The study focuses on establishing the suitable shape of ZnO nanoobjects by initiating oriented attachment (OA) process for inexpensive and eco-friendly photocatalytic decomposition of dyes. A special design of a chemical experiment was used to initiate the formation of ZnO nanosheets and nanoflowers by implementing the OA process in different conditions. The OA process taking place during the formation of ZnO nanoobjects was analysed using a complex of methods, including XRD, WPPM, FT-IR, SEM, TEM, BET, XPS and Raman spectroscopy. Special attention was paid to a specially designed computational experiment, in which the OA process was considered from the point of view of the interactions between crystallite surfaces and between a crystallite surface and ions in the reaction medium. It was established that changing the ratio of facets by regulating the OA process can significantly improve photocatalytic activity by influencing the formation processes of the activated complex and reactive oxygen species on different facets. The best photocatalytic activity was achieved for ZnO nanosheets (97 % after 90 min of visible light irradiation). ZnO nanoobjects obtained in this study were found to be non-toxic.