Fig. 1. Fabrication process of MF composites modified with different GO derivatives and the structural characterizations of various GO derivatives. (a) Digital images of pure MF, MF-GONR, MF-GOWR and MF-GO sponges prepared by the dip-coating procedure. Typical TEM images of (b) GONR, (c) GOWR and (d) GO sheets, showing different aspect ratio and morphology features. (e) FTIR, (f) XPS and (g) TGA results of various GO derivatives.

Fig. 2. Typical SEM images of pure MF and various modified MF samples at different magnifications: (a) pure MF, (b) MF-GONR, (c) MF-GOWR and (d) MF-GO sponges.

Fig. 3. Physical properties of MF sponges modified different GO derivatives. (a) Digital images of compressive process at 70 % strain and (b) cyclic compressive tests, showing excellent mechanical flexibility and reliability. (c) Photographs of water droplets on surfaces of various MF nanocomposites samples and (d) their water contact angle, indicating good surface hydrophobicity. (e) Typical burning process of the modified MF sponge, showing excellent flame resistance and good structural integrity.

Fig. 4. Flame detection process. (a) Photographs of flame detection demon processes of MF-GO sponge, and the fire alarm device was established by connecting the sample with a warning lamp and a low-voltage electrical source. (b) Electrical resistance changes of three MF sponges as a function of time and (c) fire alarm time. Danger alarm was quickly triggered in less than 3 s once the sample attacked by the flame, and continuous alarm was kept even after removing the fire resource.

Fig. 5. Structure and morphology of the modified MF sponges after the burning test. (a) Typical digital photo of the three MF sponges after burning, and SEM images of (b) MF-GONR, (c) MF-GOWR and (d) MF-GO sponges at different magnifications. The porous structure and interconnected network of the modified samples can be well kept (b2-d2), and the GO derivative on the MF skeleton can be thermally reduced during the burning process to form the conductive network, thus forming the wrinkled morphology on the skeleton.

Fig. 6. Typical photographs of fire early warning processes (detecting a hot surface) of three modified MF based devices: (a) MF-GONR, (b) MF-GOWR and (c) MF-GO sponges. The fire early warning signals can be triggered for the modified samples at a fixed high temperature condition of 300 °C (below the ignition temperature of most combustible materials), and the different GO derivatives produce different fire early-warning time.

Fig. 7. Fire early-warning alarm and resistance response. (a) Electrical resistance changes of various samples as a function of time under different temperatures from 200 to 500 °C, (b) fire early-warning alarm time and (c) resistance response time of various MF sponges at different temperatures.

Fig. 8. Structural analysis of the modified MF sponges. (a, c) Raman spectra and (c, d) FTIR results of various MF composites samples before and after the burning test.

Fig. 9. XPS C1s spectra analysis of the MF-GONR, MF-GOWR and MF-GO sponges at different conditions: (a-c) room temperature, (d-f) 350 °C treatment and (g-i) combustion.