Iron oxide nanoparticles of different shape were synthesized via an ion-mediated hydrothermal route. The addition of Zn2+ and Al3+ to the reaction system is no doubt the reason for the formation of hematite with cubic and disc structures, respectively. The growth mechanism of iron oxides is proposed. The morphology of the obtained nanostructures was analyzed by SEM and HR-TEM. The phase identification was performed by XRD and FTIR spectroscopy. Nanopowders were characterized by optical and zeta potential PZ measurements. The overall density of hydroxyl groups depends on the crystal structure and crystal faces. Placing oxides in the Rhodamine B RhB solution reduces the potential value PZ. The observed changes are the most pronounced for discs (Delta PZ = 16.2 mV) and the least pronounced for cubes (Delta PZ = 5.5 mV). A significant degree of adsorption of the dye on the surface of the discs, which confirms the presence of a significant number of hydroxyl groups responsible for surface activity. The photocatalytic activity of the obtained nanostructures investigated by photodecomposing RhB can be improved by applying H2O2 as an electron trap. Cyclic photodegradation experiments show that iron oxides with variously exposed planes can be used multiple times without losing their photocatalytic properties. Discs exhibited the most desirable photocatalytic behavior. Based on the performed addition of hydrogen peroxide, it seems that the shape of the particles affects the diffusion of H2O2 at the surface.