Comparison of Methods for Obtaining Graphene Structures

Three methods for obtaining graphene structures have been investigated: ultrasonic liquid-phase exfoliation (20–60 min), mechanical treatment in a vibratory cup mill, and Hammer’s method. An ultrasonic processing in a polyacrylonitrile/dimethylformamide solution led to a decrease in the particle size from 25.3 to 9.57 µm; the fraction of (5–20)-µm particles reached 68%, and the fraction of particles smaller than 1 µm was 2.69%. According to the atomic force microscopy data, the layer height reduced from 1.1 µm to 100 nm, and the fraction of large aggregates (>100 µm) decreased from 40 to 10%. Mechanical exfoliation with polyacrylonitrile increased the interlayer spacing to 3.609 Å in comparison with 3.373–3.376 Å, a value obtained by ultrasonic treatment. Hammer’s method demonstrated the best exfoliation (according to the X-ray diffraction and Raman spectroscopy data): I_D/I_G = 1, I_2D/I_G = 0.07, \({{I}_{{\left( {D + D'} \right)}}}\) /I_G = 0.12. Molecular modeling revealed a decrease in the specific energy of the system from 351.68 to 200.21 J/g with an increase in the C : O ratio from 38 : 1 to 111 : 1, reaching a minimum of 10.780 J/g for pure graphene.