In this work, CoAl2O4 pigments successfully were prepared via thermal decomposition method by employing green tea extract as precipitating agent and capping agent. The effects of preparation parameters such as: calcination temperature, surfactants, solvent and pH were investigated to reach the optimum conditions. The biosynthesized cobalt alumina spinel was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray energy dispersive spectroscopy (EDS), ultraviolet visible (UV-Vis) spectroscopy and vibrating sample magnetometer (VSM). The photocatalytic activity of CoAl2O4 nanostructures was compared by degradation of methylene blue in aqueous solution under UV light irradiation. Also the hydrogen storage capacity of CoAl2O4 was measured by chronopotentiometry method. The capacity of CoAl2O4 in 1 mA current and 20 cycles obtained 1100 mh/g. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.