Two-Step Mediated Electrosynthesis and Catalytic Activity of Au/Cu₂O@poly(N-vinylpyrrolidone) Nanocomposite

Efficient two-step methylviologen (MV²⁺) — mediated electrosynthesis of a nanocomposite of gold nanoparticles with copper(I) oxide stabilized by a shell of poly(N-vinylpyrrolidone) (Au/Cu₂O@PVP) was performed in DMF at room temperature at the potentials of MV^.+ radical cation generation. At the first step, the mediated reduction of Cu²⁺ ions, generated in situ by dissolution of the copper anode, in the presence of dissolved oxygen or with subsequent oxidation with oxygen, leads to Cu₂O@PVP composite containing Cu(0) and Cu₂O in a different ratio. In the latter case, the resulting composite is in the form of stable nanoroses. When AuCl is added into the resulting solutions of Cu₂O@PVP, the partial chemical reduction of AuCl by Cu(0) occurs to form Au(0) and CuCl. At the second step, the electrochemical reduction of AuCl leads to Au/Cu₂O@PVP nanocomposite not containing Cu(0), but nanoroses are preserved. Cu₂O@PVP nanoparticles are catalytically inactive in the reduction reaction of p-nitrophenol with sodium borohydride in water, and Au/Cu₂O@PVP nanocomposites exhibit catalytic activity. In the presence of cetyltrimethylammonium chloride, the catalytic activity of both types of particles sharply increases; in the case of Cu₂O@PVP, the increase is so high that the catalytic activity becomes the same as for Au/Cu₂O@PVP.