Synthesis of hybrid metal-semiconductor ultrafine particles - Photochemical deposition of silver on a ZnO colloid surface

Hybrid ZnO-Ag ultrafine particles have been synthesized via photochemical reduction of silver ions on ZnO colloids (ca. 3.8 nm mean diameter) in deaerated ethanol. The excess surface ions such as Zn2+ or OH-, which determine the charge and the structure of the double layer of ZnO particles, greatly affect the deposition behaviour of silver. When the excess ions were Zn2+, upon UV irradiation, Ag+ ions in solution were photoreduced on the ZnO surface with kinetics that accord with a mode where the acceleration of silver is proportional to the increase in the number of silver particles, resulting in the formation of very big hybrid particles (up to ca. 15 nm in diameter). When the excess ions were OH-, Ag+ ions were initially attracted to the negatively charged ZnO surface, then Ag2O was generated after UV irradiation. Further reaction results in the transformation of Ag2O into silver, leading to a damping of the exciton band of ZnO ultrafine particles, the silver being referred to as an electron trap. A combined investigation via UV-VIS and fluorescence spectrometry indicated that the interaction between the silver formed and the surface of ZnO occurred in both the above cases.