Lanthanum BiFeO _{Preparation And Visible Photocatalytic 3} Complex

In recent years,the bismuth-based semiconductor as a new type of photocatalyticmaterials become a hot spot of research because of its good catalysis under the visiblelight irradiation and has a high stability during the reaction. BiFe〇3has a narrow bandgap （2.2eV）. It has good chemical stability, and can take full advantage UV-visiblelight. Therefore, it can be used in the process of the photocatalytic treatment of organicwastewater. Besides, because of its weak ferromagnetism, the sample recovery rate ofBiFe〇3can reach80%, which is very good for repeated use. However, the wastewaterphotocatalytic degradation rate is relatively low by BiFeO₃，and the research of BFOphotocatalytic still very few. Therefore, it’s too important to improve the cuprousBiFeO₃，s photocatalytic research of the visible light activity.Paper prepared pure and modification BFO complex by the Sol-gel methodisecitric acid as the complexing agent The structure shape and spectrum characteristicwere characterized by TGA> FT-IR、XPS> XRD、UV-Vis> TG-DSC、FS.Thephotocatalytic activities were evaluated by degradation of methylene blue.（一）Experiment results show that if the sample is prepared with bismuth nitrate,ferric nitrate, citric acid, and polyethylene glycol as raw materials, Sol-gel method, theLa-BiFeO₃/Bi20₃complex powder is highly active, while its activity is further enhancedafter doping La.Using methylene blue as the target compound, considering the change of theBFO photocatalytic activity of the sample under different process conditions, such asthe calcination temperature and the doped amount, it is concluded that when thelanthanum-doped amount is15%，and the calcination temperature is500。C，theLa-BFO complex has a good crystallization property and the highest photocatalyticactivity^can be91.87%after3h light irradiation, and ultimately reach99.2%in5h.Comparing the photocatalytic activity of the La-BFO complex under the optimalcondition and the pure BFO complex with hydrothermal synthesis, we can see thatunder visible light, the degradation rate of the La-doped sample is higher than that of undoped samples. Using the degradation kinetics equation of methylene blue solution,we also analyzed the influence of different initial concentration of methylene blue onthe photocatalytic activity of the BFO complex.（二）As can be seen from the XRD characterization, the La doped BiFe〇3complex bismuth mixture is prepared by Sol-gel method, but the physical phase peak ofdoped lanthanum doesn’t appear in the XRD pattern. It shows that there is less dopedLa, which brings no change in the crystal form. From the XPS spectra of the mostactive15%doped lanthanum sample, we found La3d5/2peak at834.2and837.8eV,and La3d3/2peak in851.3and855.4eV. This indicates that part of La has entered thelattice of the BFO, and also confirms the presence of the La-0bond in the catalyst. Byanalyzing the high-resolution spectral scanning of Bi，0，and Fe, and comparing theXPS spectra database, we concluded that Bi and Fe are+3valence, and furtherconfirmed the substance is prepared by BiFe〇3and Bi2〇3. By observing the anultraviolet-visible spectrum, we found that the sample’s response range to move to thelonger wavelength region after being doped with La, and calculated that band gap ofdoped sample is lower than that of the undoped one. It demonstrates that La-doping canreduce the band gap of the BiFe〇3complex, and increase the spectral response range,thereby improving the light utilization. Comparing the BFO complex fluorescencespectra of different calcination temperatures and doped amounts, we further confirmedthe impact of different calcination temperatures, the doping amounts on thephotocatalytic activity of BFO complex.From the TG-DSC diagram can be found，BFOcomplex was stable before104。C，BiFeO₃composite weight loss rate is about60%at500°C with increasing temperature,while the La-doped sample is mass loss was53%,reduce the weight loss rate of sample.