Ultrafast Charge-Carrier Dynamics and Photocatalytic Mechanisms in Lanthanum-Doped Cerium Oxide Nanoparticles

Cerium oxide nanoparticles (nanoceria) doped with trivalent lanthanum (La) ions and synthesized by a coprecipitation process at ambient temperature were studied by steady-state and femtosecond transient absorption spectroscopy to understand the photocatalytic mechanisms of this wide band gap photocatalyst in alkaline aqueous solution. UV irradiation reduces a significant fraction of cerium ions near the surface to Ce³⁺ centers that persist for hours in air.

La doping increases the percentage of cerium ions that can be photoreduced, while also increasing the rate of photocatalytic degradation of an added dye molecule. Adding methanol eliminates dye photodegradation, showing that photogenerated hydroxyl radicals are the active species. Unexpectedly, the transient spectral signatures and dynamics of photogenerated electrons and holes are nearly unaffected by La doping.