氧化锌在硅胶表面的分散状态及ZnO/SiO_2表面酸性的研究

用X射线相定量方法测定了氧化锌在硅胶表面分散的阈值;用XPS证明ZnO是富集在样品表面的,表面的ZnO量有一定的限制,此值与X射线相定量所得的阈值相符;测定了样品的表面酸性,表明在ZnO/SiO_2表面上有单独的氧化物所没有的、较强的酸性位置,酸量也明显增加。酸量与ZnO的表面浓度相对应,阈值处表面酸量最大。提出ZnO在SiO_2表面上呈分散状态,以及分散在表面上的ZnO与载体表面相互作用形成某种酸性结构单元使样品呈现表面酸性的新观点。     

DISPERSION STATE OF ZINC OXIDE ON SURFACE OF SILICA GEL AND SURFACE ACIDITY OF ZnO/SiO_2

The dispersion threshold level of zinc oxide on silica gel was determined by X-ray quantitative phase analysis. And the results of XPS experiments show that the surface of the sample is enriched with ZnO and there is a limit for the ZnO amount dispersed on the surface. The value of this limit is corresponding with the threshold level obtained by XRD. The measurements of surfaee acidity show that there are some stronger acid sites on the surface of ZnO/SiO_2, they have not been found on the ZnO or SiO_2 individually, and the total amount of acid increases remarkably. The acidity depends on the ZnO concentration in the surface phase and reaches the maximum at the threshold value.In this paper, we propose a new point of view for the origin of the acidity on surface of the ZnO/SiO_2 samples. ZnO is well dispersed on the surface of SiO_2 gel in a monolayer state. In this situation, some new surface structure units emerge as a result of interaction between dispersed ZnO and the carrier, which are responsible