In Situ UV–Vis Spectroscopy Insights into the Role of Hole Scavengers during the Photodeposition of Uniform Gold Nanoparticles on Zinc Oxide

Photodeposition has emerged as a promising technique to grow metal nanoparticles (NPs) on semiconductors through the reduction of metal ions by photoexcited electrons. It is known that metal NPs become more uniform when holes are subtracted by a hole scavenger. However, mechanistic insights into the effect of hole scavengers on the growth kinetics and resulting material properties and the effect of the type of hole scavenger are lacking. In this work, we use in situ UV–vis transmission spectroscopy to investigate the oxygen-deficient photodeposition of Au on ZnO. These measurements reveal that the presence of ethanol as a hole scavenger leads to faster nucleation and substantially accelerates the growth of Au NPs compared to the nonscavenged case. Although the effect of adding a hole scavenger is significant, the type of hole scavenger does not play a significant role in the final Au NP morphology. Therefore, adding a hole scavenger results in a higher density of Au NPs with a well-defined localized surface plasmon resonance (LSPR) band and a homogeneous size distribution of 9 ± 3 nm. By capturing real-time NP growth dynamics, inaccessible to ex situ methods, this study shows why a hole scavenger plays a significant role in the kinetics of Au NPs formation and why they lead to better-defined Au NPs with more controlled plasmonic properties.