Continuous Synthesis of Copper Nanowires in a Stirred Tank Reactor with Reagent Recycling

Copper nanowires (CuNWs) are promising materials for electronic and thermal applications; however, their scalable synthesis remains challenging because most reported methods rely on batch processing. Herein, we demonstrate a substrate-free continuous synthesis of CuNWs in a continuously operated stirred tank reactor (CSTR) using an aqueous chemical reduction route with integrated product withdrawal and reagent recycling. A quantitative image-analysis-based quality parameter (q), combining nanowire length, diameter, and impurity content, was introduced and used as the response variable in a central composite design optimization of reagent flow rates. Under optimized conditions (EDA: 1.2 mL h –1; hydrazine: 0.2 mL h –1 ), the process produced high-aspect-ratio CuNWs (length ∼45 μm, diameter ∼170 nm) with stable reactor operation for 44 h and an overall yield of 71.5%. The recovered nanowires form stable CuNW–ethylene glycol nanofluids, exhibiting a 19.64% enhancement in thermal conductivity at 0.15 vol % loading with minimal viscosity increase.