Modification And Photocatalytic Properties Of BiOX(X=Cl,Br) Photocatalysts

As an environment-friendly, high-efficiency and energy-saving pollutantstreatment technology, Semiconductor photocatalysis shows promisingapplication in air purification and wastewater treatment, and thus is of growinginterest in the fields of environment and energy. For popularizing and applyingthis technology, it is key to explore a novel semiconductor photocatalyticmaterial which can utilize the clean sunlight effectively. In recent years, BiOXphotocatalysts have attracted extensive attention due to their open-layeredstructure and indirect transition mode thereby separating the photoinducedelectron-hole pair effectively, and then show good photocatalytic activity. Butamong the BiOX photocatalysts, BiOCl can be activated by the UV light below360nm, and BiOBr only can extend the light response range to around430nm.Considering the broad wavelength range of sunlight, the light utilizationefficiency of BiOCl and BiOBr are still very low, and greatly limited thepractical application of BiOX. Hence, more and more researchers have focusedon expanding the light response of the BiOX by using a simple and effectivemodification way, in order to improve the photocatalytic performance andfacilitate the practical application. In this dissertation, we prepared the Sn(x%)-BiOCl and Bi4O5Br2photocatalysts with enhanced visible light photocatalytic performance. Thesephotocatalysts were synthesized via a simple ion doping and stoichiometricregulation at room temperature. The as-synthesized products were characterizedby X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS),transmission electron microscopy (TEM), scanning electron microscopy (SEM),Nitrogen adsorption-desorption isotherms measuremnet and UV-Vis diffusereflectance spectra (DRS). The photocatalytic activities of Sn(x%)-BiOCl andBi4O5Br2were evaluated by the degradation of different organic under thesimulated sunlight or visible light. Main results are presented as follows:1. Sn-doped BiOCl photocatalysts were successfully synthesized viaoxidation-reduction method.1) The as-prepared Sn(x%)-BiOCl samples indexed as the tetragonal phase,with uniformly lamellar morphology composed by nanosheets. Sn existed as theform of tetra-valence, and the existence of Sn could not change the crystalstructure of BiOCl, but could narrow the band gap and enhance light responseability.2) The photocatalytic performance for the degradation rhodamine B (RhB)and benzoic acid (BA) was evaluated under visible light and under simulatedsunlight, respectively. Results showed that the photocatalytic efficiency ofSn(x%)-BiOCl was much higher than that of the pure BiOCl, and the highestphotocatalytic activity achieved at the doping amount of10%. Furthermore, Sn(10%)-BiOCl exhibited a good photochemical stability, which may beattribute to the enhance light response ability and the electron capture ability ofSn.3) According to the results of photocatalytic degradation of BA, we foundthat the optimum dosage of Sn(10%)-BiOCl was0.4g·L-1. Scavengerexperimens suggest that the active species h+and dissolved oxygen played animportant role in BAdegradation.2. A novel Bi4O5Br2photocatalyst was prepared by a simple alcoholysismethod.1) The as-synthesized micro/nano block structure of Bi4O5Br2photocatalystcould be perfectly indexed as the monoclinic crystal. The BET specific surfacearea of Bi4O5Br2is62.25m2·g-1, the porediameter is about12nm, and the bandgap is2.36eV.2) The visible light induced degradation of resorcinol (RC), bisphenol-A(BPA) and phenol indicated that the degradation efficiency of RC, BPA andphenol could reach to95.0%,97.1%,93.4%after irradiation for150min,180min,600min over Bi4O5Br2, respectively. However, only11.4%,16.9%,8.3%of RC, BPA and phenol have been decomposed by BiOBr under identicalconditions and8.5%，42.7%，20.9%by P25. The superior photocatalytic activityof Bi4O5Br2may mainly attribute to its smaller particle size, larger BET surfaceareas and narrower band gap energy.3) The optimal degradation of RC was achieved at the condition of that the initial concentration of RC was10mg·L-1, the dosage of Bi4O5Br2was2.0g·L-1,The main reactive active species was·O2-and h+in degrading RC. Furthermore,the Bi4O5Br2displayed highly photochemical stability with95%after fivecycles.