Hierarchical δ -Bi 2 O 3 /Bi 2 O 2 CO 3 composite microspheres: phase transformation fabrication, characterization and high photocatalytic performance

Novel hierarchical δ-Bi2O3/Bi2O2CO3 composite microspheres were fabricated via phase transformation under solvothermal condition. The obtained products were characterized by N2 physical adsorption, powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy, and photoluminescence emission spectroscopy. The results showed that solvothermal temperatures exerted a large influence on the phase composition and morphologic structure. Low solvothermal temperatures (120, 140 °C) produced the δ-Bi2O3 phase. When the temperature increased to 160 °C, δ-Bi2O3 began to transform to Bi2O2CO3 phase, and cabbage-like δ-Bi2O3/Bi2O2CO3 composite microspheres were produced. At 180 °C, δ-Bi2O3 totally transformed into Bi2O2CO3. Under xenon lamp irradiation, the degradation rate constant of rhodamine B over δ-Bi2O3/Bi2O2CO3 was 6.7 and 3.1 times of the δ-Bi2O3 and Bi2O2CO3, respectively. The high photocatalytic performance of the δ-Bi2O3/Bi2O2CO3 composite microspheres could be attributed to their large specific surface area, rich mesopores structures, and efficient light-harvesting capability. Moreover, the produced δ-Bi2O3/Bi2O2CO3 heterojunction can effectively restrain the recombination of photogenerated electrons and holes, which largely improved the photocatalytic performances.