In addition to photocatalytic activity, the stability of the photocatalyst is another important issue for its practical application.The catalytic test using the ZnO/rGO composite to investigate the recyclability and stability in repeated Orange II degradation experiments. After each reaction, the catalyst was collected by centrifugation, washed with water and subsequently dried at 60 ◦ C for 12 h before its reuse. As shown in Fig. 12a, 95% of Orange II was photodegraded in 2 h after the first cycle. After 15 reuses, the photocatalytic activity only slightly decreased and ca. 89% of the dye were bleached after the same reaction time. The slight decrease of activity demonstrates that the photocatalyst has a high repeatability. A SEM image of the recycled catalyst is shown in Fig. 12b and obviously indicates that no aggregation of ZnO rods occurred during photocatalysis