Preparation Of Highly Efficient Bismuth-based Photocatalysts And Their Photocatalytic Activities

Environment pollution and energy shortage had been two serious problems in modern society need human beings to solve. The photocatalytic technology was gradually developed from the 70 s, which had an important application in the field of energy and environment with the utilization of solar energy. The photocatalytic technology had received interest, due to energy saving, mild condition and absence of secondary pollution for environmental pollutants. Over the past forty years, great efforts had been devoted to design highly efficient and stable photocatalysis systems. However, poor visible light absorption efficiency and high recombination rate of electron-hole were still challenges for the commercial scale application of photocatalysis technology.With a narrow band gap, bismuth-based photocatalysts showed a strong absorption in the visible region. In this study, three methods were used to improve the photoactivity of bismuth-based photocatalysts, including the increasing of photocatalyst surface area, nonstoichiometric introducing crystal defects and semiconductor combination. Main contents and conclusions were as follows:1. Based on the the similarity crystal structure between Bi2 Mo O6 and Bi OI, Bi2 Mo O6 photocatalyst with hollow structure was prepared by in-situ transformation method using Bi OI as self-sacrificing template. The phase and morphology analysis of intermediates were surveyed during Bi OI microspheres were transformed to hollow Bi2 Mo O6 at different reaction temperature and different time. The results showed that, the best conditions for preparing Bi2 Mo O6 hollow microspheres were 8 h at 120℃. The structure, morphology, specific surface area and optical properties of Bi2 Mo O6 hollow microspheres were studied. The Bi2 Mo O6 microsphere surface was relatively loose with a hollow structure inside, and the specific surface area was 61.0 m2/g. Methyl orange(MO) was selected as a pollutant model to evaluate the visible-light-driven photocatalytic activity of the prepared materials. As a result, MO was completely degraded by Bi2 Mo O6 hollow microspheres in 80 minutes. The photocatalytic activity of Bi2 Mo O6 hollow microspheres were obviously superior to Bi2 Mo O6 sheets and the intermediates obtained at different reaction time.2. Nonstoichiometric bismuth molybdates were prepared through a solvothermal method by changing the amounts of Na2 Mo O4·2H2O, meanwhile chosing Bi(NO3)3·5H2O as the bismuth resource and controlling its amount more than needed. The structure, morphology and optical properties of the as-obtained photocatalysts were studied. The results showed that Mo vacancies may be introduced to the nonstoichiometric bismuth molybdates, leading to smaller lattice spacing and O-Mo bond ratio decreasing. The visible light absorption was enhanced with the increase of bismuth/molybdenum molar ratio, while the recombination rate of electron-hole was reduced. Rhodamine B(Rh B) was selected as a pollutant model to evaluate the visible-light-driven photocatalytic activity of the prepared materials. As a result, the photocatalyst showed higher activity with the increase of bismuth/molybdenum ratio and then decreased. The as-obtained photocatalysts with the bismuth/molybdenum ratio 2.2 showed the best photocatalytic activities. In addition, the active species and the stability of the photocatalyst were studied.3. The suitable energy band between Bi VO4 and g-C3N4(Graphitic Carbon Nitride) were beneficial for the separation of light induced electron-hole pairs in the as-formed semiconductor combination. The g-C3N4 slice layer was introduced to the surface of Bi VO4 after stripping. g-C3N4/Bi VO4 composite photocatalysts with different g-C3N4 contents were prepared by in-situ synthesis method. The structure, morphology, specific surface area and optical properties of the as-obtained photocatalysts were studied. The results showed that g-C3N4 was successfully introduced to the surface of Bi VO4. g-C3N4/Bi VO4 composite photocatalysts showed strong absorptions in the visible region. Meanwhile, the composite photocatalysts had a large specific surface area. Rhodamine B(Rh B) and phenol were selected as pollutant models to evaluate the visible-light-driven photocatalytic activity of the prepared materials. As a result, the photocatalysts showed higher activity with the increase of g-C3N4 contents and then decreased. g-C3N4/Bi VO4(5:5) composite photocatalysts showed the best photocatalytic activities, which was obviously superior to pure Bi VO4 and g-C3N4. In addition, the stability of g-C3N4/Bi VO4 composite photocatalyst was good.