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 Ag⁰ and Ag₂O in the catalyst. Ag₂O/BiFeO₃-Ag exhibits superior photocatalytic activity compared with BiFeO₃ based on the degradation of 10.4 µmol 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 Ag⁰, 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.