Growth of Supported Gold Nanoparticles in Aqueous Phase Studied by In Situ Transmission Electron Microscopy

Nanoparticle growth has long been a significant challenge in nanotechnology and catalysis, but the lack of knowledge on the fundamental nanoscale aspects of this process has made its understanding and predicting difficult, especially in a liquid phase. In this work, we successfully used liquid-phase transmission electron microscopy to image this process in real time at the nanometer scale, using an Au/TiO2 catalyst in the presence of NaCl(aq) as a case study. In situ LP-TEM clearly showed that the growth of Au nanoparticles occurred through a form of Ostwald ripening, whereby particles grew or disappeared, probably via monomer transfer, without clear correlation to particle size in contrast to predictions of classical Ostwald ripening models. In addition, the existence of a significant fraction of inert particles that neither grew, nor shrank, was observed. Furthermore, in situ TEM showed that particle shrinkage was sudden and seemed a stochastic process, while particle growth by monomer attachment was sl...