A more direct way to make catalysts: one-pot ligand-assisted aerobic stripping and electrodeposition of copper on graphite

Abstract

Electrodeposition of metals onto conductive supports such as graphite potentially provides a lower-waste method to form heterogeneous catalysts than the standard methods such as wet impregnation. Copper electrodeposition onto pressed graphite disc electrodes was investigated from aqueous CuSO₄–ethylenediamine solutions by chronoamperometry with scanning electron microscopy used to ascertain the particle sizes obtained by this method. The particle size was studied as a function of pH, CuSO₄–ethylenediamine concentration, and electrodeposition time. It was observed that decreasing the pH, copper–ethylenediamine concentration and time each decreased the size of the copper particles observed, with the smallest obtained being around 5–20 nm. Furthermore, electroless aerobic oxidation of copper metal in the presence of ethylenediamine was successfully coupled with the electrodeposition in the same vessel. In this way, deposition was achieved sequentially on up to twenty different graphite discs using the same ethylenediamine solution, demonstrating the recyclability of the ligand. The materials thus prepared were shown to be catalytically active for the mineralisation of phenol by hydrogen peroxide. Overall, the results provide a proof-of-principle that by making use of aerobic oxidation coupled with electrochemical deposition, elemental base metals can be used directly as starting materials to form heterogeneous catalysts without the need to use metal salts as catalyst precursors.