The Preparation Of High-purity Birnessite And The Study On Its Oxidative Degradation Of RhB

Based on its abundant reserves, cheap price and environmentally friendly, manganese oxides have been investigated and applied widely in industry. Especially, birnessite, a common kind of manganese oxides, possesses unique physicochemical properties for its layer structure. Birnessite has a large specific surface area, low zero charge and high cationic exchange capacity, and which is also considered as the most strong oxidizing agent among all manganese oxides.The use of refractory dyes has been influencing human survival and development seriously, so it is urgent for us to solve the problem. However, the traditional methods, such as physical adsorption cannot eliminate those dyes completely; some advanced oxidation methods, such as photocatalytic oxidation is restricted for the catalysis materials and the light sources. Based on these two reasons stated above, we hope to prepared high pure birnessite, and apply it to the degradation of organic dyes in waste water. We mainly did the work in following three section:In the first part:we prepared high pure birnessite using air oxidation process under basic condition, and choosing MnSO4, NaOH and EDTA-2Na as Mn source, alkali source and complex agent respectively. The factors on the kinds of products and its morphology were investigated, the optimal condition were following:the mole ratio of EDTA-2Na/MnSO4=1, the concentration of NaOH is 0.6 mol/L, the speed of dropping NaOH is 3 mL/min. Under those conditions, high pure birnessite with three-dimentional micrometer flower composed of ultrathin nano-sheet was obtained, and besides, its forming was speculated.In the second part:the prepared birnessite was used to degrade the organic dye RhB. The influences of the dosage of birnessite, the density of RhB and the solution pH. Typically,50 ml of RhB (10 mg/L) could be degraded completely with 10 mg sample in 10 min under pH =1 without any additives such as hydrogen peroxide, peroxysulphate or any supplementary means such as microwave, ultrasound. The degradation performance of recovered birnessite shows good activity until the fifth cycle. And the degradation mechanism was proved to be redox between bienessite and RhB.In the third part:in above two parts, we have mainly introduced the preparation of birnessite and its degradation performance. In this part, we prepared another two kind birnessites contained different alkali metal ions called Li-Bir?Na-Bir and K-Bir respectively, using EDTA instead of EDTA-2Na and corresponding alkali. A systematic characterization were done to check the relationship of different kinds of birnessites and their degradation performances.In brief, high pure birnessite was prepared using air oxidation process through introducing the complex agent EDTA-2Na, and its degradation performance of RhB was investigated. Besides, birnessites contains different alkali metal ions were synthesized, the inner factors on their degradation performances were discussed preliminarily. Due to its starting materials easily available, simple method to be synthesized and undemanding degradation conditions, the as-prepared birnessite possesses high practical value in treating environmental pollutants.