Study On CNTs Catalytic Ozone Chemical Process And Reaction Dynamic

Dyeing wastewater is characterized by high color, complex composition, high concentration of organic matter and non-biodegradable. Ozone water treatment technology can produce strong oxidizing species hydroxyl radical (OH-) during oxidation degradation of pollutants. At the same time it may complete mineralization. The pH is an important limiting factor of ozone oxidation. In order to strengthen the OH-oxide route, we selected carbon nanotubes as the heterogeneous catalyst and do research at different pH environment. We studied the change law of parameters such as the ozone decomposition kinetics in multiphase flow, important product decomposition of hydrogen peroxide (H2O2) and OH-. The degradation of model compound (methyl orange) was analyzed (including decolorizing, mineralization, etc.). The possible route of catalytic ozone oxidation was also analyzed and discussed. This may supply scientific conclusion for application of the multiphase flow catalytic oxidation system which was controlled by carbon nanotubes.In order to study of the possible catalytic process more comprehensive and comparative, the experiment was carried out in no substrate and substrate environment respectively. Firstly, we studied the stability and solubility of ozone under different pH and carbon nanotubes. At the same time, we determined the intermediate products during ozonation. The experiment selected methyl orange as the simulated dye wastewater and used ozone oxidation technique to study the effects of pH, carbon nanotubes, modified carbon nanotubes, ozone flow rate and initial substrate concentration on methyl orange decolorization behavior. We also tried to give possible reaction mechanism.In the absence of substrate conditions, the reaction of ozone decay accorded with first-order kinetics. When the pH was2.5,6.5, and8, the half-life were38.09min,44.72min and8.38min respectively. When the pH was6.5,8,9and10, the concentrations of dissolved oxygen were9.31mg/L,9.28mg/L,9.17mg/L and5.13mg/L respectively. The results indicated that the stability of ozone affected by pH. Under alkaline conditions, the decay rate accelerated and the concentration of dissolved ozone reduced. Acid conditions could also accelerate the decomposition of ozone slightly. At the pH of8, after adding untreated carbon nanotubes (CNTs-0) and the modified carbon nanotubes (CNTs-1) into reaction, the half-life of ozone were3.48min and3.10min respectively. At the pH of10, the concentrations of ozone were2.83mg/L and1.86mg/L. The results showed that carbon nanotubes could catalyze the decomposition of ozone and modified carbon nanotubes had better catalytic effects. Through the determination of the intermediate products, we found that the important intermediate products during ozonation had H2O2and OH-. After applying ozone into water for a period of time, the concentration of H2O2reached a substantially constant. In pH=8system, the concentration of H2O2was less than pH=6.5. Carbon nanotubes could slow down the decay rate of H2O2. In pH=10system, the concentration of OH-was highest. The lowest concentration of OH-was in ph=6.5system.At the pure ozone oxidation system, the initial concentration of methyl orange was30mg/L. Through comparing the degradation with pH=6.5, pH=8and pH=10systems, we could see that reaction time attains10min,8min and7min respectively when decolorization ration reaches99%. Meanwhile, TOC removal ration reached6.93%,17.42%and22.4%. This indicated that in alkaline conditions, the effect of oxidation is better. In the initial concentration of methyl orange10mg/L,50mg/L and100mg/L, reaction time attains3min,9min and30min respectively when decolorization ration reaches99%. This showed that the smaller of initial substrate concentration, the faster of decolorization. By analyzing the relationship of the concentration of methyl orange and the reaction time, we found that the reaction of ozone degradation methyl orange was first-order kinetics.In pH=10system, compared the degradation with pure ozone oxidation (O3), untreated carbon nanotubes catalytic ozonation (O3/CNTS-0) and the modified carbon nanotubes catalytic ozonation (O3/CNTS-1) systems, reaction time attains10min,6.5min and5.5min respectively when decolorization ration reaches99%. Meanwhile, TOC removal ration reaches27.33%,34.24%and35.42%. Results show that carbon nanotubes have a good effect on degradation of organic matter which has large molecules and dissolve in water. Because the substrates produce strong oxidation resistance molecular fragments during oxidation process, we did not observe the apparent efficiency removal of TOC after adding carbon nanotubes, under the condition of the experimental dose.