Achievement of safer palladium nanocrystals by enlargement of {100} crystallographic facets.

Developing catalytic and safe nanomaterials is very necessary for the reduction of potential risk to human health; however, this strategy has been found extremely challenging because the enhancement in catalytic activity of nanomaterials is inevitably accompanied with more potent cell injury. The relationship of physicochemical properties and biological responses in catalytic nanomaterials needs to be clarified at the nano-bio interface for achieving the safe application. Herein, high-energy crystallographic facets of palladium (Pd) nanocrystals that have been known to significantly contribute to the catalytic activity were introduced to attenuate the toxicity, and the underlying mechanism was unraveled. Polyhedral Pd nanocrystals with morphology evolution from truncated octahedron to cuboctahedron and cube were prepared for elaborately tuning the extents of high-energy {100} facets, and hierarchical in vitro and in vivo biological evaluation were performed to clarify that Pd nanocrystals exposed with the more {100} facets could show the less toxicity to cells and animals. Density functional theory (DFT) calculation revealed {100} facet exposure was endowed with a strong oxygen adsorption, which weakens the breakage of the water molecule and suppresses the hazardous water dissociation and hydroxyl radical generation, which was supported by electron spin resonance (ESR)-based radical evaluation and X-ray photoelectron spectroscopy (XPS)-based oxygen identification. This means high-energy facet-based catalytic Pd nanocrystals can deliver low toxicity due to their unique surface properties.