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

In recent years, with the rapid development of dye textile industry, the varieties and quantities of dye have increased a lot. Due to all kinds of new type of dyes appear constantly, printing and dyeing wastewater has become one of the important sources of water pollution. The treatment of printing and dyeing wastewater is a urgent question in the world because of its complex water quality, deep color, the large quantity of emission, hazardousness and difficultly in degradation. The efficiency of traditional treatment methods of printing and dyeing wastewater is very low and the decoloration is quite difficult. Therefore, it is one of the research direction to choose a kind of energy-efficient wastewater treatment method to treat dye wastewater.As an advanced oxidation technology, photocatalytic technology has drown more and more attention. With the optical performance of catalyst, the method makes use of light energy to decompose organic pollutants or reduce heavy metal ions, and finally achieve the goal of wastewater purification. At present, most studies are concentrated on TiO2 as photocatalyst. However, due to band gap of TiO2 is very large, which results in low utilization ratio of light energy and limits its application. Therefore, there is a trend for people to develop new type of photocatalyst with narrow band gap or make use of doping methods to broaden the scope of the absorption of photocatalyst.In this paper, on the basis of bismuth materials, Bi₂O₃ doped with rare earth Ce³⁺, Y³⁺, Ho³⁺, Eu³⁺, Nd³⁺ and Gd³⁺ were prepared successfully by the method of thermal decomposition of molecular precursor, respectively. The results of thermo gravimetric analysis and infrared spectrum analysis showed decomposition temperature of the precursors was roughly the same, and each precursor was completely decomposed under the annealing temperature 500? and yielded composite oxide photocatalyst. The XRD analysis results of all kinds of rare earth ions doped Bi₂O₃ samples showed that the doping ratio of rare earth elements has a great influence on the crystal structure of the sample. The crystalline structure of the catalyst samples may transformed from monoclinic phase to tetragonal phase or bismuth based compounds. Ultraviolet-visible diffuse reflection spectrum for all catalyst samples showed the introduction of rare earth ions can effectively reduce the band gap of Bi₂O₃ catalyst samples and expand the visible light absorption range. Fluorescence spectrum for all catalysts showed the doping of rare earth ions can inhibit the recombination of photogenerated electrons and holes and improve the light quantum efficiency. Photocatalytic degradation of methyl orange experiments showed that the potocatalytic performance of Bi₂O₃ doped with rare earth ions is obviously better than that of pure Bi2O3. The optimal catalytic efficiency was obtained when Bi₂O₃ doped with 5% gadolinium, and the decoloration rate of methyl orange was 99.0% under light irradiation of 4 hours in the presence of it.Using Gd5% as a catalyst to degrade methyl orange and methylene blue, respectively. The degradation rate were 99.0% and 76.0% for methyl orange and methylene blue, respectively. It can be seen that the catalyst is selective, and the basic reason lies in the structure of pollutant itself. The pH value of solution, dosage of catalyst and air flow rate had a great effect on the degradation of pollutants. When the pH value was 4, catalyst dosage was 0.8 g/L, and air flow rate was 1.0 L/min, the degradation rate of methyl orange was 99.14% after the illumination for 2 h in the presence of Gd5%. Catalyst stability tests showed that rare earth ions doped bismuth oxide photocatalysts have good stability, recyclability and practical application value.