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 N-2 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/S-v-ZIS) were synthesized by solvothermal method and used for photocatalytic nitrogen reduction reaction (pNRR). Without sacrificial reagent, the ammonia generation rate reached 80.6 mu mol.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 N-2-TPD, XPS and DFT calculation show that sulfur vacancy (S-v) is not only the active site of N-2 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 N-2 molecules with S-v as a bridge, so as to break the barrier and enhance the efficiency of electron injection into N-2 molecules during pNRR on heterojunction.