Select Nanocrystal Facets Activate Oxygen

Oxidation reactions between organic compounds and O₂ often require an activation step to promote O₂’s electronic configuration from a triplet ground spin state to a singlet excited state. Noble-metal nano­particles can catalyze such oxidations, but the metal’s role in electronic excitations has remained unclear. To sort out those details, Ran Long, Yujie Xiong, and coworkers at the University of Science & Technology of China studied model single-facet nanocrystals—{100}-faceted nanocubes and {111}-faceted nanooctahedrons. The team found that palladium {100} facets readily promote O₂ spin flipping and subsequent oxidations, and Pd {111} facets do not (J. Am. Chem. Soc., DOI: 10.1021/ja311739v). The group established the {100} facets’ knack for exciting O₂ in a series of electron spin resonance spectroscopy control tests on probe molecules and singlet-oxygen scavengers. They also showed that {100}-faceted Pd crystals selectively mediate glucose oxidation and human cervical cancer cell death. The group proposes that these findings, which may lead to improved catalysts and cancer treatments, can be attributed to facet-specific differences in O₂’s bond length and magnetic moment that are induced upon adsorption on the nanocrystals.