Preparation And Propetry Of Visible Light Catalyst Of Rare Earth Doped Bismuth Oxide

Dye wastewater which contains azo, aromatic compounds and heavy metals isharmful to the human and ecological environment. It has high color degree, high CODand low biodegradability, resulting in high cost and low efficiency of dye wastewatertreatment. Therefore, how to develop a cost-effective technology for the treatment ofdye wastewater has been paid a lot of attention.The semiconductor photocatalytic technique is an advanced oxidation technologyand can produce strong oxidizing active substances by energy excitation. So it canmake use of solar clean energy. Recently, many researches focus on the TiO₂asphotocatalyst. Due to band gap of TiO₂which results in low utilization of light energy,there is a limit of TiO₂application. Therefore, there is a need to develop a new type ofnarrow band gap and wide absorbance range of photocatalyst.In this study, the preparation of Bi₂O₃doped with Eu was conducted by amorphouscomplexation. Thr catalysts were made up of oxide by Bi （III） and Eu （III） and Ce（Ⅳ）.The results indicated that the influence of doping ratio on the crystal structure wassignificant. The crystal structure of Bi₂O₃and Bi_0.25(Bi_0.375Eu_0.375)O_1.5is quadrangularpolymorph and non-stoichiometric ratio of the cubic crystal with the doping ratio of1:8, respectively. High doping ratio with more Eu can induce the Bi₂O₃transformed toBi_0.25(Bi_0.375Eu_0.375)O_1.5. The Europium-doped Bi₂O₃catalyst can effectively adsorbthe visible light. The band gap of catalyst was2.75eV when the doping amount of thesample1:8and1:4. But the band gap of catalyst was increased with increasing dopingamount. The band gap of catalyst was3.3eV when the doping amount was1mol/mol.The separation ability of light-generated electron-hole was strongest when Eudoping ratio was1:4, resulting that the methyl orange degradation rate can reach97.6%. The crystallinity was increased with increasing temperature and agglomeration wasproduced. At500°C and600°C, the Bi_0.775Eu0.225O_1.5with structure of rhombichexahedron was formed. The band gap of catalyst prepared at400°C was minimumand its separation ability of light-generated electron-hole was strongest, illustratinggreat photocatalytic activity. Thus, the optimal preparation condition is temperature of400°C with5h calcinations.The structure of Bi₂O₃doped with Ce is tetragonal and transformed to cubic crystalwhen doping amount is1:1. The crystallinity decreased with increasing dopingamount. Samples prepared under different doping levels have better light absorptionat550nm. Based on the catalyst photocatalytic ability of methyl orange, the optimumdoping ratio was1:1. The monoclinic polymorph of Bi₂O₃was formed at600℃andits photocatalytic ability was less than cubic crystal of Bi₂O₃. High temperatures led toagglomeration. The band gap of samples prepared at400℃is2.35eV and effectiveseparation of photo-generated electron-hole pairs produced, resulting that highestphotocatalytic degradation of methyl orange achieved up to99%within1hour.Based on the characteristics of Bi₂O₃catalyst with different doped rare earths, itwas found that the absorption edge of Bi₂O₃doped with Ce was obviously red shiftedand the band gap decreased. Compared with Bi₂O₃doped with Eu, the Bi₂O₃dopedwith Ce had a high voltage signal, photo-generated carriers separation and transportcapabilities. The degradation of methyl orange by Bi₂O₃catalyst doped with Ce was99%within1hour, while the degradation of methyl orange by Bi₂O₃catalyst dopedwith Eu was90%within2hour. This suggested that the best photocatalyst is Bi₂O₃catalyst doped with Ce.During the photocatalytic degradation of methyl orange by Bi₂O₃catalyst dopedwith Ce, some intermediate products were produced within4hours. After that, mostof intermediate products were mineralized to NO₃^-、SO₄^2-and a few amounts ofintermediate products were still incompletely degraded. It was found that the catalysthad the adsorption capacity of methyl orange. But photosensitization phenomenonwas not detected by UV-Vis DRS.The photocatalytic degradation of methylene blueby Bi₂O₃catalyst doped with Ce was different with photocatalytic degradation of methyl orange, but similar to the reaction rate. The adsorption of methylene blue washigher than that of methyl orange. A new peak appeared in the range of575-675nm inthe UV-Vis DRS results. Adsorbed dyes and intermediates prompted catalyst producemore active sites and extend the scope of the absorbance of the catalyst. Thephotosensitizing effect existed. However, due to the degradation of fuel by catalyst,the absorption peak weakened at the575-675nm after12h reaction.Photocatalytic reaction rate increased with the increasing amount of catalyst andlight intensity, while decreased with the increasing initial concentration of reactant.The reaction fitted to the first-order kinetics and their relationship can be expressed asν=0.0113C₀^-1.459m^1.3458P^0.3332.The results showed that the reaction rate was inhibitedby Na₂SO₄, NaNO₃and NaCl, and the inhibitory effect of ions are enhanced withincreasing concentration.In general, the Bi₂O₃catalyst doped with Eu and Ce in this study had broad lightresponse range of the catalyst and high photo-generated carrier separation ability, andgood photocatalytic ability under visible light. Through the analysis of pathway andreaction condition in the photodegradation of pollutants, the relationship between thereaction rate and the different conditions was proposed in this study, aiming toprovide a theoretical basis for the application of the catalyst in future.