Preparation And Photocatalytic Performance Of BiOBr And Its Composite Materials

Nowadays, the problem of environmental pollution is one of the major social issues of sustainable development of the global economy, and it also attracts increasing attention of the scientists in the world. Among the techniques, semiconductor photocatalysis appeals to scientists’ concerns because of its environmentally friendly, low energy consumption and no secondary pollution. Titanium dioxide（TiO₂） is a semiconductor catalyst which is most widely used in the field of photocatalysis. However, due to its large band gap energy（³.2eV）, it can only be excited by ultraviolet light（λ <380 nm）, and the utilization of solar energy is limited. Therefore, it has become a new direction to develop photocatalyst with visible light response.In this thesis, tuning BiOBr with exposed（001） face and semiconductor coupling were adopted to widen the light absorption range and enhance the photogenerated electron-hole separation efficiency. The the crystalline morphology, crystal phase structure, photo-absorption property, surface microstructure, surface chemical states, surface size and separation efficiency of photogenerated carriers of as-prepared photocatalysts were characterized by field emission scanning electron microscope, energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray powder diffraction, UV-Vis diffuse reflectance spectroscopy（UV-Vis DRS）, fluorescence spectrum（PL）, specific surface area and photocurrent testing. The main points are listed as following:（1） BiOBr photocatalysts with various morphologies were synthesized by a facile hydrothermal method. The highlight of this approach was the use of ethylene glycol（EG） as the crystal growth inhibitor agent and water as the hydrolysis agent to control the growth of BiOBr nanomaterial. With this method, the BiOBr morphologies changed from microspheres to nanoplates with high exposed（001） facets could be easily tuned by adjusting the volume ratio of EG/H2 O. This method also provides a new thought for controlling morphologies. Various methods such as XRD, SEM, TEM and UV-Vis DRS were used to fully characterize the as-obtained BiOBr samples. Visible light photocatalytic degradation experiments show that BiOBr square plate revealed the highest photocatalytic activity. High exposure（001） ratio is the main factor affecting the photocatalytic activity, the surface aera is the secondary factor affecting the activity.（2） In-suit synthesis and visible-light-driven photocatalytic activity of BiOBr@Bi₂S₃. BiOBr@Bi₂S₃ core-shell structure was obtained by a facile anion exchange process to form Bi₂S₃ in situ on the surface of BiOBr hollow microspheres, which were firstly prepared by a one-step solvothermal method. By controlling the amount of sulfur source, prepared different BiOBr@Bi₂S₃ composite samples with different content of Bi₂S₃. The study shows that the composite samples show strong visible light response. Compared with BiOBr and Bi₂S₃ samples, the BiOBr@Bi₂S₃ composite samples showed significantly enhanced degradation activity under the visible light. When the mole percentage of Bi₂S₃ was 8%, the photocatalytic activity of BiOBr@Bi₂S₃ was the highest. The intimate heterojunction between BiOBr and Bi₂S₃ greatly promoted the separation of charge carriers, resulting in the superior visible-light-driven photocatalytic activity for the degradation of methyl orange（MO）. The study of active species shows that ?O2- plays a major role in the process of degradation.（3） Enhanced visible-light-driven photocatalytic reduction of Cr（VI） over QDs-CdSe/BiOBr microspheres. CdSe quantum dots were deposited on the surface of BiOBr microspheres by the chemical bath deposition method. The QDs-CdSe/BiOBr samples exhibited superior photocatalytic activities. Photocatalytic reduction of Cr（VI） showed that the photocatalytic activities of all the composite samples were higher than the pure BiOBr samples under visible light irradiation. Among the samples, the 5wt% QDs-CdSe/BiOBr sample exhibited highest photocatalytic activities, and the results also showed that the composite materials have good photocatalytic stability.