Structural engineering of highly ordered TiO2 nanotube array by periodic anodization of titanium

► Continuously fabricating multilayer TiO2 NT arrays with controllable diameter by periodic anodization. ► Periodic pulses, consisting of high and low voltages, were applied to fabricate TiO2 NTs with periodically changing morphology. ► Introducing a new way of reusing old electrolyte which was usually discarded in conventional anodization method.