吸附层对制备Ag/SiO2纳米复合材料过程的影响

分别在有水体系和无水体系中制备了Ag/SiO2纳米复合粒子，研究了吸附层对NaOH在体系中的分配、反应场所的变迁、Ag+的还原机理以及产物形貌的影响.采用电导率法测定了NaOH在SiO2表面的吸附曲线，结果表明：在有水体系中，吸附层的形成明显促进了SiO2表面对NaOH的吸附，当达到平衡时，58%的NaOH分配在SiO2表面；在无水体系中，当达到吸附平衡时仅有25%的NaOH分配在SiO2表面.溶剂置换实验结果表明：在有水体系中，吸附层是Ag生成反应进行的主要场所；在无水体系中，Ag生成反应在乙醇溶液相和SiO2表面都可以发生.利用紫外 可见光（UV Vis）光谱、X射线衍射仪（XRD）、透射电镜（TEM）和能谱仪（EDAX），对比了在有水体系和无水体系中Ag+的还原过程，阐述了吸附层对Ag+还原机理的影响.利用XRD、TEM和EDAX对Ag/SiO2最终样品进行了分析，发现在有水体系中生成的Ag粒子比在无水体系中生成的Ag粒子的粒径小，分布更加均匀.

Effect of adsorption layer on preparation process of Ag/SiO2 nanocomposite materials

Ag/SiO2 nanocomposite were synthesized in the system with additional water and in the system without water respectively.The effects of water-rich adsorption layer on distribution of NaOH,change of reaction place,mechanism of Ag reduction and characteristics of Ag were studied.The adsorption curve of NaOH was measured by electrical conductivity meter.The results indicate that the formation of adsorption layer in the system with additional water promotes the ability of silica surface to absorb NaOH.When the adsorption achieved equilibrium, the proportion of NaOH distributed on silica surface was 58% in the system with additional water,but it was only 25% in the system without water.The solventsubstituted experiments testify that reaction only takes place in the adsorption layer formed on the surface of SiO2 in the system with additional water,but in the system without water reaction takes place both in ethanol solution and on the surface of SiO2.By ultraviolet-visible(UV-Vis) adsorption spectra,X-ray diffraction(XRD),transmission electron microscopy(TEM) and energy dispersive analysis X-ray(EDAX),the mechanisms of Ag reduction reaction both in the system with additional water and in the system without water were illustrated.By XRD, TEM and EDAX,the particles of Ag formed in the adsorption layer in the system with additional water were smaller and better distributed on SiO2 than that formed in the system without water.