Fabrication of nitrogen-doped mesoporous TiO₂ layer with higher visible photocatalytic activity by plasma-based ion implantation

Nitrogen-doped porous TiO₂ layers were fabricated on the titanium substrate by plasma-based ion implantation sequentially using He, O₂ or N₂ atmospheres. Post implantation annealing at 570 °C generates a mixture of anatase with a small fraction of rutile in the implanted layer. In order to enlarge the specific surface area, a mesoporous surface structure was produced by exposing the helium bubbles at the sub-surface after removing the surface compact layer using argon ion sputtering. Nitrogen doping extends the photoresponse into the visible light region. Moreover, a lower dose of 4 × 10¹⁵ N/cm² induces a stronger visible light absorption. The photodegradation of Rhodamine B solution with visible light sources indicates that the mesopores at the fresh surfaces and nitrogen doping, both individually and in combination, contribute to an apparent increase in the photodegradation rate.