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

Francyelle De Oliveira,Lucas Nascimento,Simoni Meneghetti,Claudia Calado,Monique Da Silva,Mario Meneghetti

doi:10.21577/0103-5053.20210019

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.

Highlights

In the study reported we prepared catalytic systems based on gold nanorods (AuNRs) with different capping agents based on ammonium bromide and compered their catalytic properties on the reduction of p-nitrophenol (PNP) to p-aminophenol (PAP) under the same number of catalytic nanoparticles
We carried out a systematic study of reactions for the chemical reduction of PNP in the presence of NaBH4 and AuNRs capped with three different capping agents based on the ammonium bromide salts, CTABr, HEA16Br and HPA16Br, as catalysts
The substrate must pass through the barrier formed by the capping agents (CTABr, HEA16Br, or HPA16Br) that surrounds the AuNRs, and we suggest that the access of the substrates to the gold surface is different for each system

Summary

Introduction

In contrast to the bulk form, gold in nanometric scale presents particular chemical properties and can even be employed as a catalyst in important chemical reactions,[1,2] such as C-C and C-Het bond formation,[3,4] oxidation,[5,6] hydrogenation[7] and chemical reduction.[8,9,10] The catalytic activity of gold nanoparticles (AuNPs) is related to the large number of atoms present on the surface of the nanoparticles, i.e., large surface/volume ratios,[11] and to singular properties of these particles that arise due to quantum confinement.[12]. In the study reported we prepared catalytic systems based on gold nanorods (AuNRs) with different capping agents based on ammonium bromide and compered their catalytic properties on the reduction of p-nitrophenol (PNP) to p-aminophenol (PAP) under the same number of catalytic nanoparticles.

Results

Conclusion