The photoexcited electron transfer and photocatalytic mechanism of g-C3N4/TiO2 heterojunctions: Time-domain ab initio analysis

The control of the carrier migration in the semiconductor heterojunctions is still one of the biggest challenges for the performance improvement of photocatalysts. In this paper, we systematically studied the carrier transfer of g-C3N4/A-TiO2 (anatase) and g-C3N4/R-TiO2 (rutile) by using non-adiabatic molecular dynamics. It has been shown that the g-C3N4 could form stable interfaces with A-TiO2(101) or R-TiO2(110). Electrons migrated from the CB of TiO2 to the VB of g-C3N4 in the g-C3N4/A-TiO2 and formed a typical S-scheme heterojunction, which benefited the electron-hole recombination on the VB of g-C3N4 to relieve hole accumulation and increased the photocatalytic efficiency. In contrast, the g-C3N4/R-TiO2, a typical Type-II heterojunction, had no such notable feature. By comparing with the VB and CB edge potentials of the normal hydrogen electrode (NHE), it was found that the photoexcited electrons and holes of the g-C3N4/A-TiO2 could reduce H+ to H2 and product O2, respectively, while g-C3N4/R-TiO2 only had a better ability to produce O2. The effective tuning of the charge transfer and bandgap of the g-C3N4/TiO2 by applying electric field was also explored. We believed that these findings not only demonstrated the advantages of S- scheme heterojunctions over Type-II heterojunctions, but also facilitated the rational design of better photocatalysts.