Mass production of ZnO nanotetrapods by a flowing gas phase reaction method

We have developed a flowing gas phase reaction method for synthesizing ZnO nanotetrapods. The synthesis was carried out in a tube furnace under air pressure using air and nitrogen as reactive and carrying gases. The zinc precursor was provided by carbothermal reduction of ZnO powder. The source material transformation efficiency is higher than 90%. ZnO nanotetrapods were nucleated and grown in the gas phase via a vapor-solid mechanism. The reaction occurred at a temperature controlled to 1050-1200 °C and gas flow rate controlled to 0.7-2 L/min. The high flow rate suppressed the diffusion of growth precursors and productions towards the tube wall, and localized them into a gas phase pipe. The harvested ZnO nanotetrapods were carried by the flowing gas and collected outside of the furnace. The sizes of the nanotetrapods range from several hundred nanometers to more than 10 µm with leg diameters of 30-200 nm. The flowing gas phase reaction method provides a relatively uniformity environment for nanotetrapod growth and simplifies the product collection procedure compared with other techniques. This technique is simple and inexpensive, which is promising for realizing continuous mass production of ZnO nanotetrapods on a factory scale.