Preparation And Photocatalytic Activity Research Of Flower-Like Bi₂WO₆-Based Ternary Microsphere

Bi2WO6, a new type of visible light catalyst, is considered as one of the best photocatalytic activities in the bismuth-based compounds. Although optimizing raw material and preparation process to change the size and morphology of the Bi2WO6 can further improve the photocatalytic efficiency of the organic pollutants, the high photo-generated carrier recombination, low quantum efficiency and narrow visible light response range still limit the practical application of Bi2WO6. Therefore, modified Bi2WO6, such as doping, compositing and modifying with notable metals, is still the main research direction to further improve its visible-light photocatalytic activity.In this thesis, to solve the scientific problems of enhancing the photocatalytic efficiency of Bi2WO6, we mainly studied the Bi2WO6-based composites to form heterojunction by controlling its composition and morphology to solve the problems in the practical application. Related research results are as follows:(1) The flower-like WO3/Bi2WO6 n-n type heterojunction with high photocatalytic activity has been successfully prepared by one-step hydrothermal method and hydrothermal-calcination method, respectively, which use Bi(NO3)3·5H2O as the source of bismuth, Na2WO4·2H2O as the source of tungsten. The influence of WO3 on the crystal phase, the microstructure, morphology and photocatalytic activity has been discussed. Compared with two different methods, nanoplates of flower-like WO3-Bi2WO6 microspheres prepared by one-step hydrothermal method become denser and thinner, and the specific surface area is larger. This flower-like WO3-Bi2WO6 microspheres can provide more active site, which benefits for light absorption and adsorption of pollutants. More importantly, this simple process can reduce the cost and energy consumption. It is good for the following synthesis of Bi2WO6-based ternary hybrid composites.(2) The CuO-WO3-Bi2WO6 p-n-n type heterojunction with high visible-light photocatalytic activity has been preparated by a impregnation-calcination method, the flower-like WO3-Bi2WO6 microsphere is used as the basic materials, and the different loading content of CuO has been discussed. The UV-vis-NIR diffuse reflection spectra shows that the absorption edge of the CuO-WO3-Bi2WO6 samples change to infrared region with the increasing of CuO content, which can be attributed to the effect of interphase interaction among CuO, WO3 and Bi2WO6 in the sample. CuO-WO3-Bi2WO6 ternary hybrid photocatalysts exhibit obviously higher photocatalytic activity than that of pure Bi2WO6, WO3/Bi2WO6 and CuO/Bi2WO6 in the photodegradation of RhB, and the suitable content of CuO make the flower-like WO3/Bi2WO6 exhibit the best photocatalytic activity among all samples.(3) The flower-like BiOBr-WO3-Bi2WO6 ternary hybrids have been designed and synthesized by an effective two-step approach. Specifically, WO3 decroated Bi2WO6 are prepared by one-step hydrothermal method and subsequent BiOBr layer via a cost-effective process. The superstructure of flower-like WO3/Bi2WO6 heterojunction do not change after copling with BiOBr, and suitable BiOBr small nanoplates uniformly appear on the nanoplates and surface of Bi2WO6. The experimental results indicate that the BiOBr-WO3-Bi2WO6 composites exhibit much higher visible-light photo-catalytic activity than that of pure Bi2WO6 and WO3/Bi2WO6 binary hybrids, which is attributed to the increased surface area, tight interface contact and difference in the energy band positions. This can improve the photo-induced charge separation and enhance the photocatalytic activity after WO3, BiOBr coupled with flower-like Bi2WO6.(4) The Ag3PO4-WO3-Bi2WO6 ternary system largely improve the visible-light absorption ability of flower-like WO3/Bi2WO6, which was prepared by precipitation method using WO3-Bi2WO6 as matrix. The photocatalytic experimental results indicate that the suitable amount of Ag3PO4 modified flower-like WO3/Bi2WO6 exhibit the best visible-light catalytic activity among all samples, which can be ascribed to the cascade structure. For Ag3PO4-WO3-Bi2WO6 sample, WO3 possesses a more positive CB position than Ag3PO4 and can rapidly receive electrons from the CB of Ag3PO4 as soon as they are injected into Ag3PO4 from Bi2WO6, which can enhance the separated efficiency of photo-generated electron-hole pairs.In summary, a series of new visible light response WO3/Bi2WO6-based ternary system are constructed in this thesis. These catalysts effectively improve the visible light absorption and quantum efficiency of flower-like WO3/Bi2WO6, and provide a new way to explore new type of high efficient photocatalyst.