Immobilization of Photocatalytic ZnO Nanopowders Using Anodized Nanoporous Alumina Substrates.

Nanoporous Al₂O₃ substrates with an average pore size of about 150 nm were prepared via anodization of Aluminum plates. Depending on the anodization condition, the surface area of the anodized Al₂O₃ was increased more than six-fold. Solution-combusted ZnO nanopowders were prepared as a function of fuel/oxidant ratios. At a fuel/oxidant ratio of 0.8, ZnO powder showed excellent powder characteristics such as average particle sizes of 30 nm and spherical shape. Electrical properties of SCM ZnO nanopowders with different fuel/oxidant ratios were investigated by Hall measurement. The carrier concentration of SCM ZnO nanopowders at the fuel/oxidant ratio of 0.8, was the highest, three-fold higher than that of any commercial ZnO powders. Using spray coating, these nanopowders were coated onto Al₂O₃ substrates for immobilization. To evaluate the photo-catalytic effect, Ag ions were removed from the wastewater via photocatalysis. The photocatalytic efficiency with the SCM ZnO nanopowders on nanoporous Al₂O₃ substrates was 2.5-fold higher than that with the SCM ZnO nanopowders on normal Al₂O₃ substrates. However, commercial zinc oxide powders did not show any photocatalytic phenomena. The large difference in photocatalytic efficiency was probably attributed to the characteristics of SCM ZnO nanopowder and the large surface area of anodized Al₂O₃.