Multifunctional non-woven fabrics of interfused graphene fibres

Abstract

Carbon-based fibres hold promise for preparing multifunctional fabrics with electrical conductivity, thermal conductivity, permeability, flexibility and lightweight. However, these fabrics are of limited performance mainly because of the weak interaction between fibres. Here we report non-woven graphene fibre fabrics composed of randomly oriented and interfused graphene fibres with strong interfibre bonding. The all-graphene fabrics obtained through a wet-fusing assembly approach are porous and lightweight, showing high in-plane electrical conductivity up to ∼2.8 × 10⁴ S m^-1 and prominent thermal conductivity of ∼301.5 W m^-1 K^-1. Given the low density (0.22 g cm^-3), their specific electrical and thermal conductivities set new records for carbon-based papers/fabrics and even surpass those of individual graphene fibres. The as-prepared fabrics are further used as ultrafast responding electrothermal heaters and durable oil-adsorbing felts, demonstrating their great potential as high-performance and multifunctional fabrics in real-world applications.

Figure 1. Fabrication of GFFs via wet-fusing assembly.

(a) Continuous wet-spinning of GO staple fibres. (b) First drying of the as-spun GO fibres. (c) Re-dispersion of dried GO fibres in the mixture of H₂O and ethanol. (d) Wet-fusing assembly of GO fibres after filtration of the re-dispersed fibres. (e) A free-standing GOFF with brownish colour after drying. (f) A grey GFF after chemical reduction or thermal annealing with randomly oriented and interfused graphene fibres.

Figure 2. Mechanism of wet-fusing assembly and morphology of the as-prepared GOFFs and GFFs.

Micrographs of the re-dispersed GO fibres in a H₂O/ethanol mixture under (a) OM and (b) polarized-light optical microscopy (POM). (c) Wet-fusing of GO fibres recorded under OM and POM. Photographs of (d) a piece of thin GOFF (thickness 0.05 mm) held towards an light-emitting diode lamp, showing its porous structure and light brown colour, (e) a thick and dark brown GOFF (thickness 3 mm), (f) a thermally annealed GFF with porous feature for light and gas penetration, (g) GOFF (left) and GFF (right), indicating the slight shrinkage of lateral dimension and colour change, (h) a strip of GFF coiled around a glass rod and (i) four GFFs of different sizes and thicknesses. Scale bars, 500 μm (a,b), 150 μm (c) and 20 mm (d,f,h,i).

Figure 3. Characterization of GOFFs and GFFs.

(a) XPS spectra of the as-prepared GOFF, N₂H₄ reduced GFF and thermally annealed GFFs at 1,000, 2,000 and 3,000 °C. (b) X-ray diffraction patterns of GOFF, GFF-N₂H₄ and annealed GFFs. (c) Raman spectra of GOFF, GFF-N₂H₄ and annealed GFFs. (d) Variation of I_D/I_G in different samples. Error bars represent the s.d. of I_D/I_G for at least five measurements.

Figure 4. Electrical and thermal conductivities of GFFs.

(a) In-plane electrical and thermal conductivities of 130GFFs and 200GFFs after N₂H₄ reduction and thermal annealing at various temperatures. Error bars represent the s.d. of the conductivities of different GFFs. (b) Comparison of specific electrical conductivity (σ/ρ) and specific thermal conductivity (κ/ρ) of GFFs with selected 2D assemblies of carbon nanotube (CNT) or graphene. The units for σ, κ and ρ are S m⁻¹, W m⁻¹ K⁻¹ and g cm⁻³, respectively.

Figure 5. Microstructure of GOFFs and GFFs.

SEM images of (a) 130GOFF, (b) 130GFF-3,000 and (c) 200GFF-3,000. (d–f) Magnified images of a–c. SEM images highlighting the (g) X-type junction, (h) Y-type junction and (i) a well-preserved junction at the broken end of 130GFF-3,000. Insets in g,h depict the arrangement of graphene sheets within X-type junction and Y-type junction. Scale bars, 500 μm (a–c), 100 μm (d,e,f,i) and 50 μm (g,h).

Figure 6. Bending and stretching behaviour of GFFs.

Electrical-resistance variation of a GFF (a) at bending radius up to 1.5 mm, (b) under cyclic bending for 1,000 times and (c) performing 10 folding-releasing cycles. R₀ is the initial resistance of the GFF and ΔR is the resistance change in different states. Inset in a shows the definition of bending radius. Photos in b show photographs of a GFF in straight and bent states, respectively. Photos in c show a GFF being folded by a pair of tweezers and released. (d) Typical stress–strain curves of 130GFF-3,000 and 200GFF-3,000. Inset emphasizes details of the stress–strain curve of 130GFF-3,000. (e) Diagram of the fracture process under tensile stress. SEM images showing crack propagation through the thickness of the GFF in (f) regime II and (g) regime III. Scale bars, (f) and (g) 100 μm.

Figure 7. Electrothermal performance of GFFs.

(a) Diagram of experimental set-up for GFF electrothermal heaters. (b) Temperature profiles of a strip of GFF (4 × 2 cm²) at different applied voltages. (c) Peak values of heating-up and cooling-down rates and the corresponding saturated temperatures as a function of input electrical power density. (d) Frequency-dependent responses of a thinner GFF strip (20 × 1.5 mm²) at 0.05 and 1 Hz, with applied triangular wave and pulsed squared wave from 0 to 3 V. (e) Top: saturated temperature of a GFF heater at various voltages in flat state, 180° curved state and after bending for 100 times. Bottom: infrared pictures of the GFF heater in flat and 180° bent state. (f) Top left: temperature evolution across the central line of a water droplet with respect to time. Top right: photos indicating the concerned region from p1 to p2, and showing the evaporation of the water droplet. Bottom: infrared pictures following the droplet evaporation process.

Figure 8. Oil uptake behaviour of the GFF.

(a) Adsorption capacities of GFF for various organic liquids in term of its weight gain. (b) Photos showing violent agitation of a GFF in water, and the GFF remains intact after agitation. (c) Mild agitation of a graphene aerogel in water makes the aerogel broken into pieces. (d) Photograph of a GFF adsorbing pump oil with relatively high viscosity. (e) Fast adsorption of heptane within 1 s. The dashed line indicates the frontline of adsorbed heptane. (f) Recyclability of the GFF adsorbing felt. Combustion was applied to regenerate the GFF with adsorbate of heptane. (g) The appearance, flexibility and microstructure of GFF are not changed after 20 adsorbing-burning cycles. Scale bar, 50 μm.