Organic solvents-free and ambient-pressure drying melamine formaldehyde resin aerogels with homogeneous structures, outstanding mechanical strength and flame retardancy.

Atmospheric drying method for fabricating aerogels is considered the most promising way for casting aerogels on a large scale. However, the organic solvent exchange, remaining environmental pollution risk, is a crucial step in mitigating the impact of surface tension during the atmospheric drying process, especially for wet gel formed through the alkoxy-derived sol-gel process, such as melamine-formaldehyde resin (MF) aerogel. Herein, a tough polymer-assisted in situ polymerization was proposed to fabricate MF resin aerogel with a combination of mechanical toughness and strength, enabling it to withstand the capillary force during water evaporation. The monolithic MF resin aerogel through the sol-gel method can be directly prepared without additional network strengthening or organic solvent exchange. The resulting MF resin aerogel exhibits a homogeneous as well as hierarchical structure with macropores and mesopores (~6 µm and ~5 nm), high compressive modulus of 31.8 MPa, self-extinguishing property, and high-temperature thermal insulation with 97 % heat decrease for butane flame combustion. This work presents a straightforward and environmentally friendly method for fabricating MF resin aerogels with nanostructures and excellent performance in open conditions, exhibiting various applications.

Bio-based phytic acid/amino acid complex coating for antimicrobial and flame-retardant cotton fabrics.

Here, a novel multifunctional coating containing bio-based phytic acid (PA), L-glutamic acid (L-Glu), and trimesoyl chloride (TMC) is constructed by a simple soaking strategy, giving cotton fabrics excellent flame retardancy, washability, and antibacterial properties. The coating layer on the cotton surface was prepared via the electrostatic and hydrogen bonding between PA and L-Glu, accompanied by the interface polymerization between PA, L-Glu, and TMC. Among them, the limiting oxygen index value of the treated cotton fabrics (C2 and C2-TMC) was as high as 40 %. During the vertical flammability test, both C2 and C2-TMC cotton showed self-extinguished behavior with a short damaged length (≤50 mm). Remarkably, the LOI of C2-TMC sustained a high value (30 %) even after 300 laundering cycles, maintaining its self-extinguishing behavior in the vertical combustion test. Additionally, in the cone calorimetry test, peak heat release rate and total heat release of treated cotton were lower than control cotton. Surprisingly, after 30 or 60 laundering cycles, the C2-TMC cotton exhibited excellent antibacterial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans due to the continuous exposure of PA and L-Glu. Moreover, the coating layer on the cotton surface had little impact on the mechanical properties and feel of the fabric.

Self-evolutionary recycling of flame-retardant polyurethane foam enabled by controllable catalytic cleavage.

Polyurethane (PU) foams, pivotal in modern life, face challenges suh as fire hazards and environmental waste burdens. The current reliance of PU on potentially ecotoxic halogen-/phosphorus-based flame retardants impedes large-scale material recycling. Here, our demonstrated controllable catalytic cracking strategy, using cesium salts, enables self-evolving recycling of flame-retardant PU. The incorporation of cesium citrates facilitates efficient urethane bond cleavage at low temperatures (160 °C), promoting effective recycling, while encouraging pyrolytic rearrangement of isocyanates into char at high temperatures (300 °C) for enhanced PU fire safety. Even in the absence of halogen/phosphorus components, this foam exhibits a substantial increase in ignition time (+258.8%) and a significant reduction in total smoke release (-79%). This flame-retardant foam can be easily recycled into high-quality polyol under mild conditions, 60 °C lower than that for the pure foam. Notably, the trace amounts of cesium gathered in recycled polyols stimulate the regenerated PU to undergo self-evolution, improving both flame-retardancy and mechanical properties. Our controllable catalytic cracking strategy paves the way for the self-evolutionary recycling of high-performance firefighting materials.

Biomimetic Nanoporous Transparent Universal Fire-Resistant Coatings.

The inherent flammability of most polymeric materials poses a significant fire hazard, leading to substantial property damage and loss of life. A universal flame-retardant protective coating is considered as a promising strategy to mitigate such risks; however, simultaneously achieving high transparency of the coatings remains a great challenge. Here, inspired by the moth eye effect, we designed a nanoporous structure into a protective coating that leverages a hydrophilic-hydrophobic interactive assembly facilitated by phosphoric acid protonated amino siloxane. The coating demonstrates robust adhesion to a diverse range of substrates, including but not limited to fabrics, foams, paper, and wood. As expected, its moth-eye-inspired nanoporous structure conferred a high visible light transparency of >97% and water vapor transmittance of 96%. The synergistic effect among phosphorus (P), nitrogen (N), and silicon (Si) largely enhanced the char-forming ability and restricted the decomposition of the coated substrates, which successfully endowed the coating with high fire-fighting performance. More importantly, for both flexible and rigid substrates, the coated samples all possessed great mechanical properties. This work provides a new insight for the design of protective coatings, particularly focusing on achieving high transparency.

Catalytic polymer self-cleavage for CO2 generation before combustion empowers materials with fire safety.

Polymeric materials, rich in carbon, hydrogen, and oxygen elements, present substantial fire hazards to both human life and property due to their intrinsic flammability. Overcoming this challenge in the absence of any flame-retardant elements is a daunting task. Herein, we introduce an innovative strategy employing catalytic polymer auto-pyrolysis before combustion to proactively release CO2, akin to possessing responsive CO2 fire extinguishing mechanisms. We demonstrate that potassium salts with strong nucleophilicity (such as potassium formate/malate) can transform conventional polyurethane foam into materials with fire safety through rearrangement. This transformation results in the rapid generation of a substantial volume of CO2, occurring before the onset of intense decomposition, effectively extinguishing fires. The inclusion of just 1.05 wt% potassium formate can significantly raise the limiting oxygen index of polyurethane foam to 26.5%, increase the time to ignition by 927%, and tremendously reduce smoke toxicity by 95%. The successful application of various potassium salts, combined with a comprehensive examination of the underlying mechanisms, underscores the viability of this strategy. This pioneering catalytic approach paves the way for the efficient and eco-friendly development of polymeric materials with fire safety.

Electrocatalytic Coenhancement of Bimetallic Polyphthalocyanine-Anchored Ru Nanoclusters Enabling Efficient Overall Water Splitting at Ampere-Level Current Densities.

Efficient electrocatalysts capable of operating continuously at industrial ampere-level current densities are crucial for large-scale applications of electrocatalytic water decomposition for hydrogen production. However, long-term industrial overall water splitting using a single electrocatalyst remains a major challenge. Here, bimetallic polyphthalocyanine (FeCoPPc)-anchored Ru nanoclusters, an innovative electrocatalyst comprising the hydrogen evolution reaction (HER) active Ru and the oxygen evolution reaction (OER) active FeCoPPc, engineered for efficient overall water splitting are demonstrated. By density functional theory calculations and systematic experiments, the electrocatalytic coenhancement effect resulting from unique charge redistribution, which synergistically boosts the HER activity of Ru and the OER activity of FeCoPPc by optimizing the adsorption energy of intermediates, is unveiled. As a result, even at a large current density of 2.0 A cm-2 , the catalyst exhibits low overpotentials of 220 and 308 mV, respectively, for HER and OER. It exhibits excellent stability, requiring only 1.88 V of cell voltage to achieve a current density of 2.0 A cm-2 in a 6.0 m KOH electrolyte at 70 °C, with a remarkable operational stability of over 100 h. This work provides a new electrocatalytic coenhancement strategy for the design and synthesis of electrocatalyst, paving the way for industrial-scale overall water splitting applications.

Controllable proton-reservoir ordered gel towards reversible switching and reliable electromagnetic interference shielding.

Smart and dynamic electromagnetic interference (EMI) shielding materials possess a remarkable capacity to modify their EMI shielding abilities, rendering them invaluable in various civil and military applications. However, the present response mechanism of switch-type EMI shielding materials is slightly restricted, as it primarily depends on continuous pressure induction, thereby resulting in concerns regarding their durability and reliability. Herein, for the first time, we demonstrate a novel method for achieving solvent-responsive, reversible switching, and robust EMI shielding capabilities using a controlled proton-reservoir ordered gel. The gel contains polyaniline (PANI) and sodium alginate (SA). Initially, SA acts as a proton reservoir for PANI in an aqueous system, enhancing the doping level of PANI and improving its electrical conductivity. Additionally, PANI and SA chains respond to diverse polar solvents, such as water, acetonitrile, ethanol, n-hexane, and air, inducing distinct conformations that affect the degree of PANI conjugation and electron migration along the chains. This process is reversible and non-destructive to the polymer chain, ensuring the effective and uncompromised performance of the EMI shielding switch. We can achieve precise and reversible tuning (on/off) of EMI shielding with different effectiveness levels by manipulating the solvents within the framework. This work opens a new solvent-stimuli avenue for the development of EMI shielding materials with reliable and intelligent on/off switching capabilities.

Construction of hierarchical SiO2 microcapsule towards flame retardation, low toxicity and mechanical enhancement of epoxy resins.

A novel approach for improving the flame retardancy, smoke suppression and mechanical properties of epoxy resins (EPs) has been proposed by incorporating functionalized hollow mesoporous silica microcapsules (SHP) loaded with phosphorous silane flame retardants (SCA) and coated with polydopamine (PDA) and transition metals. The proposed approach involves a multi-level structure that combines several mechanisms to enhance the flame-retardant properties of EP. The physical barrier provided by silica serves to impede heat and mass transfer during combustion, while the catalytic carbonization effect of phosphorus and transition metals promotes the formation of a protective char layer, which acts as a barrier to further flame propagation. Incorporating a low loading amount of 3 wt% SHP into the epoxy matrix resulted in EP/SHP-3 composites with significantly improved flame retardancy, as evidenced by a limiting oxygen index of 31.5% and a V-1 rating, in contrast to the values obtained for unmodified EP, which were 23.8% and no rating, respectively. In addition, cone calorimeter test (CCT) results indicated that the total heat release, peak heat release rate and total smoke production of EP/SHP-3 decreased by 18.2%, 25.2% and 18.4%, respectively. Moreover, the improved interfacial compatibility facilitated by polydopamine assists in the dispersion and compatibility of the SHP with the epoxy matrix, leading to better mechanical properties. Herein, the addition of 1 wt% SHP to EP significantly improved its mechanical performance, with a 16.7% increase in tensile strength and a 19.2% increase in impact strength. The design of the multi-level structural approach has the potential to provide new ideas for the simultaneous improvement of fire safety as well as mechanical properties of polymers.

Gradient Hierarchical Hollow Heterostructures of Ti3C2Tx@rGO@MoS2 for Efficient Microwave Absorption.

Heterostructure engineering has emerged as a promising approach for creating high-performance microwave absorption materials in various applications such as advanced communications, portable devices, and military fields. However, achieving strong electromagnetic wave attenuation, good impedance matching, and low density in a single heterostructure remains a significant challenge. Herein, a unique structural design strategy that employs a hollow structure coupled with gradient hierarchical heterostructures to achieve high-performance microwave absorption is proposed. MoS2 nanosheets are uniformly grown onto the double-layered Ti3C2Tx MXene@rGO hollow microspheres through self-assembly and sacrificial template techniques. Notably, the gradient hierarchical heterostructures, comprising a MoS2 impedance matching layer, a reduced graphene oxide (rGO) lossy layer, and a Ti3C2Tx MXene reflective layer, have demonstrated significant improvements in impedance matching and attenuation capabilities. Additionally, the incorporation of a hollow structure can further improve microwave absorption while reducing the overall composite density. The distinctive gradient hollow heterostructures enable Ti3C2Tx@rGO@MoS2 hollow microspheres with exceptional microwave absorption properties. The reflection loss value reaches as strong as -54.2 dB at a thin thickness of 1.8 mm, and the effective absorption bandwidth covers the whole Ku-band, up to 6.04 GHz. This work provides an exquisite perspective on heterostructure engineering design for developing next-generation microwave absorbers.

A One-Step Self-Flowering Method toward Programmable Ultrathin Porous Carbon-Based Materials for Microwave Absorption and Hydrogen Evolution.

Ultrathin 2D porous carbon-based materials offer numerous fascinating electrical, catalytic, and mechanical properties, which hold great promise in various applications. However, it remains a formidable challenge to fabricate these materials with tunable morphology and composition by a simple synthesis strategy. Here, a facile one-step self-flowering method without purification and harsh conditions is reported for large-scale fabrication of high-quality ultrathin (≈1.5 nm) N-doped porous carbon nanosheets (NPC) and their composites. It is demonstrated that the layered tannic/oxamide (TA/oxamide) hybrid is spontaneously blown, exfoliated, bloomed, in situ pore-formed, and aromatized during pyrolysis to form flower-like aggregated NPC. This universal one-step self-flowering system is compatible with various precursors to construct multiscale NPC-based composites (Ru@NPC, ZnO@NPC, MoS2 @NPC, Co@NPC, rGO@NPC, etc.). Notably, the programmable architecture enables NPC-based materials with excellent multifunctional performances, such as microwave absorption and hydrogen evolution. This work provides a facile, universal, scalable, and eco-friendly avenue to fabricate functional ultrathin porous carbon-based materials with programmability.

Design of P-decorated POSS towards flame-retardant, mechanically-strong, tough and transparent epoxy resins.

Epoxy resins (EPs) are known for their durability, strength, and adhesive properties, which make them a versatile and popular material for use in a variety of applications, including chemical anticorrosion, small electronic devices, etc. However, EP is highly flammable due to its chemical nature. In this study, phosphorus-containing organic-inorganic hybrid flame retardant (APOP) was synthesized by introducing 9, 10-dihydro-9-oxa-10­phosphaphenathrene (DOPO) into cage-like octaminopropyl silsesquioxane (OA-POSS) via Schiff base reaction. The improved flame retardancy of EP was achieved by combining the physical barrier of inorganic Si-O-Si with the flame-retardant capability of phosphaphenanthrene. EP composites containing 3 wt% APOP passed the V-1 rating with a value of LOI of 30.1% and showed an apparent reduction in smoke release. Additionally, the combination of the inorganic structure and the flexible aliphatic segment in the hybrid flame retardant provides EP with molecular reinforcement, while the abundance of amino groups facilitates a good interface compatibility and outstanding transparency. Accordingly, EP containing 3 wt% APOP increased in tensile strength, impact strength, and flexural strength by 66.0 %, 78.6 %, and 32.3 %, respectively. The EP/APOP composites had a bending angle lower than 90°, and their successful transition to a tough material highlights the potential of this innovative combination of the inorganic structure and the flexible aliphatic segment. In addition, the relevant flame-retardant mechanism revealed that the APOP promoted the formation of a hybrid char layer containing P/N/Si for EP and produced phosphorus-containing fragments during combustion, showing flame-retardant effects in both condensed and vapor phases. This research offers innovative solutions for reconciling flame retardancy & mechanical performances and strength & toughness for polymers.

Growth of copper organophosphate nanosheets on graphene oxide to improve fire safety and mechanical strength of epoxy resins.

With the high integration of electronic products in our daily life, high-performance epoxy resins (EP) with excellent flame retardancy, smoke suppression, and mechanical strength are highly desired for applications. In this study, copper organophosphate nanosheets were evenly grown on the surface of graphene oxide (GO) via a self-assembly process based on coordination bonding and electrostatic interactions. The resultant nanohybrid endowed EP with satisfactory flame retardant effect and improved mechanical properties. Incorporating functionalized nanosheets of merely 1 wt% loading, the impact strength of the EP nanocomposites improved by 147% when compared to 1% EP-GO. Additionally, the nanosheets inhibited the smoke and heat release of EP, and the limiting oxygen value of EP-EGOPC reached ∼29%. The mechanism analysis verified that the existence of organophosphate and copper-containing components associated with the physical barrier of GO promoted the hybrid aromatization of the char layer, thereby improving the fire safety of epoxy matrix. This research offers a new interfacial method for designing functional nanosheets with good interface compatibility and high flame-retardant efficiency in polymers.

Fully recyclable multifunctional adhesive with high durability, transparency, flame retardancy, and harsh-environment resistance.

Recyclable/reversible adhesives have attracted growing attention for sustainability and intelligence but suffer from low adhesion strength and poor durability in complex conditions. Here, we demonstrate an aromatic siloxane adhesive that exploits stimuli-responsive reversible assembly driven by π-π stacking, allowing for elimination and activation of interfacial interactions via infiltration-volatilization of ethanol. The robust cohesive energy from water-insensitive siloxane assembly enables durable strong adhesion (3.5 MPa shear strength on glasses) on diverse surfaces. Long-term adhesion performances are realized in underwater, salt, and acid/alkali solutions (pH 1-14) and at low/high temperatures (-10-90°C). With reversible assembly/disassembly, the adhesive is closed-loop recycled (~100%) and reused over 100 times without adhesion loss. Furthermore, the adhesive has unique combinations of high transparency (~98% in the visible light region of 400-800 nm) and flame retardancy. The experiments and theoretical calculations reveal the corresponding mechanism at the molecular level. This π-π stacking-driven siloxane assembly strategy opens up an avenue for high-performance adhesives with circular life and multifunctional integration.

Comparative Study of M(â ¡)Al (M=Co, Ni) Layered Double Hydroxides for Silicone Foam: Characterization, Flame Retardancy, and Smoke Suppression.

To compare the different actions of the two representative transition metal cations of Co2+ and Ni2+ in layered double hydroxides (LDHs), CoAl-LDH and NiAl-LDH intercalated with CO32- were synthesized, and the chemical structures, microstructures, and surface areas thereof were successfully characterized. Then, the two LDHs were utilized as flame retardants and smoke suppressants for silicone foam (SiF). The densities, flame retardancy, smoke suppression, thermal stabilities, and compressive strengths of the two SiF/LDHs nanocomposites were investigated. The introduction of LDHs slightly decreased the density of SiF due to the catalytic actions of Co and Ni during the foaming process of SiF. With respect to the flame retardancy, the addition of only 1 phr of either CoAl-LDH or NiAl-LDH could effectively improve the limiting oxygen index of SiF from 28.7 to 29.6%. Based on the results of vertical flame testing and a cone calorimeter test, the flame retardancy and fire safety of the SiF were effectively enhanced by the incorporation of LDHs. In addition, owing to the good catalytic action and large specific surface area (NiAl-LDH: 174.57 m2 g-1; CoAl-LDH: 51.47 m2 g-1), NiAl-LDH revealed higher efficiencies of flame retardancy and smoke suppression than those of CoAl-LDH. According to the results of energy-dispersive X-ray spectroscopy, Co and Ni participated in the formation of protective char layers, which inhibited the release of SiO2 into the gas phase. Finally, the influences on the thermal decomposition and compressive strength for SiF resulting from the addition of LDHs are discussed.

Interfacial engineering to construct P-loaded hollow nanohybrids for flame-retardant and high-performance epoxy resins.

Nano flame retardants, as one of the key flame retardants in recent years, have been limited by poor efficiency and weak compatibility. In this study, we propose an interfacial hollow engineering strategy to tackle this problem by assembling P-phytic acid into the hollow cavity of mesoporous SiO2 grafted with a polydopamine transition metal. In this design, the grafted polydopamine-metal coatings on the hybrids can greatly improve their interface compatibility with the polymer matrix, while the loaded phytic acid in the cavity contributes to enhance flame retardancy. Consequently, the resultant hierarchical P-loaded nanohybrids show both high flame retardancy and mechanical reinforcement for the polymer. Taking epoxy resin (EP, a typical thermosetting resin used in large quantities) as a representative, at only 1 wt% loading of the nanohybrids, the impact strength of the nanocomposites improved by 35.7% compared to pure EP. Remarkably, the hybrids can simultaneously endow EP with high flame retardancy (low heat release rate) and satisfactory smoke inhibition. Additionally, the flame-retardant mechanism analysis confirmed that the nanohybrid had a better catalytic carbonization effect on promoting the highly graphitized carbon layer, thereby suppressing the fire hazard of epoxy resins. This research offers a new interfacial hollow engineering method for the construct and design of high-performance EP with nanohybrids.

A sponge heated by electromagnetic induction and solar energy for quick, efficient, and safe cleanup of high-viscosity crude oil spills.

Frequent oil spills have caused severe environmental and ecological damage. Effective cleanup has become a complex challenge owing to the poor flowability of viscous crude oils. The current method of solar heating to reduce the viscosity of heavy oil is only suitable during sunny days, while the use of Joule heating is limited by the risk of direct exposure to high-voltage electricity. Herein, we demonstrate a noncontact electromagnetic induction and solar dual-heating sponge for the quick, safe, and energy-saving cleanup of ultrahigh-viscosity heavy oil. The resulting sponge with magnetic, conductive, and hydrophobic properties can be rapidly heated to absorb heavy oil under alternating magnetic fields, solar irradiation, or both of these conditions. By constructing theoretical models and fitting the actual data, an in-depth analysis of induction and solar heating processes is carried out. The sponge has excellent resilience and stability, indicating its reusability, fast and continuous adsorption (16.17 g in 10 s), and large capacity (75-81 g/g, the highest value ever) for soft asphalt (a highly viscous crude oil). This work provides a new noncontact dual-heating strategy for heavy oil cleanup, in which absorbents use induction heating during an emergency and then switch to partial or full solar heating to save energy in sunny conditions. ENVIRONMENTAL IMPLICATION: Heavy oils stranded on the beach or floating on water can kill underwater plants by blocking sunlight, or trap water birds and other animals. Heavy oil also contains aromatic substances that are toxic to aquatic organisms. Although oil spills near shallow water cannot be cleaned up by fences or other machinery, an oil adsorbent can deal with this problem. However, common adsorbents cannot effectively absorb high-viscosity oils, such as heavy oil. In this paper, an induction and solar dual-heating sponge is developed for the effective cleanup of high-viscosity oil.

A Phosphorus-Nitrogen-Carbon Synergistic Nanolayered Flame Retardant for Polystyrene.

Polymers are widely used in our daily life; however, most of them are highly flammable. Once modified with flame retardants (FRs), polymers always have deteriorative properties in mechanical strength aspects. As a countermeasure, a novel unified phosphorus and nitrogen-containing organic nano-layered flame retardant (BA-MA) was synthesized by the assembly of biphenyl-4,4'-diphosphonic acid (BA) and melamine (MA), which was used as an additive flame retardant for polystyrene (PS) resin. The chemical structure and morphology of BA-MA were characterized, and a possible growth mechanism of the nanolayered structure was presented in detail. The resulting BA-MA with a thickness of about 60 nm can be uniformly dispersed in the PS resin, thus maintaining the mechanical properties of the material. Remarkably, under only 1 wt% loading of BA-MA, the flammability of PS can be largely reduced with a 68% reduction in the peak heat release rate. Additionally, the smoke release was also significantly inhibited. The research on flame retardant mechanisms shows that BA-MA mainly produces incombustible gas to dilute the concentration of combustibles and promote the formation of aromatic carbon layers to isolate oxygen transmission and heat transfer.

Hierarchical Ti3C2Tx@ZnO Hollow Spheres with Excellent Microwave Absorption Inspired by the Visual Phenomenon of Eyeless Urchins.

Ingenious microstructure design and rational composition selection are effective approaches to realize high-performance microwave absorbers, and the advancement of biomimetic manufacturing provides a new strategy. In nature, urchins are the animals without eyes but can "see", because their special structure composed of regular spines and spherical photosensitive bodies "amplifies" the light-receiving ability. Herein, inspired by the above phenomenon, the biomimetic urchin-like Ti3C2Tx@ZnO hollow microspheres are rationally designed and fabricated, in which ZnO nanoarrays (length: ~ 2.3 µm, diameter: ~ 100 nm) as the urchin spines are evenly grafted onto the surface of the Ti3C2Tx hollow spheres (diameter: ~ 4.2 µm) as the urchin spherical photosensitive bodies. The construction of gradient impedance and hierarchical heterostructures enhance the attenuation of incident electromagnetic waves. And the EMW loss behavior is further revealed by limited integral simulation calculations, which fully highlights the advantages of the urchin-like architecture. As a result, the Ti3C2Tx@ZnO hollow spheres deliver a strong reflection loss of - 57.4 dB and broad effective absorption bandwidth of 6.56 GHz, superior to similar absorbents. This work provides a new biomimetic strategy for the design and manufacturing of advanced microwave absorbers.