Production of N-doped anatase TiO2 on TiN-coated Ti substrates by plasma electrolytic oxidation for visible-light photocatalysts

N-doped TiO2 exhibiting visible-light photocatalytic activity is useful for many environmental and energy applications. In this work, N-doped anatase TiO2 coatings were facilely produced by plasma electrolytic oxidation using two types of nitrogen doping sources including the TiN seeding layers and the electrolytes consisting of (NaPO3)6 and NaOH mixed with various NH4OH concentrations. The TiN seeding layers were deposited on Ti foils by a unique air-based sputtering technique. Effects of the TiN seeding layers and the NH4OH concentrations added in the electrolytes on the characteristics and the resulting visible-light photocatalytic activity of obtained N-TiO2 coatings were investigated. Enhanced bandgap narrowing and visible-light photocatalytic activity for the coatings were achieved by using the TiN seeding layer and the optimum NH4OH concentration added in the electrolytes. The synergistic effects of both nitrogen doping sources were discussed. The facile controlled growth of N-doped anatase TiO2 coatings with uniform porous surface morphologies has great potentials in visible-light photocatalytic applications.