Fig. 2 shows the XRD patterns of the as-prepared ZnO-A samples. All the diffraction peaks of the prepared ZnO-A products can be well indexed to the standard card of hexagonal wurtzite ZnO structures (JCPDS No. 01-1136-1) as shown in Fig. 2. No other characteristic diffraction peaks or impurities were detected, which implies that pure ZnO was formed.