Complicated and strict protocols are followed to tune the size of gold nanoparticles (GNPs) in chemical synthesis methods. In this study, we address the polarity of solvents as a tool for tailoring the size of GNPs in the chemical reduction method. The effects of varying polarity index of the reaction medium on synthesizing gold nanoparticles by chemical reduction method have been investigated. Ethanol as a polar solvent, ethanol–water mixture as reaction medium, L-ascorbic acid as reducing agent, and polyvinylpyrrolidone as stabilizer were used to synthesize GNPs. The polarity index of the reaction medium was adjusted by changing the volume ratio of ethanol to water. UV–Vis, dynamic light scattering (DLS), and transmission electron microscopy (TEM) characterizations reveal that the growth of nanoparticles was gradually increased (~ 22 to 219 nm hydrodynamic diameter) with decreasing value of polarity index of the reaction medium (~ 8.2 to 5.2). Furthermore, the high polarity index of the reaction medium produced smaller and spherical nanoparticles, whereas lower polarity index of reaction medium results in bigger size of GNPs with different shapes. These results imply that the mechanistic of the growth, assembly, and aggregation phenomena of ligand or stabilizer-capped GNPs strongly rely on the polarity of solvent molecules. Using the proposed methodology, wide size range of GNPs with different morphology sizes can be synthesized by simply modulating the volume percentage of organic solvent in the reaction medium.

在化学合成方法中，遵循复杂而严格的协议来调整金纳米颗粒（GNP）的大小。在这项研究中，我们将溶剂的极性作为在化学还原方法中调整GNP大小的工具。研究了反应介质极性指数的变化对化学还原法合成金纳米粒子的影响。乙醇用作极性溶剂，乙醇-水混合物作为反应介质，L-抗坏血酸作为还原剂，聚乙烯吡咯烷酮作为稳定剂用于合成GNP。通过改变乙醇与水的体积比来调节反应介质的极性指数。UV-Vis，动态光散射（DLS），透射电子显微镜（TEM）表征表明，随着反应介质极性指数的降低（〜8.2至5.2），纳米颗粒的生长逐渐增加（流体动力学直径约为22至219 nm）。此外，反应介质的高极性指数产生较小且球形的纳米颗粒，而反应介质的较低极性指数导致较大尺寸的具有不同形状的GNP。这些结果暗示配体或稳定剂封端的GNP的生长，组装和聚集现象的机理强烈依赖于溶剂分子的极性。使用所提出的方法，可以通过简单地调节反应介质中有机溶剂的体积百分比来合成具有不同形态大小的宽范围GNP。