Highly efficient Z-scheme structured visible-light photocatalyst constructed by selective doping of Ag@AgBr and Co3O4 separately on {010} and {110} facets of BiVO4: Pre-separation channel and hole-sink effects

To improve the visible-light photocatalytic activity and photo-carriers separation of BiVO4, highly efficient Z scheme structured visible-light photocatalyst Ag@AgBr/BiVO4/Co3O4 was constructed by selective doping of Ag@AgBr and Co3O4 on {010} and {110} facets of BiVO4. Due to the different energy levels of conduction band (CB) and valence band (VB) between {010} facet and {110} facet, BiVO4 could act as the 'pre-separation channel' to achieve spatial charge separation. Such pre-separation channel effect improved photo-electrons transfer from BiVO4(010) facets to electron mediator (Ag) for subsequent recombination with holes of AgBr. Thus, the photo-induced electrons of AgBr could be accumulated on CB for reduction of O-2 to O-center dot(2)-. On the other hand, holes of BiVO4 accumulated on {110} facets were captured by deriving-hole-type co-catalysts Co3O4 for organics oxidation. In addition, Ag not only served as the electron mediator of Z-scheme but also improve the visible-light utilization due to SPR-effect. Being attributed to the synergistic effect of pre-separation channel and deriving-hole-type co-catalysts, Z-scheme structured Ag@AgBr/BiVO4/Co3O4(0.15 wt%) achieved high photo-degradation rate of organics. Even after 9th cycles, Ag@AgBr/BiVO4/Co3O4(0.15 wt%) could still photo degraded more than 90% of OTC within 24 min. DRS, PL and photoelectrochemical analyses also confirmed the improvement of visible-light utilization and charge separation of Ag@AgBr/BiVO4/Co3O4. The radical trapping experiments and EPR demonstrated that both superoxide radical (O-center dot(2)-) and holes (h(+)) were main active species for organics photodegradation. In summary, this work not only constructed a highly efficient Z-scheme structured visible-light photocatalyst, but also provided a new method to diminish the photo-carriers recombination by pre-separation channel and hole-sink effects.