Sized-controlled Pd nanoflowers by a non-classical growth mechanism combining the LaMer and DLVO theories and their catalytic activities

Abstract

We describe the synthesis of Pd nanoflowers in a single reaction step by reducing PdCl42-(aq) with hydroquinone. Simply by controlling the reaction temperature, we could obtain monodisperse Pd nanoflowers with well-defined shapes and sizes. Based on the detected product morphology, crystallinity, and several control experiments, a novel non-classical mechanism based on both LaMer and DLVO theories was established. Specifically, Pd nanoclusters were produced at the initial stages of the reaction, followed by their fusion to form larger polycrystalline Pd nanoparticles. These polycrystalline Pd nanoparticles served as seeds for further Pd deposition and attachment of Pd nanoclusters to generate Pd nanoflowers. In this procedure, the control over the temperature enabled us to tune the ionic strength of the solution (control over the fraction of PdCl42- and K+ ions present in the solution), which affected the attachment and aggregation steps, leading to Pd nanoflowers with controlled sizes and morphologies. When these nanomaterials were employed as nanocatalysts for electrooxidation of ethanol, the 12 nm-Pd nanoflowers were the best catalyst in terms of both activity and peak potential.