Characterization of the ZnO samples obtained at pH of the reaction solution of 13.8: (a) XRD pattern and (b) SEM imageSEM images of ZnO samples obtained at different pH values of the reaction solutions: (a) 13.1, (b) 13.6, (c) 13.7Illustration of a possible growth mechanism of the ZnO microflowersPhotocatalytic performance of ZnO based photocatalysts for degrading MB; the ZnO nanocrystals were obtained at different pH values of the reaction solutions: (a) 13.1, (b) 13.6, (c) 13.7, (d) 13.8