Bio-based synthesis of oxidation resistant copper nanowires using an aqueous plant extract

Copper nanowires have recently emerged as promising nanomaterials for transparent conducting electrodes applications, however, their production commonly involves the use of harmful reagents. In this study, we describe for the first time a simple and cost-effective bio-based synthesis of copper nanowires using an aqueous plant extract (Eucalyptus globulus) as the reducing/stabilizing agent and oleic acid and oleylamine as surfactants. Well-dispersed crystalline copper nanowires (lambda(max) = 584-613 nm) were obtained with average diameters in the nanometric range (44 and 145 nm) and lengths in the micrometric range (from 5 to dozens of micrometres) using extract concentrations between 10 and 50 mg mL(-1). Moreover, the aspect ratio of these nanowires can be adjusted (from around 14-20 to 160-400) by changing the experimental conditions, namely the use of oleic acid. Phenolic compounds were found to have a key role in this bioreduction process allowing to obtain practically only nanowires (without other morphologies). Nevertheless, the use of oleic acid/oleylamine is essential to manipulate their size and aspect ratio. Most importantly, these bio-based copper nanowires were found to be resistant under storage in ethanol and when submitted to air exposure, both for 2 weeks, certainly due to the adsorption of antioxidant biomolecules (phenolic) at their surface, thus avoiding the use of other polymeric protective layers. The conductivity of the CuNWs was found to be 0.009 S cm(-1). As a result, this study opens a new standpoint in this field, closing the door to the use of hazardous reagents and synthetic polymeric protective layers, on the production of stable copper nanowires with potential application as conductive materials. (C) 2019 Elsevier Ltd. All rights reserved.