Catalysis in Silver Nanocube Formation: The Role of Iron Ions in Non-Polar Solvents

Plasmonics is a rapidly growing field of research based on plasmonic nanostructures. To exploit the full potential of this fascinating class of materials, it is indispensable to tune and optimize the properties of these structures, which requires precise knowledge and optimization of their synthesis processes. Plasmonic silver nanocubes for applications in nonpolar media are obtained by an AgCl-mediated hot-injection method. In this process, catalysis by Fe species is of central importance, as the Fe species influence the reaction in multiple ways, enabling a finely balanced control of the nanocube synthesis. Using electron microscopy, optical spectroscopy, and X-ray photoelectron spectroscopy, it is shown that the Fe species not only direct the reaction of the Ag precursor to the formation of AgCl nanoparticles instead of icosahedral Ag nanoparticles but also enhance the reduction rate of AgCl, from which the Ag nanocubes are formed and grow. Based on these results, a detailed reaction mechanism is proposed. An additional comparison of the effects of different metal ions on the reaction shows that iron ions are highly likely to be specific as catalysts for this synthesis. The results also indicate that the Fe ions are likely present in the form of an organic iron complex, catalyzing the chloride transfer.