纳米银枝晶的液相辐射还原与自组装生长机理

Liquid-phase irradiation reduction and self-assembly growth mechanism of silver nanodendrites

以聚乙烯醇(PVA)作稳定剂,采用g-射线液相辐射还原制备具有精细分形结构的树枝状纳米银枝晶,利用透射电子显微镜(TEM)、高分辨率的透射电镜(HRTEM)、选区电子衍射(SAED)、X射线衍射(XRD)对其形貌结构进行表征,探讨树枝状纳米银枝晶的合成条件和生长机理。结果表明,PVA浓度是形成纳米银枝晶的关键因素。对于硝酸银浓度0.02 mol/L、异丙醇浓度1.0 mol/L、吸收剂量75 kGy的反应体系,适宜的PVA浓度为2.5%~5.0%。纳米银颗粒浓度是控制纳米银枝晶形成的另一个主要因素。控制吸收剂量(30~75 kGy)和硝酸银浓度(0.02 mol/L)可以提供适宜的纳米银颗粒浓度。作为自由基清除剂的异丙醇,通过与PVA相互作用影响纳米银枝晶的生长。纳米银枝晶的自组装生长机理可以描述为"还原聚集成核并生长形成多面体近球形初级粒子,初级粒子聚集融合形成孪晶、雪花状晶粒等次级粒子,次级粒子继续与初级粒子聚集融合形成树枝状纳米银枝晶"3个步骤。

Silver nanodendrites of fine fractal structure were prepared under γ-ray liquid-phase irradiation with polyvinyl alcohol（PVA） as stabilizer. The morphology of the structure was characterized by Transmission electron microscope, High-resolution transmission electron microscope, Selective electron diffraction, and X-ray diffraction. The synthesis conditions and growth mechanism of the silver nanodendrites were studied. The results showed that PVA concentration was a key factor influencing the formation of the silver nanodendrites. In a reaction system with concentration of AgNO3, isopropanol at 0.02 mol/L and 1.0 mol/L, respectively, and absorbed dose of 75 kGy, the suitable concentration of PVA was between 2.5% and 5.0%. The silver nanoparticle concentration was another major factor affecting the formation of the silver nanodendrites. A suitable concentration of silver nanoparticles could be obtained with the concentration of silver nitrate at 0.02 mol/L and the absorbed dose between 30 kGy and 75 kGy. As a free radical scavenger, isopropanol affected the growth of the silver nanodendrites by interacting with PVA. The self-assembly growth mechanism of the silver nanodendrites could be described in three steps. Firstly, silver ions aggregated, nucleated, and grew to form polyhedral near-spherical primary particles. Secondly, the primary particles aggregated to form secondary particles such as twins and snowflake-like grains. Finally, the secondary particles aggregated with the primary particles to form silver nanodendrites.