SrTiO3-graphene nanocomposites were prepared via photocatalytic reduction of graphene oxide by UV light-irradiated SrTiO3 nanoparticles. Fourier transformed infrared spectroscopy analysis indicates that graphene oxide is reduced into graphene. Transmission electron microscope observation shows that SrTiO3 nanoparticles are well assembled onto graphene sheets. The photocatalytic activity of as-prepared SrTiO3-graphene composites was evaluated by the degradation of acid orange 7 (AO7) under a 254-nm UV irradiation, revealing that the composites exhibit significantly enhanced photocatalytic activity compared to the bare SrTiO3 nanoparticles. This can be explained by the fact that photogenerated electrons are captured by graphene, leading to an increased separation and availability of electrons and holes for the photocatalytic reaction. Hydroxyl (·OH) radicals were detected by the photoluminescence technique using terephthalic acid as a probe molecule and were found to be produced over the irradiated SrTiO3 nanoparticles and SrTiO3-graphene composites; especially, an enhanced yield is observed for the latter. The influence of ethanol, KI, and N2 on the photocatalytic efficiency was also investigated. Based on the experimental results, ·OH, h+, and H2O2 are suggested to be the main active species in the photocatalytic degradation of AO7 by SrTiO3-graphene composites.PACS61.46. + w; 78.67.Bf; 78.66.Sq
Z-scheme Ag2S/BiFeO3 heterojunction composites were successfully prepared through a precipitation method. The morphology and microstructure characterization demonstrate that Ag2S nanoparticles (30–50 nm) are well-decorated on the surfaces of polyhedral BiFeO3 particles (500–800 nm) to form Ag2S/BiFeO3 heterojunctions. The photocatalytic and photo-Fenton catalytic activities of the as-derived Ag2S/BiFeO3 heterojunction composites were evaluated by the degradation of methyl orange (MO) under visible-light irradiation. The photocatalytic result indicates that the Ag2S/BiFeO3 composites exhibit much improved photocatalytic activities when compared with bare Ag2S and BiFeO3. The optimum composite sample was observed to be 15% Ag2S/BiFeO3 with an Ag2S mass fraction of 15%. Furthermore, the addition of H2O2 can further enhance the dye degradation efficiency, which is due to the synergistic effects of photo- and Fenton catalysis. The results of photoelectrochemical and photoluminescence measurements suggest a greater separation of the photoexcited electron/hole pairs in the Ag2S/BiFeO3 composites. According to the active species trapping experiments, the photocatalytic and photo-Fenton catalytic mechanisms of the Ag2S/BiFeO3 composites were proposed and discussed.
In this work, oxygen vacancies were introduced onto the surface of BiFeO3 nanoparticles by NaBH4 reduction method to yield oxygen-deficient BiFeO3−x samples. Comprehensive analysis on the basis of high-resolution transmission electron microscopy (HRTEM) observation and X-ray photoelectron spectrum (XPS) confirms the existence of surface oxygen vacancies on the BiFeO3−x nanoparticles. The photocatalytic activity of as-prepared BiFeO3−x samples was evaluated by the decolorization of rhodamine B (RhB) under simulated sunlight irradiation. The experimental results indicate that the photocatalytic activity of samples is highly related to the NaBH4 reduction time, and the BiFeO3−x sample reduced for 40 min exhibits the highest photocatalytic efficiency, which is much higher than that of pristine BiFeO3 nanoparticles. This can be explained by the fact that the surface oxygen vacancies act as photoinduced charges acceptors and adsorption sites suppress the recombination of photogenerated charges, leading to an increasing availability of photogenerated electrons and holes for photocatalytic reaction. In addition, the obtained BiFeO3−x sample exhibits good photocatalytic reusability.
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