Formation of self-inhibiting copper(II) nanoparticles in an autocatalytic Fenton-like reaction.

Cu(II)-catalysed decomposition of hydrogen peroxide at alkaline pH in the presence of etidronic acid (HEDP) showed a sigmoid kinetic profile typical of autocatalytic reactions. However, the reaction abruptly stopped well before all hydrogen peroxide had decomposed, and further addition of Cu(II) and HEDP did not restart the reaction. Results of a mechanistic study suggest that the reaction involves the formation of an active catalyst which decomposes hydrogen peroxide and oxidizes HEDP. Once all HEDP has been consumed, the active complex triggers Cu(II) aggregation to form remarkably stable but catalytically inactive nanoparticles. The nanoparticles were found to be basic Cu(II) phosphate/carbonate. They exhibit self-poisoning behaviour in the hydrogen peroxide decomposition and undergo seed-mediated growth upon addition of further Cu(II).