Abstract:

Photocatalytic ammonia generation via nitrogen reduction reaction (NRR) is a green and prospective nitrogen fixation technique. However, NRR is often hampered by the high N₂ adsorption/activation energies and is accompanied by a slow kinetics oxygen evolution reaction (OER). Herein, a robust Bi₂S₃/OV-Bi₂MoO₆ S-scheme heterojunction is constructed using a simple in-situ anion exchange process, which enables oxygen vacancy (OVs) abundant Bi₂MoO₆ microspheres with surface deposited Bi₂S₃. The as-fabricated Bi₂S₃/OV-Bi₂MoO₆ functioned as an effective photocatalyst to convert N₂-to-NH₃ under mild conditions. The photocatalytic NH₃/NH₄⁺ production rate reached 126 μmol g_cat^-1 under visible light for 2.5 h with 2% of Bi₂S₃/OV-Bi₂MoO₆ photocatalyst, which was 8-fold higher than pristine Bi₂MoO₆. Furthermore, the as-fabricated Bi₂S₃/Bi₂MoO₆ heterojunction exhibited good selectivity, high stability and reproducibility. The excellent photocatalytic NRR performance was ascribed to the Bi₂S₃/Bi₂MoO₆ heterojunction formed subsequent to the strong interaction between Bi₂S₃ and Bi₂MoO₆. The OVs facilitated the chemical adsorption process allowing activation of N₂ molecule on the Bi₂S₃/Bi₂MoO₆. Simultaneously, the S-scheme heterojunction prolonged the lifetime of photogenerated carriers, accelerated the electrons/holes spatial separation and accumulation on the Bi₂S₃ (reduction) and Bi₂MoO₆ side (oxidation), respectively, thus strengthening both OER and NRR half-reactions. This simple in-situ anion exchange method offers a novel technique for strengthening OER and NRR half-reactions in Bi-based photocatalysts for effective photocatalytic ammonia generation.

Key words: Anion exchange method, Bi₂S₃/Bi₂MoO₆ s-scheme heterojunction, Nitrogen activation, Photocatalytic ammonia generation