Photocatalytically driven dissolution of macroscopic metal surfaces. Part 1: Silver

We present the first observation of photocatalytically driven, hydrogen peroxide mediated, dissolution of a macroscopic metal surface. Specifically, we report on the dissolution of silver in the presence of photocatalytically generated H2O2 produced by ultra-band gap illumination of TiO2 at 365 nm in the presence of O2. Direct measurements of photocatalytically generated H2O2 in the TiO2 suspensions studied indicate that peroxide concentration never exceeds 32 μmol dm−3. However, comparison of electrochemical quartz crystal microgravimetrically determined rates of Ag dissolution with rates recorded from solutions spiked with H2O2 indicates that dissolution occurs at a rate equivalent to a bulk solution concentration of ∼100 mmol dm−3 H2O2. This suggests that a local enhancement occurs in the rate of photocatalytically induced metal dissolution on surfaces under direct illumination, which is attributed to two causes: (i) local modification of the TiO2 by deposition of dissolved Ag, so increasing its efficiency for peroxide generation; and (ii) peroxide generation local to the electrode surface mitigating against photolytic loss reactions seen to occur in the solution bulk. The photoinduced dissolution process is found to be both highly controllable/light switchable and spatially specific.