In summary CeOx BiVO composite photocatalysts with heterojunction structure
The peak with the largest intensity attributed to the pure BiVO4 appeared at around 600 nm, which was also actually a character PL peak of the monoclinic BiVO4 and . The luminescence corresponded to the recombination of the hole formed in the O 2p band and the ARRY-380 in the V 3d band. The intensity of the PL peaks decreased after the heterojunction nanostructure formation in the CeOx/BiVO4 series of composites ( Fig. 11). With the Ce mass ratio increasing from 1 wt.% to 5.7 wt.% in the heterojunction, the PL peak intensity declined and the lowest peak intensity was observed for the 5.7 wt.% CeOx /BiVO4 composite. It implied that the recombination of the photogenerated electrons–holes was greatly suppressed. The peak intensity raised again when the cerium content further increased. This intensity remained highly consistent with the photocatalytic performance of the samples ( Fig. 6 and Fig. 7). Most importantly, the blue shift of peaks to the lower wavelength after cerium was introduced was clearly observed ( Fig. 11). This shift was related to the change of the Ce ion valence from 4+ to 3+ corresponding to the transition of the electrons from the 4f band to the valence band of CeO2  and . To the best of our knowledge, this is the first study to show that the process of photogenerated electrons trapped by valence-variable ions in the semiconductor was indirectly proved by the change in the photoluminescence spectrum, albeit having been recently proposed  and . The higher number of shifts to a lower wavelength implied the better effect of cerium species on separating electron–holes, which corresponded to a better photocatalytic performance.