Construction of multifunctional MoSe2 hybrid towards the simultaneous improvements in fire safety and mechanical property of polymer

Catalytic chemistry inspired hollow carbon nanofibers loaded with NiS/Ni as high-performance and safe Li+ reservoir

Transition metal sulfides (TMSs) based anodes hold a very broad application prospect in lithium ion batteries (LIBs). In this work, the catalytic effect of metallic nickel at high temperature was used to generate hollow carbon nanofibers loaded with NiS and Ni (denoted as NiS/Ni@HCNF). The heteroatoms doped carbon fibers buffer the huge volumetric change of NiS during the discharge/charge process, and enhance the ion transport efficiency and electrical conductivity. In addition, the high specific surface area brought by the hollow carbon nanofibers can accelerate the electrolyte penetration and speed up the transport of ions as well as electrons. When used as anode of half cell, this electrode gives 958.5 and 612.9 mAh/g after running 1000 cycles under 1 and 2 A/g, showing the extremely-low attenuation rates of 0.0483 % per cycle and 0.0643 % per cycle, respectively. Impressively, NCM//NiS/Ni@HCNF battery shows the discharge capacity of 187.6 mAh/g at 1st cycle. Regarding the next 100 cycles, the relatively-high discharge capacities (>110 mAh/g) and coulombic efficiency (CE) values (>96 %) are discerned. It is noted that the usage of NiS/Ni@HCNF electrode improves the activation energy for thermal runaway, corroborating the elevated thermal safety of battery.

Hollow Superstructure In Situ Assembled by Single-Layer Janus Nanospheres toward Electromagnetic Shielding Flame-Retardant Polyurea Composites

A dodecahedral superstructure consisting of a single layer of Janus spheres containing ZIF-67 nanodots is prepared by in situ polymerization, with ZIF-67 and bio-based phytic acid (PA) as templates and dopants. It is used to improve the flame retardant, electromagnetic (EMI) shielding, and thermal conductivity properties of polyurea (PUA). By adding 5 wt% polyaniline@cobalt phytate-2.0 (PANI@Co-PA-2.0), the peak of heat release rate and the peak of smoke production rate are reduced by 54.9 and 59.9%, respectively. The peak of CO and CO2 production also decreased by 46.2 and 53.1%, respectively. A decrease in the absorption intensity of aliphatic and aromatic volatiles is also observed. The fire safety of PUA is greatly improved. In addition, PUA/PANI@Co-PA-2.0 exhibits an EMI shielding capability of 22.4 dB with the help of reduced graphene oxide, which confirms the possibility of PUA material application in the field of electromagnetic shielding. The 5 wt% filler increases the tensile strength of the PUA matrix to 6.3 MPa, and the composite material obtains good thermal conductivity. This work provides a viable method for the preparation of a flame-retardant, conductive, and electromagnetic refractory PUA substrate.

Synergistic effects of core-shell structured piperazine pyrophosphate microcapsules on fire safety and mechanical property in styrenic thermoplastic elastomer

In this study, core-shell structured piperazine pyrophosphate (PAPP) is designed to enhance the fire safety and mechanical property of styrenic thermoplastic elastomer (TPE) composites. The PAPP is microencapsulated with carbon nanotube modified melamine-formaldehyde resin to prepare core-shell structured flame retardants (MT@PAPP). Due to the excellent compatibility between the MT@PAPP and TPE matrix, the mechanical property of TPE/MT@PAPP is improved. Compared with TPE, the peak heat release rate and peak smoke production rate of TPE/MT@PAPP are decreased by 78.5% and 60.0%, respectively. Thus, the core-shell structured piperazine pyrophosphate microcapsule strategy provides an excellent approach to obtain high-performance TPE composites.

Three-dimensional micro-nanostructures based on binary transitional metal sulfides with doped carbon protector enabled high-performance and safe batteries

The lack of suitable Li⁺ reservoirs and the risk of thermal runaway have hindered the extended use of lithium-ion batteries. Although utilizing Li₄Ti₅O₁₂ or TiO₂ can improve the thermal safety, their low theoretical capacities compromise the electrochemical performance of the cell. In this study, a three-dimensional micro-nanostructure based on binary transitional metal sulfides (TMSs) with a doped carbon protector (SnS/Co₉S₈@HC) is designed. When operating at 0.1-1 A g^-1, the SnS/Co₉S₈@HC cell exhibits a high inceptive capacity of 1104.8 mAh g^-1 with a high coulomb efficiency of 97.1%. Even after 1000 cycles, it delivers a relatively-high capacity of 450.3 mAh g^-1, indicating a low capacity decay rate of 0.033% per cycle (from the 2nd to the 1000th cycle). The thermal runaway actions of the cells with graphite and SnS/Co₉S₈@HC anodes are investigated. The results demonstrate that the cell with the SnS/Co₉S₈@HC anode exhibits a significantly reduced maximum thermal runaway temperature of 473.5 ± 6.2℃ and maximum temperature increasing rate of 15.1 ± 0.6 °C min^-1 compared to the graphite cell. This indicates that SnS/Co₉S₈@HC cell holds higher thermal safety. The potential of SnS/Co₉S₈@HC as sodium ion batteries anode is also investigated. The results indicate an initial capacity of 631.7 mAh g^-1, with a low capacity decay rate of 0.063% per cycle when operating at 2 A g^-1. This work may be enlightening for constructing multi-phase TMSs based hierarchical structure towards superior and safe energy storage.

Designing of trimetallic-phase ternary metal sulfides coupled with N/S doped carbon protector for superior and safe Li/Na storage

Traditional transition metal sulfides (TMSs) have shown favorable potentials in energy storage. Nevertheless, its further usage is plagued by the issues of particle breakage and large volume change. In this work, the nanostructured ternary TMSs coupled with N/S doped carbon protector (NiCoFe-S@NSC) is delicately designed via compositional regulation and spatial structure protection strategies. As lithium ion batteries anode, this electrode gives an impressive capacity of 995.7 mAh/g after running 1000 cycles at 1 A/g. More importantly, NiCoFe-S@NSC electrode still shows a discharge capacity of 221.94 mAh/g after running 20,000 cycles at 10 A/g, reflecting an extremely-low capacity decay rate of 0.0377 ‰ per cycle. As sodium ion batteries anode, a high initial discharge capacity of 896.4 mA h g^-1 can be found. Even after running 400 cycles at 5 A/g, the electrode still displays a reversible capacity of 334.5 mAh/g with outstanding coulombic efficiency above 98.0 %. Impressively, LiNi_xCo_yMn_1-x-yO₂//NiCoFe-S@NSC full cell gives incipient discharge/charge capacities of 186.89/240.18 mAh/g. Moreover, the discharge capacities for the following 100 cycles remain above 150 mAh/g. Thermal runaway tests also demonstrate the higher thermal safety of cells with NiCoFe-S@NSC electrode, accompanying with the promoted activation energy.

Ligand-Mediated Exfoliation and Antibacterial Activity of 2H Transition-Metal Dichalcogenides

Transition-metal dichalcogenides (TMDs) exists mainly in two polymorphs, namely, 1T (metallic) and 2H (semiconducting). To tailor the characteristics and practical utility of TMDs for different applications, functionalization is essential. In our earlier studies, we have shown that functionalized 1T and 2H MoS₂ exhibit exceptionally high antibacterial activity. The functionalization and related biological applications of other 1T (chemically exfoliated) TMDs were reported, but regarding other 2H TMDs, the functionalization and antibacterial activity are not explored yet. Hence, here we prepared functionalized 2H TMDs such as WS₂, WSe₂, and MoSe₂ other than MoS₂ by using a positively charged thiolate surfactant ligand. Further, functionalized 2H TMDs were utilized for antibacterial activity against Gram-positive and Gram-negative bacteria for a comparative antibacterial analysis. Interestingly, we found disparity in activity among the functionalized 2H TMDs, that is, MoS₂ shows higher activity than WS₂ followed by MoSe₂ and WSe₂. The intracellular reactive oxygen species measurement was found to be in the order MoS₂ > WS₂ > MoSe₂ > WSe₂, which is solely responsible for variation in the activity of functionalized TMDs. These results indicate that the easy functionalization of all types TMDs by using thiol ligand and importance of core material should be considered while designing functionalized material for specific applications.

TPU-based porous heterostructures by combined techniques

The production of thermoplastic polyurethane-based porous heterostructures combining physical foaming with fused deposition modeling is detailed in this contribution. The choice of combining these two techniques lies in the possibility of creating objects endowed with a dual-scale structure at millimeter scale by fused deposition modeling and at microscopic scale by gas foaming. Thermal stability and rheological properties of the neat polymer were studied prior to foaming to design a suitable processing protocol and three different combined techniques are proposed: pressure quench, temperature rise and direct 3D foam printing. Foam morphologies were evaluated by SEM and foamed samples were characterized by thermal and mechanical analyses to highlight the differences among the combined processing techniques. Samples foamed via pressure quench exhibit the highest degree of crystallinity and a uniform cell morphology, also resulting in the largest stiffness. The results presented in this contribution open up the possibility of producing objects with complex geometry and porosity architecture at the dual scale.

The improvement of fire safety performance of flexible polyurethane foam by Highly-efficient P-N-S elemental hybrid synergistic flame retardant

Herein, three different phosphorus-containing compounds (methyl phosphoryl dichloride, phenyl phosphoryl dichloride and phenyl dichlorophosphate) were reacted with 2-aminobenzothiazole respectively, and a series of synergistic flame retardants with phosphorus, nitrogen and sulfur elements were synthesized, named MPBT, PPBT and POBT respectively. Then, they were added to prepare flame-retardant flexible polyurethane foam (FPUF). Through the analysis of thermal stability, pyrolysis, heat release and smoke release behavior, the influence of different phosphorus-containing structures on the flame-retardant performance of FPUF was studied, and their flame-retardant mechanism was explored in detail. Among them, MPBT had the highest flame retardant efficiency with the same addition amount (10 wt%). The limiting oxygen index (LOI) value of PU/10.0% MPBT reached 22.5 %, and it successfully passed the vertical burning test. Subsequently, the addition amount of MPBT was increased and the best comprehensive performance of flame-retardant FPUF was explored. The results showed that the LOI value of PU/15.0% MPBT was increased to 23.5%. As for PU/15.0% MPBT, the peak heat release rate (PHRR) was 453 KW/m², which was reduced by 46.64 %; and the flame retardancy index (FRI) value was also increased to 6.88. At the same time, the mechanical properties of flame-retardant FPUF were studied. The tensile strength of PU/15.0% MPBT reached 170 KPa, and the permanent deformation of FPUF/10% MPBT was only 4 %, showing its excellent resilience. The above results show that this phosphorus-containing element hybrid synergistic flame retardant (MPBT) has a very good application prospect in the field of flame-retardant polymer materials.

Electrochemical Heteroatom-Heteroatom Bond Construction

Heteroatom-heteroatom linkage, with S-S bond as a presentative motif, served a crucial role in biochemicals, pharmaceuticals, pesticides, and material sciences. Thus, preparation of the privileged scaffold has always been attracting tremendous attention from the synthetic community. However, classic protocols suffered from several drawbacks, such as toxic and unstable agents, poor functional group tolerance, multiple steps, and explosive oxidizing regents as well as the transitional metal catalysts. Electrochemical organic synthesis exhibited a promising alternative to the traditional chemical reaction due to the sustainable electricity can be employed as the traceless redox agents. Hence, toxic and explosive oxidants and/or transitional metals could be discarded under mild reaction with high efficiency. In this context, a series of electrochemical approaches for the construction of heteroatom-heteroatom bond were reviewed. Notably, most of the cases illustrated the dehydrogenative feature with the clean energy molecules hydrogen as the sole by-product.

Durable electromagnetic interference (EMI) shielding ramie fabric with excellent flame retardancy and Self-healing performance

Although more and more attention has been paid to electromagnetic interference (EMI) shielding fabric materials due to increasing electromagnetic waves pollution, little attention to their fire safety behavior and durability in practical use. Herein, durable EMI shielding ramie fabric with flame retardant and self-healing performance were fabricated by depositing ammonium polyphosphate (APP)/polyethyleneimine (PEI) layer, MXene sheets and polycaprolactone (PCL) layer. The resultant multifunctional fabric could self-extinguish and the peak heat release rate (pHRR) value reduced about 74.3% for the modified ramie fabric that contains about 12 wt% of PEI/APP bilayer compared with pure ramie fabric. Furthermore, the ramie fabric coated by a increasing amount of MXene sheets changed from insulating to conductive, thus gradually improving their EMI shielding performance, which exhibit a high electrical conductivity of 900.56 S/m with an outstanding SE value of 35 dB at a 1.2 mg/cm² content in the X-band. Besides, When the multifunctional fabric was cut off under external force, it could achieve self-healing and the EMI shielding performance can recover to 34 dB due to the low melting point and good fluidity of PCL. Thus, this multifunctional fabric holds great promise for wearable intelligent cloth, EMI shielding and other fields.

Barrier function of graphene for suppressing the smoke toxicity of polymer/black phosphorous nanocomposites with mechanism change

Recently, black phosphorous (BP) nanosheets as an emerging nanomaterial have presented significant fire safety improvement in polymer nanocomposites. However, as elemental phosphorus, fire safety improvement effect of BP nanosheets on polymer composites builds on the conversion of gaseous pyrolysis products into smoke particles, which inevitably promotes the formation and release of smoke particles. From the perspective of overall fire safety improvement, it is vital to simultaneously suppress the heat release and smoke production of polymer/BP composites. Herein, melamine-mediated graphene/black phosphorous nanohybrids (GNS/MA/BP) were fabricated through electrostatic-driving self-assembly process and introduced into polyether thermoplastic polyurethane (TPU). During combustion, the barrier function provided by thermally stable layered structure of graphene (GNS) enables more pyrolysis products of BP nanosheets to be kept within condensed phase and react with polymer matrix. Compared to pure TPU, the incorporated hierarchical nanostructure (GNS/MA/BP-2) decreases PHRR, THR, and total CO₂ release of TPU composite by 54.7%, 23.5%, and 32.5%, respectively. Beside, in contrast to TPU-BP composite, the release rate of toxic smoke and CO gas of TPU-GNS/MA/BP-2 composite are reduced by 46.7% and 49.4%. With barrier function of graphene, the heat and smoke release behavior of polymer/BP nanocomposites is effectively suppressed.

Construction of Charring-Functional Polyheptanazine towards Improvements in Flame Retardants of Polyurethane

Nitrogen-containing flame retardants have been extensively applied due to their low toxicity and smoke-suppression properties; however, their poor charring ability restricts their applications. Herein, a representative nitrogen-containing flame retardant, polyheptanazine, was investigated. Two novel, cost-effective phosphorus-doped polyheptazine (PCN) and cobalt-anchored PCN (Co@PCN) flame retardants were synthesized via a thermal condensation method. The X-ray photoelectron spectroscopy (XPS) results indicated effective doping of P into triazine. Then, flame-retardant particles were introduced into thermoplastic polyurethane (TPU) using a melt-blending approach. The introduction of 3 wt% PCN and Co@PCN could remarkably suppress peak heat release rate (pHRR) (48.5% and 40.0%), peak smoke production rate (pSPR) (25.5% and 21.8%), and increasing residues (10.18 wt%→17.04 wt% and 14.08 wt%). Improvements in charring stability and flame retardancy were ascribed to the formation of P-N bonds and P=N bonds in triazine rings, which promoted the retention of P in the condensed phase, which produced additional high-quality residues.

Engineering MXene surface with POSS for reducing fire hazards of polystyrene with enhanced thermal stability

High-performance MXene-based polymer nanocomposites are highly desirable for diverse industry applications due to their exceptional mechanical, thermal and other properties. Nevertheless, it remains an intractable challenge to create flame retardant polymer/MXene nanocomposites due to the difficulty to achieve uniform dispersion of MXenes. Here, we reported a facile strategy for the surface manipulation of two-dimensional titanium carbide nanosheets (Ti₃C₂T_x) with 3-aminopropylheptaisobutyl-polyhedral oligomeric silsesquioxane (AP-POSS) (POSS-Ti₃C₂T_x) through electrostatic interactions. The POSS-Ti₃C₂T_x is steadily dispersed in many polar solvents. Upon incorporated into polystyrene (PS), the combined effect of AP-POSS and MXene makes the resultant PS nanocomposites exhibit significantly improved thermal and thermoxidative stability, e.g. 22 °C and 39 °C increases in the temperature at 5 wt% mass loss under nitrogen and air, respectively. Meanwhile, a 39.1 % reduction in the peak heat release rate, a respective 54.4 % and 35.6 % reduction in the peak CO production rate and the peak CO₂ production rate was achieved, which are superior to those of its own and previous counterparts. This outstanding fire safety is attributed to the combination of adsorption, catalytic and barrier effects of POSS-Ti₃C₂T_x. Hence, as-designed functionalized MXenes can be effectively applied in PS to formulate multifunctional polymer nanocomposites attractive for wide potential applications.

Enhanced Fire Safety of Rigid Polyurethane Foam via Synergistic Effect of Phosphorus/Nitrogen Compounds and Expandable Graphite

In order to explore highly efficient flame-retardant rigid polyurethane foam (RPUF), phosphorus/nitrogen compounds and expandable graphite (EG) were successfully incorporated into RPUF by a free one-spot method. The combustion results showed that the fire safety of the RPUF samples was remarkably improved by the addition of phosphoric/nitrogen compounds and EG. With the incorporation of 22.4 wt.% phosphorus/nitrogen compounds and 3.2 wt.% EG, the RPUF composites achieved UL-94 V-0 rating. Besides, the total heat release and total smoke release of RPUF composites were reduced by 29.6% and 32.4% respectively, compared to those of the pure RPUF sample. PO• and PO2• together with nonflammable gaseous products were evolved from phosphoric/nitrogen compounds in the gas phase, which quenched the flammable free radicals in the matrix and diluted the concentration of combustible gaseous products generated from PRUF during combustion. The compact char residues which acted as excellent physical barriers were formed by catalysis of EG and phosphoric/nitrogen compounds in the condense phase. The fire hazard of RPUF was significantly reduced by the synergistic effect of phosphorus-nitrogen compounds and EG. This work provides a promising strategy to enhance the fire safety of RPUF.

Nacre-biomimetic graphene oxide paper intercalated by phytic acid and its ultrafast fire-alarm application

A novel nacre-like flame-retardant paper based on graphene oxide (GO), and phytic acid (PTA) is fabricated via evaporation-induced self-assembly. This facile method is time saving and low energy consuming. A facile approach is proposed to improve thermal oxidative stability of GO paper by in situ phosphorus doping during flame exposure. Then fire-alarm system is designed based on the high-temperature thermal reduction characteristic of GO. The GO paper functionalized with PTA (GO-PTA) can provide ultrasensitive, reliable and longtime fire early-warning signal. Fire alarm can be triggered at approximately 0.50 s when GO-PTA samples are attacked by fire. Phosphorus atoms are in situ doped into graphene layers during fire exposure, endowing GO-PTA paper with outstanding thermal oxidative stability, and thus alarm duration time of GO is greatly improved. The work develops advanced fire detection and early-warning sensors that provide reliable and continuous signals, which provide more available time for fire evacuation.

Organic Aluminum Hypophosphite/Graphitic Carbon Nitride Hybrids as Halogen-Free Flame Retardants for Polyamide 6

The novel organic aluminum hypophosphite (ALCPA) and its hybrid (CNALCPA) with graphitic carbon nitride (g-C3N4) were successfully synthesized and applied as halogen-free flame retardants in polyamide 6 (PA6). Their structures, morphology, thermal stability, and fire properties were characterized. Results showed that both ALCPA and CNALCPA had good flame retardancy. PA6/CNALCPA composites achieved a high limited-oxygen-index (LOI) value of 38.3% and a V-0 rating for UL94 at 20 wt % loading, while PA6/ALCPA composites could reach a V-1 rating for UL94. The flame-retardant mechanism was also studied. On the one hand, the incorporation of g-C3N4 produced more gas-phase products, which indicated a gas-phase mechanism. On the other hand, g-C3N4 could catalyze the thermal degradation of ALCPA and PA6 to form a compact char layer that was evidence for a solid-phase mechanism. The tensile test of the PA6 composites also displayed good mechanical properties.

Impact of graphene oxide on epoxy resin characteristics

The incorporation of a small part of graphene oxide (GO) offers an appropriate fire retardant for thermally conductive epoxy (EP) resin composites, which is verified by the upper limiting oxygen index of 24.5% and other standard flame-retardant tests. The smoke production rate, total smoke production (TSP), and the smoke density of EP composites were reduced with additional GO. The increased efficiency of fire resistance and smoke suppression is primarily due to the formation of physical barrier and compactness of the developed GO char layers, serving as an effective barrier layer that increases the fire resistance, and the thermal steadiness of the char layers derives from the effect of GO inclusion. The barrier impact of GO and the limited mobility of polymer chains are crucial factors in increasing thermal stability and reduction of generating dangerous carbon monoxide during burns. The thermal stability increased and the peak heat release rate, total heat release, TSP, and the largest smoke density value reduced to 52.5%, 43.6%, 33.9%, and 44.2%, correspondingly, compared with pure EP. The tensile strength and elongation at break of EP composites were enhanced by 23% and 8.4% compared with pure EP, respectively.

Anisotropic, low-tortuosity and ultra-thick red P@C-Wood electrodes for sodium-ion batteries

Red phosphorus (P) is considered to be the most suitable electrode for sodium-ion batteries due to its low cost, earth abundance and high theoretical capacity. Numerous studies have focused on improving the low conductivity and the extremely large volume change of red P during the cycling process. However, these strategies heavily decrease the P mass loading in the electrode. Herein, inspired by natural wood, we successfully develop an ultra-thick bulk red Phosphorus@Carbon-Wood (red P@C-Wood) electrode via the vaporization-condensation process. The sodium-ion batteries assembled with the fabricated red P@C-Wood electrode provide a high areal capacity of 18 mA h cm^-2 (≈5 times those of other reported electrodes) and the P mass loading of up to 8.4 mg cm^-2 (≥2 times those of other reported electrodes). The combination of red phosphorus and carbonized wood provides a new strategy for people to improve the areal energy density of lithium and sodium batteries.

A DVD-MoS2/Ag2S/Ag Nanocomposite Thiol-Conjugated with Porphyrins for an Enhanced Light-Mediated Hydrogen Evolution Reaction

We have recently demonstrated in a previous work an appreciable photoelectrocatalytic (PEC) behavior towards hydrogen evolution reaction (HER) of a MoS₂/Ag₂S/Ag nanocomposite electrochemically deposited on a commercial writable Digital Versatile Disc (DVD), consisting therefore on an interesting strategy to convert a common waster product in an added-value material. Herein, we present the conjugation of this MoS₂/Ag₂S/Ag-DVD nanocomposite with thiol-terminated tetraphenylporphyrins, taking advantage of the grafting of thiol groups through covalent S-S bridges, for integrating the well-known porphyrins photoactivity into the nanocomposite. Moreover, we employ two thiol-terminated porphyrins with different hydrophilicity, demonstrating that they either suppress or improve the PEC-HER performance of the overall hybrid, as a function of the molecule polarity, sustaining the concept of a local proton relay. Actually, the active polar porphyrin-MoS₂/Ag₂S/Ag-DVD hybrid material presented, when illuminated, a better HER performance, compared to the pristine nanocomposite, since the porphyrin may inject photoelectrons in the conduction band of the semiconductors at the formed heterojunction, presenting also a stable operational behavior during overnight chopped light chronoamperometric measurement, thanks to the robust bond created.

Natural antioxidant functionalization for fabricating ambient-stable black phosphorus nanosheets toward enhancing flame retardancy and toxic gases suppression of polyurethane

Herein, as a natural antioxidant, tannin (TA) is firstly used to functionalize black phosphorous (BP) nanosheets to improve the ambient stability and toxic suppression, thus decreasing the fire hazards of polymer materials. Compared to pure BP nanosheets, higher temperature for thermal oxidation decomposition is achieved for TA-BP nanosheets, directly confirming the ambient stability of TA-BP nanosheets. Meanwhile, from high resolution TEM and XPS results, TA-BP nanosheets after being exposed at air for 10 days present well-organized crystal structure and low PO_x bonds content. Cone calorimeter results illustrate that the incorporation of 2.0 wt% TA-BP nanosheets significantly decreases the peak value of heat release rate (-56.5 %), total heat release (-43.0 %), CO₂ concentration (-57.3 %) of TPU composite. Meanwhile, with addition of low to 1.5 wt%, the release of highly-toxic CO gas is significantly suppressed, confirmed by lower peak value (0.52 mg/m³) and decreased total release amount (-55.1 %). The obviously enlarged tensile strength (36.7 MPa) and desirable elongation at break (622 %) are also observed. This strategy not only firstly adopts bio-based antioxidant to impart excellent environmental stability for BP nanosheets, but also promotes the promising potentials of BP nanosheets in the fire safety application of polymer composites.

Coordination-Driven Hierarchical Assembly of Hybrid Nanostructures Based on 2D Materials

2D materials have received tremendous scientific and engineering interests due to their remarkable properties and broad-ranging applications such as energy storage and conversion, catalysis, biomedicine, electronics, and so forth. To further enhance their performance and endow them with new functions, 2D materials are proposed to hybridize with other nanostructured building blocks, resulting in hybrid nanostructures with various morphologies and structures. The properties and functions of these hybrid nanostructures depend strongly on the interfacial interactions between 2D materials and other building blocks. Covalent and coordination bonds are two strong interactions that hold high potential in constructing these robust hybrid nanostructures based on 2D materials. However, most 2D materials are chemically inert, posing problems for the covalent assembly with other building blocks. There are usually coordination atoms in most of 2D materials and their derivatives, thus coordination interaction as a strong interfacial interaction has attracted much attention. In this review, recent progress on the coordination-driven hierarchical assembly based on 2D materials is summarized, focusing on the synthesis approaches, various architectures, and structure-property relationship. Furthermore, insights into the present challenges and future research directions are also presented.

Combination of black phosphorus nanosheets and MCNTs via phosphoruscarbon bonds for reducing the flammability of air stable epoxy resin nanocomposites

As a rising star of two-dimensional material, black phosphorus (BP) has attracted tremendous attention in applications of photovoltaics, transistors and batteries due to its unique characteristics. Inspiring, we developed a simple strategy to fabricate BP-MCNTs as highly promising inorganic phosphorus-based flame retardant. After incorporation 2 wt% BP-MCNTs11(the mass ratio of BP:MCNTs=1:1) nanohybrid, the peak of heat release rate and total heat release of EP nanocomposites reduced by 55.81% and 41.17% at a phosphorus content of only 1 wt%, and the comprehensive index FGI for evaluating the flame retardant of materials decreased from 17.35 to 6.97. In addition, the typical flammable volatile are suppressed significantly, and the first stage of carbon monoxide release is disappeared. The improvement of fire safety and inhibition of smoke toxicity could be attributed to the the synergistic effects of nano-barrier, catalytic charring and radicals trapping of BP-MCNTs nanohybrid. More importantly, BP hybrid with MCNTs and wrapped in EP matrix which formed effective isolation protection against the ambient degradation. Raman spectra and SEM results confirmed that EP/BP-MCNTs performed enhanced ambient stability than EP/BP-BS nanocomposites after three months. This study demonstrates its great potential for preparation of air-stable BP based nanocomposites with enhanced fire safety.

Nacre-Inspired Tunable Electromagnetic Interference Shielding Sandwich Films with Superior Mechanical and Fire-Resistant Protective Performance

With the rapidly increasing development of portable device hardware and flexible electronics, ultrathin electromagnetic interference (EMI) shielding films with a combination of high flexibility and excellent mechanical properties are noticeably required. In addition to minimizing the electromagnetic wave pollution problem, the fire hazards caused by accidental electrical leakage or aging are also a cause of extensive concern. Inspired by nacre and sandwich structure, herein, we fabricated for the first time an electrical insulating sandwich-structured film based on Ca ion cross-linked sodium alginate (SA)-montmorillonite (MMT) and Ti₃C₂T_x MXene through a step-by-step vacuum-assisted filtration process. This novel design strategy not only maintains the inner EMI shielding network but also can act as an excellent fire-resistant barrier to protect the electronic device in case of accidental fire. Compared with the pure Ti₃C₂T_x layer, such kind of sandwich film can effectively maintain the EMI shielding performance (50.01 dB), dramatically enhance the mechanical properties (84.4 MPa), and exhibit excellent fire-resistant performance. Especially, compared with the film composed of mixture, the EMI shielding effectiveness value is only 55% that of sandwich films. Besides, it functions well under long-term heat aging test at 80 °C. Therefore, this unique design provides a novel EMI material strategy to facilitate its future applications in flexible electronics.

MXene/chitosan nanocoating for flexible polyurethane foam towards remarkable fire hazards reductions

MXene/chitosan nanocoating for flexible polyurethane foam (PUF) was prepared via layer-by-layer (LbL) approach. MXene (Ti₃C₂) ultra-thin nanosheets were obtained through etching process of Ti₃AlC₂ followed by exfoliation. The deposition of MXene/chitosan nanocoating was conducted by alternatingly immersing the PUF into a chitosan solution and a Ti₃C₂ aqueous dispersion, which resulted in different number of bilayers (BL) ranging from 2, 5 and 8. Owing to the utilization of ultra-thin Ti₃C₂ nanosheets, the weight gain was only 6.9% for 8 BL coating of PUF, which minimised the unfavourable impact on the intrinsic properties of PUF. The Ti₃C₂/chitosan coating significantly reduced the flammability and smoke releases of PUF. Compared with unmodified PUF, the 8 BL coating reduced the peak heat release rate by 57.2%, alongside with a 65.5% reduction in the total heat release. The 8 BL coating also showed outstanding smoke suppression ability with total smoke release decreased by 71.1% and peak smoke production rate reduced by 60.3%, respectively. The peak production of CO and CO₂ gases also decreased by 70.8% and 68.6%, respectively. Furthermore, an outstanding char formation performance of 37.2 wt.% residue was obtained for 8 BL coated PUF, indicating the excellent barrier and carbonization property of the hybrid coating.

Fabrication of an anode composed of a N, S co-doped carbon nanotube hollow architecture with CoS2 confined within: toward Li and Na storage

Over the years, transition metal chalcogenides (TMCs) have attracted ample attention from researchers on account of their high theoretical capacity, through which they show great potential for use in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Nevertheless, there are some serious obstacles (particle pulverization and large volume change) still in the way to achieving satisfactory cycling performance and rate property. Here, we report the preparation of a N, S co-doped carbon nanotube hollow architecture confining CoS₂ (CoS₂/NSCNHF) derived from bimetal-organic-frameworks. The rationally designed structure possesses excellent Li⁺/Na⁺ storage performances. Further investigation of the Li⁺/Na⁺ storage behavior indicated the presence of a partial pseudocapacitive contribution, facilitating the fast Li⁺/Na⁺ interaction/extraction process and thus giving it superb electrochemical property. This work may represent an important step forward in the fabrication of MOF-derived hierarchical hybrids combined with a hollow structure and TMCs to help such TMCs achieve their potential in energy storage systems.