Visible-light-driven superhydrophilicity by interfacial charge transfer between metal ions and metal oxide nanostructures.

Single-crystalline rutile nanorods were synthesized by a facile acid treatment on titanate nanotubes. These rutile nanorods could be highly dispersed in water to form a stable colloidal solution. Cu(2+) ions were grafted onto these rutile nanorods, and the Cu(2+)-grafted nanorods could absorb visible light by the interfacial charge transfer between the valence band of rutile TiO(2) and surface-modified Cu(2+) ions. Transparent thin films of Cu(2+)-grafted nanorods were coated on substrates by a facile spin-coating method. These films exhibited superhydrophilic conversion under visible light irradiation.