The two-step electrosynthesis of nanocomposites of Ag, Au, and Pd nanoparticles with iron(ii) oxide-hydroxide

Abstract

The two-step electrosynthesis of metal nanoparticle (MNP, M = Ag, Pd, and Au) nanocomposites with iron oxide-hydroxide FeO-xFe(OH)₂ was investigated. The first step of the amorphous FeO-xFe(OH)₂ synthesis in an undivided cell using a soluble Fe-anode and dissolved atmospheric oxygen as the reagent proceeds efficiently in a DMSO medium. The second step of mediated electrosynthesis of MNPs in the resulting solution of FeO-xFe(OH)₂ depends on the nature of the mediator. When p-benzoquinone (BQ) is used as a mediator, the mediated reduction of M^z+ does not occur. If the mediator is methylviologen (MV²⁺), MNP electrosynthesis in the absence and presence of cetyltrimethylammonium chloride (CTAC) proceeds efficiently. The M/FeO-xFe(OH)₂ nanocomposites are obtained in bulk solution. In the case of the Ag nanocomposite in the absence of CTAC, AgNPs are large particles with a size of 49 ± 17 nm (TEM), and the metal crystallite size is 10–19 nm. In the synthesis of Pd, Au nanocomposites stabilized with CTAC, the formed large aggregates consist of smaller metal particles (7 ± 1 nm (Pd), 14 ± 6 nm (Au)), and the metal crystallites sizes are 3–6 nm (Pd) and 8–13 nm (Au). The Pd@CTAC/FeO-xFe(OH)₂ nanocomposite exhibits high catalytic activity in the p-nitrophenol reduction reaction by sodium borohydride, which increases with increasing concentration of CTAC.