Removal of surfactant and capping agent from Pd nanocubes (Pd-NCs) using tert-butylamine: its effect on electrochemical characteristics

Abstract

Synthesis of shape-controlled nanoparticles of precious metals with defined size is well-established in the literature and the control over shape and size is achieved using surfactants and capping agents. However, a clean surface without impurities is required for realistic applications. In the present investigation, palladium nanocubes are synthesized using poly(vinylpyrrolidone) and potassium bromide. A novel method for cleaning the nanoparticle surface, i.e., treatment with tert-butylamine is reported. For comparison, a part of the untreated sample is subjected to the commonly used method of heat-treatment in an oxygen atmosphere for surface cleaning. The XPS and FTIR spectra of the heat-treated sample show incomplete removal of PVP and complete removal of Br⁻ and the XRD pattern suggests oxide formation on the Pd surface. Treatment with tert-butylamine provides a clean surface free of PVP and Br⁻. Cleanliness of the surface is further confirmed by the voltammograms and ORR activities in 0.1 M HClO₄. We conclude that tert-butylamine can be an effective solvent for the removal of PVP and a reagent for Br⁻ ions because of its ability to form a quaternary ammonium salt.