Ultra-sensitive fan-folded thermally expandable surface reduced graphene oxide strips for fire early warning response

The increasingly frequent fire has brought serious harm to the safety of human life and property. The development of fire early warning materials with super sensitive temperature response has always been an urgent need in the field of fire safety. Herein, a surface reduced graphene oxide strip (RGOS) was fabricated by a simple chemical reduction and used as a fire early warning sensor via the facile fan-folding method. By controlling the reduction time of graphene oxide (GO) in the system of HI/CH3COOH/H3PO2, phosphorus-containing RGOS with different reduction degrees can be obtained. Compared with the pure GO strips, the RGOS exhibits improved flame retardancy. Structural observation and thermal analysis show that the introduction of phosphorus and the reduced graphene oxide (RGO) layer formed by surface reduction effectively inhibit the thermal degradation of the internal GO layer after encountering a high-temperature attack. More importantly, different from the previous GO-based sensors that rely on resistance transformation to generate fire alarm response, the fan-folded RGOS can rapidly expand to trigger a conductive contact after encountering high temperature or flame, thus providing an ideal fire early alarm response (∼3 s for 150 ℃, ∼0.5 s for flame). This work suggests that the RGOS is promising in the development of advanced materials as smart sensors for fire early warning.