  Gold-decorated TiO$_2$ nanotubes were used for the photocatalytic abatement
of Hg(II) in aqueous solutions. The presence of dewetted Au nanoparticles
induces a strong enhancement of photocatalytic reduction and scavenging
performances, with respect to naked TiO$_2$. In the presence of chlorides, a
massive formation of Hg2Cl2 nanowires, produced from Au nanoparticles, was
observed using highly Au loaded photocatalysts to treat a 10 ppm Hg(II)
solution. EDS and XPS confirmed the nature of the photo-produced nanowires. In
the absence of chlorides and/or at lower Hg(II) starting concentrations, the
scavenging of mercury proceeds through the formation of Hg-Au amalgams. Solar
light driven Hg(II) abatements up to 90% were observed after 24h. ICP-MS
analysis revealed that the removed Hg(II) is accumulated on the photocatalyst
surface. Regeneration of Hg-loaded exhaust photocatalysts was easily performed
by anodic stripping of Hg(0) and Hg(I) to Hg(II). After four
catalytic-regeneration cycles only a 10% decrease of activity was observed.
