Heterojunction of n-type Sr2TiO4 with p-type Bi5O7I with enhanced photocatalytic activity under irradiation of simulated sunlight

Abstract In this study, n-type Sr 2 TiO 4 and p-type Bi 5 O 7 I, which have identical layered structures, were coupled and loaded with Ag to form a heterojunction photocatalyst. The synthesized Ag-loaded Bi 5 O 7 I/Sr 2 TiO 4 heterojunction composite showed higher photocatalytic activity toward the degradation of methyl orange (MO) dye under irradiation of simulated sunlight than did a bare Sr 2 TiO 4 sample. X-ray diffraction, UV–vis diffuse reflectance spectroscopy, and scanning electron microscopy analyses revealed that under alkaline conditions, bismuth ions penetrate into the Bi 5 O 7 I/Sr 2 TiO 4 heterojunction and replace titanium ions owing to pH changes and the identical layered structures of Bi 5 O 7 I and Sr 2 TiO 4 , thus causing a reduction in the band-gap energies. Loading of Ag nanoparticles as a co-catalyst onto the Sr 2 TiO 4 surface did not yield a p - n heterojunction or cause any improvement in the photocatalytic degradation activity. However, owing to the p - n junction, the internal built-in electric field within the space charge region at the Bi 5 O 7 I/Sr 2 TiO 4 interface, and the electron-capture ability of Ag and localized surface plasmon resonance effect, the photo-excited electrons and holes separated and migrated effectively and the photocatalytic activity increased significantly. These results reveal that the Ag-loaded Bi 5 O 7 I/Sr 2 TiO 4 heterojunction can serve as a promising photocatalyst.