Three-Dimensional MOFs@MXene Aerogel Composite Derived MXene Threaded Hollow Carbon Confined CoS Nanoparticles toward Advanced Alkali-Ion Batteries

Sandwich-structured continuous ZIF-8/Ti3C2 MXene/ZIF-8 for efficient sterilization: Enhanced photocatalytic activity, photothermal effect, and environmental safety

The development of effective water purification systems is crucial for controlling and remediating environmental pollution, especially in terms of sterilization. Herein, we demonstrate elaborately designed composite nanosheets with a sandwich structure, composed of two-dimensional (2D) Ti3C2 MXene nanosheet core and conformal ZIF-8 ultrathin outer layers, and their potential applications in photocatalytic sterilization. The study results indicate that the conformal ZIF-8-MXene nanosheet exhibits an expanded light absorption range (826 nm), improved photothermal conversion efficiency (6.2 °C s-1), and photocurrent response, thus boosting photocatalytic sterilization efficiency (6.63 log10 CFU mL-1) against Escherichia coli under simulated sunlight within 90 min. Interestingly, 2D ZIF-8 layers exhibit positive zeta potential (19 mV), good hydrophilicity (40.6°), and local photogenerated-hole accumulation, possessing efficient bacteria-trapping efficiency. Membrane filters fabricated from optimized composite nanosheets exhibit an outstanding bacteria-trapping and sterilization efficiency (almost 100 %) against Escherichia coli under simulated sunlight within 30 min of the flow photocatalytic experiments. This work not only presents a rational structural design of the conformal and ultrathin anchoring of ZIF-8 onto a 2D conductive material for bacteria-trapping and sterilization, but also opens new opportunities for using metal-organic frameworks in photocatalytic disinfection of drinking water.

Recent Progress in MOF-Aerogel Fabrication and Applications

Recent advancements in metal-organic frameworks (MOFs) underscore their significant potential in chemical and materials research, owing to their remarkable properties and diverse structures. Despite challenges like intrinsic brittleness, powdered crystalline nature, and limited stability impeding direct applications, MOF-based aerogels have shown superior performance in various areas, particularly in water treatment and contaminant removal. This review highlights the latest progress in MOF-based aerogels, with a focus on hybrid systems incorporating materials like graphene, carbon nanotube, silica, and cellulose in MOF aerogels, which enhance their functional properties. The manifold advantages of MOF-based aerogels in energy storage, adsorption, and catalysis are discussed, with an emphasizing on their improved stability, processability, and ease of handling. This review aims to unlock the potential of MOF-based aerogels and their real-world applications. Aerogels are expected to reshape the technological landscape of MOFs through enhanced stability, adaptability, and efficiency.

Designing a Se-intercalated MOF/MXene-derived nanoarchitecture for advancing the performance and durability of lithium-selenium batteries

Lithium-selenium batteries have emerged as a promising alternative to lithium-sulfur batteries due to their high electrical conductivity and comparable volume capacity. However, challenges such as the shuttle effect of polyselenides and high-volume fluctuations hinder their practical implementation. To address these issues, we propose synthesizing Fe-CNT/TiO2 catalyst through high-temperature sintering of an amalgamated nanoarchitecture of carbon nanotubes decorated metal-organic framework (MOF) and MXene, optimized for efficient selenium hosting, leveraging the distinctive physicochemical properties. The catalytic features inherent in the porous Se@Fe-CNT/TiO2 nanoarchitecture were instrumental in promoting efficient ion and electron transport, and lithium-polyselenide kinetics, while its inherent porosity could play a crucial role in inhibiting electrode stress during cycling. This nanoarchitecture exhibits remarkable battery performance, retaining 99.7% of theoretical capacity after 425 cycles at 0.5 C rate and demonstrating 95.8% capacity retention after 2000 cycles at 1 C rate, with ∼100% Coulombic efficiency. Additionally, the Se@Fe-CNT/TiO2 electrode exhibited an impressive recovery of 297.5 mAh/g (97.9%) capacity after undergoing 450 cycles at a charging rate of 10 C and a discharging rate of 1 C. This synergistic integration of MOF- and MXene-derived materials unveils new possibilities for high-performance and durable LSeBs, thus advancing electrochemical energy storage systems.

Ti─O─C Bonding at 2D Heterointerfaces of 3D Composites for Fast Sodium Ion Storage at High Mass Loading Level

3D composite electrodes have shown extraordinary promise as high mass loading electrode materials for sodium ion batteries (SIBs). However, they usually show poor rate performance due to the sluggish Na+ kinetics at the heterointerfaces of the composites. Here, a 3D MXene-reduced holey graphene oxide (MXene-RHGO) composite electrode with Ti─O─C bonding at 2D heterointerfaces of MXene and RHGO is developed. Density functional theory (DFT) calculations reveal the built-in electric fields (BIEFs) are enhanced by the formation of bridged interfacial Ti─O─C bonding, that lead to not only faster diffusion of Na+ at the heterointerfaces but also faster adsorption and migration of Na+ on the MXene surfaces. As a result, the 3D composite electrodes show impressive properties for fast Na+ storage. Under high current density of 10 mA cm-2, the 3D MXene-RHGO composite electrodes with high mass loading of 10 mg cm-2 achieve a strikingly high and stable areal capacity of 3 mAh cm-2, which is same as commercial LIBs and greatly exceeds that of most reported SIBs electrode materials. The work shows that rationally designed bonding at the heterointerfaces represents an effective strategy for promoting high mass loading 3D composites electrode materials forward toward practical SIBs applications.

Advanced Insights on MXenes: Categories, Properties, Synthesis, and Applications in Alkali Metal Ion Batteries

The development and optimization of promising anode material for next-generation alkali metal ion batteries are significant for clean energy evolution. 2D MXenes have drawn extensive attention in electrochemical energy storage applications, due to their multiple advantages including excellent conductivity, robust mechanical properties, hydrophilicity of its functional terminations, and outstanding electrochemical storage capability. In this review, the categories, properties, and synthesis methods of MXenes are first outlined. Furthermore, the latest research and progress of MXenes and their composites in alkali metal ion storage are also summarized comprehensively. A special emphasis is placed on MXenes and their hybrids, ranging from material design and fabrication to fundamental understanding of the alkali ion storage mechanisms to battery performance optimization strategies. Lastly, the challenges and personal perspectives of the future research of MXenes and their composites for energy storage are presented.

A precisely Assembled Wall-Like Architecture for High Lithium/Sodium Storage

MXene nanosheets and ordered porous carbons both have their own advantages and disadvantages. Assembling and combining the advantages of the two will be a good choice for battery electrode hosts of active materials. In this work, an electrostatic separation-adsorption strategy is proposed to realize the ordered alternating self-assembly of MXene nanosheets and ordered porous carbon (MPOC), obtaining a unique wall-like porous material with a high conductivity and interconnected porous nanostructure, which strengthens the transfer rate of electrons and ions simultaneously. Meanwhile, the introduction of N-doping from porous carbon into MPOC prolongs the cycle life. When use red phosphorus (RP) as active materials, the MPOC@RP anode exhibited high-capacity output (2454.3 and 2408.1 mAh g-1 in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) at 0.1 C) and long cycle life (the decay rates per cycle of 0.028% and 0.036% after 1500 and 1200 cycles at 2 C in LIBs and SIBs respectively). The successful application in RP anodes displays great potential in other electrode materials such as silicon, sulfur, selenium, and so on. Meanwhile, this strategy is also effective to design other composites materials like MXene and carbon nanotubes, MXene and Graphene, and so on.

Ultrathin nitrogen-doped carbon Ti3C2Tx-TiN heterostructure derived from ZIF-8 nanoparticles sandwiched MXene for high-performance capacitive deionization

Rational design of high-performance electrode materials is crucial for enhancing desalination performance of capacitive deionization (CDI). Here, ultrathin nitrogen-doped carbon/Ti3C2Tx-TiN (NC/MX-TiN) heterostructure was developed by pyrolyzing zeolite imidazolate framework-8 (ZIF-8) nanoparticles sandwiched MXene (ZSM), which were formed by assembling ultrafine ZIF-8 nanoparticles with size of 20 nm on both sides of MXene nanosheets. The introduction of ultrasmall ZIF-8 particles allowed for in situ nitridation of the MXene during pyrolysis, forming consecutive TiN layers tightly connected to the internal MXene. The two-dimensional (2D) heterostructure exhibited remarkable properties, including high specific surface area and excellent conductivity. Additionally, the resulting TiN demonstrated exceptional redox capability, which significantly enhanced the performance of CDI and ensured cycling stability. Benefiting from these advantages, the NC/MX-TiN exhibited a maximum adsorption capacity of 45.6 mg g-1 and a steady cycling performance in oxygenated saline water over 50 cycles. This work explores the rational design and construction of MXene-based 2D heterostructure and broadens new horizons for the development of novel CDI electrode materials.

Heterostructures Assembled from Bi2O2CO3 and MXene for Boosted Potassium-Ion Storage by Arousing the Built-in Electric Field

Bismuth-based materials have been recognized as the appealing anodes for potassium-ion batteries (PIBs) due to their high theoretical capacity. However, the kinetics sluggishness and capacity decline induced by the structure distortion predominately retard their further development. Here, a heterostructure of polyaniline intercalated Bi2O2CO3/MXene (BOC-PA/MXene) hybrids is reported via simple self-assembly strategy. The ingenious design of heterointerface-rich architecture motivates significantly the interior self-built-in electric field (IEF) and high-density electron flow, thus accelerating the charge transfer and boosting ion diffusion. As a result, the hybrids realize a high reversible specific capacity, satisfying rate capability as well as long-term cycling stability. The in/ex situ characterizations further elucidate the stepwise intercalation-conversion-alloying reaction mechanism of BOC-PA/MXene. More encouragingly, the full cell investigation further highlights its competitive merits for practical application in further PIBs. The present work not only opens the way to the design of other electrodes with an appropriate working mechanism but also offers inspiration for built-in electric-field engineering toward high-performance energy storage devices.

Metal-Organic Framework-Based Materials for Advanced Sodium Storage: Development and Anticipation

As a pioneering battery technology, even though sodium-ion batteries (SIBs) are safe, non-flammable, and capable of exhibiting better temperature endurance performance than lithium-ion batteries (LIBs), because of lower energy density and larger ionic size, they are not amicable for large-scale applications. Generally, the electrochemical storage performance of a secondary battery can be improved by monitoring the composition and morphology of electrode materials. Because more is the intricacy of a nanostructured composite electrode material, more electrochemical storage applications would be expected. Despite the conventional methods suitable for practical production, the synthesis of metal-organic frameworks (MOFs) would offer enormous opportunities for next-generation battery applications by delicately systematizing the structure and composition at the molecular level to store sodium ions with larger sizes compared with lithium ions. Here, the review comprehensively discusses the progress of nanostructured MOFs and their derivatives applied as negative and positive electrode materials for effective sodium storage in SIBs. The commercialization goal has prompted the development of MOFs and their derivatives as electrode materials, before which the synthesis and mechanism for MOF-based SIB electrodes with improved sodium storage performance are systematically discussed. Finally, the existing challenges, possible perspectives, and future opportunities will be anticipated.

Dual-Confinement Effect of Nanocages@Nanotubes Suppresses Polysulfide Shuttle Effect for High-Performance Lithium-Sulfur Batteries

The shuttle effect of lithium polysulfides (LiPSs) severely hinders the development and commercialization of lithium-sulfur batteries, and the design of high-conductive carbon fiber-host material has become a key solution to suppress the shuttle effect. In this work, a unique Co/CoN-carbon nanocages@TiO2-carbon nanotubes structure (NC@TiO2-CNTs) is constructed using an electrospinning and nitriding process. Lithium-sulfur batteries using NC@TiO2-CNTs as cathode host materials exhibit high sulfur utilization (1527 mAh g-1 at 0.2 C) and can still maintain a discharge capacity of 663 mAh g-1 at a high current density of 5 C, and the capacity loss is only 0.056% per cycle during 500 cycles at 1 C. It is worth noting that even under extreme conditions (sulfur-loading = 90%, surface-loading = 5.0 mg cm-2 (S), and E/S = 6.63 µL mg-1), the lithium-sulfur batteries can still provide a reversible capacity of 4 mAh cm-2. Throughdensity functional theory calculations, it has been found that the Co/CoN heterostructures can adsorb and catalyze LiPSs conversion effectively. Simultaneously, the TiO2 can adsorb LiPSs and transfer Li+ selectively, achieving dual confinement for the shuttle effect of LiPSs (nanocages and nanotubes). The new findings provide a new performance enhancement strategy for the commercialization of lithium-sulfur batteries.

Co─Mn Bimetallic Nanowires by Interfacial Modulation with/without Vacancy Filling as Active and Durable Electrocatalysts for Water Splitting

Active and stable nonnoble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are required for water splitting by sustainable electricity. Here, Mn bonded with O and P is incorporated to modulate Co3S4 and Co2P respectively to enhance the catalytic activity and extend the catalyst lifetime. Mn3O4 adjusts the electronic structure of Co3S4 and Co atom fills the oxygen vacancy in Mn3O4. The interfacial interaction endows Co3S4/Mn3O4 to a lower reaction barrier due to ideal binding energies for OER intermediates. Structure stability of active sites and enhanced Co─S bonds by Operando Raman spectroscopy and theoretical calculations reduce the dissolution of Co3S4/Mn3O4, resulting in a lifetime of 500 h at 50 mA cm-2 for OER. The modulation of Co2P by MnP weakens the interaction between Co sites and adsorbed H*, achieving a high activity under a large current for HER. The assembled electrolyzer affords 50 mA cm-2 at 1.58 V and exhibits a lifetime of 350 h at 50 mA cm-2. The calculations disclose the electron interaction for the activity and stability, as well as the enhanced conductivity. The findings develop new avenues toward promoting catalytic activity and stability, making Co─Mn bimetallic nanowires efficient electrocatalysts for nonnoble water electrolyzers.

Elastic MXene conductive layers and electrolyte engineering enable robust potassium storage

The precisely engineered structures of materials greatly influence the manifestation of their properties. For example, in the process of alkali metal ion storage, a carefully designed structure capable of accommodating inserted and extracted ions will improve the stability of material cycling. The present study explores the uniform distribution of self-grown carbon nanotubes to provide structural support for the conductive and elastic MXene layers of Ti3C2Tx-Co@NCNTs. Furthermore, a compatible electrolyte system has been optimized by analyzing the solvation structure and carefully regulating the component in the solid electrolyte interphase (SEI) layer. Mechanistic studies demonstrate that the decomposition predominantly controlled by FSI- leads to the formation of a robust inorganic SEI layer enriched with KF, thus effectively inhibiting irreversible side reactions and major structural deterioration. Confirming our expectations, Ti3C2Tx-Co@NCNTs exhibits an impressive reversible capacity of 260 mA h g-1, even after 2000 cycles at 500 mA g-1 in 1 M KFSI (DME), surpassing most MXene-based anodes reported for PIBs. Additionally, density functional theory (DFT) calculations verify the superior electronic conductivity and lower K+ diffusion energy barriers of the novel superstructure of Ti3C2Tx-Co@NCNTs, thereby affirming the improved electrochemical kinetics. This study presents systematic evaluation methodologies for future research on MXene-based anodes in PIBs.

Layered CoS@NC in situ loaded onto Ti3C2Tx MXene as an efficient lithium-ion battery anode

Due to its large capacity and relatively high conductivity, cobalt sulfide has been considered an excellent electrode material for lithium-ion batteries, but its extreme volume change during charging and discharging and lower conductivity than graphite limits its development. In this work, composite nanosheets of MXene and N-doped carbon-confined cobalt sulfide nanosheets (CoS@NC/MXene) were synthesized by growing the Co metal-organic framework of ZIF-67 onto MXene sheets, followed by sulfidation treatment. Different from normal ZIF-67 generally prepared in methanol, this work fabricates ZIF-67 in aqueous solution, which induces ZIF-67 to undergo some degree of hydrolysis and form more dispersed Co layered hydroxides mounted onto MXene. Also, the MXene incorporation imparts better water stability to ZIF-67(Co) and helps maintain its morphology during the sulfidation. CoS@NC/MXene has a conductive network supported by MXene and enhanced by NC, as well as a 3D hierarchical porous structure offered by the rational combination of its components. These favorable characteristics allow CoS@NC/MXene to deliver a capacity of 691 mA h g-1 at 200 mA g-1 in the 100th cycle and retain the specific capacity of 382 mA h g-1 at a higher current density of 8000 mA g-1.

Hollow Carbon and MXene Dual-Reinforced MoS2 with Enlarged Interlayers for High-Rate and High-Capacity Sodium Storage Systems

Sodium-ion batteries (SIBs) and sodium-ion capacitors (SICs) are promising candidates for cost-effective and large-scale energy storage devices. However, sluggish kinetics and low capacity of traditional anode materials inhibit their practical applications. Herein, a novel design featuring a layer-expanded MoS2 is presented that dual-reinforced by hollow N, P-codoped carbon as the inner supporter and surface groups abundant MXene as the outer supporter, resulting in a cross-linked robust composite (NPC@MoS2 /MXene). The hollow N, P-codoped carbon effectively prevents agglomeration of MoS2 layers and facilitates shorter distances between the electrolyte and electrode. The conductive MXene outer surface envelops the NPC@MoS2 units inside, creating interconnected channels that enable efficient charge transfer and diffusion, ensuring rapid kinetics and enhanced electrode utilization. It exhibits a high reversible capacity of 453 mAh g-1 , remarkable cycling stability, and exceptional rate capability with 54% capacity retention when the current density increases from 100 to 5000 mA g-1 toward SIBs. The kinetic mechanism studies reveal that the NPC@MoS2 /MXene demonstrates a pseudocapacitance dominated hybrid sodiation/desodiation process. Coupled with active carbon (AC), the NPC@MoS2 /MXene//AC SICs achieve both high energy density of 136 Wh kg-1 at 254 W kg-1 and high-power density of 5940 W kg-1 at 27 Wh g-1 , maintaining excellent stability.

N-Doped Carbon Nanonecklaces with Encapsulated BiOCl Nanoparticles as High-Rate Anodes for Lithium-Ion Batteries

The unique two-dimensional layered structure of BiOCl makes it highly promising for energy storage applications. In this study, we successfully synthesized BiOCl nanoparticles encapsulated in N-doped carbon nanonecklaces (BiOCl NPs/N-CNNs) using well-established electrospinning and solvothermal substitution. As an anode material for lithium-ion batteries, BiOCl NPs/N-CNNs exhibited enhanced rate performance, delivering a capacity of 220.2 mA h g-1 at 8 A g-1. Furthermore, it demonstrated remarkable long cycle stability, retaining a capacity of 200.5 mA h g-1 after 9000 cycles with a discharge rate of 8.0 A g-1. The superior electrochemical performance can be attributed to the stacked layered structure of BiOCl, facilitated by van der Waals force, as well as the ingenious nanonecklace structures. These structures not only provide fast ion diffusion pathways but also enhance electrolyte penetration and offer more active sites for Li+ insertion and extraction. Additionally, the nanonecklace structure prevents the aggregation of nanopolyhedra, promoting the complete reaction of BiOCl with Li+. Moreover, the unique nanopolyhedron structure alleviates the stress caused by the volume expansion of Bi nanoparticles during cycling and reduces the internal resistance of the electrode.

Recent advances and promise of MXene-based composites as electrode materials for sodium-ion and potassium-ion batteries

With the increasing demand for sustainable energy and concerns about the scarcity of lithium resources, sodium and potassium ion batteries have emerged as promising alternative energy storage technologies. MXene, as a novel two-dimensional material, possesses exceptional electrical conductivity, high surface area, and tunable structural features that make it an ideal candidate for high-performance electrode materials. However, its limited theoretical capacity hinders its widespread application. To overcome this limitation, MXene has been combined with other materials through synergistic effects between different components to enhance the overall electrochemical performance and expand its application in sodium/potassium ion batteries. Recently, substantial advancements have been realized in the exploration of MXene-based composites as energy storage materials, encompassing their synthesis, design, and the comprehension of charge storage mechanisms. This paper aims to propose a comprehensive summary of the latest developments in MXene-based composites as electrode materials for sodium ion batteries and potassium ion batteries, with a particular emphasis on the enhanced physicochemical properties resulting from composite formation. Moreover, the challenges faced by MXene materials in sodium ion batteries and potassium ion batteries are thoroughly discussed, and future research directions to further advance this field are proposed.

NiM (Sb, Sn)/N-doped hollow carbon tube as high-rate and high-capacity anode for lithium-ion batteries

Alloy-type materials are regarded as prospective anode replacements for lithium-ion batteries (LIBs) owing to their attractive theoretical capacity. However, the drastic volume expansion leads to structural collapse and pulverization, resulting in rapid capacity decay during cycling. Here, a simple and scalable approach to prepare NiM (M: Sb, Sn)/nitrogen-doped hollow carbon tubes (NiMC) via template and substitution reactions is proposed. The nanosized NiM particles are uniformly anchored in the robust hollow N-doped carbon tubes via NiNC coordination bonds, which not only provides a buffer for volume expansion but also avoids agglomerating of the reactive material and ensures the integrity of the conductive network and structural framework during lithiation/delithiation. As a result, NiSbC and NiSnC exhibit high reversible capacities (1259 and 1342 mAh/g after 100 cycles at 0.1 A/g) and fascinating rate performance (627 and 721 mAh/g at 2 A/g), respectively, when employed as anodes of LIBs. The electrochemical kinetic analysis reveals that the dominant lithium storage behavior of NiMC electrodes varies from capacitive contribution to diffusion contribution during the cycling corresponding to the activation of the electrode exposing more NiM sites. Meanwhile, M (Sb, Sn) is gradually transformed into stable NiM during the de-lithium process, making the NiMC structure more stable and reversible in the electrochemical reaction. This work brings a novel thought to construct high-performance alloy-based anode materials.

Effect of Zr on the Microstructure and High-Temperature Phase Separation Evolution of SiOC Aerogels

SiZrOC aerogels were synthesized through the pyrolysis of the zirconium source-doped SiOC system using zirconyl chloride octahydrate (ZrOCl2·8H2O) at temperatures ranging from 900 to 1300 °C. This study investigates the microstructure evolution and phase separation of SiOC and SiZrOC aerogels during the pyrolysis process. Upon pyrolysis, both aerogels exhibited a Si-O-C structure with a high thermal stability. The introduction of zirconium elements significantly enhanced the pore volume (3.20 cm3/g) and porosity (96.0%) and reduced the thermal conductivity (0.023 W·m-1·K-1) of the organic-inorganic precursor aerogel. Moreover, the three-dimensional pore structure was retained even under high-temperature pyrolysis conditions. SiZrOC-1100 displayed a high specific surface area of 273.52 m2/g, a high pore volume of 1.70 cm3/g, and a low thermal conductivity of 0.033 W·m-1·K-1. At high temperatures, the SiZrOC phase transformation produces tetragonal ZrO2, which inhibits the graphitization process of free carbon and the growth of SiC grains. Furthermore, the phase separation process of the SiOxCy matrix structure generated oxygen-rich SiOxC4-x units, while carbon-rich SiOxC4-x units were negligible below a pyrolysis temperature of 1200 °C. Between 900 and 1200 °C, SiZrOC is composed of amorphous SiOC, amorphous ZrO2, microcrystalline t-ZrO2, and free carbon phase. These findings provide valuable insights into the preparation of high-performance SiOC aerogels.

Laser-Induced MXene-Functionalized Graphene Nanoarchitectonics-Based Microsupercapacitor for Health Monitoring Application

Microsupercapacitors (micro-SCs) with mechanical flexibility have the potential to complement or even replace microbatteries in the portable electronics sector, particularly for portable biomonitoring devices. The real-time biomonitoring of the human body's physical status using lightweight, flexible, and wearable micro-SCs is important to consider, but the main limitation is, however, the low energy density of micro-SCs as compared to microbatteries. Here using a temporally and spatially controlled picosecond pulsed laser, we developed high-energy-density micro-SCs integrated with a force sensing device to monitor a human body's radial artery pulses. The photochemically synthesized spherical laser-induced MXene (Ti3C2Tx)-derived oxide nanoparticles uniformly attached to laser-induced graphene (LIG) act as active electrode materials for micro-SCs. The molecular dynamics simulations and detailed spectroscopic analysis reveal the synergistic interfacial interaction mechanism of Ti-O-C covalent bonding between MXene and LIG. The incorporation of MXene nanosheets improves the graphene sheet alignment and ion transport while minimizing self-restacking. Furthermore, the micro-SCs based on a nano-MXene-LIG hybrid demonstrate high mechanical flexibility, durability, ultrahigh energy density (21.16 × 10-3 mWh cm-2), and excellent capacitance (∼100 mF cm-2 @ 10 mV s-1) with long cycle life (91% retention after 10 000 cycles). Such a single-step roll-to-roll highly reproducible manufacturing technique using a picosecond pulsed laser to induce MXene-derived spherical oxide nanoparticles (size of quantum dots) attached uniformly to laser-induced graphene for biomedical device fabrication is expected to find a wide range of applications.

Metal-Organic Framework Gels for Adsorption and Catalytic Detoxification of Chemical Warfare Agents: A Review

Chemical warfare agents (CWAs) have brought great threats to human life and social stability, and it is critical to investigate protective materials. MOF (metal-organic framework) gels are a class with an extended MOF architecture that are mainly formed using metal-ligand coordination as an effective force to drive gelation, and these gels combine the unique characteristics of MOFs and organic gel materials. They have the advantages of a hierarchically porous structure, a large specific surface area, machinable block structures and rich metal active sites, which inherently meet the requirements for adsorption and catalytic detoxification of CWAs. A series of advances have been made in the adsorption and catalytic detoxification of MOF gels as chemical warfare agents; however, overall, they are still in their infancy. This review briefly introduces the latest advances in MOF gels, including pure MOF gels and MOF composite gels, and discusses the application of MOF gels in the adsorption and catalytic detoxification of CWAs. Meanwhile, the influence of microstructures (pore structures, metal active site, etc.) on the detoxification performance of protective materials is also discussed, which is of great significance in the exploration of high-efficiency protective materials. Finally, the review looks ahead to next priorities. Hopefully, this review can inspire more and more researchers to enrich the performance of MOF gels for applications in chemical protection and other purification and detoxification processes.

Mott-Schottky MXene@WS2 Heterostructure: Structural and Thermodynamic Insights and Application in Ultra Stable Lithium-Sulfur Batteries

Due to the "shuttle effect" and low conversion kinetics of polysulfides, the cycle stability of lithium sulfur (Li-S) battery is unsatisfactory, which hinders its practical application. The Mott-Schottky heterostructures for Li-S batteries not only provide more catalytic/adsorption active sites, but also facilitate electrons transport by a built-in electric field, which are both beneficial for polysulfides conversion and long-term cycle stability. Here, MXene@WS2 heterostructure was constructed by in-situ hydrothermal growth for separator modification. In-depth ultraviolet photoelectron spectroscopy and ultraviolet visible diffuse reflectance spectroscopy analysis reveals that there is an energy band difference between MXene and WS2 , confirming the heterostructure nature of MXene@WS2 . DFT calculations indicate that the Mott-Schottky MXene@WS2 heterostructure can effectively promote electron transfer, improve the multi-step cathodic reaction kinetics, and further enhance polysulfides conversion. The built-in electric field of the heterostructure plays an important role in reducing the energy barrier of polysulfides conversion. Thermodynamic studies reveal the best stability of MXene@WS2 during polysulfides adsorption. As a result, the Li-S battery with MXene@WS2 modified separator exhibits high specific capacity (1613.7 mAh g-1 at 0.1 C) and excellent cycling stability (2000 cycles with 0.0286 % decay per cycle at 2 C). Even at a high sulfur loading of 6.3 mg cm-2 , the specific capacity could be retained by 60.0 % after 240 cycles at 0.3 C. This work provides deep structural and thermodynamic insights into MXene@WS2 heterostructure and its promising prospect of application in high performance Li-S batteries.

ZnS/CoS@C Derived from ZIF-8/67 Rhombohedral Dodecahedron Dispersed on Graphene as High-Performance Anode for Sodium-Ion Batteries

Metal sulfides are highly promising anode materials for sodium-ion batteries due to their high theoretical capacity and ease of designing morphology and structure. In this study, a metal-organic framework (ZIF-8/67 dodecahedron) was used as a precursor due to its large specific surface area, adjustable pore structure, morphology, composition, and multiple active sites in electrochemical reactions. The ZIF-8/67/GO was synthesized using a water bath method by introducing graphene; the dispersibility of ZIF-8/67 was improved, the conductivity increased, and the volume expansion phenomenon that occurs during the electrochemical deintercalation of sodium was prevented. Furthermore, vulcanization was carried out to obtain ZnS/CoS@C/rGO composite materials, which were tested for their electrochemical properties. The results showed that the ZnS/CoS@C/rGO composite was successfully synthesized, with dodecahedrons dispersed in large graphene layers. It maintained a capacity of 414.8 mAh g-1 after cycling at a current density of 200 mA g-1 for 70 times, exhibiting stable rate performance with a reversible capacity of 308.0 mAh g-1 at a high current of 2 A g-1. The excellent rate performance of the composite is attributed to its partial pseudocapacitive contribution. The calculation of the diffusion coefficient of Na+ indicates that the rapid sodium ion migration rate of this composite material is also one of the reasons for its excellent performance. This study highlights the broad application prospects of metal-organic framework-derived metal sulfides as anode materials for sodium-ion batteries.

MXene Derivatives for Energy Storage and Conversions

Associated with the rapid development of 2D transition metal carbides, nitrides, and carbonitrides (MXenes), MXene derivatives have been recently exploited and exhibited unique physical/chemical properties, holding promising applications in the areas of energy storage and conversions. This review provides a comprehensive summarization of the latest research and progress on MXene derivatives, including termination-tailored MXenes, single-atom implanted MXenes, intercalated MXenes, van der Waals atomic layers, and non-van der Waals heterostructures. The intrinsic relationship between structure, properties, and corresponding applications for MXene derivatives are then emphasized. Finally, the essential challenges are addressed and perspectives for the MXene derivatives are also discussed.

Fabrication, Performance, and Potential Applications of MXene Composite Aerogels

Aerogel, known as one of the remarkable materials in the 21st century, possesses exceptional characteristics such as high specific surface area, porosity, and elasticity, making it suitable for a diverse range of applications. In recent years, MXene-based aerogels and MXene composite aerogels as functional materials have solved some limitations of traditional aerogels, such as improving the electrical conductivity of biomass and silicon aerogels, further improving the energy storage capacity of carbon aerogels, enhancing polymer-based aerogels, etc. Consequently, extensive research efforts have been dedicated to investigating MXene-based aerogels, positioning them at the forefront of material science studies. This paper provides a comprehensive review of recent advancements in the preparation, properties, and applications of MXene-based composite aerogels. The primary construction strategies employed (including direct synthesis from MXene dispersions and incorporation of MXene within existing substrates) for fabricating MXene-based aerogels are summarized. Furthermore, the desirable properties (including their applications in electrochemistry, electromagnetic shielding, sensing, and adsorption) of MXene composite aerogels are highlighted. This paper delves into a detailed discussion on the fundamental properties of composite aerogel systems, elucidating the intricate structure-property relationships. Finally, an outlook is provided on the opportunities and challenges for the mass production and functional applications of MXene composite aerogels in the field of material engineering.

Collaborative Interface Optimization Strategy Guided Ultrafine RuCo and MXene Heterostructure Electrocatalysts for Efficient Overall Water Splitting

Developing highly active and robust electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) is crucial for the large-scale utilization of green hydrogen. In this study, a collaborative interface optimization guided strategy was employed to prepare a metal-organic framework (MOF) derived heterostructure electrocatalyst (MXene@RuCo NPs). The obtained electrocatalyst requires overpotentials of only 20 mV for the HER and 253 mV for the OER to deliver a current density of 10 mA/cm² in alkaline media, respectively, and it also exhibits great performance at high current density. Experiments and theoretical calculations reveal that the doped Ru introduces second active sites and decreases the diameter of nanoparticles, which greatly enhances the number of active sites. More importantly, the MXene/RuCo NPs heterogeneous interfaces in the catalysts exhibit great synergistic effects, decreasing the work function of the catalyst and improving the charge transfer rate, thus reducing the energy barrier of the catalytic reaction. This work represents a promising strategy for the development of MOF-derived highly active catalysts to achieve efficient energy conversion in industrial applications.

Metal-Organic Framework Composites and Their Derivatives as Efficient Electrodes for Energy Storage Applications: Recent Progress and Future Perspectives

Metal-organic frameworks (MOFs) have been important electrochemical energy storage (EES) materials because of their rich species, large specific surface area, high porosity and rich active sites. Nevertheless, the poor conductivity, low mechanical and electrochemical stability of pristine MOFs have hindered their further applications. Although single component MOF derivatives have higher conductivity, self-aggregation often occurs during preparation. Composite design can overcome the shortcomings of MOFs and derivatives and create synergistic effects, resulting in improved electrochemical properties for EES. In this review, recent applications of MOF composites and derivatives as electrodes in different types of batteries and supercapacitors are critically discussed. The advantages, challenges, and future perspectives of MOF composites and derivatives have been given. This review may guide the development of high-performance MOF composites and derivatives in the field of EES.

Low volume expansion hierarchical porous sulfur-doped Fe2O3@C with high-rate capability for superior lithium storage

Ingenious morphology design and doping engineering have remarkable effects on enhancing conductivity and reducing volume expansion, which need to be improved by transition metal oxides serving as anode materials for lithium-ion batteries. Herein, S_0.15-Fe₂O₃@C nano-spindles with a hierarchical porous structure are obtained by carbonizing MIL-88B@PDA and subsequent high-temperature S-doping. Kinetic analysis showed that S-doping increases capacitive contribution, enhances charge transfer capability and accelerates Li⁺ diffusion rate. Therefore, the S_0.15-Fe₂O₃@C electrode exhibits superior lithium storage performance with a remarkable specific capacity of 1014.4 mA h g^-1 at 200 mA g^-1, ultrahigh rate capability of 513.1 mA h g^-1 at 5.0 A g^-1, and excellent cycling stability of 842.3 mA h g^-1 at 1.0 A g^-1 after 500 cycles. Moreover, the size of S_0.15-Fe₂O₃@C particles barely changed after 50 cycles, indicating an extremely low volume expansion, related to the carbon shell, fine Fe₂O₃ nanoparticles, abundant voids inside, and improved kinetics. This strategy can be applied to other metal oxides for synthesizing anodes with high-rate capability and low volume expansion.

Hoya-like Hierarchical Porous Architecture as Multifunctional Phosphorus Anode for Superior Lithium-Sodium Storage

Designing nanostructured hosts with the merits of high conductivity, strong trapping ability, and long-term durability to improve the insulating nature and extreme volume change of red phosphorus (RP) is a promising option for the development of high-performance lithium/sodium-ion batteries (LIBs/SIBs). Here, a multifunctional RP immobilizer is proposed and fabricated, which comprises a nitrogen-doped hollow MXene sphere (NM) planted with the dual-sided porous carbon network (DCNM). In such a configuration, the highly conductive macroporous NM not only facilitates fast electron transport but also acts as the capturing center to entrap polyphosphide through strong chemical adsorption, while the uniformly distributed micromesoporous carbon network in or out of the sphere provides reliable RP accommodation and alleviates the volume expansion, as well as creates interpenetrating ion diffusion and electron transport channels. Benefiting from the synergistic effect of the triple-shelled architecture and the exclusive restraint, the Hoya-like DCNM@RP anode exhibits significantly enhanced electrochemical performances for LIBs and SIBs, delivering a combination of high reversible capacity, splendid rate properties, and extended cycling performance: up to 1800 cycles with 0.01% per cycle capacity decay for LIBs and 0.024% per cycle over 1000 cycles for SIBs at 2 C.

Preparation of VCo-MOF@MXene composite catalyst and study on its removal of ciprofloxacin by catalytically activating peroxymonosulfate: Construction of ternary system and superoxide radical pathway

The synergistic effect between transition metal active centers and the generation of multiple removal pathways has a significant impact on the catalytic activation efficiency of peroxymonosulfate. In this work, a kind of composite catalyst was prepared by growing VCo-metal-organic frameworks (VCo-MOF) in-situ on the surface of Ti3C2Tx by a solvothermal method. The morphology and structure are characterized by Transmission Electron Microscope (TEM), Energy Dispersion Spectrum (EDS), Atomic Force Microscope (AFM), etc. Response surface methodology was used to optimize the experimental conditions. Only 5 mg catalyst can be used to effectively activate PMS and remove 96.14 % ciprofloxacin (CIP, 20 mg/L) within 30 min. The removal effect of catalyst on CIP in different actual water environment was explored. In addition, the fluorescence spectrum test also verified the effective removal of ciprofloxacin. V-Co-Ti ternary system provides a wealth of active sites for CIP removal. Cyclic voltammetry (CV) and lear sweep voltammetry (LSV) tests showed the existence of the electron transfer pathway. The results of density functional theory (DFT) calculation show that VCo-MOF@Ti3C2Tx has excellent adsorption and activation ability for PMS. At the same time, the hydrophilicity of the catalyst makes PMS more inclined to react with water molecules, which promotes the formation of a unique superoxide radical path.

Solar-Driven Reversible Hydrogen Storage

The lack of safe and efficient hydrogen storage is a major bottleneck for large-scale application of hydrogen energy. Reversible hydrogen storage of light-weight metal hydrides with high theoretical gravimetric and volumetric hydrogen density is one ideal solution but requires extremely high operating temperature with large energy input. Herein, taking MgH₂ as an example, a concept is demonstrated to achieve solar-driven reversible hydrogen storage of metal hydrides via coupling the photothermal effect and catalytic role of Cu nanoparticles uniformly distributed on the surface of MXene nanosheets (Cu@MXene). The photothermal effect of Cu@MXene, coupled with the "heat isolator" role of MgH₂ indued by its poor thermal conductivity, effectively elevates the temperature of MgH₂ upon solar irradiation. The "hydrogen pump" effect of Ti and TiH_x species that are in situ formed on the surface of MXene from the reduction of MgH₂ , on the other hand, plays a catalytic role in effectively alleviating the kinetic barrier and hence decreasing the operating temperature required for reversible hydrogen adsorption and desorption of MgH₂ . Based on the combination of photothermal and catalytic effect of Cu@MXene, a reversible hydrogen storage capacity of 5.9 wt% is achieved for MgH₂ after 30 cycles using solar irradiation as the only energy source.

Highly Performant Electromagnetic Absorption at the X Band Based on Co@NCS/Ti3C2Tx Composites

Electromagnetic waves at the X band (8.2-12.4 GHz) play significant roles in military applications such as radar, satellite, and wireless communication. However, within this band range, the developed performance of electromagnetic absorption (EMA) is still unsatisfied, and it is hard to settle the corresponding problems on radar stealth and electromagnetic pollution. Herein, we demonstrate a state-of-the-art EMA property of -82.6 dB at 8.24 GHz with 2.57 mm thickness and 30 wt % paraffin filling ratio. For this purpose, an optimal Co@NCS/Ti₃C₂T_x composite is prepared by an electrostatic self-assembly approach through compelling Co-loading of nitrogen-doped carbon sheets (Co@NCS) derived from the pyrolysis of ZIF-67 (CoZn) with 2D Ti₃C₂T_x MXene nanosheets. Experimental results show that the highly efficient EMA performance of this Co@NCS/Ti₃C₂T_x composite originates from the large surface area for multiple reflection and electromagnetic wave scattering, from abundant defects sites for dipole and interfacial polarization, and from the optimizing impedance matching by the combination of Co magnetic nanoparticles and conductive NCS/Ti₃C₂T_x composite. These results confirm that the as-fabricated composites possess scientific and practical values for EMA applications at the X band, paving the way for developing highly performant electromagnetic absorbers toward specific microwave bands.

Functional MXene-Based Materials for Next-Generation Rechargeable Batteries

MXenes are seen as an exceptional candidate to reshape the future of energy with their viable surface chemistry, ultrathin 2D structure, and excellent electronic conductivity. The extensive research efforts bring about rapid expansion of the MXene families with enriched functionalities, which significantly boost performance of the existing energy-storage devices. In this review, the strategies that are developed to functionalize the MXene-based materials, including tailoring their microstructure by ions/molecules/polymers-initiated interaction or self-assembly, surface/interface engineering with dopants or functional groups, constructing heterostructures from MXenes with various materials, and transforming them into a series of derivatives inheriting the merits of the MXene precursors are highlighted. Their applications in emerging battery technologies are demonstrated and discussed. With delicate functionalization and structural engineering, MXene-based electrode materials exhibit improved specific capacity and rate capability, and their presence further suppresses and even eliminates dendrite formation on the metal anodes, which lengthens the lifespan of the rechargeable batteries. Meanwhile, MXenes serve as additives for electrolytes, separators, and current collectors. Finally, some future directions worth of exploration to address the remaining challenging issues of MXene-based materials and achieve the next-generation high-power and low-cost rechargeable batteries are proposed.

MXene-Based Porous Monoliths

In the past decade, a thriving family of 2D nanomaterials, transition-metal carbides/nitrides (MXenes), have garnered tremendous interest due to its intriguing physical/chemical properties, structural features, and versatile functionality. Integrating these 2D nanosheets into 3D monoliths offers an exciting and powerful platform for translating their fundamental advantages into practical applications. Introducing internal pores, such as isotropic pores and aligned channels, within the monoliths can not only address the restacking of MXenes, but also afford a series of novel and, in some cases, unique structural merits to advance the utility of the MXene-based materials. Here, a brief overview of the development of MXene-based porous monoliths, in terms of the types of microstructures, is provided, focusing on the pore design and how the porous microstructure affects the application performance.

Metal-organic framework nanocrystal-derived hollow porous materials: Synthetic strategies and emerging applications

Metal-organic frameworks (MOFs) have garnered multidisciplinary attention due to their structural tailorability, controlled pore size, and physicochemical functions, and their inherent properties can be exploited by applying them as precursors and/or templates for fabricating derived hollow porous nanomaterials. The fascinating, functional properties and applications of MOF-derived hollow porous materials primarily lie in their chemical composition, hollow character, and unique porous structure. Herein, a comprehensive overview of the synthetic strategies and emerging applications of hollow porous materials derived from MOF-based templates and/or precursors is given. Based on the role of MOFs in the preparation of hollow porous materials, the synthetic strategies are described in detail, including (1) MOFs as removable templates, (2) MOF nanocrystals as both self-sacrificing templates and precursors, (3) MOF@secondary-component core-shell composites as precursors, and (4) hollow MOF nanocrystals and their composites as precursors. Subsequently, the applications of these hollow porous materials for chemical catalysis, electrocatalysis, energy storage and conversion, and environmental management are presented. Finally, a perspective on the research challenges and future opportunities and prospects for MOF-derived hollow materials is provided.

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MOFs have garnered multi-disciplinary attention due to their unique inherent properties

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Various synthetic strategies of MOFs-derived hollow porous materials are summarized

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Emerging applications of MOFs-derived hollow porous materials are reviewed

Dual Regulation of Metal Doping and Adjusting Cut-Off Voltage for MoSe2 to Achieve Reversible Sodium Storage

MoSe₂ , as a typical 2D material, possesses tremendous potential in Na-ion batteries (SIBs) owing to larger interlayer distance, more favorable band gap structure, and higher theoretical specific capacity than other analogs. Nevertheless, the low intrinsic electronic conductivity and irreversible conversion of discharged products of Mo/Na₂ Se to MoSe₂  seriously hamper its electrochemical performance. Herein, through a facile hydrothermal method combined with calcination process, Sn-doped MoSe₂  nanosheets grown on graphene substrate in the vertical direction are fabricated. Benefiting from the improved electronic conductivity contributed by the abundant defects and expanded interlamellar spacing of MoSe₂  originated from Sn doping, combined with a smart strategy of raising discharge cut-off voltage to 0.2 V during the actual performance testing for SIBs, the as-fabricated anode material delivers superior Na-ions storage performance in terms of electrons/ions transfer, reversible sodium storage as well as cycle stability. An ultra-stable reversible specific capacity of 268.5 mAh g^-1 at 1 A g^-1 can be maintained after 1600 cycles. Moreover, the great sodium storage property in the SIB full-cell system of the as-obtained nanocomposite illustrates practical potential. Density functional theory calculation and in situ/ex situ measurements are employed to further reveal the storage mechanism and process of Na-ions.

Laminated Structural Engineering Strategy toward Carbon Nanotube-Based Aerogel Films

Aerogel films with a low density are ideal candidates to meet lightweight application and have already been used in a myriad of fields; however, their structural design for performance enhancement remains elusive. Herein, we put forward a laminated structural engineering strategy to prepare a free-standing carbon nanotube (CNT)-based aerogel film with a densified laminated porous structure. By directional densification and carbonization, the three-dimensional network of one-dimensional nanostructures in the aramid nanofiber/carbon nanotube (ANF/CNT) hybrid aerogel film can be reconstructed to a laminated porous structure with preferential orientation and consecutively conductive pathways, resulting in a large specific surface area (341.9 m²/g) and high electrical conductivity (8540 S/m). Benefiting from the laminated porous structure and high electrical conductivity, the absolute specific shielding effectiveness (SSE/t) of a CNT-based aerogel film can reach 200647.9 dB cm²/g, which shows the highest value among the reported aerogel-based materials. The laminated CNT-based aerogel films with an adjustable wetting property also exhibit exceptional Joule heating performance. This work provides a structural engineering strategy for aerogel films with enhanced electric conductivity for lightweight applications, such as EMI shielding and wearable heating.

Perspectives and Trends in Advanced MXenes-Based Optical Biosensors for the Recognition of Food Contaminants

Fabricating novel biosensing constructs with high sensitivity and selectivity is highly demanded in food contaminants detection. In this prospect, various nanostructured materials were envisaged to build (bio)sensors with superior sensitivity and selectivity. The desirable biocompatibility, brilliant mechanical strength, ease of surface functionalization, as well as tunable optical and electronic features, portray 2D MXenes as versatile scaffolds for biosensing. In this review, we overviewed the state-of-the-art MXenes-based optical biosensing devices to detect mycotoxins, pesticide residues, antibiotic residues, and food borne-pathogens from foodstuff and environmental matrices. Firstly, the synthesis methods and surface functionalization/modification of MXenes are discussed. Secondly, according to the target analytes, we categorized and presented a detailed account of the newest research progress of MXenes-based optical probes for food contaminants monitoring. The efficiency of all the surveyed probes was assessed on the basis of important factors like response time, detection limit (DL), and sensing range. Lastly, the necessity and requirements for future advances in this emerging MXenes material are also given, followed by challenges and opportunities. We hope that this study will bridge the gap between nanotechnology and food science, offering insights for engineers or scientists in both areas to accelerate the progress of MXenes-based materials for food safety detection.

Element-Doped Mxenes: Mechanism, Synthesis, and Applications

Heteroatom doping can endow MXenes with various new or improved electromagnetic, physicochemical, optical, and structural properties. This greatly extends the arsenal of MXenes materials and their potential for a spectrum of applications. This article comprehensively and critically discusses the syntheses, properties, and emerging applications of the growing family of heteroatom-doped MXenes materials. First, the doping strategies, synthesis methods, and theoretical simulations of high-performance MXenes materials are summarized. In order to achieve high-performance MXenes materials, the mechanism of atomic element doping from three aspects of lattice optimization, functional substitution, and interface modification is analyzed and summarized, aiming to provide clues for developing new and controllable synthetic routes. The mechanisms underlying their advantageous uses for energy storage, catalysis, sensors, environmental purification and biomedicine are highlighted. Finally, future opportunities and challenges for the study and application of multifunctional high-performance MXenes are presented. This work could open up new prospects for the development of high-performance MXenes.

An Open-Ended Ni3 S2 -Co9 S8 Heterostructures Nanocage Anode with Enhanced Reaction Kinetics for Superior Potassium-Ion Batteries

Sulfides are perceived as promising anode materials for potassium-ion batteries (PIBs) due to their high theoretical specific capacity and structural diversity. Nonetheless, the poor structural stability and sluggish kinetics of sulfides lead to unsatisfactory electrochemical performance. Herein, Ni₃ S₂ -Co₉ S₈ heterostructures with an open-ended nanocage structure wrapped by reduced graphene oxide (Ni-Co-S@rGO cages) are well designed as the anode for PIBs via a selective etching and one-step sulfuration approach. The hollow Ni-Co-S@rGO nanocages, with large surface area, abundant heterointerfaces, and unique open-ended nanocage structure, can reduce the K⁺ diffusion length and promote reaction kinetics. When used as the anode for PIBs, the Ni-Co-S@rGO exhibits high reversible capacity and low capacity degradation (0.0089% per cycle over 2000 cycles at 10 A g^-1 ). A potassium-ion full battery with a Ni-Co-S@rGO anode and Prussian blue cathode can display a superior reversible capacity of 400 mAh g^-1 after 300 cycles at 2 A g^-1 . The unique structural advantages and electrochemical reaction mechanisms of the Ni-Co-S@rGO are revealed by finite-element-simulation in situ characterizations. The universal synthesis technology of bimetallic sulfide anodes for advanced PIBs may provide vital guidance to design high-performance energy-storage materials.