Electrospun polyacrylonitrile nanofibers as graphene oxide quantum dot precursors with improved photoluminescent properties

Graphene oxide quantum dots were synthesized from carbonization, ultrasonic peeling, and oxidation of electrospun polyacrylonitrile (PAN) nanofibers. By energy scattering X-ray spectroscopy, a strong increase/decrease in the carbon/oxygen concentration was found during the stabilization stage and during carbonization, which resulted in the formation of carbon-enrich nanofibers. FTIR spectroscopy and Raman scattering results of electrospun PAN nanofibers demonstrated changes in structural and optical properties during the carbonization process. By X-ray diffraction was found that after the carbonization and oxidation processes of the PAN nanofibers, they showed a hexagonal graphene structure with two main crystallographic directions (002) and (101). The formation of graphene oxide quantum dots resulting from the ultrasonic exfoliation process was demonstrated by TEM with nanocrystal sizes of 10.98 nm, which were obtained after the ultrasonic exfoliation of carbonized/graphitized PAN nanofibers in highly oxidizing solvents. The absorbance in the UV spectral region showed a band at approximately 265 nm, which was assigned to the π→π* excitation of the π bonds of aromatic C[dbnd]C, and another band at 325 nm that was assigned to the n→π* transition of C[dbnd]O bonds, showing the presence of graphene oxide quantum dots (GOQDs). By Raman scattering is found that the synthesized GOQDs have a density of 22.6 ppm of crystalline defects, which indicates a higher order in their crystal lattices. The fluorescence and photoluminescence of the graphene oxide quantum dots showed radiative bands associated with possible crystalline defects in the graphene oxide quantum dot network, the radiative emissions of which correspond to the blue spectral region. The preparation protocol is simple and the yield of graphene oxide quantum dots is high.