fig2

Figure 2. (A-C) SEM images of (A) CNT, (B) O-CNT, and (C) SG-CNT; (D-F) TEM images of (D) CNT, (E) O-CNT, and (F) SG-CNT; and (G) schematics of oxygen functional groups in CNT (left), O-CNT (middle), and SG-CNT (right).