The superior photocatalytic activity of Nb doped TiO/g-CN direct Z-scheme system for efficient conversion of CO into valuable fuels.

In this study, we firstly aimed to use Nb as dopant to dope into the TiO lattice in order to narrow band gap energy or enhance photocatalytic activity of the Nb-TiO. Then, the prepared Nb-TiO was combined with g-CN to establish Nb-TiO/g-CN direct Z-scheme system for superior reduction of CO into valuable fuels even under visible light. The obtained results indicated that the band gap energy of the Nb-TiO (2.91 eV) was lower than that of the TiO (3.2 eV). In the successfully established Nb-TiO/g-CN direct Z-scheme system, the photo-excited e in the CB of the Nb-TiO combined with the photo-excited h in the VB of the g-CN preserving the existence of e in the CB of the g-CN and h in the VB of Nb-TiO, and thereby, the system produced numerous amount of available e/h pairs for the reduction of CO into various valuable fuels. In addition, the produced e of the Nb-TiO/g-CN existing in the CB of the g-CN, which the potential energy is approximately -1.2 V, would be strong enough for the reduction of CO to generate not only CH and CO but also HCOOH. Among established Nb-TiO/g-CN materials, the 50Nb-TiO/50 g-CN material was the best material for the CO reduction.