Synthesis of mesoporous flower-like iron oxide nanostructures from iron alkoxide precursor and their application in the catalytic reduction of 4-nitrophenol

Abstract

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 Fe3O4, γ-Fe2O3, 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 N2 adsorption–desorption analysis showed that the surface area of the as-synthesized mesoporous flower-like FeOOH, Fe3O4, γ-Fe2O3 and α-Fe nanostructures were 232 m2g−1, 128 m2g−1, 80 m2g−1, and 80 m2g−1, respectively. The nanostructures' porosity and morphology, due to the replacement of bulky glycolate molecules with smaller water molecules, were also investigated. The as-prepared nanostructures' catalytic activity was examined in the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 as the reducing agent. The kinetic study was shown all as-prepared nanostructures exhibited high catalytic activity with pseudo-first-order kinetic constants of 0.0099, 0.0054, 0.0038, and 0.0027 s−1 for mesoporous flower-like FeOOH, α-Fe, γ-Fe2O3, and Fe3O4 nanostructure, respectively. Mesoporous flower-like FeOOH, due to having more rate constant rather than other catalysts, was separated easily by centrifugation and was recycled 4 times with an increased reaction time to 7 min in the final cycle. We deduced that specific surface area, morphology, and crystal structure played an essential role in reducing 4-NP to 4-AP reaction.