| Nowadays, researches on photocatalytic activity of Bi2WO6 under visible light irradiation have just started, and it has caused wide concerns in the fields of photocatalysts due to its various advantages such as the ablity to make full use of the visible light, high photocatalytic activity, decreasing energy consumption, cost saving, and easiness of industrialization. Therefore, it is important to study the photocatalytic activity of Bi2WO6 under visible light irradiation in view of the environment. Moreover, photocatalysts with different micro-morphology may perform different photocatalytic activities and different photocatalysis mechanisms. At the same time, Bi2WO6 is also a kind of multifunctional material which has potential applications such as photoluminescence, microwave applications, optical fibers, scintillator materials, and catalysis, thus, exploring synthesis of Bi2WO6 with different micro-morphology not only has important significance to discuss the effects of morphology on the photocatalytic activity but also will provide a basis to expand its application in other fields.This paper mainly focuses on the synthesis, photocatalytic activity, stability and doping modification of Bi2WO6 photocatalytsts, and the synthesis and activity of Bi2WO6 with different morphology in the aim of obtaining photocatalysts with high activity under visible light irradiation, providing a basis for practical application, and providing a method to synthesize material for the application in other fields.Nano-Bi2WO6 powders were synthesized by a hydrothermal method. The influence of synthesis conditions such as temperature, pH value, reaction time, calcination, microwave treatment and ultrasonic treatment on photocatalytic activity have been investigated. As a result, the optimum preparation process of Bi2WO6 was as following: the origin pH value 2 is the favourable choice, reaction time is 24h, the temperature is 120°C, and without any other treatment. In addition, the suitable magnitude of the photocatalysts used in the photocatalytic process is determined to be 0.5 g/l( initial concentration of RhB, 1×10-5).Stability of photocatalysts is one of the most important influence factors for their further application, as a matter of fact, it is the instability of many highly efficient photocatalysts that have hindered their further application. Products of side reactions or changes in the catalyst structure lead to deactivation during the photocatalytic process of some catalysts. Recently, we have found that perovskite compounds such as BaFeO3 and SrFeO3 endured serious photochemical erosion due to the FeO6.structure. Noting the perovskite-like slab of WO6 in Bi2WO6, in view of the doubt whether it is a common phenomenon existing in the field of perovskite-type compound photocatalysts, whether there are some occurrence regularitys, it is necessary to probe the stablity of Bi2WO6 to provide a theoretical foundation for the stability evaluation and a basis for the further practical application. A careful investigation has been carried out into stablity of Bi2WO6 during photodegradation of rhodamine-B. It is found that, the recycled catalysts exhibited almost the same high photocatalytic activity as it did during the maiden catalytic process and showed stable composition structure pre-and post photodegradation, proving that Bi2WO6 was stable against photocorrosion. As a perovskite-type compound, comparing with those instable perovskite compounds, of which the prominent examples were BaFeO3 and SrFeO3, a conclusion can be drawn that the transition metal B in BO6 plays an important role in the stablity of this kind photocatalysts and the stablity of Bi2WO6 can be attributed to the jarless oxidation state of W in WO6. It is suggesting that element in the B-site with a stable oxidation state is a favourable choice when we are designing new perovskite-type compound photocatalysts.Obviously, Bi2WO6 not only showed a fairly high photocatalytic activity, but also performed a high stability during the photocatalytic process. In order to extend the visible light absorption region and improve solar efficiency, Bi2WO6 was modified by doping ions. First, different types of ions were doped. It is found that various doping could improve the catalytic properties, moreover, among them, Pb2+, and Zr4+ are more active. Then, different concentrations of Pb2+ and Zr4+were doped to determine the optimal concentration. The results revealed that 1%Pb2+ and 0.5% Zr4+ doping exhibited the highest photochemical activity under visible-light irradiation respectively.Although numerous morphological studies have been conducted for many kinds of materials, the development of synthesis methods, control of size and morphology, and assembly of desired nanostructure still remains a challenge in this field. Very recently, simple nanostructures of Bi2WO6 including low-dimensional nanoparticles, nanorods, and nanoplates were attained accordingly, however, PEG surfactant was little reported as an assistant. In this study, special three-dimensional Bi2WO6 has been successfully synthesized under the assistance of PEG, and the photoactivities of the as-prepared samples were investigated, furthermore, a possible growth mechanism of different samples is proposed on the basis of results of morphologies observation. It is found that different amount of surfactant made the morphology of samples range from flower like assembly to random clew-like structures, and samples showed different activities due to the effects of different morphology on the mobility and recombination of charge carriers. In addition, it is under the assistant of the surfactant that enable it overcome the surface free energy to form the special morphology of Bi2WO6, When the ratio of the volume of PEG200 and water was 6:15, the clew-like microspheres built by nanosheet alignment were synthesized. The clew-like sample showed the highest activity among samples prepared in the presence of surfactant, suggesting its high photo-quantum efficiency. It is also found that the more surfactant is added, the more dense packing the three-dimensional morphology of the samples was inclined to. It is believed that the synthesis of special uniform Bi2WO6 microspheres will also provide a basis for the potential application in the other fields.BiOBr as a new type of photocatalyst with high photocatalytic activity attained in the presence of CTAB in our experiment was also investigated. The prepared sample was of special morphology, at the same time, compared with Bi2WO6 attained in the presence of surfactant, the BET surface area of BiOBr is relatively small, but showed higher photocatalytic activity, suggesting that it has high mobility and low recombination of charge carriers during the photocatalytic process. |
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