Impacts that pH and metal ion concentration have on the synthesis of bimetallic and trimetallic nanorods from gold seeds

Abstract

This paper describes the synthesis of Au–Ag bimetallic and Au–Ag–Hg trimetallic nanorods (NRs) from gold NRs, which acted as seeds, under alkaline conditions (pH ≥ 8.0) and in the presence of hexadecyltrimethylammonium bromide (CTAB), ascorbic acid, and other metal ions. The Hg²⁺, Fe³⁺, and Co²⁺ ions are stable at pH ≥ 8.5 in the presence of 200 mM glycine; these conditions allow investigations into their roles during the syntheses of the NRs. We prepared a number of differently colored NRs by controlling the pH and the nature and concentration of the metal ion. Mercury ions, which have a higher reduction potential and form a more stable complex with glycine, are reduced and deposited on the gold NRs to form Au–Ag–Hg trimetallic NRs; we confirmed this situation by performing inductively coupled plasma-mass spectrometry and energy dispersive X-ray measurements. In addition, we have demonstrated that the size and shape of the Au–Ag–Hg trimetallic NRs can be tuned by controlling the Hg²⁺ concentration.