ZnO nanoparticles were prepared by hydrothermal method from the source materials of zinc chloride and ammonium hydroxide. Precursor solution pH was varied to 7,9,11 and 13 by the addition of ammonium solution and the solution was hydrothermally treated at 150 degrees C for 3 h. Further prepared samples were annealed at 400 degrees C for 3 h. X-ray diffraction technique was employed to study the structure and crystalline nature of synthesized nanoparticles. Diffuse Reflectance Spectroscopy studies revealed that optical band gap of ZnO is slightly varied due to the effect of size of the particle. Field emission scanning electron microscope images showed that the prepared ZnO nanoparticles acquired spindle like nanorods, hexagonal disk, porous nanorods and nanoflower structures due to the effect of pH of the precursor solution. Photocatlytic activity of the prepared ZnO nanoparticles was evaluated for Rhodamine B (RhB) dye which showed 94% of degradation and good stability for five cycles. (C) 2016 Elsevier B.V. All rights reserved.