2.2 Preparation of the SCG
The SCG was dried in a 105 °C oven for 24 h, and then the dried SCG was
heat treated in a tube furnace under nitrogen and air atmosphere at 240
°C for 1.5 h with the heating speed of 5 °C·min-1,
respectively. The obtained SCG were named as NSCG and ASCG corresponding
to the heat treatment atmosphere of nitrogen and air separately.