Hierarchical Nanocomposites Derived from Nanocarbons and Layered Double Hydroxides ‐ Properties,Synthesis, and Applications

The combination of one‐dimensional and two‐dimensional building blocks leads to the formation of hierarchical composites that can take full advantages of each kind of material, which is an effective way for the preparation of multifunctional materials with extraordinary properties. Among various building blocks, nanocarbons (e.g., carbon nanotubes and graphene) and layered double hydroxides (LDHs) are two of the most powerful materials that have been widely used in human life. This Feature Article presents a state‐of‐the‐art review of hierarchical nanocomposites derived from nanocarbons and LDHs. The properties of nanocarbons, LDHs, as well as the combined nanocomposites, are described first. Then, efficient and effective fabrication methods for the hierarchical nanocomposites, including the reassembly of nanocarbons and LDHs, formation of LDHs on nanocarbons, and formation of nanocarbons on LDHs, are presented. The as‐obtained nanocomposites derived form nanocarbons and LDHs exhibited excellent performance as multifunctional materials for their promising applications in energy storage, nanocomposites, catalysis, environmental protection, and drug delivery. The fabrication of LDH/carbon nanocomposites provides a novel method for the development of novel multifunctional nanocomposites based on the existing nanomaterials. However, knowledge of their assembly mechanism, robust and precise route for LDH/nanocarbon hybrid with well designed structure, and the relationship between structure, properties, and applications are still inadequate. A multidisciplinary approach from the scope of materials, physics, chemistry, engineering, and other application areas, is highly required for the development of this advanced functional composite materials.     

Thin‐Layered Photocatalysts

Semiconductor photocatalysis, a green and sustainable technology, is of great significance for solving environmental pollution and energy shortages. However, the common problems of inefficient light harvesting, rapid recombination of electron–hole pairs, and low surface reactive reaction sites for photocatalysts urgently need to be solved. In this regard, thin‐layered photocatalysts are considered to be one of the most promising candidates for addressing these issues, due to their unique surface and electronic properties. In this review, the various strategies for constructing thin‐layered photocatalysts are summarized, and emphasis is given to approaches for optimizing the photocatalytic performance of the thin‐layered materials, which can be classified into surface engineering and junction construction. In addition, the photocatalytic applications of thin‐layered materials, i.e., water splitting, CO₂ reduction, nitrogen fixation, and molecule oxygen activation, are summarized. Finally, based on current achievements in thin‐layered photocatalysts, their future development and challenges are discussed.     

Layered Materials in the Magnesium Ion Batteries: Development History,Materials Structure,and Energy Storage Mechanism

Layered crystal materials have blazed a promising trail in the design and optimization of electrodes for magnesium ion batteries (MIBs). The layered crystal materials effectively improve the migration kinetics of the Mg²⁺ storage process to deliver a high energy and power density. To meet the future demand for high-performance MIBs, significant work has been applied to layered crystal materials, including crystal modification, mechanism investigation, and micro/nanostructure design. Herein, this review presents a comprehensive overview of layered crystal materials applied to MIBs, from development history to current applications. It focuses on the relationship between the layered crystal structure and the energy storage mechanism. Meanwhile, recent achievements in the design principles of layered crystal materials and their application to electrodes are summarized. Finally, future perspectives on the application of layered materials in MIBs are presented. The overview of the development process and structural characteristics contributes to a thorough understanding of these materials, while a discussion of design strategies and practical applications can inspire further research. Therefore, this review provides guidance and assistance for constructing high-performance MIBs.     

In Situ Exfoliated,N‐Doped,and Edge‐Rich Ultrathin Layered Double Hydroxides Nanosheets for Oxygen Evolution Reaction

The number of catalytically reactive sites and their intrinsic electrocatalytic activity strongly affect the performance of electrocatalysts. Recently, there are growing concerns about layered double hydroxides (LDHs) for oxygen evolution reaction (OER). Exfoliating LDHs is an effective method to increase the reactive sites, however, a traditional liquid phase exfoliation method is usually very labor‐intensive and time‐consuming. On the other hand, proper heteroelement doping and edge engineering are helpful to tune the intrinsic activity of reactive sites. In this work, bulk CoFe LDHs are successfully exfoliated into ultrathin CoFe LDHs nanosheets by nitrogen plasma. Meanwhile, nitrogen doping and defects are introduced into exfoliated ultrathin CoFe LDHs nanosheets. The number of reactive sites can be increased efficiently by the formation of ultrathin CoFe LDHs nanosheets, the nitrogen dopant alters the surrounding electronic arrangement of reactive site facilitating the adsorption of OER intermediates, and the electrocatalytic activity of reactive sites can be further tuned efficiently by introducing defects which increase the number of dangling bonds neighboring reactive sites and decrease the coordination number of reactive sites. With these advantages, this electrocatalyst shows excellent OER activity with an ultralow overpotential of 233 mV at 10 mA cm^?2.     

Engineering the Thermal Conductivity of Functional Phase‐Change Materials for Heat Energy Conversion,Storage, and Utilization

Thermal energy storage technologies based on phase‐change materials (PCMs) have received tremendous attention in recent years. These materials are capable of reversibly storing large amounts of thermal energy during the isothermal phase transition and offer enormous potential in the development of state‐of‐the‐art renewable energy infrastructure. Thermal conductivity plays a vital role in regulating the thermal charging and discharging rate of PCMs and improving the heat‐utilization efficiency. The strategies for tuning the thermal conductivity of PCMs and their potential energy applications, such as thermal energy harvesting and storage, thermal management of batteries, thermal diodes, and other forms of energy utilization, are summarized systematically. Furthermore, a research perspective is given to highlight emerging research directions of engineering advanced functional PCMs for energy applications.     

Advanced Flexible Materials from Nanocellulose

With the increase of environmental pollution and depletion of fossil fuel resources, the utilization of renewable biomass resources for developing functional materials or fine chemicals is of great value and has attracted considerable attention. Nanocellulose, as a well-known renewable nanomaterial, is regarded as a promising nano building block for advanced functional materials owing to its unique structure and properties, as well as natural abundance. Typically, its high mechanical strength, structural flexibility, reinforcing capabilities, and tunable self-assembly behavior makes it highly attractive to fabricate flexible materials for various applications. Herein, the recent progress in the design, properties, and applications of advanced flexible materials from nanocellulose is comprehensively summarized. The preparation and properties of nanocellulose are first briefly introduced and discuss its merits in fabricating flexible materials. Then, various advanced flexible materials from nanocellulose are introduced, and the critical role of nanocellulose in constructing flexible materials is highlighted based on its intrinsic properties. After that, their applications in energy storage, electronics, sensor, biomedical, thermally insulating, photonic devices, etc., are presented. At last, the outlook of the current challenges and future perspectives for developing nanocellulose-derived flexible materials are discussed.     

State-of-the-Art Progress in Diverse Black Phosphorus-Based Structures: Basic Properties,Synthesis, Stability,Photo- and Electrocatalysis-Driven Energy Conversion

Over the past few decades, the design and development of advanced catalysts for efficient energy conversion technologies have undergone extensive study. Black phosphorus (BP) is considered to be one of the most promising catalysts, exhibiting remarkable performance and drawing significant attention, because of its extraordinary physicochemical properties: a unique layered structure, anisotropic structure, tunable direct bandgap, and ultrahigh charge mobility. In this review, the fundamentals of bulk BP, single- and few-layer phosphorene, and BP quantum dots are briefly introduced, along with their crystal structure, optical and electrical properties, stability, and synthetic methods. Furthermore, recent progress toward diverse BP-based materials for photo- and electrocatalysis for renewable energy is summarized, specifically focusing on water splitting, CO₂ conversion, and nitrogen fixation. Finally, the challenges ahead for these BP-based catalysts are also emphasized, alongside and perspectives on their further development as part of the this fast-flourishing renewable energy field.     

Strategic Design of Clay‐Based Multifunctional Materials: From Natural Minerals to Nanostructured Membranes

Nature not only carefully prepares ingenious raw materials but also continuously inspires and guides human beings to create a wide variety of intelligent materials. As the most abundant mineral resource on earth, clay minerals are no longer synonymous with ceramics and cements. Many natural clay minerals can be exfoliated into single‐ or few‐layered nanosheets with exquisite physicochemical properties, which can be reassembled into functional membranes with a macroscopic controllable size and microscopic ordered structure. They are thus used in many fields including chemistry, biology, energy, and environmental science. Strategic design represents one of the key processes to enhance the value of clay minerals and broaden their applications. In this work, the three frequently used approaches of exfoliation are highlighted and the six routes of assembly including casting, dip‐coating, spray coating, vacuum filtration, electrophoretic deposition, and 3D printing are compared. The corresponding principles and advantages are summarized. Representative applications of clay‐based multifunctional membranes in protection, separation, responsiveness, flexible electronics, and energy conversion are presented. The challenges and future perspectives of the clay‐based multifunctional membranes are discussed.     

Pristine Metal–Organic Frameworks and their Composites for Renewable Hydrogen Energy Applications

Metal–organic frameworks (MOFs) have emerged as ideal multifunctional platforms for renewable hydrogen (H₂) energy applications owing to their tunable chemical compositions and structures and high porosity. Their advanced component species and porous structure contribute greatly to the enhanced activity, electrical conductivity, photo response, charge-hole separation efficiency, and structural stability of MOF materials, which are promising for practical H₂ economy. In this review, we mainly introduce design strategies for the enhancement of electro-/photochemical behaviors or adsorption performance of porous MOF materials for H₂ production, storage, and utilization from compositional perspective. Following these engineering strategies, the correlation between composition and property-structure-performance of pristine MOFs and their composite with advanced components is illustrated. Finally, challenges and directions of future development of related MOFs and MOF composites for H₂ economy are provided.     

Hierarchical Composites of Single/Double‐Walled Carbon Nanotubes Interlinked Flakes from Direct Carbon Deposition on Layered Double Hydroxides

Three‐dimensional hierarchical nanocomposites consisting of one‐dimensional carbon nanotubes (CNTs) and two‐dimensional lamellar flakes (such as clay, layered double hydroxides) show unexpected properties for unique applications. To achieve a well‐designed structure with a specific function, the uniform distribution of CNTs into the used matrix is a key issue. Here, it is shown that a hierarchical composite of single/double‐walled CNTs interlinked with two‐dimensional flakes can be constructed via in‐situ CNT growth onto layered double hydroxide (LDH) flakes. Both the wall number and diameter of the CNTs and the composition of the flakes can be easily tuned by changing the proportion of the transition metal in the LDH flakes. Furthermore, a structure with continuously interlinked CNT layers alternating with lamellar flakes is obtained after compression. The hierarchical composite is demonstrated to be an excellent filler for strong polyimide films. This study indicates that LDH is an extraordinary catalyst for the fabrication of hierarchical composites with high‐quality single/double‐walled CNTs. The as‐obtained CNTs/calcined LDHs nanocomposite is a novel structural platform for the design of mechanically robust materials, catalysts, ion‐transportation, energy‐conversion, and other applications.     

Layered Oxide Cathodes Promoted by Structure Modulation Technology for Sodium‐Ion Batteries

Considering the ever‐growing climatic degeneration, sustainable and renewable energy sources are needed to be effectively integrated into the grid through large‐scale electrochemical energy storage and conversion (EESC) technologies. With regard to their competent benefit in cost and sustainable supply of resource, room‐temperature sodium‐ion batteries (SIBs) have shown great promise in EESC, triumphing over other battery systems on the market. As one of the most fascinating cathode materials due to the simple synthesis process, large specific capacity, and high ionic conductivity, Na‐based layered transition metal oxide cathodes commonly suffer from the sluggish kinetics, multiphase evolution, poor air stability, and insufficient comprehensive performance, restricting their commercialization application. Here, this review summarizes the recent advances in layered oxide cathode materials for SIBs through different optimal structure modulation technologies, with an emphasis placed on strategies to boost Na⁺ kinetics and reduce the irreversible phase transition as well as enhance the store stability. Meanwhile, a thorough and in‐depth systematical investigation of the structure–function–property relationship is also discussed, and the challenges as well as opportunities for practical application electrode materials are sketched. The insights brought forward in this review can be considered as a guide for SIBs in next‐generation EESC.     

Wood‐Derived Materials for Advanced Electrochemical Energy Storage Devices

Over the past decade, wood‐derived materials have attracted enormous interest for both fundamental research and practical applications in various functional devices. In addition to being renewable, environmentally benign, naturally abundant, and biodegradable, wood‐derived materials have several unique advantages, including hierarchically porous structures, excellent mechanical flexibility and integrity, and tunable multifunctionality, making them ideally suited for efficient energy storage and conversion. In this article, the latest advances in the development of wood‐derived materials are discussed for electrochemical energy storage systems and devices (e.g., supercapacitors and rechargeable batteries), highlighting their micro/nanostructures, strategies for tailoring the structures and morphologies, as well as their impact on electrochemical performance (energy and power density and long‐term durability). Furthermore, the scientific and technical challenges, together with new directions of future research in this exciting field, are also outlined for electrochemical energy storage applications.     

Nanocellulose-Based Functional Materials: From Chiral Photonics to Soft Actuator and Energy Storage

Nanocellulose is currently in the limelight of extensive research from fundamental science to technological applications owing to its renewable and carbon-neutral nature, superior biocompatibility, tailorable surface chemistry, and unprecedented optical and mechanical properties. Herein, an up-to-date account of the recent advancements in nanocellulose-derived functional materials and their emerging applications in areas of chiral photonics, soft actuators, energy storage, and biomedical science is provided. The fundamental design and synthesis strategies for nanocellulose-based functional materials are discussed. Their unique properties, underlying mechanisms, and potential applications are highlighted. Finally, this review provides a brief conclusion and elucidates both the challenges and opportunities of the intriguing nanocellulose-based technologies rooted in materials and chemistry science. This review is expected to provide new insights for nanocellulose-based chiral photonics, soft robotics, advanced energy, and novel biomedical technologies, and promote the rapid development of these highly interdisciplinary fields, including nanotechnology, nanoscience, biology, physics, synthetic chemistry, materials science, and device engineering.     

Thermal Transport in 2D Semiconductors—Considerations for Device Applications

The discovery of graphene has stimulated the search for and investigations into other 2D materials because of the rich physics and unusual properties exhibited by many of these layered materials. Transition metal dichalcogenides (TMDs), black phosphorus, and SnSe among many others, have emerged to show highly tunable physical and chemical properties that can be exploited in a whole host of promising applications. Alongside the novel electronic and optical properties of such 2D semiconductors, their thermal transport properties have also attracted substantial attention. Here, a comprehensive review of the unique thermal transport properties of various emerging 2D semiconductors is provided, including TMDs, black‐ and blue‐phosphorene among others, and the different mechanisms underlying their thermal conductivity characteristics. The focus is placed on the phonon‐related phenomena and issues encountered in various applications based on 2D semiconductor materials and their heterostructures, including thermoelectric power generation and electron–phonon coupling effect in photoelectric and thermal transistor devices. A thorough understanding of phonon transport physics in 2D semiconductor materials to inform thermal management of next‐generation nanoelectronic devices is comprehensively presented along with strategies for controlling heat energy transport and conversion.     

Production and Patterning of Liquid Phase–Exfoliated 2D Sheets for Applications in Optoelectronics

2D materials (2DMs), which can be produced by exfoliating bulk crystals of layered materials, display unique optical and electrical properties, making them attractive components for a wide range of technological applications. This review describes the most recent developments in the production of high‐quality 2DMs based inks using liquid‐phase exfoliation (LPE), combined with the patterning approaches, highlighting convenient and effective methods for generating materials and films with controlled thicknesses down to the atomic scale. Different processing strategies that can be employed to deposit the produced inks as patterns and functional thin‐films are introduced, by focusing on those that can be easily translated to the industrial scale such as coating, spraying, and various printing technologies. By providing insight into the multiscale analyses of numerous physical and chemical properties of these functional films and patterns, with a specific focus on their extraordinary electronic characteristics, this review offers the readers crucial information for a profound understanding of the fundamental properties of these patterned surfaces as the millstone toward the generation of novel multifunctional devices. Finally, the challenges and opportunities associated to the 2DMs' integration into working opto‐electronic (nano)devices is discussed.     

Fast Photoresponse from 1T Tin Diselenide Atomic Layers

Atomically layered 2D crystals such as transitional metal dichalcogenides (TMDs) provide an enchanting landscape for optoelectronic applications due to their unique atomic structures. They have been most intensively studied with 2H phase for easy fabrication and manipulation. 1T phase material could possess better electrocatalytic and photocatalytic properties, while they are difficult to fabricate. Herein, for the first time, the atomically layered 1T phase tin diselenides (SnSe₂, III‐IV compound) are successfully exfoliated by the method of mechanical exfoliation from bulk single crystals, grown via the chemical vapor transport method without transport gas. More attractively, the high performance atomically layered SnSe₂ photodetector has been first successfully fabricated, which displays a good responsivity of 0.5 A W^?1 and a fast photoresponse down to ≈2 ms at room temperature, one of the fastest response times among all types of 2D photodetectors. It makes SnSe₂ a promising candidate for high performance optoelectronic devices. Moreover, high performance bilayered SnSe₂ field‐effect transistors are also demonstrated with a mobility of ≈4 cm² V^?1 s^?1 and an on/off ratio of 10³ at room temperature. The results demonstrate that few layered 1T TMD materials are relatively stable in air and can be exploited for various electrical and optical applications.     

Biocatalytic Metal–Organic Frameworks: Prospects Beyond Bioprotective Porous Matrices

Biocatalytic metal–organic framework (MOF) composites, synthesized by interfacing MOFs with biocatalytic components, possessing the unprecedented synergetic properties that are hard to achieve via conventional strategies, represent one of the next‐generation composite materials for diverse biotechnological applications. Research on the applications of biocatalytic MOFs is still in its preliminary stage, with a wide variety of studies focusing on the bioprotection role of MOFs. However, their diversity of building units, molecular‐scale tunability, modular synthetic routes, and more detailed understanding of the heterogeneous MOF‐biointerface could even lead to completely new applications and potentials beyond the current imagination. The most recent progress in biocatalytic MOFs presents ground‐breaking applications in smart and tunable biocatalysis, precision nanomedicine, vaccine and gene delivery, biosensing, and nano‐biohybrids. Herein, the general and advanced synthesis strategies for improving the material properties of biocatalytic MOFs, from tuning biocatalytic activity to framework stability to synergistic properties with other materials, are summarized. Then, the latest state‐of‐the‐art applications of the biocatalytic MOF systems and recent advanced developments that are shaping this emerging field are surveyed. Finally, to define promising research directions, a critical evaluation and future prospects for the potential applications of biocatalytic MOFs are provided.     

Advanced Antiscaling Interfacial Materials toward Highly Efficient Heat Energy Transfer

The energy problem has been a matter of some concern worldwide over the past 20 years. On the opposite side of energy production, energy loss is another crucial problem of current energy due to the low efficiency of heat transfer from scale deposition. However, less attention has been paid on the further development of advanced antiscaling interfacial materials, which may provide promising ways to save energy by reducing scale fouling. Herein, the development of antiscaling strategies is summarized from the basic theories and fabrication methods to antiscaling interfacial materials with potential applications. First, the mechanism of scale formation and the corresponding effect on thermal conductivity are introduced. Second, the typical fabrication approaches of antiscaling interfacial materials are briefly described. Finally, the performance, potential applications, future challenges, and opportunities of the advanced antiscaling interfacial materials are comprehensively discussed.     

Investigating Local Structure in Layered Double Hydroxides with 17O NMR Spectroscopy

A new method based on the “memory effect” for efficient and economical ¹⁷O labeling of layered double hydroxides (LDHs) is introduced. High‐quality ¹⁷O solid‐state NMR spectra are obtained, for the first time, for LDHs prepared with only several hundred microliters of ¹⁷O‐enriched H₂O. The ¹⁷O resonances due to the different oxygen ions in the structure of LDHs can be resolved with better resolution than the results obtained from ¹H ultrafast magic angle spinning (MAS) NMR spectroscopy. The results show clear evidence for Al–O–Al avoidance. Since only intermediate MAS speeds and fields are used, this new approach can be incorporated easily with a variety of dipolar recoupling schemes to explore the key interactions and applications of LDHs.     

Two-dimensional air-stable CrSe2 nanosheets with thickness-tunable magnetism

Since Geim et al.firstly separated graphene from graph-ite by mechanical exfoliation method in 2004,the research of two-dimensional (2D) van der Waals (vdW) layered materials has begun[1].Compared with three-dimensional materials,2D vdW layered materials exposing the most atoms to exterior are more sensitive to external control and have the great po-tential applications in electronic,optoelectronic and electro-chemical area[2].