Ambient‐pressure‐dried (APD) preparation of transition metal carbide/nitrides (MXene) aerogels is highly desirable yet remains highly challenging. Here, ultrathin, high‐strength‐to‐weight‐ratio, renewable cellulose nanofibers (CNFs) are efficiently utilized to assist in the APD preparation of ultralight yet robust, highly conductive, large‐area MXene‐based aerogels via a facile, energy‐efficient, eco‐friendly, and scalable freezing‐exchanging‐drying approach. The strong interactions of large‐aspect‐ratio CNF and MXene as well as the biomimetic nacre‐like microstructure induce high mechanical strength and stability to avoid the structure collapse of aerogels in the APD process. Abundant functional groups of CNFs facilitate the chemical crosslinking of MXene‐based aerogels, significantly improving the hydrophobicity, water resistance, and even oxidation stability. The ultrathin, 1D nature of the CNF renders the minimal MXenes’ interlayered gaps and numerous heterogeneous interfaces, yielding the excellent conductivity and electromagnetic interference (EMI) shielding performance of aerogels. The synergies of the MXene, CNF, and abundant pores efficiently improve the EMI shielding performance, photothermal conversion, and absorption of viscous crude oil. This work shows great promises of the APD, multifunctional MXene‐based aerogels in electromagnetic protection or compatibility, thermal therapy, and oil‐water separation applications.

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In this paper, a triazine‐based flame retardant (TAT) was synthesized from cyanuric chloride and aniline. Its chemical structure was characterized by Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance, and elemental analysis. Two kinds of novel intumescent flame‐retardant epoxy systems were obtained with the incorporation of TAT and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) or hexa‐phenoxy‐cyclotriphosphazene (HPCP). The flame retardancy of the obtained epoxy samples was evaluated using limited oxygen index, vertical burning (UL94), and cone calorimeter tests. The results indicated that there was a synergistic effect between TAT and DOPO or HPCP. The flame‐retardant mechanism was investigated by thermogravimetric analysis (TGA), thermogravimetric analysis/infrared spectrometry (TGA‐FTIR) coupled with the morphology and chemical analysis of the char residues. During combustion, DOPO or HPCP decomposed to release phosphorus‐containing free radicals with quenching effect. The morphology study showed that the introduction of DOPO or HPCP promoted the carbonization of epoxy matrix and the formation of a phosphorus‐containing viscous char layer, while the pyrolysis gases derived from the decomposition of TAT caused the char layer to expand. The main reason of the promotion of flame retardancy of epoxy samples was that the simultaneous addition of TAT and DOPO or HPCP led to the formation of a compact and intumescent char layer that restricted the transfer of heat and combustible volatiles and simultaneously protected the underlying matrix.

A novel phosphorus‐containing, nitrogen‐containing, and sulfur‐containing reactive flame retardant (BPD) was successfully synthesized by 1‐pot reaction. The intrinsic flame‐retardant epoxy resins were prepared by blending different content of BPD with diglycidyl ether of bisphenol‐A (DGEBA). Thermal stability, flame‐retardant properties, and combustion behaviors of EP/BPD thermosets were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL94 vertical burning test, and cone calorimeter test. The flame‐retardant mechanism of BPD was studied by TGA/infrared spectrometry (TGA‐FTIR), pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS), morphology, and chemical component analysis of the char residues. The results demonstrated that EP/BPD thermosets not only exhibited outstanding flame retardancy but also kept high glass transition temperature. EP/BPD‐1.0 thermoset achieved LOI value of 39.1% and UL94 V‐0 rating. In comparison to pure epoxy thermoset, the average of heat release rate (av‐HRR), total heat release (THR), and total smoke release (TSR) of EP/BPD‐1.0 thermoset were decreased by 35.8%, 36.5% and 16.5%, respectively. Although the phosphorus content of EP/BPD‐0.75 thermoset was lower than that of EP/DOPO thermoset, EP/BPD‐0.75 thermoset exhibited better flame retardancy than EP/DOPO thermoset. The significant improvement of flame retardancy of EP/BPD thermosets was ascribed to the blocking effect of phosphorus‐rich intumescent char in condensed phase, and the quenching and diluting effects of abundant phosphorus‐containing free radicals and nitrogen/sulfur‐containing inert gases in gaseous phase. There was flame‐retardant synergism between phosphorus, nitrogen, and sulfur of BPD.