The detailed process of the graphene sheet fabrication was
described in our previous work [40]. In briefly, GIC (a conventional
expanded graphite based on H2SO4) was took into the muffle
furnace, and kept the temperature about 900 C for 60 s, worm-like
graphite was obtained, then the worm-like graphite was dispersed
in ethanol for 5 h (h) by ultrasonic exfoliation, and we can get the
graphite nanoflake after the filtration (the filter paper with 45 mm
pore size) and vacuum drying process. Then, the graphite nanoflake
was dispersed into the oleum for 5 h to weaken the graphite
interlayer force, next we diluted the oleum by ice water and filtrated
the solution, subsequently we shifted the treated graphite
nanoflake in the H2O2 aqueous solution about 2 h with 5e10 wt%,
again by filtration and vacuum drying treatment, then the graphite
nanoflake were transferred in ethylene glycol solution for layers
insertion, after filtration, then the intercalation graphite nanoflake
were brought into the muffle furnace at 600 C about 120 min
(mins) for the second thermal expansion. After the thermal
expansion, the graphite nanoflake were put in a furnace with gas
(H2:N2 ¼ 5:95) for reduction about 2 h at 920 C. After the thermal
reduction procedure, the reduced graphite nanoflake were shifted
into the N-Methyl pyrrolidone (NMP) solution by ultrasonic exfoliation
about 12 h with mechanical stirring about 200 rounds per
minute, finally, the graphene sheet powder can be realized after the
filtration and vacuum drying process. All the filter papers were
used in this part with 40 mm pores.