Doping rare earth cations with an additional chemical reduction synergistically weakened the photocatalytic performance of ceria.

Chemical reducing or rare earth cations (RE) doping was normally employed to promote the photocatalytic performance of ceria, aimed to evaluate their cooperation influences, ceria was obtained by decomposing homogenously RE (RE = La, Sm, and Y)-doped CeCOOH in H. XPS and EPR results evidenced that the excess oxygen vacancies (OVs) were formed in RE-doped CeO compared to the un-doped ceria. However, all the RE-doped ceria unexpectedly showed an impeded photocatalytic activity towards to methylene blue (MB) photodegradation. The 5% Sm-doped ceria had the best MB photodegradation ratio of 81.47% after 2-h reaction in all RE-doped samples, which was lower than that of 87.24% for the un-doped ceria. After doping RE cations and chemical reducing, the band gap of ceria were almost narrowed, while the PL spectra and photo-electro characterizations indicated that the separation efficiency of photo-excited e/h (electrons/holes) was reduced. The RE dopants and formed excess OVs including inner and surface OVs was proposed to promote the recombination of e/h which further hindered the generation of active species of ·O and ·OH, and finally weakened the photocatalytic activity of ceria.