Mechanochemical synthesis of nanocrystalline SnO₂–ZnO photocatalysts

Mechanochemical processing of anhydrous chloride precursors with Na 2 CO 3 has been investigated as a means of manufacturing nanocrystalline SnO 2 doped ZnO photocatalysts. High-energy milling and heat-treatment of a 0.1SnCl 2 +0.9ZnCl 2 +Na 2 CO 3 +4NaCl reactant mixture was found to result in the formation of a composite powder consisting of oxide grains embedded within a matrix of NaCl. Subsequent washing with deionized water resulted in removal of the NaCl matrix phase and partial hydration of the oxide reaction product with the consequent formation of ZnSn(OH) 6 . The extent of this hydration reaction was found to decrease in a linear fashion with the temperature of the post-milling heat-treatment over the range of 400–700 °C. For a heat-treatment temperature of 700 °C, the SnO 2 doped ZnO powder was found to exhibit significantly higher photocatalytic activity than either single-phase SnO 2 or ZnO powders that were synthesized using similar processing conditions. The heightened photocatalytic activity of the SnO 2 doped ZnO was attributed to its higher specific surface area and the enhanced charge separation arising from the coupling of ZnO with SnO 2 .