Surface heterogeneity dictates radical reactivity: adsorption and oxidation pathways on platinum nanoparticles

The reactions of hydroxyl (OH˙) and carbonate (CO₃˙^-) radicals with Pt⁰ nanoparticles suspended in aqueous solution were investigated using pulse radiolysis. The results reveal that two distinct reaction pathways occur in parallel: (1) adsorption of radicals on metallic Pt⁰ surface sites; (2) oxidation of Pt^II species located in surface oxide/hydroxide domains formed during nanoparticle synthesis. On bare Pt⁰ surfaces, both radicals adsorb exothermically with significant electron transfer from the metal to the radical species. Pulse radiolysis experiments show that the oxidation of the surface oxide/hydroxide domains produces characteristic transient absorption bands at 390 and 700 nm, whose kinetics are consistent with the formation and subsequent disproportionation of Pt^III species. Hydrogen treatment of the nanoparticles removes these oxidized domains and eliminates the corresponding spectral features, confirming their origin. These findings demonstrate that radical reactions with metal nanoparticles may involve both metallic surface sites and oxidized surface domains that commonly form during aqueous nanoparticle synthesis. Consequently, both adsorption and surface redox pathways must be considered when analyzing radical-nanoparticle interactions.