Green, sustainable, and room-temperature synthesis of silver nanowires using tannic acid – Kinetic and parametric study

This study reports the green, room-temperature and light-assisted synthesis of silver nanowires (AgNWs) using tannic acid as both the reducing and capping/stabilizing agents. Although the green synthesis of silver nanowires can offer several advantages in terms of simplicity, environmental friendliness, and cost-effectiveness, most of these processes suffer from substantial variability due to uncertain experimental factors, which makes their reproduction challenging. One of the factors that is often neglected in such processes is light, which can significantly affect the synthesis process and as a result alter the morphology of the final nanostructures. In this study, three different light conditions including dark (0 LUX), partially illuminated (90 LUX), and fully illuminated (676 LUX) were considered for the synthesis of silver nanostructures, and the change in morphology with respect to light intensity was evaluated. The results suggested that light intensity can significantly change the reduction capability of tannic acid, and that a relatively weak illumination condition is necessary for the growth of AgNWs when tannic acid is used as the reducing agent. The AgNWs were found to have an average diameter and length of 24.4 ± 6.6 nm and 11.4 ± 3.2 µm, respectively in partially illuminated condition. The synthesized silver nanostructures and nanowires were characterized using scanning electron microcopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and UV–visible spectroscopy (UV–vis). In addition, the consumption of Ag+ ions for all illumination conditions was measured to observe how the reduction rate is affected by illumination. The results suggested that the reduction rate has a direct relation with respect to light intensity. The Ag+ concentration with respect to time was analyzed by the pseudo-first order kinetics model, a modified pseudo-first order model previously introduced by Finke and Watzky, and a new proposed empirical model. Furthermore, the effect of other factors such as the tannic acid/silver nitrate molar ratio, pH, and stirring rate were investigated to observe how the morphology of silver nanostructures and the yield of AgNWs change. Considering tannic acid, a green and abundantly available compound, as the only reducing and capping/stabilizing agent, while using merely light as a reduction assisting input, this procedure can serve as a useful approach towards the scalable, inexpensive, and sustainable synthesis of AgNWs with relatively high yield and aspect ratio, which has not been reported before to the best of the authors’ knowledge. The green and sustainably synthesized AgNWs are promising candidates for manufacturing a new generation of transparent conductive films (TCFs) known as eco-friendly transparent conductive films (Eco-TCFs) for electronic applications. This study will shed light to the industrially-relevant sustainable metal nanostructures synthesis and fundamentally contributes to the advancement of the green nanotechnology field. These fundamental advances will eventually seek to solve two critical problems, namely that of capital investment and environmental footprints of metal nanostructures synthesis.