Multifunctional MXene-coated cotton fabric with enhanced thermopower for smart fire protection

Titanium carbide (MXene) nanosheet is one of the most promising early fire-warning materials but limited by its relatively low thermopower. Doping modification is an effective method to improve its thermoelectric efficiency. Herein, a novel enhanced thermopower flame-retardant cotton fabric (HTE@CF) was fabricated by dip-coating of MXene, tannic acid (TA), and calcium chloride (CaCl2) via layer-by-layer assembly. It was found that HTE@CF exhibited high thermopower. When the temperature difference was 120 °C, its maximum thermoelectric voltage was as high as 3.72 mV, and the Seebeck coefficient was more than 39.4 μV/K, which was about 900% higher than those of MXene/TA@CF. HTE@CF displayed accurate temperature response and sensitive fire-warning performance. When being burned, it quickly triggered the fire-warning system within 3 s. More importantly, HTE@CF exhibited outstanding flame retardancy. Its limiting oxygen index (LOI) was as high as 35.3%, and its structure remained stable when exposed to the flame for 60 s. Furthermore, due to the high conductivity of MXene and CaCl2, HTE@CF showed good piezoresistive sensing capability. Our work provides new insights for the preparation of multifunctional and smart fire protection cotton fabrics.