Conformational changes in self-assembled monolayers of 4-pyridineethanethiol and 2-aminoethanethiol on the gold nanoparticle-graphene oxide composite and advantages in Hg(II) determination

Abstract

In this study, the advance in modification of glassy carbon electrode (GCE) has been further developed for enhancing advantages in Hg(II) determination by differential pulse voltammetry. A composite of gold nanoparticles (AuNPs) and graphene oxide (GO) was first produced under the reduced potential of Au(III). The composite was then modified with self-assembled monolayer (SAMs) of 4-pyridineethanethiol (PET), which followed by an introduction of 2-aminoethanethiol (AET). Properties of the synthesized AuNPs and the modified SAMs were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), and infrared reflection absorption spectroscopy. The results indicated that the presence of GO did not only increase the active surface area, but also involved in the intermolecular interactions. The latter property which is similar to the role of AET led to reduction of the highly ordered state of alkyl chains and conformations of terminated groups in alkanethiolates. This postulation was in good agreement with the interaction energy calculated by density functional theory (DFT). The influence of various parameters on the voltammetric response of Hg(II) was also investigated. Under the optimized conditions, the modified GCE offered higher sensitivity in the Hg(II) determination. The linear correspondence of the peak current response to the concentration of Hg(II) was from 0.149 to 17.421 nM with a correlation coefficient of 0.999, and with the detection limit of 0.012 nM (signal/noise = 3). The modified GCE was also employed to determine Hg(II) in sampled water collected in different local areas, which showed satisfactory results.