Hierarchically ordered networks comprising crystalline ZrO2 tubes through sol–gel mineralization of eggshell membranes

A facile sol–gel coating procedure has been successfully applied for the ZrO2 coating of eggshell membranes (ESM), resulting in hierarchically ordered thin films with a macroporous network structure comprising crystalline ZrO2 tubes. This hierarchical material, which was obtained through sol–gel mineralization of the ESM template and subsequent calcination at 600 uC, was characterized by XRD, SEM, TEM, HRTEM, and nitrogen sorption measurements. It has been shown that this ZrO2 material exhibits a macroscopic morphology of a film with a thickness about 15 mm; the film has a microstructure of macroporous networks composed of interwoven ZrO2 microtubes with diameters less than 1.0 mm; the tube walls consist of tetragonal ZrO2 nanocrystals with an average crystallite size about 6 nm. It shows a specific surface area of 55 m g and a BET average pore size of 7.0 nm, which is mostly due to the ZrO2 nanocrystals constituting the tube walls. It has also been shown that calcination of the initial ESM/zirconium precursor hybrid at 700 uC resulted in significant fusion between neighboring ZrO2 tubes accompanying a tetragonal-to-monoclinic phase transformation of zirconia.