Synthesis of Au Nanorods through Prereduction with Curcumin: Preferential Enhancement of Au Nanorod Formation Prepared from CTAB-Capped over Citrate-Capped Au Seeds

Abstract

Despite seed-mediated growth approach being the state of art method for synthesis of gold nanorods, the mechanism of gold nanorod formation to control final aspect ratio of the nanorods is not yet well understood. In this work, formation of Au nanorods has been investigated using curcumin, a hydrophobic molecule, as secondary reducing agent, instead of popularly used hydrophilic ascorbic acid. It is found that the nature of the secondary reducing agent plays a crucial role in preferential enhancement of Au nanorod formation. Although in the seed-mediated growth approach the concentration of curcumin has similar effect on Au nanorod formation as observed for ascorbic acid earlier, the combination of the nature of the capping agent of seed particles as well as that of the secondary reducing agent determines the final aspect ratio of the nanorods. Hydrophobic (secondary) reducing agent, curcumin, prefers CTAB capped seed solution compared with citrate capped seed solution. The mechanism of nanorod formation has been explored. AgNO3 is known to enhance the aspect ratio of the nanorod formation when the ascorbic acid and citrate capped seed method is used; however, in contrast when curcumin is used, AgNO3 encourages nanorod formation for only CTAB capped seed solution but discourages nanorod formation for citrate capped seed solution. A mechanism has been suggested for this discrepancy. Present results help to gain more understanding of the formation process by bringing new insight in the mechanism of Au nanorod formation through seed-mediated growth approach, which may trigger better design of nanomaterials. © 2015 American Chemical Society.