| The magnetic spinel MnFe2O4 of porous structure was prepared by using the egg white as foaming agent with a sol-gel process, and the same process applied to the Ag-doped spinel MnFe2O4 (Molar fraction should be 0.5%, 1%, 2% and 5% respectively). It was prepared five kinds of catalyst and were used on the the degradation of dibutyl phthalalte (DBP, a kind of organic contaminant) in the water by the catalytic ozonation.Meanwhile, the performance of catalyst was compared and studied.In this paper, XRD?FTIR?SEM?BET?XPS?EDS?VSM and other characterization methods were used to study the properties, structure and surface morphology of the catalysts..The results showed that the catalyst was porous structure and specific surface area was very large. This indicated Ag+ had entered into the lattice structure and replaced the space position of Mn2 . The phenomenon could be called the tetrahedral site (A-site) doped. The oxygen lattice defects became aggravate with increasing amount of silver-doped. The magnetic of catalysts decreased after silver-doped, but still belonged to the ferrimagnetic category.Furthermore, the performance of the five kinds of catalysts for catalytic ozone degradation of DBP had been carried on the experimental study, comparing Ag-doped catalytic properties after reinforcement effect. The results showed that the optimum property was 0.5%Ag/MnFe2O4 compared with MnFe2O4, and DBP removal rate increased by 23.6%.Different initial pH value of wastewater, different concentrations of DBP, catalyst dosage,water common ions and other factors were also studied, which showed that in the five kinds of catalytic system, the optimum result was the initial pH near the catalyst isoelectric point(pHpzc = 7.3), the dosage of 10 mg/L. The removal rate of DBP decreased with the increasing of initial DBP concentration. Water common ions such as Na+?Mg2+?Ca2+ and NO3- had no effect on the DBP removal, but Cl- would slightly depress the catalytic effect. In addition, the experiment research of catalyst reuse performance and homogeneous of metal ions dissolution indicated that the catalystcould still maintain a high catalytic performance after being repeatedly used for five times, and the dissolved metal ions had no effect on the catalytic systems. The results showed that the catalytic systems equaled to the pseudo-first-order reaction kinetics, and it was consistent with the proof of catalytic effect. Pseudo-first-order reaction kinetics constants k and the rate of ozone utilization R had the linear relationship under different catalytic systems and different conditions.With the help of Raman spectroscopy, electrochemical workstation and XPS analysis,and combining with phosphate and tert-butanol experimental results, the reaction mechanism between the catalyst and the ozone molecules was analyzed and the catalytic properties of Ag-doped MnFe2O4 enhancement mechanism was also comprehensive studied. The results showed that the catalytic process of ozone: firstly, hydroxy of water was adsorped on the catalyst surface. A five-member ring was formed by ozone molecules combining with surface hydroxyl groups to induce the decomposition of ozone molecules producing large amounts of reactive intermediate groups (HO2-·,·OH etc.),relying on strong oxidizing groups OH to degrade DBP. After the silver entered into MnFe2O4, on the one hand, the defect of lattice oxygen could be increased so as to enhancing the adsorption capacity of MnFe2O4 surface hydroxyl groups. On the other hand, it was indicated silver had played the role of the bridge to transferring electron in catalytic reaction, reducing the activation energy of of catalysts, and accelerating the production of -OH to enhance the degradation effecoxidation-reduction process between catalysts and ozone molecules, and improving reducibility t of DBP. The continuously produced intermediates Ag would consume part of -OH, so the larger content of the Ag-doped had a negative effect on the DBP removal, but the overall catalytic effect was better than MnFe2O4.There should be large improvement in DBP removal after small amout of Ag-doped of MnFe2O4. |
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