there exists only an evident broadening bulge in
a range of 20–301, indicating that the carbon spheres are in a form of agraphitic carbon. Type II
adsorption isotherm was obtained through N2 adsorption as shown in Fig. 3c, implying the non-
porous nature of carbon spheres. The BET specific surface area of the carbon spheres was calculated
to be about 15 m2 .