Nano-sized ZnO powder was synthesized by solution combustion method (SCM). Using this ZnO nanopowder as a photocatalyst, it was tried to recover silver from the silver-plating wastewater that was discharged by noble metal plating industries. The photocatalytic efficiency of ZnO nanopowder, as one of optical properties, was compared with other photocatalysts such as commercial TiO2 and commercial ZnO. The ZnO nanopowder showed three folds higher photocatalytic efficiency than any other commercial photocatalysts. Other electro-optical measurements such as photoluminescence (PL) measurement, electrical resistivity and carrier concentration measurement also showed very consistent results. The recovery of gold from gold plating wastewater was also tried. The recovery efficiency was improved by about 25% by adding methanol as a scavenger to the gold plating wastewater. It took 45 min to completely recover gold from the wastewater. (C) 2003 Kluwer Academic Publishers.