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ZnO nanopowder was synthesized by a unique method which is called solution combustion method (SCM). This nanopowder was used for a photocatalyst to decompose nitrate that is a toxic pollutant in wastewater. It has been known that TiO2, the most popular photocatalyst, does not decompose the nitrate. In this paper, however, the SCM ZnO nanopowder decomposed about 13% of nitrate. Furthermore, adding methanol as a hole scavenger, the decomposition rate was enhanced by about 5 times. On the other hand, it has been reported that the photocatalytic reduction reaction of nitrate produces ammonia as a final product. The present results, however, suggest that the final product is non-toxic nitrogen gas rather than the toxic ammonia. These results would be very valuable for drinking water purification.

ZnGa 2 O 4 phosphors were synthesized by both SCM (solution combustion method) and SSRM (solid state reaction method). The characteristics of the both ZnGa 2 O 4 phosphors were investigated by TGA (Thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5 fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn +2 ions. The highest PL peak was observed with Mn +2 ions of 0.003 mole fraction. The peak was shifted from blue (470 nm) to green (513 nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels.

In this study, ZnO nanopowder was synthesized by solution-combustion method (SCM). The photocatalytic gold recovery efficiency by this SCM ZnO nanopowder was about 6 fold higher compared to the case by the state of the art commercial TiO 2 nanopowder. The purity of recovered gold was about 99.6% in weight% and 98.8% in atomic%. Furthermore, the ZnO nanopowder synthesis method and gold recovery process are very cost-effective. Especially, in this study it was tried to recover gold metal ions from not simulated wastewater but real plating wastewater. This technology is therefore very viable to obtain high purity gold from plating wastewater.

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