Photocatalytic recovery of Ag ions from wastewater using ZnO nanopowders immobilized on microporous alumina substrates

ZnO nanopowders were synthesized by solution combustion method (SCM) and their average particle size was about 30 nm. They were immobilized on microporous alumina substrates by spray coating. The microporous alumina substrates were prepared by anodization and the average pore size was about 150 nm. Ag ions were tried to be recovered from waste photograph developing solution by photocatalytic reaction. Three kinds of samples were prepared to compare their photocatalytic efficiency: commercial ZnO powders (slurry type reaction), SCM ZnO powders immobilized on normal alumina substrates and SCM ZnO powders immobilized on anodized alumina substrates. The commercial ZnO powders without immobilization did not show any photocatalytic reaction even though they have maximum surface area. This is probably ascribed to their poor crystalline quality. However, the Ag ion recovery rate by SCM ZnO powders immobilized on anodized alumina substrates was about 2.5 times higher than that by SCM ZnO powders immobilized on normal alumina substrates. This big difference in photocatalytic efficiency is probably due to the large surface area of the anodized alumina. This result was correspondent to photoluminescence measurement results.