Interfacial charge transfer effects of α-Fe2O3/Cu2O heterojunction and enhancement mechanism of its photocatalytic oxidation

Abstract

In order to construct Cu2O based heterostructures with high efficiency of interfacial charge transfer and clarify the enhancing mechanism of its photocatalytic performance for degrading antibiotics, and reveal the characteristics of band reconstruction and the photocatalytic reaction path, the α-Fe2O3/Cu2O heterojunction was established based on hydrothermal method. The crystal plane structure, morphological state, photoelectric conversion properties and photocatalytic degradation kinetics of α-Fe2O3/Cu2O heterojunction were revealed by XRD, XPS, UV-Vis, BET, SEM, TEM and RSM, and the reconstruction principles of bandgap formations of heterojunction were analyzed by the density function theory. The reaction intermediates of levofloxacin were distinguished with HPLC-MS/Ms, and the reactive sites and photocatalytic oxidation paths of levofloxacin were clarified from the frontier electron density calculation. It turned out that the constructed α-Fe2O3/Cu2O heterojunction emerged high energy (111) preferred crystal plane orientation and significantly enhanced the specific surface area and visible spectral excitation efficiency. The micromorphologies of Cu2O, M1-Cu2O, M2-Cu2O and M3-Cu2O crystals were cube, irregular polyhedron and approximate sphere, respectively. The introduction of Fe 3d hybrid orbital in α-Fe2O3/Cu2O heterojunction widened the band gap of Cu2O microcrystals, resulting in the migration of spectral absorption edging to high energy level and causing blueshift. Photogenerated superoxide radicals and hydroxyl radicals were the dominant active species for photocatalytic oxidation of levofloxacin. The removal rate of levofloxacin by α-Fe2O3/Cu2O heterojunction could still reach more than 70% after eight cycles and show high material durability. The ring opening reaction process and decarboxylic reaction of quinolone group and piperazine side chain were the main pathways for photocatalytic oxidation of levofloxacin. This study systematically revealed the interfacial charge transfer characteristics and photocatalytic reaction mechanism of α-Fe2O3/Cu2O heterojunction.