S vacancies act as a bridge to promote electron injection from Z-scheme heterojunction to nitrogen molecule for photocatalytic ammonia synthesis

The low efficiency of photogenerated electron injection into N2 molecule is the key problem to limit the improvement of activity for photocatalytic ammonia synthesis of heterojunction materials. In this paper, BiVO4/ZnIn2S4 direct Z-scheme heterojunction rich in sulfur vacancies (BVO/Sv-ZIS) were synthesized by solvothermal method and used for photocatalytic nitrogen reduction reaction (pNRR). Without sacrificial reagent, the ammonia generation rate reached 80.6 μmol·g−1·h−1, which is 3.5 times and 4.5 times higher than that of pristine BVO and ZIS, respectively. The results of N2-TPD, XPS and DFT calculation show that sulfur vacancy (Sv) is not only the active site of N2 chemisorption, but also can capture photogenerated electrons and change the local electronic structure on the surface of heterojunction. The photogenerated electrons are continuously transferred to N2 molecules with Sv as a bridge, so as to break the barrier and enhance the efficiency of electron injection into N2 molecules during pNRR on heterojunction.