Graphene Oxide and Hydroxyapatite Nanowire-Based Asymmetric Nanocomposite Papers with Heat-Induced Color and Resistance Switching for Dual-Mode Early Fire Warning

Graphene oxide (GO) fire warning sensors have received much attention in the last 5 years. However, GO sensors still suffer from a high response temperature (above 100 °C) and short duration time of fire warning. In this work, an asymmetric nanocomposite paper based on color and resistance switching was developed to overcome these issues. The top surface consists of poly(pentacosadiynoic acid) [poly(PCDA)] and hydroxyapatite (HAp) nanowires, which gives the alarm by a color change from purple to red at 55 °C due to the conformational distortion of the poly(PCDA) backbone. On the other hand, the bottom surface is made of 3-aminopropyltriethoxysilane (APTES)-modified GO nanosheets and HAp nanowires, which sends out alerts within 1 s in fire by means of resistance change due to the thermal reduction of GO. It is found that the APTES molecules effectively enhance flame retardancy of GO by releasing nonflammable gases and producing a protective solid barrier. As a result, long-lasting fire warning has been realized.