Multifunctional porous titanium oxide coating with apatite forming ability and photocatalytic activity on a titanium substrate formed by plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was used to make a multifunctional porous titanium oxide (TiO₂) coating on a titanium substrate. The key finding of this study is that a highly crystalline TiO₂ coating can be made by performing the PEO in an ammonium acetate (CH₃COONH₄) solution; the PEO coating was formed by alternating between rapid heating by spark discharges and quenching in the solution. The high crystallinity of the TiO₂ led to the surface having multiple functions, including apatite forming ability and photocatalytic activity. Hydroxyapatite formed on the PEO coating when it was soaked in simulated body fluid. The good apatite forming ability can be attributed to the high density of hydroxyl groups on the anatase and rutile phases in the coating. The degradation of methylene blue under ultraviolet radiation indicated that the coating had high photocatalytic activity. - Highlights: • A highly crystalline TiO₂ coating could be made by PEO in a CH₃COONH₄ solution. • Inorganic ion-free electrolyte was a key to make the highly crystalline TiO₂ coating. • The high crystallinity led to apatite forming ability and photocatalytic activity