Surface Facet of Palladium Nanocrystals: A Key Parameter to the Activation of Molecular Oxygen for Organic Catalysis and Cancer Treatment

In many organic reactions, the O₂ activation process involves a key step where inert ground triplet O₂ is excited to produce highly reactive singlet O₂. It remains elusive what factor induces the change in the electron spin state of O₂ molecules, although it has been discovered that the presence of noble metal nanoparticles can promote the generation of singlet O₂. In this work, we first demonstrate that surface facet is a key parameter to modulate the O₂ activation process on metal nanocrystals, by employing single-facet Pd nanocrystals as a model system. The experimental measurements clearly show that singlet O₂ is preferentially formed on {100} facets. The simulations further elucidate that the chemisorption of O₂ to the {100} facets can induce a spin–flip process in the O₂ molecules, which is achieved via electron transfer from Pd surface to O₂. With the capability of tuning O₂ activation, we have been able to further implement the {100}-faceted nanocubes in glucose oxidation. It is anticipated that this study will open a door to designing noble metal nanocatalysts for O₂ activation and organic oxidation. Another perspective of this work would be the controllability in tailoring the cancer treatment materials for high ¹O₂ production efficiency, based on the facet control of metal nanocrystals. In the cases of both organic oxidation and cancer treatment, it has been exclusively proven that the efficiency of producing singlet O₂ holds the key to the performance of Pd nanocrystals in the applications.