Fig. 2 provides the TEM images of CNF-1, CNF-2 and CNF-3, which clearly shows that the CNF with a length in several micrometers and a width in 5-10 nm wide were successfully extracted from the DCSBs both with and without pre-treatment. Moreover, the width of CNF-2 and CNF-3 is much smaller than that of CNF-1 as shown in Fig. 2b and c. This can be attributable to the pre-treatment of DCSBs before TEMPO-oxidized. It can be concluded that the pre-treatment of cellulosic fiber is not essential in the process of the preparation of CNF, but it has great influence on the size of resultant CNF.