Intelligent cyclic fire warning sensor based on hybrid PBO nanofiber and montmorillonite nanocomposite papers decorated with phenyltriethoxysilane

Poly(p-Phenylene Benzobisoxazole) Nanofiber: A Promising Nanoscale Building Block Toward Extremely Harsh Conditions

Since the invention and commercialization of poly(p-phenylene benzobisoxazole) (PBO) fibers, numerous breakthroughs in applications have been realized both in the military and aerospace industries, attributed to its superb properties. Particularly, PBO nanofibers (PNFs) not only retain the high performance of PBO fiber but also exhibit impressive nanofeatures and desirable processability, which have been extensively applied in extreme scenarios. However, no review has yet comprehensively summarized the preparation, applications, and prospective challenges of PNFs to the best of our knowledge. Herein, the two fabrication pathways to acquire PNFs from bottom-up to top-down approaches are critically overviewed; the significant advantages and the problem caused simultaneously of the protonation approach compared with other methods are revealed. Besides, the construction strategies of multidimensional PNF-based advanced composites, including 1D fiber, 2D film/nanopaper, and 3D gel, are discussed. Moreover, the outstanding mechanical, insulating, and thermal stability properties of PNFs facilitate their extensive applications in thermal protection, electrical insulation, batteries, and flexible wearable devices, which are further comprehensively introduced. Finally, the perspective and challenges of the fabrication and application of PNFs are highlighted. It demonstrates that the PNFs as one of the promising high-performance nanoscale building blocks can be fully competent using extremely harsh conditions.

Multi-crosslinked gelatin-based composite hydrogel featuring high thermoelectric performance and excellent flame retardancy for intelligent fire-warning system

The frequency occurrence of building fires necessitates response materials with high flame retardancy and temperature sensitivity. Herein, we synthesized a gelatin/poly(acrylamide-co-acrylic acid)/lithium bromide/sodium phytate/glycerol hydrogel (Gly-GAPL) using in situ radical polymerization and solvent exchange techniques. Gly-GAPL exhibits notable thermoelectric performance (the Seebeck coefficient: 8.66 mV/K), temperature sensitivity, commendable mechanical properties and flame retardancy. Remarkably, Gly-GAPL features a rapid response time, triggering an alarm within 2 s upon exposure to flame. Gly-GAPL is highly resistant to ignition and significantly enhances the fire resistance of wood coated with it. Furthermore, its high transparency, impressive water retention and adhesion further underscore its potential as a flame-retardant coating for various inflammable materials. Given its outstanding thermoelectric performance and temperature sensitivity, an early fire-warning system is rapidly activated, promptly sending alerts to smart devices. This work introduces a novel strategy for developing smart flame retardancy materials and advances the applications of ionic hydrogels in early fire-warning systems.

A Conductive and Anti-impact Composite for Flexible Piezoresistive Sensors

Flexible piezoresistive sensors, which can convert specific mechanical information (such as compression, bending, tensile, and torsion) into a resistance value change signal through the piezoresistive effect, have attracted more and more attention. However, how to achieve the simple, low-cost fabrication of a piezoresistive sensor is still a challenge. Herein, we report a facile strategy that introduces conductive carbon black (CB) and shear thickening gel (SG) composite into a melamine sponge (MS) to generate an MS-SG-CB composite with a unique force-electric coupling effect. A flexible sensor derived from the MS-SG-CB composite can not only accurately identify deformation signals during static stretching and compression while monitoring human movement status in real time but also recognize electrical signals under dynamic impact in a very short time (6 ms). The 3 × 3 flexible array built on this basis can accurately identify the mass and position of heavy objects. Furthermore, based on the flame-retardant properties of MS, the flame-retardant ammonium polyphosphate (APP) is further introduced into MS-SG-CB to obtain MS-SG-CB-APP composite with excellent flame retardancy and stable temperature electrical response behavior, expanding its application in the field of high temperature trigger alarm.

Surface Engineering of Superparamagnetic Graphene Oxide Nanosheet as a Chemically Tunable Platform for Facial Biofuel Production by Lipase

In this research, we utilized an efficient approach to synthesize superparamagnetic graphene oxide (SPGO) rapidly in a one-pot method using microwave irradiation of graphene oxide (GO), urea, and Fe(III) ion. Tannic acid (TA) was introduced to the surface of SPGO through a straightforward and eco-friendly process. Methods were devised to furnish GO nanosheets and modify their surfaces with TA in an environmentally friendly manner. Two series of nanosheets, namely, SPGO/TA-COOH and SPGO/TA-IM, were engineered on the surface and used for immobilizing lipase enzyme. Through various analytical tools, the unique biocatalysts SPGO/TA-COOH/L and SPGO/TA-IM/L were confirmed. These biocatalysts exhibited enhanced stability at high temperatures and pH levels compared with free lipase. They also demonstrated prolonged storage stability and reusability over four months and seven cycles, respectively. Furthermore, the catalytic activity of immobilized lipase showed minimal impairment based on kinetic behavior analysis. The kinetic constants of SPGO/TA-IM/L were determined as Vmax = 0.24 mM min-1, Km = 0.224 mM, and kcat = 0.8 s-1. Additionally, the efficiency of biocatalysts for biodiesel production from palmitic acid was studied, focusing on various reaction parameters, such as temperature, alcohol to palmitic acid molar ratio, water content, and lipase quantity. The esterification reaction of palmitic acid with methanol, ethanol, and isopropanol was tested in the presence of SPGO/TA-COOH/L and SPGO/TA-IM/L, and the corresponding esters were obtained with a yield of 30.6-91.6%.

Rational Design of Amorphous Carbon-Coated Laminar-Structured Wood for Integrating Repeatable Early Fire Detection and High-Temperature Affordable Flexible Pressure Sensing in One System

High-temperature affordable flexible polymer-based pressure sensors integrated with repeatable early fire warning service are strongly desired for harsh environmental applications, yet their creation remains challenging. This work proposed an approach for preparing such advanced integrated sensors based on silver nanoparticles and an ammonium polyphosphate (APP)-modified laminar-structured bulk wood sponge (APP/Ag@WS). Such integrated sensors demonstrated excellent fire warning performance, including a short response time (minimum of 0.44 s), a long-lasting alarm time (>750 s), and reliable repeatability. Moreover, it achieved high-temperature affordable flexible pressure sensing that exhibited an almost unimpaired working range of 0-7.5 kPa and a higher sensitivity (in the low-pressure range, maximum to 226.03 kPa-1) after fire. The high stability was attributed to reliable structural elasticity, and the wood-derived amorphous carbon is capable of repeatable fire warnings. Finally, a Ag@APP/WS-based wireless fire alarm system that realized reliable house fire accident detection was demonstrated, showing great promise for smart firefighting application.

Facile Preparation of Lightweight Natural Rubber Nanocomposite Foams with High Wear Resistance

The light weight and excellent mechanical properties of rubber foam means that it is widely applied in the aerospace, automobile, and military industries. However, its poor wear resistance contributes directly to a short service life and a waste of resources. Therefore, the design and development of high-wear-resistance rubber foam are of great importance. In this work, some nanoclay/rubber composite foams were prepared by blending NR/EPDM with different kinds of nanoclays containing layered double hydroxide (LDH), montmorillonite (MMT), and attapulgite (ATP) to indicate the effects of the kinds of nanoclays on the wear resistance and mechanical properties of nanoclay/rubber composite foams. The kinds of nanoclay/rubber composite foams were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The results showed that nanoclay has heterogeneous nucleation in composite foamed materials. The wear resistance of the composite foam materials with added nanoclay was significantly improved, and the MMT of the lamellar structure (increased by 43.35%) and LDH (increased by 38.57%) were significantly higher than the ATP of the rod-like structure (increased by 13.04%). The improvement in the wear resistance of the matrix was even higher. Compared with other foams, the wear resistance of the OMMT-NR/EPDM foam (increased by 58.89%) with a lamellar structure had the best wear resistance. Due to the increase in the lamellar spacing of the modified OMMT, the exfoliation of worn rubber molecular chains has little effect on the adjacent molecular chains, which prevents the occurrence of crimp wear and further improves the wear resistance of composite foaming materials. Therefore, this work lays the foundation for the manufacturing of rubber foams for wear-resistant applications.

Nanoscale-controlled organicinorganic hybrid spheres for comprehensive enrichment of ultratrace chlorobenzenes in marine and fresh water

The size of the adsorbent has the potential to influence extraction performance, but the size effect at the nanoscale is still poorly understood. In this study, organic-inorganic hybrid nanospheres (OIHNs) with controllable nanoscale sizes of 30, 50, and 100 nm were successfully prepared. These materials were further fabricated as solid phase microextraction (SPME) coatings with similar thicknesses, and coupled with gas chromatography-mass spectrometry (GC-MS) to investigate their extraction performance. The results showed that the extraction capacities of OIHNs for chlorobenzenes (CBs) and polycyclic aromatic hydrocarbons (PAHs) were much better than those of their corresponding derived carbon materials, despite the smaller specific surface areas and lower porosities of them. In addition, the enrichment performance increased significantly with decreasing particle size, and the OIHN-30 coating demonstrated the best performance, with enrichment factors ranging from 1098 to 6853 for CBs. Finally, a highly sensitive and practical analytical method was established with a wide linear range of 0.5-5000 ng·L-1, and the limits of quantification (LOQs) were 0.43-1.7 ng·L-1. The determinations of ultratrace CBs in five marine water samples and five fresh water samples were realized successfully. This study is expected to contribute to a deep understanding of the environmental effects of nanoparticles and the design of high-performance adsorbents.

Sustainable biomass-based composite biofilm: Sodium alginate, TEMPO-oxidized chitin nanocrystals, and MXene nanosheets for fire-resistant materials and next-generation sensors

Efficient utilization of natural biomass for the development of fireproof materials and next-generation sensors faces various challenges in the field of fire safety and prevention. In this study, renewable sodium alginate (SA), TEMPO-oxidized chitin nanocrystals (TOChNs), and MXene nanosheets were employed to fabricate a sustainable, flexible, and flame-retardant composite biofilm, donated as STM, utilizing a simple and environmentally friendly evaporation-induced self-assembly technique. The incorporation of SA, TOChNs, and MXene in a weight ratio of 50/10/40 led to improved mechanical properties of the resulting STM-40 films, as evidenced by increased tensile strength and Young's modulus values of approximately 36 MPa and 4 GPa, respectively. Notably, these values were approximately 3 and 11 times higher than those observed for the pure SA film. Moreover, the STM-40 films demonstrated highly sensitive fire alarm capabilities, exhibiting a superior flame alarm response time of 0.6 s and a continuous alarm time of approximately 492 s when exposed to flames. The STM exhibited exceptional flame retardancy due to the synergistic carbonization between MXene and SA/TOChNs, resulting in a limiting oxygen index of 45.0 %. Furthermore, its maximum heat release rate decreased by over 90.1 % during the test. This study presents a novel approach for designing and developing fire-retardant fire alarm sensors by utilizing natural biomass.