Electronic structure regulation and built-in electric field synergistically strengthen photocatalytic nitrogen fixation performance on Ti-BiOBr/TiO₂ heterostructure

At present, industrial synthetic ammonia was still obtained through the Hubble-Bosch process, with large energy consumption. It is a research hotspot to realize green synthetic ammonia by using solar energy. The difficulty of photocatalytic ammonia synthesis was that the photo-excited electrons have not enough energy to active N≡N. In this study, Ti was doped into BiOBr by one-step hydrothermal method, which was oxidized into TiO₂ when the doping amount reaches the maximum, in situ forming Ti_0.31B_0.69OB/TiO₂ composites. Benefiting from the synergistic effect of Ti doping and S-scheme heterojunction, the synthetic ammonia efficiency of Ti_0.31B_0.69OB/TiO₂-11.96 reached 1.643 mmol·g⁻¹_cat at mild conditions and without hole scavenger for up to 7 h, the efficiency of synthetic ammonia is 115 times, 10.5 times and 3.3 times of that of BiOBr, Ti_0.31B_0.69OB and TiO₂, respectively. Specifically, DFT calculation confirms that Ti doping accurately refine the electronic structure of BiOBr, facilitate nitrogen adsorption activation and reduce hydrogenation reaction energy barrier, thus accelerating the reaction kinetics of photocatalytic nitrogen reduction (NRR). Meanwhile, constructing S-scheme heterojunction boosts the separation and transfer of photogenerated electron–hole pairs, improving the reduction ability of electrons in the conduction band of TiO₂ and the oxidation ability of holes in the valence band of Ti_0.31B_0.69OB.