Preparation Of AgI-ZnO Nanocomposites And Their Properties

As we all know, crystal defects have tremendous effect on the crystal structure, and doping is an effective means to obtain the crystal defects. In oxides with nano-crystalline structure, the point defects can be obtained by doping other elements, and the surface defects can be obtained by doping other compounds. So far, both point and surface defects have been paid much attention to about their doping methods and the improvement to the structure sensitive of crystal. However, research of the design, control, type and change of the multiplex defects is insufficient, and it has been an emerging subject in the field of crystal materials.In the paper, the nano-powders of AgI-ZnO composites were prepared by liquid precipitation method and at the same time, multiplex defect composed by point defect and surface defect can also be obtained. The multiplex defect was characterized by XPS, XRD, ESR and Raman, and based on this, we investigated the thermal catalytic and the photo catalytic properties of the AgI-ZnO nanocomposites, realized the assessment of the effect of the multiplex defect to the crystal material properties.The followings are the main research work and results.(1) AgI-ZnO nanocomposites with different doping rates of AgI are prepared by precipitation method. The results of TG-DSC, SEM and TEM indicated that when the doping rate of AgI is 0.3%, the product with a good dispersion and uniform size 50 nm could be obtained after calcining the precursor at 350℃for 1 h. XRD analysis revealed that ZnO existed in the nanocomposites had a wurtzite structure and a high crystallinity. The precipitation is an effective method for the compound of AgI and metal oxides.(2) Based on the analytical tools of XPS, ESR and Raman, it can be concluded that AgI was stuffed in the lattice of ZnO. Compared with the pure ZnO, the oxygen vacancy concentration in AgI-ZnO increased and the sample of 0.3% was the highest one. In addition, with the doping rate of AgI increased, the crystallization degree of ZnO was weakened but the lattice structure hadn't change.(3) As a thermal catalyst, AgI-ZnO nanocomposite was used to decompose AP. The results showed that composite of 0.3% which could make the high-decomposition temperature of AP decreased from 433.6℃to 301.8℃had the best catalytic properties. Moreover, the high-decomposition temperature would continue reduce to 293℃when the add content of nanocomposite came to the best one of 5.0%. Dynamic analysis revealed that the adding of nanocomposite to AP leaded to a reduction of apparent activation energy from 164.50 kJ/mol to 86.34 kJ/mol, and the reaction rate constant also improved greatly. As a photo catalyst, the nanocomposite was used to degrade MB. As the doping rate of AgI increased, the photo catalytic effect became better. Compared to pure nano-ZnO, the nanocomposite catalyst increased the absorption of visible-light. The addition of catalyst in the solution had a minor effect to the photo catalytic result. Even though the sample is reused for 6 times, the degradation rate of MB after reacting for 35 min could also reach to 98%. Therefore, AgI-ZnO nanocomposite showed an excellent catalytic performance, and the research made a new exploration to the application of compound materials of AgI and metal oxides.(4) Analyze the catalytic reaction mechanism of the nanocomposite, the results revealed that there are two very important factors which affect the reaction, one is the electron transfer rate and the other is the concentration of oxygen defects. During the thermal catalytic decomposition process of AP, they both play a positive role and have the same direction. When degraded the MB dye, the increase of the concentration of oxygen defects benefited the positive reaction, however, too high rate of the electron transfer can resulted in two competitive function. On one hand, that would reduce the probability of the compound of electron and hole, and therefore enhanced the photo catalytic effect. On the other hand, the electron lost the original reduction effect, and that wasn't conducive to the degradation. Competition of the two respects caused that the improvement of the photo catalytic wasn't significant like that of the thermal catalytic. The paper completed the characterization of the AgI-ZnO nanocomposites prepared by precipitation, the construction and the properties of multiplex defects existed in the nanocomposites. The work provides a reference to the preparation of interface defects in functional nanomaterials.