Mesoporous flower-like FeOOH nanostructure was synthesized via hydrolysis of flower-like iron glycolate in aqueous methylamine solution and ethanol as a solvent with a molar ratio of 1: 350: 52: 44. Then mesoporous flower-like FeOOH nanostructure was transformed into mesoporous flower-like Fe 3 O 4, γ-Fe 2 O 3, and α-Fe nanostructures using reductive annealing under Ar or air atmosphere by adjusting the process factors such as reaction temperature and time. The nanostructures were studied and characterized by XRD, SEM, TEM, TGA, and BET analysis. The N 2 adsorption–desorption analysis showed that the surface area of the as-synthesized mesoporous flower-like FeOOH, Fe 3 O 4, γ-Fe 2 O 3 and α-Fe nanostructures were 232 m 2 g− 1, 128 m 2 g− 1, 80 m 2 g− 1, and 80 m 2 g− 1, respectively. The nanostructures' porosity and morphology, due to the replacement of bulky glycolate molecules with …