, as a proof-of-concept, a solid-state gas-steamed metal-organic-framework approach is designed to fabricate carbon cages with controlled openings on walls, and N, P dopants. Taking advantage of the fabricated carbon cages with large openings on their walls for enhanced kinetics of mass transport and N, P dopants within the carbon matrix for favoring chemical adsorption of Zn ions, when used as carbon cathodes for advanced aqueous Zn-ion hybrid supercapacitors (ZHSCs), such open carbon cages (OCCs) display a wide operation voltage of 2.0 V and an enhanced capacity of 225 mAh g^-1 at 0.1 A g^-1 . Also, they exhibit an ultralong cycling lifespan of up to 300 000 cycles with 96.5% capacity retention. Particularly, such OCCs as electrode materials lead to a soft-pack ZHSC device, delivering a high energy density of 97 Wh kg^-1 and a superb power density of 6.5 kW kg^-1 . Further, the device can operate in a wide temperature range from -25 to + 40 °C, covering the temperatures for practical applications in daily life.

Metal-Organic Frameworks-Derived Nitrogen-Doped Porous Carbon Nanocubes with Embedded Co Nanoparticles as Efficient Sulfur Immobilizers for Room Temperature Sodium-Sulfur Batteries

Room temperature sodium-sulfur (RT Na-S) batteries are considered a promising candidate for energy-storage due to their high energy-density and low-cost. However, the shutting effect of polysulfides and sluggish kinetics of sulfur redox reactions still severely limit their practical implementation. Herein, a new type of 3D hierarchical porous carbonaceous nanocubes is reported as efficient sulfur hosts, composed of carbon nanotubes (CNT) and Co nanoparticles (NPs) uniformly embedded into a nitrogen-doped carbon matrix (NC). Because of the high specific surface area, large degree of graphitization, and the synergetic effects between Co NPs and N-doping, the as-designed CNTs/Co@NC electrodes not only significantly increase polysulfides immobilization, but also efficiently catalyze sulfur redox reactions, as confirmed by experimental results and DFT calculations. When tested in a RT Na-S battery, the S@CNTs/Co@NC-0.25 cathode demonstrates outstanding electrochemical performance, achieving high initial specific capacity of 1200.3 mAh g^-1 at 0.1 C, remarkable rate capability up to 5.0 C (474.2 mAh g^-1 ), and superior cyclic performance of 450.5 mAh g^-1 (292 mAh g^-1 ) after 400 cycles at 1.0 C (5.0 C). The integration of a 3D hierarchical porous architecture with well-dispersed Co NPs of an electro-catalyst provides valuable insights based on structure-adsorption-catalysis engineering for advanced RT Na-S batteries.

Metal-Organic Framework-Derived Trimetallic Nanocomposites as Efficient Bifunctional Oxygen Catalysts for Zinc-Air Batteries

Transition-metal-based multifunctional catalysts have attracted increasing attention owing to high possibilities of substituting the expensive noble-metal-based catalysts in various scenarios. Multivariate metal-organic frameworks (MTV-MOFs) are ideal precursors to prepare multimetallic nanocomposites with high catalytic activity since the uniform distribution and precise regulation of mixed metal centers, as well as the consequent strong synergistic effect, could be readily achieved. Herein, a Mn/Co/Ni trimetallic catalyst (MnCoNi-C-D) with a hollow rhombic dodecahedron shape was synthesized via pyrolysis of the corresponding trimetallic-based MTV-MOF. The catalyst shows outstanding electrochemical activity toward the oxygen reduction reaction including a half-wave potential of 0.82 V and superior tolerance against methanol as well as high stability in an alkaline medium, and its oxygen evolution reaction activity also surpasses a RuO₂ catalyst. Moreover, primary and rechargeable zinc-air batteries based on MnCoNi-C-D delivered preferable performances compared with commercial Pt/C-RuO₂, including higher peak power density (116.4 mW cm^-2), higher specific capacity (841.3 mAh g^-1), higher open-circuit potential (OCV) (1.46 V), and better stability for more than 180 h. A comprehensive comparison was also conducted to prove the necessity of employing the MTV-MOF as the precursor and investigate the intrinsic superiority of the catalyst.