Engineering Migration Pathway for Effective Separation of Photogenerated Carriers on Multicomponent Heterojunctions Coated with Nitrogen-Doped Carbon

Multicomponent NiTiO₃/A-TiO₂/R-TiO₂ photocatalysts coated with nitrogen-doped carbon (N-C/NiTiO₃/A-TiO₂/R-TiO₂) for efficient H₂ production were fabricated by directly pyrolyzing NH₂-MIL-125(Ni/Ti) metal–organic framework microrods. Owing to the synergistic effect of the N-doped carbon coating layer and multicomponent heterojunctions, the H₂ production rate of N-C/NiTiO₃/A-TiO₂/R-TiO₂ was even higher than that of its Pt-containing counterpart (Pt/NiTiO₃/A-TiO₂/R-TiO₂). N-C/NiTiO₃/A-TiO₂ and N-C/NiTiO₃/R-TiO₂ as control photocatalysts were also prepared by simply adjusting the calcination temperature of NH₂-MIL-125(Ni/Ti) in air atmosphere. The H₂ production rate followed the order of N-C/NiTiO₃/A-TiO₂/R-TiO₂>N-C/NiTiO₃/A-TiO₂>N-C/NiTiO₃>R-TiO₂, which indicates that the multicomponent heterojunction plays a key role in photocatalytic H₂ generation. The mechanism for the influence of the multicomponent heterojunction on photocatalytic activity was investigated in combination with molecular simulations, which showed that N-C/NiTiO₃/A-TiO₂/R-TiO₂ has a so-called double type II heterojunction providing a perfect step-by-step migration pathway for effective separation of photogenerated electrons and holes. This work presents a simple and effective method for synthesizing efficient multicomponent photocatalysts.