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. PACS 61.46. + 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 BiFeO_3−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 BiFeO_3−x nanoparticles. The photocatalytic activity of as-prepared BiFeO_3−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 BiFeO_3−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 BiFeO_3−x sample exhibits good photocatalytic reusability.

In this work, we have synthesized BiOCl nanoplates (diameter 140–220 nm, thickness 60–70 nm) via a co-precipitation method, and then created Bi nanoparticles (diameter 35–50 nm) on the surface of BiOCl nanoplates via a NaBH₄ reduction method. By varying the NaBH₄ concentration and reaction time, the evolution of Bi nanoparticles was systematically investigated. It is demonstrated that with increasing the NaBH₄ concentration (at a fixing reaction time of 30 min), BiOCl crystals are gradually reduced into Bi nanoparticles, and pure Bi nanoparticles are formed at 120 mM NaBH₄ solution treatment. At low-concentration NaBH₄ solutions (e.g., 10 and 30 mM), with increasing the reaction time, BiOCl crystals are partially reduced into Bi nanoparticles, and then the Bi nanoparticles return to form BiOCl crystals. At high-concentration NaBH₄ solutions (e.g., 120 mM), BiOCl crystals are reduced to Bi nanoparticles completely with a short reaction time, and further prolong the treatment time leads to the transformation of the Bi nanoparticles into a two-phase mixture of BiOCl and Bi₂O₃ nanowires. The photodegradation performances of the samples were investigated by choosing rhodamine B (RhB) as the model pollutant and using simulated sunlight as the light source. It is demonstrated that an enhanced photodegradation performance can be achieved for the created Bi@BiOCl hybrid composites with appropriate NaBH₄ treatment. The underlying photocatalytic mechanism was systematically investigated and discussed.

In this work, ternary all-solid-state Z-scheme g-C₃N₄/carbon nanotubes/Bi₂Fe₄O₉ (g-C₃N₄/CNT/BFO) composites with enhanced photocatalytic activity were prepared by a hydrothermal method. The morphology observation shows that ternary heterojunctions are formed in the g-C₃N₄/CNT/BFO composites. The photocatalytic activity of the samples for the degradation of acid orange 7 was investigated under simulated sunlight irradiation. It was found that the ternary composites exhibit remarkable enhanced photocatalytic activity when compared with bare BFO and g-C₃N₄/BFO composites. The effect of the CNT content on the photocatalytic performance of the ternary composites was investigated. The photocatalytic mechanism of g-C₃N₄/CNT/BFO was proposed according to the photoelectrochemical measurement, photoluminescence, active species trapping experiment and energy-band potential analysis. The results reveal that the introduction of CNT as an excellent solid electron mediator into the ternary composites can effectively accelerate the electron migration between BFO and g-C₃N₄. This charge transfer process results in highly-efficient separation of photogenerated charges, thus leading to greatly enhanced photocatalytic activity of g-C₃N₄/CNT/BFO composites. Furthermore, the g-C₃N₄/CNT/BFO composites also exhibit highly-efficient photo-Fenton-like catalysis property.

In this work, Ag3PO4 microparticles were decorated onto the surface of BiFeO3 microcuboids through a precipitation method to obtain p-Ag3PO4/n-BiFeO3 heterojunction composites. The composites were employed for the degradation of acid orange 7 (AO7) under visible-light irradiation. It is found that the composites exhibit much higher photocatalytic efficiency than bare BiFeO3. Meanwhile, the intrinsical visible-light-driven photocatalytic activity of Ag3PO4/BiFeO3 composites was further confirmed by the degradation of phenol. In addition, the photo-Fenton-like catalysis property of the composite was also evaluated. The photocurrent analysis indicates that the combination of BiFeO3 with Ag3PO4 leads to the inhibition of recombination of photoinduced electrons and holes. The obvious enhancement in the photocatalytic activity of the composite is mainly ascribed to the efficient photogenerated charge separation and interfacial charge migration caused by the formation of Ag3PO4/BiFeO3 p-n heterojunctions.