Fire‐Resistant Structural Material Enabled by an Anisotropic Thermally Conductive Hexagonal Boron Nitride Coating

Fire retardant coatings have been proven effective at reducing the heat release rate (HRR) of structural materials during burning; yet effective methods for increasing the ignition temperature and delay time prior to burning are rarely reported. Herein, a strong, fire‐resistant wood structural material is developed by combining a densification treatment with an anisotropic thermally conductive flame‐retardant coating of hexagonal boron nitride (h‐BN) nanosheets to produce BN‐densified wood. The thermal management properties created by the BN coating provide fast, in‐plane thermal diffusion, slowing the conduction of heat through the densified wood, which improves the material's ignition properties. Compared with densified wood without the BN coating, a 41 °C enhancement in ignition temperature (T_ig), a twofold increase in ignition delay time (t_ig), and a 25% decrease in the maximum HRR of BN‐densified wood can be achieved. As a proof of concept for scalability, the pieces of the BN‐densified wood are fabricated with a length larger than 25 cm, width greater than 15 cm, and thickness more than 7 mm. The improved thermal management, fire resistance, mechanical strength, and scalable production of BN‐densified wood position it as a promising structural material for safe and energy‐efficient buildings.     

Hybrid Materials from Ultrahigh‐Inorganic‐Content Mineral Plastic Hydrogels: Arbitrarily Shapeable,Strong, and Tough

Natural mineralized structural materials such as nacre and bone possess a unique hierarchical structure comprising both hard and soft phases, which can achieve the perfect balance between mechanical strength and shape controllability. Nevertheless, it remains a great challenge to control the complex and predesigned shapes of artificial organic–inorganic hybrid materials at ambient conditions. Inspired by the plasticity of polymer‐induced liquid precursor phases that can penetrate and solidify in porous organic frameworks for biomineral formation, here a mineral plastic hydrogel is shown with ultrahigh silica content (≈95 wt%) that can be similarly hybridized into a porous delignified wood scaffold, and the resultant composite hydrogels can be manually made into arbitrary shapes. Subsequent air drying well preserves the designed shapes and produces fire‐retardant, ultrastrong, and tough structural organic–inorganic hybrids. The proposed mineral plastic hydrogel strategy opens an easy and eco‐friendly way for fabricating bioinspired structural materials that compromise both precise shape control and high mechanical strength.     

On the unexpected role of oxygen in the generation of microlens arrays with self‐developing photopolymers

Recent results have shown the interest in self‐developing photopolymers as optical storage materials. Their main advantage is the absence of a wet chemical post‐treatment to reveal the latent images. The self‐generating character of a sensitive layer is studied for the fabrication of refractive microlens arrays in the visible range. The kinetic of radical‐induced photopolymerization, the effect of molecular oxygen on the reaction rate and the properties of the final photopolymer are outlined. The results focus on the process of relief development and the role of atmospheric oxygen during the generation of refractive microlenses. A structural characterization of micro‐optical elements is investigated. Copyright © 2000 John Wiley & Sons, Ltd.     

Magnetically Enhanced Mechanical Stability and Super‐Size Effects in Self‐Assembled Superstructures of Nanocubes

Artificial materials from the self‐assembly of magnetic nanoparticles exhibit extraordinary collective properties; however, to date, the contribution of nanoscale magnetism to the mechanical properties of this class of materials is overlooked. Here, through a combination of Monte Carlo simulations and experimental magnetic measurements, this contribution is shown to be important in self‐assembled superstructures of magnetite nanocubes. By simulating the relaxation of interacting macrospins in the superstructure systems, the relationship between nanoscale magnetism, nanoparticle arrangement, superstructure size, and mechanical stability is established. For all considered systems, a significant enhancement in cohesive energy per nanocube (up to 45%), and thus in mechanical stability, is uncovered from the consideration of magnetism. Magnetic measurements fully support the simulations and confirm the strongly interacting character of the nanocube assembly. The studies also reveal a novel super‐size effect, whereby mechanically destabilization occurs through a decrease in cohesive energy per nanocube as the overall size (number of particles) of the system decreases. The discovery of this effect opens up new possibilities in size‐controlled tuning of superstructure properties, thus contributing to the design of next‐generation self‐assembled materials with simultaneous enhancement of magnetic and mechanical properties.     

Nitrogen‐Doped Cobalt Oxide Nanostructures Derived from Cobalt–Alanine Complexes for High‐Performance Oxygen Evolution Reactions

Taking advantage of the self‐assembling function of amino acids, cobalt–alanine complexes are synthesized by straightforward process of chemical precipitation. Through a controllable calcination of the cobalt–alanine complexes, N‐doped Co₃O₄ nanostructures (N‐Co₃O₄) and N‐doped CoO composites with amorphous carbon (N‐CoO/C) are obtained. These N‐doped cobalt oxide materials with novel porous nanostructures and minimal oxygen vacancies show a high and stable activity for the oxygen evolution reaction. Moreover, the influence of calcination temperature, electrolyte concentration, and electrode substrate to the reaction are compared and analyzed. The results of experiments and density functional theory calculations demonstrate that N‐doping promotes the catalytic activity through improving electronic conductivity, increasing OH^? adsorption strength, and accelerating reaction kinetics. Using a simple synthetic strategy, N‐Co₃O₄ reserves the structural advantages of micro/nanostructured complexes, showing exciting potential as a catalyst for the oxygen evolution reaction with good stability.     

Understanding and Controlling the Self‐Folding Behavior of Poly (N‐Isopropylacrylamide) Microgel‐Based Devices

Poly(N‐isopropylacrylamide) (pNIPAm) microgel‐based materials can be fabricated that self‐fold into three‐dimensional structures in response to changes in the environmental humidity. The materials are composed of a semi‐rigid polymer substrate coated with a thin layer of Au; the Au layer is subsequently coated with a pNIPAm‐based microgel layer and finally covered with a solution of polydiallyldimethylammonium chloride (pDADMAC). The pDADMAC layer contracts upon drying causing the material to deform (typically bending); this deformation is completely reversible over many cycles as the environmental humidity is systematically varied. Here, by varying the size and aspect ratio of the polymer substrate, it is possible to develop a set of empirical rules that can be applied to predict the material's self‐folding behavior. From these rules, materials that self‐fold from two‐dimensional, flat objects into discrete three‐dimensional structures, which are fully capable of unfolding and folding multiple times in response to humidity, are designed.     

Self‐Compensated Insulating ZnO‐Based Piezoelectric Nanogenerators

Remarkable enhancement of piezoelectric power output from a nanogenerator (NG) based on a zinc oxide (ZnO) thin film is achieved via native defect control. A large number of unintentionally induced point defects that act as n‐type carriers in ZnO have a strong influence on screening the piezoelectric potential into a piezoelectric NG. Here, additional oxygen molecules bombarded into ZnO lead to oxygen‐rich conditions, and the n‐type conductivity of ZnO is decreased dramatically. The acceptor‐type point defects such as zinc vacancies created during the deposition process trap n‐type carriers occurring from donor‐type point defects through a self‐compensation mechanism. This unique insulating‐type ZnO thin film‐based NGs (IZ‐NGs) generates output voltage around 1.5 V that is over ten times higher than that of an n‐type ZnO thin film‐based NG (around 0.1 V). In addition, it is found that the power output performance of the IZ‐NG can be further increased by hybridizing with a p‐type polymer (poly(3‐hexylthiophene‐2,5‐diyl):phenyl‐C₆₁‐butyric acid methyl ester) via surface free carrier neutralization.     

A Highly Conductive Cationic Wood Membrane

Here, a highly conductive cationic membrane is developed directly from natural wood via a two‐step process, involving etherification and densification. Etherification bonds the cationic functional group (? (CH₃)₃N⁺Cl^?) to the cellulose backbone, converting negatively charged (ξ‐potential of ?27.9 mV) wood into positively charged wood (+37.7 mV). Densification eliminates the large pores of the natural wood, leading to a highly laminated structure with the oriented cellulose nanofiber and a high mechanical tensile strength of ≈350 MPa under dry conditions (20 times higher than the untreated counterpart) and ≈98 MPa under wet conditions (×5.5 increase compared to the untreated counterpart). The nanoscale gaps between the cellulose nanofibers act as narrow nanochannels with diameters smaller than the Debye length, which facilitates rapid ion transport that is 25 times higher than the ion conductance of the natural wood at a low KCl concentration of 10 × 10^?3 m . The demonstrated cationic wood membrane exhibits enhanced mechanical strength and excellent nanofluidic ion‐transport properties, representing a promising direction for developing high‐performance nanofluidic material from renewable, and abundant nature‐based materials.     

Macroscopic and Mechanically Robust Hollow Carbon Spheres with Superior Oil Adsorption and Light‐to‐Heat Evaporation Properties

Hollow carbon spheres (HCSs) represent a special class of functional materials, to which intense interest has been paid in the fields of materials science and chemistry. A major problem with these materials is the lack of sufficient particle engineering and mechanical strength for practical applications and the difficulty of up‐scaling. Herein, we report a general, template‐free, phase‐separation approach, in which the liquid–liquid phase‐inversion process and a gas‐foaming process are coupled for the first time, for fast and continuous processing of uniform HCSs. The obtained HCSs have particle sizes on the millimeter scale, and a hierarchical structure with an interpenetrating, open‐porous, carbon shell and huge external voids, therefore permitting rapid transport of molecules into, throughout, and out of the hollow structure. By evenly dispersing the CNTs in the precursor solution, CNT‐reinforced HCSs can be achieved with significantly enhanced mechanical strength, hydrophobicity, and electronic and thermal properties. The resulting CNT‐reinforced HCSs offer a viable route to remove the engine oil from water in a fixed‐bed system. Moreover, these floatable HCSs can receive and convert sunlight to heat at the water–air interface, resulting in a great enhancement in solar evaporation rate compared to conventional bulk heating schemes.     

Universal Behavior and Electric‐Field‐Induced Structural Transition in Rare‐Earth‐Substituted BiFeO3

The discovery of a universal behavior in rare‐earth (RE)‐substituted perovskite BiFeO₃ is reported. The structural transition from the ferroelectric rhombohedral phase to an orthorhombic phase exhibiting a double‐polarization hysteresis loop and substantially enhanced electromechanical properties is found to occur independent of the RE dopant species. The structural transition can be universally achieved by controlling the average ionic radius of the A‐site cation. Using calculations based on first principles, the energy landscape of BiFeO₃ is explored, and it is proposed that the origin of the double hysteresis loop and the concomitant enhancement in the piezoelectric coefficient is an electric‐field‐induced transformation from a paraelectric orthorhombic phase to the polar rhombohedral phase.     

Rotatable Aggregation‐Induced‐Emission/Aggregation‐Caused‐Quenching Ratio Strategy for Real‐Time Tracking Nanoparticle Dynamics

Real‐time tracking of the dynamics change of self‐assembled nanostructures in physiological environments is crucial to improving their delivery efficiency and therapeutic effects. However, such tracking is impeded by the complex biological microenvironment leading to inhomogeneous distribution. A rotatable fluorescent ratio strategy is introduced that integrates aggregation‐induced emission (AIE) and aggregation‐caused quenching (ACQ) into one nanostructured system, termed AIE and ACQ fluorescence ratio (AAR). Following this strategy, an advanced probe, PEG^5k‐TPE₄‐ICGD₄ (PTI), is developed to track the dynamics change. The extremely sharp fluorescent changes (up to 4008‐fold) in AAR allowed for the clear distinguishing and localization of the intact state and diverse dissociated states. The spatiotemporal distribution and structural dynamics of the PTI micelles can be tracked, quantitatively analyzed in living cells and animal tissue by the real‐time ratio map, and be used to monitor other responsive nanoplatforms. With this method, the dynamics of nanoparticle in different organelles are able to be investigated and validated by transmission electron microscopy. This novel strategy is generally applicable to many self‐assembled nanostructures for understanding delivery mechanism in living systems, ultimately to enhance their performance in biomedical applications.     

Self‐Propagating Domino‐like Reactions in Oxidized Graphite

Graphite oxide (GO) has received extensive interest as a precursor for the bulk production of graphene‐based materials. Here, the highly energetic nature of GO, noted from the self‐propagating thermal deoxygenating reaction observed in solid state, is explored. Although the resulting graphene product is quite stable against combustion even in a natural gas flame, its thermal stability is significantly reduced when contaminated with potassium salt by‐products left from GO synthesis. In particular, the contaminated GO becomes highly flammable. A gentle touch with a hot soldering iron can trigger violent, catastrophic, total combustion of such GO films, which poses a serious fire hazard. This highlights the need for efficient sample purification methods. Typically, purification of GO is hindered by its tendency to gelate as the pH value increases during rinsing. A two‐step, acid–acetone washing procedure is found to be effective for suppressing gelation and thus facilitating purification. Salt‐induced flammability is alarming for the fire safety of large‐scale manufacturing, processing, and storage of GO materials. However, the energy released from the deoxygenation of GO can also be harnessed to drive new reactions for creating graphene‐based hybrid materials. Through such domino‐like reactions, graphene sheets decorated with metal and metal oxide particles are synthesized using GO as the in situ power source. Enhanced electrochemical capacitance is observed for graphene sheets loaded with RuO₂ nanoparticles.     

Complex‐Shaped Cellulose Composites Made by Wet Densification of 3D Printed Scaffolds

Cellulose is an attractive material resource for the fabrication of sustainable functional products, but its processing into structures with complex architecture and high cellulose content remains challenging. Such limitation has prevented cellulose‐based synthetic materials from reaching the level of structural control and mechanical properties observed in their biological counterparts, such as wood and plant tissues. To address this issue, a simple approach is reported to manufacture complex‐shaped cellulose‐based composites, in which the shaping capabilities of 3D printing technologies are combined with a wet densification process that increases the concentration of cellulose in the final printed material. Densification is achieved by exchanging the liquid of the wet printed material with a poor solvent mixture that induces attractive interactions between cellulose particles. The effect of the solvent mixture on the final cellulose concentration is rationalized using solubility parameters that quantify the attractive interparticle interactions. Using X‐ray diffraction analysis and mechanical tests, 3D printed composites obtained through this process are shown to exhibit highly aligned microstructures and mechanical properties significantly higher than those obtained by earlier additively manufactured cellulose‐based materials. These features enable the fabrication of cellulose‐rich synthetic structures that more closely resemble the exquisite designs found in biological materials grown by plants in nature.     

One‐Pot Synthesis of Antimony‐Embedded Silicon Oxycarbide Materials for High‐Performance Sodium‐Ion Batteries

Sodium‐ion batteries have recently attracted intensive attention due to their natural abundance and low cost. Antimony is a desirable candidate for an anode material for sodium‐ion batteries due to its high theoretical capacity (660 mA h g^?1). However, the utilization of alloy‐based anodes is still limited by their inherent huge volume changes and sluggish kinetics. The Sb‐embedded silicon oxycarbide (SiOC) composites are simply synthesized via a one‐pot pyrolysis process at 900 °C without any additives or surfactants, taking advantage of the superior self‐dispersion properties of antimony acetate powders in silicone oil. The structural and morphological characterizations confirm that Sb nanoparticles are homogeneously embedded into the amorphous SiOC matrix. The composite materials exhibit an initial desodiation capacity of around 510 mA h g^?1 and maintained an excellent capacity retention above 97% after 250 cycles. The rate capability test reveals that the composites deliver capacity greater than 453 mA h g^?1, even at the high current density of 20 C rate, owing to the free‐carbon domain of SiOC material. The electrochemical and postmortem analyses confirm that the SiOC matrix with a uniform distribution of Sb nanoparticles provides the mechanical strength without degradation in conductive characteristics, suppressing the agglomeration of Sb particles during the electrochemical reaction.     

Self‐Doping Fullerene Electrolyte‐Based Electron Transport Layer for All‐Room‐Temperature‐Processed High‐Performance Flexible Polymer Solar Cells

To achieve high‐performance large‐area flexible polymer solar cells (PSCs), one of the challenges is to develop new interface materials that possess a thermal‐annealing‐free process and thickness‐insensitive photovoltaic properties. Here, an n‐type self‐doping fullerene electrolyte, named PCBB‐3N‐3I, is developed as electron transporting layer (ETL) for the application in PSCs. PCBB‐3N‐3I ETL can be processed at room temperature, and shows excellent orthogonal solvent processability, substantially improved conductivity, and appropriate energy levels. PCBB‐3N‐3I ETL also functions as light‐harvesting acceptor in a bilayer solar cell, contributing to the overall device performance. As a result, the PCBB‐3N‐3I ETL‐based inverted PSCs with a PTB7‐Th:PC₇₁BM photoactive layer demonstrate an enhanced power conversion efficiency (PCE) of 10.62% for rigid and 10.04% for flexible devices. Moreover, the device avoids a thermal annealing process and the photovoltaic properties are insensitive to the thickness of PCBB‐3N‐3I ETL, yielding a PCE of 9.32% for the device with thick PCBB‐3N‐3I ETL (61 nm). To the best of one's knowledge, the above performance yields the highest efficiencies for the flexible PSCs and thick ETL‐based PSCs reported so far. Importantly, the flexible PSCs with PCBB‐3N‐3I ETL also show robust bending durability that could pave the way for the future development of high‐performance flexible solar cells.     

A Generic Conversion Strategy: From 2D Metal Carbides (MxCy) to M‐Self‐Doped Graphene toward High‐Efficiency Energy Applications

This study first presents a subtle thermal‐chlorination strategy for a universal transformation of abundant 2D metal carbides (M_xC_y, e.g., Cr₃C₂, Mo₂C, NbC, and VC) to 2D graphene and M‐self‐doped graphene (MG). The as‐obtained MG endows a transparent sheet architecture of one to four atomic layers. Simultaneously, MG with different M amounts is synthesized by tuning the chlorination parameters. Among them, the novel and representative Cr‐self‐doped graphene with optimal Cr amount (4.81 at%) demonstrates the outstanding electrochemical performance. It presents an energy density of 686 W h per kg electrode and a power density of more than 391 W per kg electrode as anode material of Li ion batteries, and four‐fold activity against the commercial iridium oxide electrode toward oxygen evolution reaction as well as a comparable oxygen reduction reaction performance to the commercial platinum catalyst. Moreover, this method is readily scalable to produce graphene and MG electrode materials on industrial levels.     

Superplastic Air‐Dryable Graphene Hydrogels for Wet‐Press Assembly of Ultrastrong Superelastic Aerogels with Infinite Macroscale

Highly compressible graphene‐based monoliths with excellent mechanical, electrical, and thermal properties hold great potential as multifunctional structural materials to realize the targets of energy‐efficiency, comfort, and safety for buildings, vehicles, aircrafts, etc. Unfortunately, the ultralow mechanical strength and limited macroscale have hampered their practical applications. Herein, ultrastrong superelastic graphene aerogel with infinite macroscale is obtained by a facile wet‐press assembly strategy based on the novel superplastic air‐dryable graphene hydrogel (SAGH). The SAGH with isotropic, open‐cell, and highly porous microstructure is carefully designed by a dual‐template sol–gel method. Countless SAGH “bricks” can be assembled together orderly by press to form the strongly combined wet‐press assembled graphene aerogel (WAGA) “wall” after air‐drying. The WAGA with highly oriented, dense, multiple‐arch microstructure possesses arbitrary macroscale, outstanding compressive strength (47 MPa, over 10 times higher than the best ever reported), super elasticity (>97% strain), and high conductivity (378 S m^?1). The strong adhesion is attributed to the tightly face‐to‐face contacted graphene interfaces caused by wet‐press and air‐drying. The WAGAs prove to be excellent multifunctional structural materials in the fields of high pressure/strain sensor, tunable mechanical energy absorber, high‐performance fire‐resistance, and thermal insulation. This facile strategy is easily extended to fabricate other similar metamaterials.     

Scalable Synthesis of Multifunctional Epidermis‐Like Smart Coatings

Bioinspired self‐healing materials provide a sustainable solution for mitigating catastrophic failure and prolonging service time, but such potential may be largely offset by the tedious fabrication process that can hardly be scaled up. It is shown that a scalable doctor blade coating process may be used for the synthesis of multifunctional epidermis‐like smart coatings. The industry‐compatible technique not only preserves the biomimetic bilayer design with largely improved film production efficiency but also allows readily adjusted film compositions and structures for optimizing the synergetic healing performance and mechanical properties. Variable amounts of montmorillonite clay nanosheets can be incorporated in the top hard layer for achieving a high modulus (34.3 ± 1.4 GPa) and hardness (1.65 ± 0.09 GPa), which also affect the number of scratch‐healing cycles by controlling the decay rate of upward polymer diffusion from the soft bottom layer. These high‐performance smart coatings are transparent, bactericidal, and show good adhesions to various substrates including glass, plastics, and fiberboard. When used as a surface protection for fiberboard, excellent flame‐retardant properties are demonstrated thanks to the dominant presence of clay nanosheets. It is believed that this work may provide important guidance for transforming interesting biomimetic design into practical manufacturing.     

Halogenated Antimonene: One‐Step Synthesis,Structural Simulation,Tunable Electronic and Photoresponse Property

Surface functionalization is considered to be an effective and versatile strategy to tailor intrinsic electronic and optoelectronic properties of 2D materials. In this work, surface‐decorated few‐layer antimonene is synthesized by a one‐step electrochemical exfoliation and synchronous halogenation method in halogen‐containing an ionic liquid–based electrolyte at room temperature. The prepared halogenated antimonene nanosheets are composed of oxygen‐ and halogen‐decorated amorphous and crystalline domains. The structural reconstructions and evolutions of halogenated antimonene are further revealed by ab initio molecular dynamics simulations and first‐principles calculations. The band structures and optical properties of antimonene can be tailored after amorphization and surface functionalization, depending on the reactivity of different halogens. The photoresponse performance of the halogenated antimonene is further evaluated by photoelectrochemical measurement. Exhibiting self‐powered photoresponse behavior, their photocurrent density increases with the increases of external bias potential and light intensity. This work proposes a new idea of tuning the optoelectronic properties of 2D materials by synchronous halogenation in the facile one‐step electrochemical synthesis process. Benefiting from this facile synthesis procedure, the halogenation of antimonene may shed light on chemical functionalization of other 2D materials for electronic and optoelectronic applications.