TEM characterization of iron-oxide-coated ceramic membranes

Commercially available porous alumina–zirconia–titania ceramic (AZTC) membranes having a titania surface coating were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and the Brunauer–Emmett–Teller (BET) method. TEM photomicrographs showed the as-received AZTC membrane to be a multi-layered structure consisting of a porous alumina–zirconia–titania core having ultrafine pore sizes, coated by an additional layer of nanoporous titania. Electron diffraction studies revealed an amorphous surface titania layer while the underlying AZTC membrane was crystalline. The AZTC membranes were coated 20, 30, 40, 45, or 60 times with iron oxide (Fe 2 O 3 ) nanoparticles, after which the membranes were sintered in air at 900 °C for 30 min. TEM revealed a relatively uniform nanoporous Fe 2 O 3 coating on the sintered, coated membranes, where the Fe 2 O 3 coating thickness increased with increasing number of layers. Electron diffraction patterns showed the Fe 2 O 3 coating to be crystalline in nature. This was confirmed by the XRD results showing the structure to be α-Fe 2 O 3 , while the AZTC membrane was a mixture of the anatase and rutile phase of TiO 2 as well as ZrO 2 and corundum, Al 2 O 3 . The average pore size of the underlying AZTC membrane increased after the Fe 2 O 3 -coated membrane was sintered. The nanoporosity in the sintered Fe 2 O 3 coating increased until 40 layers, beyond which no significant increases in the average pore size were observed. The iron-oxide-coated membrane improved catalytic properties when used in combination with ozone to treat water. The optimal benefit, in terms of water treatment efficacy, was found at 40 layers of Fe 2 O 3 .