Thermally induced fire early warning aerogel with efficient thermal isolation and flame‐retardant properties

Expanded Properties and Applications of Porous Flame-Retardant Polymers Containing Graphene and Its Derivatives

With the integration and miniaturization of modern equipment and devices, porous polymers, containing graphene and its derivatives, with flame-retardancy have become a research hotspot. In this paper, the expanded properties and high-end applications of flame-retardant porous materials containing graphene and its derivatives were discussed. The research progress regarding graphene-based porous materials with multiple energy conversion, thermal insulation, an electromagnetic shielding property, and a high adsorption capacity were elucidated in detail. The potential applications of materials with the above-mentioned properties in firefighter clothing, fire alarm sensors, flexible electronic skin, solar energy storage, energy-saving buildings, stealth materials, and separation were summarized. The construction strategies, preparation methods, comprehensive properties, and functionalization mechanisms of these materials were analyzed. The main challenges and prospects of flame-retardant porous materials containing graphene and its derivatives with expanded properties were also proposed.

Visualizing and sorbing Hg(II) with a cellulose-based red fluorescence aerogel: Simultaneous detection and removal

Both sensing and removal of Hg(II) are important to environment and human health in view of the high toxicity and wide applications of mercury in industry. This study aims to develop a cellulose-based fluorescent aerogel for simultaneous Hg(II) sensing and removal via conveniently cross-linking two nanomaterials cellulose nanocrystals and bovine serum albumin-functionalized gold nanoclusters (BSA-AuNCs) with epichlorohydrin. The aerogel exhibited strong homogeneous red fluorescence at the non-edged regions under UV light due to highly dispersed BSA-AuNCs in it, and its fluorescence could be quenched by Hg(II). Through taking pictures with a smartphone, Hg(II) in the range of 0-1000 μg/L could be quantified with a detection limit of 12.7 μg/L. The sorption isotherm of Hg(II) by the aerogel followed Freundlich model with an equation of Qe = 0.329*Ce1/0.971 and a coefficient of 0.999. The maximum sorption capacity can achieve 483.21 mg/g for Hg(II), much higher than many reported sorbents. The results further confirmed Hg(II) strong sorption and sensitive detection are due to its complexation and redox reaction with the chemical groups in aerogels and its strong fluorescence quenching effect. Due to extensive sources and low cost, cellulose is potential to be developed into aerogels with multiple functions for sophisticated applications.

Construction of Multifunctional Hierarchical Biofilms for Highly Sensitive and Weather-Resistant Fire Warning

Multifunctional biofilms with early fire-warning capabilities are highly necessary for various indoor and outdoor applications, but a rational design of intelligent fire alarm films with strong weather resistance remains a major challenge. Herein, a multiscale hierarchical biofilm based on lignocellulose nanofibrils (LCNFs), carbon nanotubes (CNTs) and TiO2 was developed through a vacuum-assisted alternate self-assembly and dipping method. Then, an early fire-warning system that changes from an insulating state to a conductive one was designed, relying on the rapid carbonization of LCNFs together with the unique electronic excitation characteristics of TiO2. Typically, the L-CNT-TiO2 film exhibited an ultrasensitive fire-response signal of ~0.30 s and a long-term warning time of ~1238 s when a fire disaster was about to occur, demonstrating a reliable fire-alarm performance and promising flame-resistance ability. More importantly, the L-CNT-TiO2 biofilm also possessed a water contact angle (WCA) of 166 ± 1° and an ultraviolet protection factor (UPF) as high as 2000, resulting in excellent superhydrophobicity, antifouling, self-cleaning as well as incredible anti-ultraviolet (UV) capabilities. This work offers an innovative strategy for developing advanced intelligent films for fire safety and prevention applications, which holds great promise for the field of building materials.

Construction of porous structure-based carboxymethyl chitosan/ sodium alginate/ tea polyphenols for wound dressing

Polysaccharide-based materials with porous structure were selected as the basic skeleton to prepare a flexible and biodegradable wound dressing. The carboxymethyl chitosan/sodium alginate/tea polyphenols (CC/SA/TP) with a two-layer porous structure exhibits a variety of performances. The specific combined structure with ordered and lamellar porous structure was constructed by high-speed homogenized foaming, Ca²⁺ crosslinking and two-step freeze-drying methods. Moreover, the CC/SA/TP porous structure owns better shape retention and recovery because of the 3D network with an "egg-box" structure formed by impregnation. Tea polyphenols are efficiently encapsulated into a porous structure and released in a sustained pattern. After storing for 60 days, the CC/SA/TP porous structure still exhibits great suitable water vapor transmittance, efficient antibacterial activity and ultrarapid antioxidant activity. Meanwhile, the relatively low differential blood clotting index (BCI) and cytotoxicity of the CC/SA/TP porous structure indicate that it possesses the possibility of adjusting and controlling wound bleeding. The test results reveal that the CC/SA/TP porous structure might be expected to play a great potential role in biomedical applications of wound dressing.

Bio-Based Porous Aerogel with Bionic Structure and Hydrophobic Polymer Coating for Efficient Absorption of Oil/Organic Liquids

Increasing contamination risk from oil/organic liquid leakage creates strong demand for the development of absorbents with excellent hydrophobicity and absorption capacity. Herein, bagasse was carbonized to form porous char with a special structure of array-style and vertically perforated channels, and then the activation process enlarged the pore volume of the char. With the cooperation of low-surface-energy polydimethylsiloxane and diatomaceous earth particles, the modified activated carbon aerogel (MACA) was fabricated by modifying the surface coating and mastoid structure on the bagasse char. Moreover, the MACA demonstrates high porosity oil-water separation, hydrophobicity, and considerable absorption capacity (4.06–12.31 g/g) for gasoline and various organic solvents. This work converts agricultural waste into an efficient porous adsorbent, offering a scalable and commercially feasible solution to solving the leakages of oil/organic solvents.

Recent Advances on Early-Stage Fire-Warning Systems: Mechanism, Performance, and Perspective

Early-stage fire-warning systems (EFWSs) have attracted significant attention owing to their superiority in detecting fire situations occurring in the pre-combustion process. Substantial progress on EFWSs has been achieved recently, and they have presented a considerable possibility for more evacuation time to control constant unintentional fire hazards in our daily life. This review mainly makes a comprehensive summary of the current EFWSs, including the working mechanisms and their performance. According to the different working mechanisms, fire alarms can be classified into graphene oxide-based fire alarms, semiconductor-based fire alarms, thermoelectric-based fire alarms, and fire alarms on other working mechanisms. Finally, the challenge and prospect for EFWSs are briefly provided by comparing the art of state of fire alarms. This work can propose a more comprehensive understanding of EFWSs and a guideline for the cutting-edge development direction of EFWSs for readers.

High-Performance Liquid Crystalline Polymer for Intrinsic Fire-Resistant and Flexible Triboelectric Nanogenerators

Flammability is a great challenge in the fields of electronics. The emergence of triboelectric nanogenerators (TENGs) provides a safe way to harvest environmentalally friendly energy and convert it into more secure power sources. Especially, polymer-based TENGs significantly accelerate the practical application of self-powered flexible electronics. However, most of the existing polymeric materials for TENGs are easily flammable and melt, dripping, in a fire scenario, and cannot be reused after combustion, which greatly limits the application of TENGs under extreme conditions. Herein, a fire-resistant TENG based on all-aromatic liquid crystalline poly(aryl ether ester) (LCP_AEE ) synthesized via simple and efficient one-pot melt polycondensation is reported. The highly rigid main chain of LCP_AEE endows the LCP-TENG with outstanding anti-dripping, temperature- and fire-resistance. The resultant LCP-TENG exhibits excellent electrical output performance, which is attributed to the high dielectric constant (ε' = 4.8) and fibrous-structured morphology of LCP_AEE . The device can maintain over 65% of open-circuit voltage even after 16 s combustion (≈520 °C). Consequently, this work offers a novel strategy for tailoring the TENGs toward a secure power generator and electronics with fire hazard reduction, and potential application in firefighting, personal protection, and other extreme temperature environments.

Recent Advances in Sensors for Fire Detection

Fire is indeed one of the major contributing factors to fatalities, property damage, and economic disruption. A large number of fire incidents across the world cause devastation beyond measure and description every year. To minimalize their impacts, the implementation of innovative and effective fire early warning technologies is essential. Despite the fact that research publications on fire detection technology have addressed the issue to some extent, fire detection technology still confronts hurdles in decreasing false alerts, improving sensitivity and dynamic responsibility, and providing protection for costly and complicated installations. In this review, we aim to provide a comprehensive analysis of the current futuristic practices in the context of fire detection and monitoring strategies, with an emphasis on the methods of detecting fire through the continuous monitoring of variables, such as temperature, flame, gaseous content, and smoke, along with their respective benefits and drawbacks, measuring standards, and parameter measurement spans. Current research directions and challenges related to the technology of fire detection and future perspectives on fabricating advanced fire sensors are also provided. We hope such a review can provide inspiration for fire sensor research dedicated to the development of advanced fire detection techniques.

Fire Intumescent, High-Temperature Resistant, Mechanically Flexible Graphene Oxide Network for Exceptional Fire Shielding and Ultra-Fast Fire Warning

Smart fire alarm sensor (FAS) materials with mechanically robust, excellent flame retardancy as well as ultra-sensitive temperature-responsive capability are highly attractive platforms for fire safety application. However, most reported FAS materials can hardly provide sensitive, continuous and reliable alarm signal output due to their undesirable temperature-responsive, flame-resistant and mechanical performances. To overcome these hurdles, herein, we utilize the multi-amino molecule, named HCPA, that can serve as triple-roles including cross-linker, fire retardant and reducing agent for decorating graphene oxide (GO) sheets and obtaining the GO/HCPA hybrid networks. Benefiting from the formation of multi-interactions in hybrid network, the optimized GO/HCPA network exhibits significant increment in mechanical strength, e.g., tensile strength and toughness increase of ~ 2.3 and ~ 5.7 times, respectively, compared to the control one. More importantly, based on P and N doping and promoting thermal reduction effect on GO network, the excellent flame retardancy (withstanding ~ 1200 °C flame attack), ultra-fast fire alarm response time (~ 0.6 s) and ultra-long alarming period (> 600 s) are obtained, representing the best comprehensive performance of GO-based FAS counterparts. Furthermore, based on GO/HCPA network, the fireproof coating is constructed and applied in polymer foam and exhibited exceptional fire shielding performance. This work provides a new idea for designing and fabricating desirable FAS materials and fireproof coatings.

An Ultralight Self-Powered Fire Alarm e-Textile Based on Conductive Aerogel Fiber with Repeatable Temperature Monitoring Performance Used in Firefighting Clothing

Firefighting protective clothing is an essential equipment that can protect firefighters from burn injuries during the firefighting process. However, it is still a challenge to detect the damage of firefighting protective clothing at an early stage when firefighters are exposed to excessively high temperature in fire cases. Herein, an ultralight self-powered fire alarm electronic textile (SFA e-textile) based on conductive aerogel fiber that comprises calcium alginate (CA), Fe₃O₄ nanoparticles (Fe₃O₄ NPs), and silver nanowires (Ag NWs) was developed, which achieved ultrasensitive temperature monitoring and energy harvesting in firefighting clothing. The resulting SFA e-textile was integrated into firefighting protective clothing to realize wide-range temperature sensing at 100-400 °C and repeatable fire warning capability, which could timely transmit an alarm signal to the wearer before the firefighting protective clothing malfunctioned in extreme fire environments. In addition, a self-powered fire self-rescue location system was further established based on the SFA e-textile that can help rescuers search and rescue trapped firefighters in fire cases. The power in the self-powered fire location system was offered by an SFA e-textile-based triboelectric nanogenerator (TENG). This work provided a useful design strategy for the preparation of ultralight wearable temperature-monitoring SFA e-textile used in firefighting protective clothing.

Serendipity discovery of fire early warning function of chitosan film

Transparent chitosan (CS) film is prepared and its application in high temperature/fire warning is discussed. NaCl-doped chitosan (CS-NaCl) film shows excellent performance in real-time temperature monitoring and fire warning. The temperature warning of CS-NaCl film can be triggered under approximately 50 °C, and it has a good repeatable warning performance under high-temperature conditions. The CS composite film exhibits an ultra-sensitive (0.4 s) warning under fire attacking. A possible electrical conduction and fire-alarm mechanisms are proposed. The addition of NaCl increases the number of charge carriers, which improves the ionic conductivity of the composite film. This study provides a possibility for the application of CS in the field of fire warning.

Recent Advances in the Synthesis and Application of Three-Dimensional Graphene-Based Aerogels

Three-dimensional graphene-based aerogels (3D GAs), combining the intrinsic properties of graphene and 3D porous structure, have attracted increasing research interest in varied fields with potential application. Some related reviews focusing on applications in photoredox catalysis, biomedicine, energy storage, supercapacitor or other single aspect have provided valuable insights into the current status of Gas. However, systematic reviews concentrating on the diverse applications of 3D GAs are still scarce. Herein, we intend to afford a comprehensive summary to the recent progress in the preparation method (template-free and template-directed method) summarized in Preparation Strategies and the application fields (absorbent, anode material, mechanical device, fire-warning material and catalyst) illustrated in Application of 3D GAs with varied morphologies, structures, and properties. Meanwhile, some unsettled issues, existing challenges, and potential opportunities have also been proposed in Future Perspectives to spur further research interest into synthesizing finer 3D GAs and exploring wider and closer practical applications.

Multifunctional MXene/Chitosan-Coated Cotton Fabric for Intelligent Fire Protection

Multifunctional intelligent fireproof cotton fabrics are urgently demanded in the era of the Internet of Things. Herein, a novel high fire safety cotton fabric (denoted as MXene/CCS@CF) with temperature sensing, fire-warning, piezoresistivity, and Joule heating performance was developed by coating MXene nanosheet and carboxymethyl chitosan (CCS) via an eco-friendly layer-by-layer assembly method. Benefiting from the thermoelectric characteristic and high conductivity of MXene nanosheet, MXene/CCS@CF exhibited accurate wide-range temperature sensing performance. When being burned, it could repeatedly trigger the fire-warning system in less than 10 s. More importantly, MXene/CCS@CF showed outstanding flame retardancy because of the synergistic carbonization between MXene and CCS. The limiting oxygen index of MXene/CCS@CF was as high as 45.5%, and the char length was only 33 mm after the vertical burning test. Meanwhile, its peak heat release rate reduced more than 66%. Besides, the obtained fabric could detect a variety of human motions. Moreover, the controllable Joule heating performance enabled the fabric to be used in extreme cold weather. This work provides a facile approach to fabricating a next-generation high fire safety cotton fabric, showing promising applications in firefighting, home automation, and smart transportation.