Designing, Preparation, And Photocatalytic Performance Of Novel Bismuth Semiconductor Nanocomposites

Since Titania was found to be an effectual photocatalyst by Prof. Fujishima at 1967, much more semiconductors have been applied in the region of the photocatalysis which also has been an important method to explore the character of carriers in semiconductors.Among these semiconductors, bismuth semiconductor has been widely studied, which is attributed to its visible-light responsibility, photostability, non-toxicity and eco-friendly. However, the problems like relatively higher recombination rates of electron–hole pairs, low utilization of visible light, low quantum efficiency have limited the application of bismuth semiconductor in industries.To deal with these problems of bismuth semiconductor in the photocatalysis, we designed and synthesized a series of BiVO₄, Bi₂WO₆ and Bi₂O₃ nanoparticles; improved the utilization of visible light and quantum efficiency, and lowed the recombination rate of electron–hole pairs mainly through compositing with another semiconductor or/and doping with non-metal ions; explored the separation and transfer mechanism of electron–hole pairs. The main contents and results are listed below:1. BiVO₄/Bi₂WO₆ composite photocatalysts with virus-like structures, pure BiVO₄ and Bi₂WO₆ nanoparticles were prepared through a simple solvothermal synthesis, without using any surfactant and template. The morphology formation and photocatalytic activity of the composites were explored as a function of the molar percentage of BiVO₄. The results showed that the BiVO₄/Bi₂WO₆ composite with a 50% molar percentage of BiVO₄ exhibited an excellent photocatalytic degradation of Rhodamine B, the degradation percentage can reach 91% within 60 min. A photo-induced interfacial charge transfer process for the separation and transport of the photogenerated electron–hole pairs has been demonstrated to play a critical role in the enhanced photocatalytic performance of the BiVO₄/Bi₂WO₆ composites.2. N-doped Bi₂O₃/g-C₃N₄ composite photocatalysts were prepared via a cost effective and eco-friendly ultrasonic dispersion method. It was shown that N-doped Bi₂O₃ nanoparticles were perfectly coated by thin g-C₃N₄ layers. Under visible-light irradiation, the optimum photocatalytic activity of the composite with 66.7 wt% of g-C₃N₄ is almost 4.6 times as high as that of pure g-C₃N₄ and 8.2 times of Bi₂O₃, and the RhB degradation efficiency can reach 94.4% in 15 min. The dramatically improved performance of the composite can be attributed to an enhancement of visible-light absorption and a synergistic effect of N-doped Bi₂O₃ nanoparticles and g-C₃N₄ coatings.3. Bi₂O₃/a-Fe₂O₃ composite photocatalysts with nanosphere structures were prepared through a simple one-step solvothermal synthesis, without using any surfactant and template. The morphology formation and photocatalytic activity of the composites were explored as a function of the molar percentage of a-Fe₂O₃. The results of TEM and SEM showed that the composite nanospheres were constructed with nanoparticles. The photocatalysis results showed that these composite nanospheres showed better photocatalysis activity than pure Bi₂O₃ and a-Fe₂O₃. Especially, Bi₂O₃/a-Fe₂O₃ composites with a 30% molar percentage of a-Fe₂O₃ exhibited an excellent photocatalytic degradation of RhB, whose degradation percentage reached 95% within 60 min. The dramatically improved performance of composites can be attributed to the enhanced visible-light absorption for the introduction of a-Fe₂O₃ and proper carrier transport structures between Bi₂O₃ and a-Fe₂O₃ nanoparticles like heterjunctions which improve the separation rate of photo-generated electron-hole pairs.