BiVO4 powders with hierarchical structures were prepared by the microwave hydrothermal method at different pHs, using Bi(NO3)3·5H2O and NH4VO3 as raw materials. The results show that, when the pH value of the precursor is 0.59, the as-prepared powders are monoclinic BiVO4 crystals with octahedron and decahedron morphologies. Spherical and polyhedral BiVO4 with particle sizes in the range of 2-4 μm can be prepared under the strong acid condition (pH = 0.70-1.21) and possess a mixed crystal consisting of tetragonal and monoclinic phases, whereas rodlike and dendritic BiVO4 with a pure monoclinic phase can be obtained within a very wide pH range (pH = 4.26-9.76). The phase transformation from tetragonal phase to monoclinic phase occurs at pH 3.65. At pH >9.76, the powders are the nonstoichiometric crystals between the mixed-phase BiVO4 and non-BiVO4. The photocatalytic efficiencies were evaluated by the degradation of Rhodamine B (RhB) under UV and simulated sunlight irradiation. The corresponding relationship among pH values of the precursor, crystalline phase, morphology, and photocatalytic performance of the powders was also discussed.

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The process, by which three kinds of bismuth ferrites (BiFeO 3 , Bi 25 FeO 40 , and Bi 25 FeO 40 -BiFeO 3 ) were synthesized for 1 h through a microwave hydrothermal method by changing the KOH concentration and the temperature, is summarized in this article. The as-prepared bismuth ferrite powders were characterized by the X-ray diffraction, the field emission scanning electron microscopy, and the transmission electron microscope, and the band gaps, specific surface areas, photocatalytic and magnetic properties were explored as well. The results showed that the degradation degree of methyl orange using BiFeO 3 , Bi 25 FeO 40 , and Bi 25 FeO 40 -BiFeO 3 as catalyst were 35%, 52%, and 90% at 2 h, respectively, and the magnetizations of the three powders were 0.07, 3.17, and 0.55 emu/g, respectively. This indicated that the porous cubic Bi 25 FeO 40 -BiFeO 3 powder has the best photocatalytic property of the three, making it useful as a new type of photocatalytic material which can be easily recycled by magnetic separation.

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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.