Photocatalytic performance of Bi2VO5.5/Bi2O3 laminated composite films under simulated sunlight irradiation

Bi2VO5.5/Bi2O3 laminated composite thin films with each different layer numbers were prepared on fused silica substrates by chemical solution deposition method with a following rapid annealing process. The phase structure, surface morphology, absorption spectrum and photocatalytic degradation characteristics of the thin films were characterized. X-ray diffraction patterns show that the laminated thin films are consist of polycrystalline Bi2O3 films and c-axis oriented Bi2VO5.5 films. With the increasing of the number of Bi2VO5.5 layers as well as the decrease of the number of Bi2O3 layers, the absorption spectrum of the composite film shifted towards the longer wavelength side. Meanwhile, under simulated sunlight, the degradation ability of the thin films to Methylene Blue gradually increased and reach a maximum at appropriate layer ratio. The optimal laminated composite thin film with the highest degradation rate are 6 layers of Bi2VO5.5 films superposed upon 2 layers of Bi2O3 films. The degradation rate decreases only by 2% after the 5 cycles of degradation. The reasons for the enhancement of the photocatalytic properties of the thin film can be attribute to the laminated structure and the matching energy level, which are benefit for the transferring of photo-induced electrons. According to fitting results of the band gap and the XPS valence band spectrum, the mechanism of photocatalytic degradation of MB for Bi2VO5.5/Bi2O3 laminated composite films irradiation are analyzed. Under simulated sunlight irradiation, the photogenerated electrons on the conduction band of the Bi2O3 can transfer to the conduction band of Bi2VO5.5. Meanwhile, the photogenerated holes on the valence band of Bi2VO5.5 can also be migrated to the valence band of Bi2O3, thus suppress the recombination, prolong the lifetime of photo-generated carriers, and increase the photocatalytic degradation efficiency.