Laser-induced enhancement of the surface hardness of nanoparticulate TiO2 self-cleaning layer

We here report that the abrasion resistance of nanoparticulate TiO₂ self-cleaning layers can be highly enhanced without a considerable loss of photocatalytic capability. TiO₂ coating layers solution-deposited onto the glass substrate were irradiated by a pulsed ultraviolet (UV) laser at 355 nm, which modified the surface morphologies via laser-induced local melting of TiO₂ nanoparticles. The surface hardness, measured by pencil scratch test, improved with increasing laser power (P). While an unmodified TiO₂ layer revealed a hardness of 6B, it increased to 2H after the surface was irradiated at P = 0.3 W. Almost all of the stearic acid deposited on an unmodified sample disappeared after UV exposure for 12 h. The photocatalytic decomposition was slowed down on laser-irradiated TiO₂ surfaces and this is attributed to the reduction of specific surface areas as a result of the morphological modifications. However, a TiO₂ layer hardened to 2H still exhibited fairly good photocatalytic activity, decomposing more than 75% of the stearic acid after exposure for the same duration.