Photoelectric activity of a Bi₂O₃/Bi₂WO₆-xF₂x heterojunction prepared by a simple one-step microwave hydrothermal method.

Abstract

NH4F/Bi2WO6 powders were prepared by a simple one-step microwave hydrothermal method at different reaction temperatures, using Bi(NO3)3·5H2O and Na2WO4·2H2O as raw materials and NH4F as an additive agent. Their photoelectric activities were also investigated via the degradation of Rhodamine B (RhB). The results indicate that when the reaction temperature increases to 220 and 240 °C, the orthorhombic Bi2WO6 phase with space group Pca21 and cubic Bi2O3 phase with space group Pn3̅m appear. Raman spectroscopy, SEM, TEM, and XPS results also confirm the existence of a Bi2O3/Bi2WO6-xF2x heterojunction at higher temperature. Greater than 95% photodegradation of RhB under the exposure of simulated sunlight is achieved within 90 min with the Bi2O3/Bi2WO6-xF2x heterojunction prepared at 220 °C, which displays remarkably promoted photocatalytic activities. The electrochemical impedance spectra and photocurrent results also prove that efficient charge separation and better electron transport properties are achieved by the Bi2O3/Bi2WO6-xF2x heterojunction film prepared at 220 °C. In addition, the mechanism of the crystal growth and formation of the p-n junction between p-type Bi2O3 and n-type Bi2WO6 were also discussed.