| Semiconductor photocatalytic technology has attracted much attention since TiO2 was first reported for water splitting in 1972. This technology provides an ideal method for environmental treatments and energy application. Nowadays, developed countries have struggled to solve the increasingly severe environmental problems, including the pollution of water, atmosphere and soil. However, the photocatalytic technology must overcome some limits. For instance, poor solar energy convertion and low quantum yield of TiO2, as well as separation and recovery difficulty. Therefore, the work of exploring a new style of catalysts and improving the rate of solar energy convertion and quantum yield of TiO2 through modification is imminent. BiOBr have ignited the interests of the scientific workers due to its good photocatalytic activity under visible light, low economic consumption and non-toxic. Furthermore, it was widely used in the photocatalytic technology because of its special structures. In this paper, BiOBr, nitrate vapor pre-treated carbon nanotubes loaded with BiOBr and rare earth elements modified BiOBr were synthesized in ionic liquids, respectively. In addition, modified TiO2 was also prepared successfully. The result samples were characterized by XRD, SEM, HR-TEM, PL, EPR, XPS, and UV-vis adsorption spectra. The photocatalytic activity and the mechanisms of catalysts were evaluated in terms of the degradation of methyl orange. The contents are as follows:(1) The photocatalytic degradation of methyl orange was evaluated through BiOBr synthesized in ionic liquids. The results showed that chain length of ionic liquids and anions have effects on the process of BiOBr synthesis. The optimum parameters of BiOBr preparation are as follows:1-butyl-3-methylimidazolium bromide acts as both solvents and templates, the mole ratio of Bi to Br is 2 to 3. The reaction temperature and time is 433K and 8 hours, respectively. The degradation of MO can reach to 94.0% under 4 hours’ irradiation. Whereas, different chain length of ionic liquids results in the change of proportion of BiOBr (011) facets, which will also lead to the regularly change of degradation of methyl orange under visible light. It can be concluded that BiOBr with lower proportion of (011) facts exhibits the best performance among the degradation under visible light.(2) BiOBr was modified by MCNTs pretreated by nitrite vapor. According to our experiments, it was found that reaction temperature, reaction time and different chain length of ionic liquids have effects on the BiOBr synthesis. Compared with each other, the optimum conditions of BiOBr synthesis are as follows:1-hexadecyl-3-methylimidazolium bromide acts as both solvents and templates, the reaction time and temperature is 16 hours and 433K, respectively. The degradation rate of MO can reach to 95% by the products in 4 hours under visible light.(3) BiOBr was modified by rare earth (Re) elements. Adding the REn+ into the procedure of BiOBr synthesis, we can collect the x%Re/BiOBr (x=0,0.5,1,1.5,2). The photocatalytic activity was evaluated in terms of methyl orange with a concentration of 20mg/L. The results showed that as the doping content increase, RE/BiOBr exhibits a first decrease and then increase performance in terms of methyl orange degradation under visible light. It can be ascribed to the 4f orbits and the activities of the electrons in 4f orbits.(4) Loading multi-walled carbon nanotubes (MCNTs) and/or Phosphotungstic acid (HPW) with TiO2 was performed by sol-gel method. The photocatalytic activities of the catalysts were evaluated via experiment on ultraviolet light degradation methyl orange. An optimum value reached at the HPW/TiO2 molar ratios is 0.08 in the presence of 0.025g MCNTs/0.03mol TiO2. With this co-doped catalyst composites, the decomposition ratios of methyl orange solution reaches 93.7% after 2.5h photocatalytic reaction, compared to 64.9% for pure TiO2 and 83.7% for MCNTs/TiO2.(5) Metal organic macromolecule (MOM) was used to molerate the TiO2. The composites can response to visible light, which have a higher photocatalytic activity than that of single TiO2. Through the experiments, the degradation rate of methyl orange can reach to more than 60% after 6h. |
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