Color adjustable, mechanically robust, flame-retardant and weather-resistant TiO₂/MMT/CNF hierarchical nanocomposite coatings toward intelligent fire cyclic warning and protection

Fire safety and protection are very important but still show a critical global challenge. Developing smart fire warning materials with combined passive flame retardancy and active fire alarm response is promising for reducing or avoiding serious fire disasters. Various nano-fillers (e.g., graphene oxide and MXene) based composite coatings have proven to be effective for monitoring critical fire risk of various combustible materials; however, they still show some shortages, for example, high cost, black color, poor weather resistance and complicated fabricating process. Here, we report a green, cost-effective and large-scale strategy for fabricating water-based 3D-titania/2D-montmorillonite/1D-celluose nanofiber (TiO2/MMT/CNF) hierarchical nanocomposite coatings with adjustable color, mechanical robustness, good flame retardancy, long-term weather resistance and sensitive fire cyclic alarming response. The formation of strong chemical bonding and hydrogen bonding interactions among polyethylene glycol molecules and multi-scale nano-fillers together with silane surface modification can produce good mechanical flexibility (folded crane), surface hydrophobicity (water contact angle of 152 degrees) and exceptional flame resistance (good structure integrity after 120 s flame exposure). Notably, the optimized nanocomposite coatings exhibit ultrafast fire alarm response (<3.5 s) and stable fire cyclic alarming capability via the possible band transition of the TiO2 network under flame. Further, such color-adjustable nanocomposite coatings can be easily fabricated for large-scale production, and they show excellent stable flame retardancy and stable fire cyclic warning response even after more than one-year outdoor exposure. This work provides a promising and green fire-warning nanocomposite coatings with combined passive-active functionalities for fire warning and protection.