Hydrothermal synthesis of conductive copper nanowires: effect of oleylamine and dextrose concentrations

One-dimensional (1-D) metallic nanoparticles (i.e., nanowires, nanorods) exhibit unique properties and are useful in a variety of applications. 1-D copper nanowires (CuNWs) exhibit excellent electrical conductivity making them an economical alternative in applications that typically employ silver or gold nanowires. In this study, CuNWs were synthesized via an environmentally benign and scalable hydrothermal synthesis method using CuCl₂ (CuP) as a copper precursor. Oleylamine (OAm) and dextrose (D) were employed as capping and reducing agents, respectively. The focus of this work was to investigate the influence of varying CuP : OAm and CuP : D molar ratios during synthesis on the nanowire growth, morphology, and electrical conductivity. A series of synthesis trials were conducted by only varying CuP : OAm or CuP : D molar ratios, while keeping all other reaction conditions constant. Morphological analysis of the synthesized products suggests that both OAm and D are essential for the formation of CuNWs. A synthesis conducted at a 1 : 3.75 : 1.1 CuP : OAm : D molar ratio produced nanowires with average diameter of 96 nm, while higher OAm concentration resulted in CuNWs with larger diameters. X-ray diffraction analysis confirmed the crystalline nature of the synthesized CuNWs, with diffraction peaks corresponding well to those of FCC copper. The capping of CuNWs with OAm was confirmed through FTIR spectroscopy. Thermogravimetric (TGA) studies on CuNWs show that OAm content in CuNWs increases with increasing CuP : OAm molar ratio during synthesis. The electrical conductivity of CuNW pellets was found to decrease with increasing CuP : OAM molar ratio during synthesis. The highest conductivity of 1.38 × 10⁵ S cm^-1 was exhibited in the sample made using 1 : 3.75 : 1.1 CuP : OAm : D molar ratio. Furthermore, holding CuNWs pellets under ambient conditions for 60 days did not affect their electrical conductivity.