(257e) Continuous Tannin-Mediated Synthesis of Silver Nanostructures

Green methods for the synthesis of silver nanostructures have been receiving significant attention due to their non-hazardous, environmentally-friendly, and low-cost characteristics. Silver nanostructures can be synthesized using bacteria, fungus, yeast, viruses, vitamins, algae, plants and other natural compound or microorganism containing functional groups with reduction and capping capabilities. However, unlike conventional chemical and physical methods, the challenges in green synthesis process are broad size distribution, non-homogeneous morphologies, and low yield of synthesized silver nanostructures. Synthesis using plant extracts has emerged as a promising versatile method for improvement of the synthesis processes, as an alternative for current chemical and physical methods. However, the mechanism through which the reduction, nucleation, and nanoparticle growth occur is still obscure.

In this work, by using tannin as a strong reducing agent, we aim to demonstrate a facile and low-cost method for the synthesis of silver nanostructures and describe what are the most significant factors controlling the synthesis process using both in-situ and ex-situ characterization techniques. We show, how the size and morphology of the synthesized silver nanostructures change based on different reaction conditions. The in-situ Fourier-transform infrared spectroscopy (FTIR) is used to observe how different functional groups are changing during the course of reaction. In addition to that, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy
(SEM), Energy Dispersive X-Ray (EDX), and Ultraviolet–visible Spectroscopy (UV-vis) are used to characterize size and morphology of the synthesized silver nanostructures. The findings from these characterization techniques are essential to find the reaction mechanism behind the synthesis process.

It is found that the process does not need any capping agent to direct the anisotropic growth of the nanoparticles to form one-dimensional (1D) silver nanostructures such as nanorods (NRs) and Nanowires (NWs). However, the 1D silver nanostructure yield is low, and we illustrate how the application of continuous millifluidic reactors can increase their yield and can overcome the challenges in batch synthesis through control of a uniform reaction environment in a small reaction volume. These novel reactor systems offer similar advantages as microfluidic ones while being easier to fabricate, simpler to reconstruct, and even more adaptable for in-situ monitoring characterizations. Larger surface to volume ratio and precisely controlled flow patterns that consequently increase heat and mass transfer rate, coupled with inherent safety are among other advantages of flow millifluidic platforms.