Facile fabrication of freestanding through-hole ZrO2 nanotube membranes via two-step anodization methods

► Freestanding and tubular ZrO2 membrane was prepared by anodization. ► Two methods were used to fabricate the two-end opened ZrO2 membranes. ► Potential shock method and reducing potential method were adopted. The growth mechanisms of the two-end opened ZrO2 nanotube arrays were investigated.