Most recently, the research group led by Prof. Yujie Xiong elucidated that surface facet of palladium nanocrystals is a key parameter to the activation of molecular oxygen, in collaborations with the National Synchrotron Radiation Laboratory. This progress has been published in J. Am. Chem. Soc. 2013, 135, 3200.
The activation of molecular oxygen (O2) on the surface of heterogeneous catalysts plays a central role in a wide variety of oxidation reactions. In the organic systems, the interaction of organic molecules with O2 is essentially limited by the spin state of O2, caused by spin-conservation restrictions. In this work, it has been demonstrated that the surface facet of metal nanocrystals is a key parameter for tuning their activities of generating singlet oxygen. The surface facets may alter the chemisorption state of oxygen on metal surface, and in turn, cause the changes in the spin state of oxygen through electron transfer from Pd surface to O2. To experimentally examine the adsorption state of O2 on Pd surface, near-edge X-ray absorption fine structure (NEXAFS) spectra of O2 adsorbed on different Pd crystal surface have been collected. This characterization by Prof. Wensheng Yan reveals that the bond length of O2 on {100} facet is slightly larger than that on {111}, which is consistent with the simulation findings. The facet-dependent activities of metal nanocrystals presented in this work provide guidance for designing high-performance catalysts for organic reactions. Another contribution of this work is the controllability in tailoring the cancer treatment materials for high 1O2 production efficiency, based on the facet control of metal nanocrystals. It is anticipated that this finding will pave new way for designing cancer therapy agents by tailoring the surface facets of other metal nanostructures.
Upon its publication in JACS, this work was highlighted by the Chemical & Engineering News on February 25, 2013, entitled by “SELECT NANOCRYSTAL FACETS ACTIVATE O2”. This work was supported by the National Natural Science Foundation of China (NSFC), the Recruitment Program of Global Experts and the CAS Hundred Talent Program.

Schematic illustrating the facet-dependent activity of Pd nanocrystals in activating molecular oxygen