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

摘要

In many organic reactions, the O_2 activation process involves a key step where inert ground triplet O_2 is excited to produce highly reactive singlet O_2. It remains elusive what factor induces the change in the electron spin state of O_2 molecules, although it has been discovered that the presence of noble metal nanoparticles can promote the generation of singlet O_2. In this work, we first demonstrate that surface facet is a key parameter to modulate the O_2 activation process on metal nanocrystals, by employing single-facet Pd nanocrystals as a model system. The experimental measurements clearly show that singlet O_2 is preferentially formed on {100} facets. The simulations further elucidate that the chemisorption of O_2 to the {100} facets can induce a spin-flip process in the O_2 molecules, which is achieved via electron transfer from Pd surface to O_2. With the capability of tuning O_2 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 O_2 activation and organic oxidation. Another perspective of this work would be the controllability in tailoring the cancer treatment materials for high ~1O_2 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 O_2 holds the key to the performance of Pd nanocrystals in the applications.