Unraveling the structural and composition properties associated with the enhancement of the photocatalytic activity under visible light of Ag2O/BiFeO3-Ag synthesized by microwave-assisted hydrothermal method

BiFeO3 is synthesized for the first time via a microwave-assisted hydrothermal method along with a thermal treatment to incorporate Ag nanoparticles (Ag2O/BiFeO3-Ag). SEM and TEM micrographs demonstrate that Ag nanoparticles are homogenously dispersed on BiFeO3, while XRD reveals a reduction in size of the average crystallite size when Ag is impregnated on the material in comparison with the pristine BiFeO3 phase. Raman analysis indicates the substitution of Bi by Ag atoms into the lattice, while XPS analysis discloses the presence of Ag-0 and Ag2O in the catalyst. Ag2O/BiFeO3-Ag exhibits superior photocatalytic activity compared with BiFeO(3 )based on the degradation of 10.4 mu mol L-1 Rhodamine B (RhB) under simulated visible light irradiation. The enhancement on the photocatalytic performance was attributed to a surface plasmon resonance effect efficiently transferring photogenerated electrons from BiFeO3 to Ag-0, and photogenerated holes from a heterojunction formed between BiFeO3 and Ag2O. An energy diagram of the system is established based on the band-gap, conduction and valence bands of BiFeO3 and Ag2O. The stability of the Ag2O/BiFeO3-Ag catalyst leading to RhB-photodegradation was monitored during six consecutive cycles. Experiments conducted with scavengers (isopropyl alcohol, ascorbic acid and coumarin) reveal hydroxyl radical formation as the primary oxidant species of RhB.