Made of environmentally friendly, nonflammable materials, the smart fire alarm wallpaper uses fire-resistant inorganic paper based on ultralong hydroxyapatite nanowires (HNs) and graphene oxide (GO) thermosensitive sensors. At room temperature, the thermosensitive sensors are electrical insulators; however, when exposed to heat, they become electrically conductive, enabling the triggering of an alarm.
This contrasts with common commercial wallpaper materials, which – being made of plant cellulose fibers or synthetic polymers – are often highly flammable. According to the researchers, the fire-resistant wallpaper is white in color, mechanically robust, and highly flexible, enabling it to be processed into various shapes, dyed with different colors, and printed with a commercial printer.
The wallpaper is based on hydroxyapatite – a mineral that is the main inorganic constituent of tooth enamel and bone. While normally brittle and rigid in structure, previous research had shown that the material could be made highly flexible by forming ultralong nanowires with it. Such ultralong hydroxyapatite nanowires, say the researchers, are “a promising kind of biomaterial with many advantages such as high biocompatibility, high flexibility, good mechanical properties, high thermal stability, and fire resistance.”
Requirements for the wallpaper’s thermosensitive sensor included flexibility, fire retardance, and rapid response and steady performance in the flame. The researchers chose a graphene-oxide ink-based thermosensitive sensor fabricated onto the wallpaper’s back surface by a simple drop-casting process.
The sensor is then connected to an alarm, so if a fire occurs – heating the sensor and causing it to begin to conduct electricity – the alarm goes off. The researchers tweaked the sensor to avoid it burning out too quickly by modifying the graphene oxide with polydopamine — a material based on the hormone and neurotransmitter dopamine, found in living organisms – resulting in a sensor that could respond to fire in about two seconds and have a prolonged alarm time of more than five minutes.
Looking ahead, the researchers plan to scale up production of the wallpaper, as well as investigate other applications, such as preserving important paper documents, energy, air purification, water treatment, environment protection, anti-counterfeiting, flexible electronics, and biomedical uses. For more, see “Fire Alarm Wallpaper Based on Fire-Resistant Hydroxyapatite Nanowire Inorganic Paper and Graphene Oxide Thermosensitive Sensor“