ZnO nanostructures were synthesized by the decomposition of ZnC2O4 center dot 2H(2)O that was prepared using a precipitation reaction between Zn2+ and three different precipitating agents (H2C2O4, Na2C2O4, and (NH4)(2)C2O4). The ZnO powders prepared using H2C2O4 as the precipitating agent had the highest surface area and showed the highest photocatalytic degradation efficiency of methylene blue and reactive orange aqueous solutions. The cytotoxicities of the dye solutions after photocatalysis under blacklight illumination were also tested using L929 mouse fibroblast cells. The treated methylene blue solution showed a lower cytotoxicity than its untreated solution. However, this method was probably not effective with the reactive orange as an ionic dye because there was a repulsive force between the negative charges of the reactive orange and the cell membrane of L929 cells. (C) 2016 Elsevier B.V. All rights reserved.