吸附相反应技术制备Ag纳米粒子的反应机理

利用吸附相反应技术在SiO2表面制备Ag粒子, 研究了温度变化对载体表面NaOH的吸附、生成Ag的反应过程以及产物Ag粒子形貌的影响. NaOH的吸附率测定结果表明, 吸附平衡时间随着温度升高而增加. 温度升高加快了NaOH与Si—O—Si的反应, 使得NaOH的平衡吸附率不随吸附层的破坏而减少. 采用实时在线UV-Vis光谱研究了Ag粒子的生成过程, 发现温度超过40 ℃时, 反应体系中Ag出现的时间、Ag粒子的浓度和粒径分布范围都发生较大变化. 样品的TEM和XRD分析也表明, 当体系温度超过40 ℃时SiO2表面Ag粒子出现了团聚, 其晶粒粒径也出现了突变. 温度升高导致表面吸附层破坏, 使得Ag的生成场所从吸附层转移到SiO2表面, 最终导致Ag的反应机理和粒子形貌的变化.

Reaction Mechanism of Preparation of Ag Nanoparticles by Adsorption Phase Reaction Technique

Ag nanoparticles were prepared on SiO2 surface at different temperatures via adsorption phase reaction technique. The influence of temperature on adsorption of NaOH, reduction reaction of Ag and morphology of Ag nanoparticles was studied. Measurement results of adsorbed NaOH indicate that adsorption of NaOH needed more time to reach equilibrium with temperature increasing. The reaction of NaOH with Si—O—Si became more rapid due to increase of temperature, which resulted in little change of equilibrium percentage of NaOH with decrease of adsorption layer. The reduction reaction of Ag was characterized by UV-Vis adsorption spectra. The results suggest that when temperature reached 40 ℃, induction time, concentration and size distribution of Ag nanopartcles all changed greatly. When temperature increased to 40 ℃, there was great glomeration in morphology of sample analyzed by TEM and a sharp increase appeared in grain size gained by XRD. Adsorption layer was destroyed with temperature increasing, which resulted in the generation region of Ag nanoparticles transferred from adsorption layer to SiO2 surface. Moreover this change of reaction region resulted in the great change of reduction reaction mechanism of Ag and morphology of particles.