Fillers (Acetylene black (AB), Carbon black (CB), Carbon
brush (CBh) and Graphite (GT)) were dried at 100 o
C in vacuum
oven for 3 h to remove the moisture content. It was mixed with
saturated acid consisting of sulfuric acid and concentrated nitric
acid in a volume ratio of 3:1 for 10–15 h. Nitric acid serves as an
oxidizer and sulfuric acid as an intercalant. The mixture was
stirred from time to time to get the uniform intercalation of each
flake. The mixture was carefully washed and filtrated with water
until the pH level of solution reached 7 (neutral). After washing,
acid-treated flakes were dried at temperature 100 o
C in a vacuum
oven for 5 h.