(536a) Continuous Green Millifluidic Synthesis of Ag Nanostructures

The synthesis of nanomaterials can be done by several chemical and physical methods including but not limited to microwave assisted, hydrothermal, heat evaporation, chemical reduction, photochemical reduction, electrochemical reduction, and so on. While nanomaterials can be successfully synthesized using these techniques, there are numerous drawbacks including high cost and the application of toxic solvents and external reducing agents, excessive material conversion, sophisticated equipment, and high-energy requirements. However, green synthesis approaches aim to achieve sustainable development of nanomaterials through the application of natural products such as reducing sugars with inherent growth terminating, stabilizing, and capping characteristics. Among different metal nanoparticles, silver nanoparticles (AgNPs) have unique and outstanding shape and size-dependent electrical, thermal, optical, catalytic, optoelectronic, and biological characteristics, which make them exceptional for several applications in a variety of fields. The morphology and structure characteristics of Ag nanostructure including size, uniformity, aspect ratio, and purity have a strong effect on the final performance of Ag nanostructure-based devices. However, green synthesis control in producing Ag nanostructure is still a challenge in batch reactor along with batch-to-batch variability. We have shown that millifluidic reactor can overcome many of the challenges in batch synthesis through control of a uniform chemical and thermal environment in a small reaction volume with the goal of reducing their final cost by an order of magnitude through the application of less expensive water based reducing agents at lower reaction temperature in a continuous manner.

The purpose of this work is continuous green synthesis of Ag nanostructures using sugar and different artificial sweeteners as reducing agent to maximize yield of synthesized AgNPs and control their morphology. Aqueous solution of AgNO₃ has been used as Ag precursor in the presence of white sugar, brown sugar, and several artificial sweeteners such as Splenda, Sweet’n Low, Caribou Coffee, and Whole Earth as reducing agent to synthesize AgNPs at low temperature in a millifluidic reactor. Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), Energy-Dispersive X-ray Spectroscopy (EDX), and Scanning Electron Microscopy (SEM) have been utilized to show the morphology and size of the synthesized AgNPs. It was shown that the Maui Raw Turbinado brown sugar can act as both a reducing agent and a capping agent to synthesize One-dimensional (1D) Ag nanostructures even in the absence of a capping agent such as polyvinyl pyrrolidine (PVP). The main ingredients of this reducing agent have been used in a small-scale batch reactor for reaction mechanism investigation by using TEM characterization and in-situ Ultraviolet–visible (UV-vis) spectroscopy to find the functional groups that allow the production of 1D Ag nanostructures using this specific brown sugar.