ABSTRACT
ZnO nanopowder was synthesized by a solution combustion method. This nanopowder was char- acterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), four point probe, Hall measurement and photocatalytic reaction. The nanopowder was also investigated after heat-treating at 400 °C and 700 °C. The carrier concentrations were 8 x 10(20) cm(-3), 6 x 10(21) cm(-3) and 1.5 x 10(18) cm(-3) for the non heat-treated, the 400 °C heat-treated and the 700 °C heat-treated ZnO nanopowders respectively. Electrical resistivities of 1 Ω cm, 0.6 Ω cm and 2.6 Ω cm were obtained for the three kinds of heat-treated ZnO nanopowders respectively. These three kinds of nanopowders were then employed as photocatalysts to recover silver ions from wastewater. At 5 min of photocatalytic reaction time, the reaction removed 66.7%, 100% and 10.8% of the silver ions. The carrier concentration and photocatalytic efficiency of the 400 °C heat-treated one were 7.5 fold and 1.5 fold higher than those of the non heat-treated one respectively. However, the 700 °C heat-treated one showed far worse values than the non heat-treated one. This phenomenon was explained by carrier trap centers.
