Fig. 1

Structure characterizations of NCNFs by electron microscopies. a, b SEM and c TEM images of NCNF-650. HRTEM images of NCNF-650 (d), NCNF-950 (e), and NCNF-1100 (f). g–j Images of element mapping of C, N, and O for NCNF-650. Scale bars: 2 µm (a); 200 nm (b); 50 nm (c); 5 nm (d–f); 100 nm (g)