PdO Doping Tunes Band-Gap Energy Levels as Well as Oxidative Stress Responses to a Co3O4 p-Type Semiconductor in Cells and the Lung

We demonstrate through PdO doping that creation of heterojunctionson Co3O4 nanoparticles can quantitatively adjust band-gap and Fermi energylevels to study the impact of metal oxide nanoparticle semiconductor properties on cellular redox homeostasis and hazard potential. Flame spray pyrolysis (FSP) was used to synthesize a nanoparticle library in which the gradual increase in the PdO content (0–8.9%) allowed electron transfer from Co3O4 to PdO to align Fermi energylevels across the heterojunctions. This alignment was accompanied by free hole accumulation at the Co3O4 interface and production of hydroxyl radicals. Interestingly, there was no concomitant superoxide generation, which could reflect the hole dominance of a p-type semiconductor. Although the electron flux across the heterojunctionsinduced upward band bending, the Ec levels of the doped particles showed energy overlap with the biological redox potential (BRP). This allows electron capture from the redox couples that maintain the BRP from −4....