Sunflower seed hull was
first washed with distilled water to get
rid of the dust and other impurities adsorbed on the surface and
then dried at 100 C. Two ZnCl2 solutions were prepared by
dissolving 40 or 60 g ZnCl2 in 100 mL distilled water. To each of
them, 20 g SSH was added, yielding the impregnation ratio
between ZnCl2 and SSH of 2 or 3, respectively. The complete
impregnation of SSH in ZnCl2 solution was realized by ultrasonic
vibration for 2 h and then statically soaking for another 24 h. The
mixtures were dried in an oven
first at 80 C for 12 h and then at
120 C for 12 h, followed by hand-grinding into powders with an
agate mortar. The activations were performed in a horizontal tube
furnace at 550 C or 650 C for 1 h under protection of
flowing pure
argon (99.99%). The temperature was held at 400 C for half an hour
during heating before it reached the target temperature to get the
SSH precursor more sufficiently wetted by ZnCl2. The resultants
were washed with 0.1 M HCL, followed by distilled water until
neutrality. The
final carbon products were named as S-2-550, S-2-
650, S-3-550 and S-3-650, respectively, depending on the
impregnation ratio between ZnCl2 and SSH (denoted by the
middle number) and the activation temperature (denoted by the
end number) used to perform the activation.