Effects of ZnO nanopowder dispersion on photocatalytic reactions for the removal of Ag+ ions from aqueous solution

ZnO nanopowders were prepared by solution-combustion method (SCM). The SCM ZnO nanopowders were treated by five different dispersants. They were used as photocatalysts to remove Ag⁺ ions from used photographic developing solutions. The Ag⁺ ion removal rates by the dispersed SCM ZnO nanopowders were then compared with those by other photocatalyst powders such as commercial ZnO(Junsei, Japan), P25 TiO₂ (Degussa, Germany) and TiO₂ powder prepared by homogeneous precipitation process at low temperature (HPPLT). The dispersion of SCM ZnO nanopowders in the solution enhanced the Ag⁺ ion removal rate up to about 13 folds compared with P25 TiO₂ nanopowders and 2 folds to SCM ZnO nanopowders without dispersion. Sodium hexametaphosphate was the most effective dispersant among them.