Gold Nanorods Capped with Different Ammonium Bromide Salts on the Catalytic Chemical Reduction of p-Nitrophenol

Abstract

It is known that the reactivity of the nanocatalytic systems is related to the particle size and shape and also to the features of the capping agents on the nanostructures. In this study, gold nanorods (AuNRs) were synthesized by the seed-mediated method using different tetraalkylammonium bromide salts as capping agents, that are, cetyltrimethylammonium (CTABr), N,N-dimethyl-N‑cetyl-N-(2-hydroxyethyl)ammonium (HEA16Br), and N,N-dimethyl-N-cetyl- N-(2-hydroxypropyl)ammonium (HPA16Br), and used as catalyst for the chemical reduction of p-nitrophenol (PNP) in the presence of NaBH4. The catalytic systems were characterized by ultraviolet-visible (UV-Vis) absorption spectroscopy and transmission electron microscopy (TEM). The effect of the ammonium bromide-based capping agent on the catalytic activity of AuNRs was evaluated by performing the chemical reduction of p-nitrophenol in the presence of excess NaBH4 in aqueous medium. Under the reaction conditions employed, the catalytic systems displayed detectable subtle differences in terms of induction times and apparent activation energy (Ea) values. These results show that slight changes carried out in the chemical structure of the capping agent are able to imprint even slightly modification of the kinetic parameter of the catalytic reaction.

Polyethylenimine as a Versatile Simultaneous Reducing and Stabilizing Agent Enabling One-Pot Synthesis of Transition-Metal Nanoparticles: Fundamental Aspects and Practical Implications

“…21,22 From the catalytic point of view, the adverse impact of capping agents is a consensus because it hampers the access of the reactants to the catalyst surface, 23,24 although their presence is inevitable to promote colloidal stability. The catalytic performance is influenced by the chemical nature of the stabilizer 25 and the respective degree of coating (how densely the metallic nanoparticles are coated by the polymer chains). 26 The key influence of the polymer capping was also evidenced by us with regard to biological properties.…”