(386c) Green Synthesis of One-Dimensional Silver Nanostructures Using Tannic Acid Simultaneously As Reducing, Stabilizing, and Capping Agent-Parametric Study

The green synthesis of metallic nanostructures has risen as a promising alternative for the conventional chemical and energy-intensive methods. Most novel green methods include the use of biological reagents such as living microorganisms (e.g. bacteria, fungus, microalgae), or plant-based reagents such as vitamins, sugars, and bark/leave extracts, to name a few. Plant-based reagents are more favorable in terms of higher conversion rate of metal ions to metal atoms, non-pathogenic behavior, and process simplicity. Tannins are a particular group of plant-based polyphenols that can be used simultaneously as reducing, stabilizing, and capping agents for the synthesis of metallic nanoparticles at room temperature. Despite the few studies carried out on the synthesis of silver nanowires (AgNWs) using tannins, the effect of different reaction conditions as well as underlying mechanisms need more investigation and in-depth analysis.

In this work, we report using tannic acid, which is a hydrolysable form of tannin, for the synthesis of AgNWs at room temperature without using any external capping agent or stabilizer. We have investigated the effect of different reaction conditions including tannic acid concentration, silver precursor concentration, pH, and stirring rate. Such factors were analyzed to identify the most optimal condition for the synthesis of silver nanowires with the highest yield. Furthermore, the photosensitivity of the reduction reaction is analyzed by investigating the effect of light. In addition, a kinetic study was performed using the UV-Visible spectroscopy (UV-Vis) to analyze the reduction kinetics at different illumination conditions. The Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-Ray (EDX) were also used to characterize the size and morphology of AgNWs, and to compare the yield of AgNWs corresponding to different reaction conditions.

The results demonstrated that the tannic acid-mediated reduction process is highly photosensitive, and the rate of reduction (Ag⁺ conversion to Ag⁰) can be significantly affected by environmental light. We also report the synthesis of AgNWs with moderate to high yield at acidic conditions, controlled by the amount of light being transmitted into the system. Furthermore, the kinetic analysis sheds light on the reduction process and aims to illustrate how the reduction rate can be used as a quantitative knob to maximize the concentration of multiple twinned seeds that are favorable for the one-dimensional (1D) nanostructures growth including AgNWs. The synthesized AgNWs can be used for the preparation of electrically conductive materials such as transparent conductive films (TCFs) for flexible electronics.