SEM images of SiO2/C composite (Fig. 4) show sponge type microstructure composed of many pores, whose average pore diameter size is about 2 nm. This confirms that SiO2/C is composed by a silica network intercrossed with a carbonaceous network and both are independent and self-supported. The apparent particle size is 200–300 nm as reported in the literature (Lv et al., 2013).