Preparation Of Heterogeneous Fenton Catalytic Materials Of Co/Fe Hydrotalcite And Study On Degradation Of Dye Wastewater

With the development of people's living standards and technology,industrial wastewater has become a major problem in the field of modern environmental protection,especially in the light industry in the textile printing and dyeing industry produced by a large number of dyes containing wastewater,due to the darker,pH range,Composition is more complex and so on,has become more difficult to deal with industrial waste water and the greatest impact on people's lives one of the industrial wastewater.Therefore,this paper combined with the traditional Fenton reagent without selective oxidation,mineralization,the advantages of fast and hydrotalcite surface area,cheap,simple production process advantages,the synthesis of four different metal ions containing hydrotalcite,and its the study.Found that they all have a relatively good hydrotalcite crystal structure.CoFe-LDHs and MnFe-LDHs have better crystal form and less impurities.Thermogravure In aqueous solutions,hydrotalcite catalysts have good thermal stability.It was found from the ICP analysis that the hydrotalcite catalyst reacted in the aqueous solution,dissolution was less,the catalyst was more stable,and no large metal ion was lost,causing secondary pollution.And the catalyst has good recyclability.And the catalyst in a wide range of pH can be stable in the aqueous solution,can be a high participation in the reaction.The degradation effect of CoFe hydrotalcite was better than that of CoFe hydrotalcite,CoMn hydrotalcite,Ni Mn hydrotalcite and MnFe hydrotalcite,and the decolorization rate was higher.Therefore,CoFe-LDHs as a catalyst.In the study of the catalyst dosage,it was found that the rate of the reaction increased with the increase of the catalyst dosage.However,when the dosage was more than 0.5g/L,the collision between the catalyst and the catalyst increased,So that the effective reaction area is reduced,so the catalyst dosage is 0.5g/L.The effect of pH on the reaction is more complex,showing a tendency to rise first and then increase.Probably because at lower and higher pH,the catalyst will be weakly dissolved,resulting in a homogeneous reaction but an increase inthe reaction rate.In the lower and higher pH range,the absolute value of the Zeta potential of the hydrotalcite in the water is relatively high,so the catalyst can be more stable in the water,so that the reaction area reaches the maximum,and thus the reaction rate is large.The effect of hydrogen peroxide on the reaction is also great,specifically when the hydrogen peroxide dosage is less than 0.2mL / L,with the increase in dosage,the reaction rate will increase;when hydrogen peroxide When the dosage is more than 0.2mL/L,the reaction rate decreases with the increase of hydrogen peroxide content.Therefore,the dosage of hydrogen peroxide is0.2m L/L.The study of the kinetics and thermodynamics of the degradation process shows that the degradation reaction is better than the first-order reaction,and the enthalpy change in the reaction is greater than zero,indicating that the reaction is endothermic,and thus the reaction temperature will increase the reaction speed,And Gibbs free energy is less than zero,indicating that the reaction at normal temperature difference pressure for the spontaneous reaction process.As the chemical reaction process must be accompanied by physical changes.Heterogeneous catalysis must be accompanied by the adsorption process,the study of the adsorption process found.The kinetic study shows that the adsorption process is quasi-secondary,and it can be seen that half of the decolorization rate is provided by adsorption.In the TOC test,it was found that the decolorization of the dye in the reaction did not equal to that at the beginning of the reaction,the chromophore group of the dye macromolecule was interrupted and degraded as an intermediate product of the organic small molecule.As the reaction proceeded,Organic small molecules are oxidized degradation gradually become the main reaction,so the ratio of TOC and decolorization rate will gradually increase.The possible reaction mechanism and reaction process can be deduced by EPR and GC-MS.First,after the catalyst and hydrogen peroxide are added to the reaction system,the dye(direct red 23)and hydrogen peroxide will reach the surface of the hydrotalcite and the pores therein due to diffusion and adsorption.Since the direct red 23 is ionizable in water to produce a sulfonic acid group,it is a negatively charged dye,and thehydrotalcite indicates that the positive surface of the hydrotalcite is due to the fact that there are more positive charges of the metal positive ions that can not be neutralized by the interlayer anions Positive electrification.Thus,the negatively charged direct red 23 molecule is adsorbed on the surface of the hydrotalcite.And hydrogen peroxide molecules because of the smaller size,it will not only adsorb on the surface of the catalyst,will also enter the internal channel of hydrotalcite.After the hydrogen peroxide reaches the layered structure of the hydrotalcite,the iron ions and cobalt ions on the laminate react with Fenton or Fenton.Cobalt ions and iron ions can be priced,and then produce complex free radicals with hydrogen peroxide,and finally generate a high oxidation of hydroxyl radicals.And hydroxyl radicals will give priority to attack the unsaturated bond in the dye,so that the dye molecules into smaller stable organic small molecules,the final hydroxyl radical oxidation of water and carbon dioxide is completely fully mineralized,to achieve the purpose of degradation.It can be seen that CoFe-LDHs as a heterogeneous catalyst have a good effect in the heterogeneous catalytic degradation of the direct red 23 solution and can be used as a potential industrial catalyst.