Ambient-temperature synthesis of nanocrystalline ZnO and its application in the generation of hydrogen

The conditions leading to the direct formation of nanocrystalline ZnO particles from aqueous solutions at 25 °C are presented. The synthesis of ZnO was made possible by the suitable selection of the solution chemistry and the control of the alkaline conditions established during the formation and conversion of the precursor solid. XRD and FT-IR analyses revealed that the progressive removal of molecular and coordinated water from the precursor basic zinc sulphate and the diminution of sulphate contents took place at a temperature as low as 25 °C, making unnecessary any further thermal treatment of the as-synthesized powders. SEM observations evidenced the formation of sub-micron aggregates of ZnO (sizes below 100 nm). Depending on synthesis and precipitation conditions, it was possible to decrease the crystallite size from 25 down to 11 nm. The ambient-temperature ZnO nanocrystals were used in the photo-catalytic generation of hydrogen from alkaline Na2S aqueous solutions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)