Controlling Low Temperature Aqueous Synthesis of ZnO. 2. A Novel Continuous Circulation Reactor

A novel low temperature continuous circulation reactor for synthesizing ZnO from aqueous solutions has been developed. The reactor is based on the solubility behavior of ZnO predicted by the thermodynamic calculations presented in part I of this series. The chemistry used is simple and nontoxic, and because the reactor operates in a closed loop, no waste byproducts are produced. Experimental results confirm that the reactor is capable of synthesizing epitaxial ZnO at atmospheric pressure and temperatures well below the boiling point of water. It was possible to control the growth rate, yield, and morphology of the ZnO produced by adjusting variables, such as pH, ammonia concentration, temperature, heating rate, hold time, and recirculation rate. The experimental results obtained are shown to be in qualitative agreement with the calculations reported in part 1.