The representative SEM images of ZnO product are shown in Fig. 3. As can be seen, the ZnO product with sheet shape (Fig. 3a and b; c and d) was obtained when the mass ratios of NaOH to Zn(CH3COO)2 were 1:2 and 1:1. The thickness of the sheet was about 30 nm and the ZnO sheet was made up of small nanoparticles with well dispersion and close packed, which were clearly visible in Fig. 3b and d. ZnO rod (see Fig. 3e) was obtained when the mass ratio of NaOH to Zn(CH3COO)2 reached 2:1. The ZnO rod was hexagonal structure with smooth surface. Moreover, most of the hexagonal rod had a pointed end, and the surface of ZnO rod was very smooth which can be seen in Fig. 3f. The ZnO hexagonal rod with a diameter of 1–2 lm and a length of 10 lm in Fig. 3g was obtained when the mass ratio of NaOH to Zn(CH3COO)2 was continued increased to 4:1. The surface of these rod was not smooth, and was consisted of small particles about 20–30 nm and some pores, as can be clearly seen in Fig. 3h. The reason may be due to the etching of superfluous NaOH of the reaction system on the surface of ZnO rod.