Multifunctional enhancement strategy for MXene-based fire alarm sensors via interlocked “brick/mortar” structure of dimension-hybrid nanoparticle system

MXene-based fire-responsive composites are promising candidates for next-generation fire alarm sensors with high sensitivity and good mechanical properties. However, the low dispersibility and inherent thermal oxidation of MXene combined with the unsuitable spatial scale of polymer particles in hybrid systems impede the rapid response and alarm duration when suffering a fire. Herein, a strategy based on an interlocked “brick/mortar” structure was proposed for integrating faster response, high sensitivity, and longer duration in flames via a dimension-hybrid nanoparticle network, which was assembled by 2D MXene, 1D cellulose nanocrystals (CNCs), and ammonium polyphosphate (APP). The CNCs with a high aspect ratio of 114 and close length to MXene assisted uniform dispersion of MXene and coupled with APP impeding thermal oxidation of MXene. This assembled MXene/CNC@APP sensor can quickly trigger an alarm signal via substance conversion from insulating to conductive within 1.79 s when suffering a high thermal of 260 °C from fire, thus sensitive fire identification and rapid response were obtained. This MXene/CNC@APP film also maintained good mechanical performance with a tensile strength of 52.5 MPa and elongation at a break of 7.6%, which combined excellent flame retardancy leading to a continuous fire alarm signal over 442 s of the sensor in the fire. This multifunctional integrated enhancement strategy for MXene-based sensors may be conducive to the upgrade of fire alarm systems for better safeguarding of life and property.