Engineering cross-linking by coal-based graphene quantum dots toward tough, flexible, and hydrophobic electrospun carbon nanofiber fabrics

Polyacrylonitrile-derived electrospun carbon nanofiber fabrics (ECNFs) are believed to have great potentials in many aspects. However, the un-optimized/limited strength and flexibility considerably hinder their practical applications. We find that the tensile strength, Young's modulus, and flexibility of the ECNFs can be significantly improved by the simple addition of coal-based graphene quantum dots (CGQDs) to a spinning solution. The Young's modulus of the CGQD-added ECNF is enhanced by more than 7 times than that of pure polyacrylonitrile-derived one. However, the improvement is barely observed when oxygen-bearing functional groups on the CGQDs are removed by chemical reduction. Characterized by scanning electron microscopy; X-ray diffraction; and Raman, Fourier-transform infrared, and X-ray photoelectron spectroscopies, we propose that the CGQDs act as cross-linking agents because of their abundant oxygen-bearing functional groups and good chemical reactivity, resulting in the formation of dense, strong, and flexible carbon skeleton. Moreover, the hydrophobicity of the ECNFs is also gradually improved with the increase in CGQD content. This is ascribed to the increase in diameter of the carbon nanofibers. The ECNF prepared under the optimized condition shows a water contact angle of approximately 142°. Thus, it can be used for efficient and endurable gravity-driven oil/water separation.