Pathways of Quantum Dot Degradation during Photocatalysis

CdS QDs are widely employed as photocatalysts for reactions such as hydrogen evolution, and its degradation under aerobic, aqueous conditions is well understood. However, despite evidence of aggregation and precipitation of CdS QD photocatalysts under inert conditions, catalyst speciation and degradation are under-explored. In this work, we demonstrate that during a reductive dehalogenation reaction, CdS QDs undergo surface ligand etching, leading to loss of colloidal stability and the formation of micro-crystalline cadmium metal deposits. We hypothesize that this results from the accumulation of electrons on the QD surface. In addition, we demonstrate a high catalytic TOF of 0.67 s-1 and show evidence of mild surface sulfur oxidation and formation of an ammonium salt by-product of the hole quencher. This work adds to our atomic-level understanding of the reactions occurring at the QD surface during photocatalysis and ultimately uncovers design principles that will allow the design of more stable and efficient catalysts.