Effect Of Preparation Condition Of Mo/LDHs Catalyst On Degradation Of Cationic Orchid And Mechanism

As the development of technology, dyes had been widely used everywhere. Much attention have been focused on catalytic wet air oxidation(CWAO) for degradation of the complex components, high concentration and biorefractory dye wastewater. Unfortunately, it requires high temperature and high pressure. In this paper, the Mo/LDHs catalyst we prepared by different preparation method of Layered Double Hydroxide(LDHs) support or different p H in the impregnation process showed high catalytic activity for decoloration of cationic orchid X-BL at room temperature and atmosphere by CWAO. The effect of preparation condition for the structure and morphology of catalyst was investigated and the mechanism of CWAO was also discussed. The results was shown as follows.(1) The support of LDHs was prepared with traditional precipitation, hydrothermal synthesis, sol-gel and urea co-precipitation, respectively. Then the prepared Mo/LDHs catalyst with Mo loaded by impregnation method were characterized by N2 adsorption technique, X-ray diffraction, Zeta-potentials, X-ray photoelectron spectrum, thermogravimetric analysis and transmission electron microscopy. It turned out that the catalyst prepared with traditional precipitation and hydrothermal synthesis method hold the optimal catalytic activity with decoloration rate of 84.23% and 84.83% respectively. The specific surface area of these two catalysts is 2.806 m2/g and 3.908 m2/g, respectively and the active components of Mo exists as Na2 Mo O4, Na2Mo2O7 and Mo O3. The high removal efficiency could be attribute to the low Zeta potential and the high degree of Mo dispersion.(2) The effect of p H in the impregnation process on the phase formation, structure and catalytic potential of Mo/LDHs catalysts synthesized by the co-precipitation and impregnation method was evaluated. The materials were characterized by X-ray diffraction, UV–vis diffuse re?ectance spectroscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy and N2 adsorption technique. The experimental result showed that the Mo/LDHs catalysts prepared under p H = 7 shows the highest catalytic activity with 94.6% of decolorization and 86.7% of TOC removal ef?ciency. The characterization of the prepared Mo/LDHs catalysts showed that speciation diagram of Mo species in aqueous solution as a function of p H value. At basic p H(p H > 8), Mo O 42- was the main anionic in the solution. Hn Mo7O24m- was formed with the decrease of p H values ranging from 8 to 4 due to the combination of H+ and Mo7O246-. Molybdenum was present as solid of H2 Mo O4 when p H value was below 4.0. The Mo species existed in Mo/LDHs catalysts with p H=7 in the impregnation process was the mixture of Na2 Mo O4, Na2Mo4O13 and Na2Mo2O7 with tetrahedral Mo structure and hexavalent Mo shape.(3) Response surface methodology result was shown that the p H value in the reaction, the initial concentration of dye and the dosage of catalyst were the key factors remarkably influencing catalytic activity. The optimum conditions of the CWAO process was with p H value of 5,the initial dye concentration of 100mg/L and catalyst dosage of 1g/L accompanying by the maximum decoloration of 99.56%. Meanwhile the consequence of the kinetic of Mo/LDHs catalyst for degradation of cationic orchid X-BL by CWAO under room temperature and atmosphere showed that the constant rate of the reaction was-4104.98? and the activation energy of the process was-191.60J/mol.