Synergy of dopants and defects in ultrathin 2D carbon nitride sheets to significantly boost the photocatalytic hydrogen evolution

An approach of thermal annealing of atomically thin CNs in Se vapor is used to narrow the bandgap of 2D CNs and realize strong visible light absorption. The results show that the presence of both the selenium dopants and nitrogen vacancies in Se-CNs matrix could contribute to a narrowed bandgap and extended absorption as well as greatly enhanced photocatalytic activity. [Display omitted] •This is a facile strategy to realize the broad absorption of CNs photocatalyst.•The method can dramatically extend the absorption of CNs from 418 to 574 nm.•HER activity of Se-CNs photocatalyst significantly exceeds that of CNs. Atomically thin 2D carbon nitride sheets (CNs) can improve the photocatalytic performance due to their high specific surface area, exposed active sites, and nano-scaled diffusion path of the charge transferred to surface. However, in practical application, 2D CNs photocatalysts always suffer the low solar absorption. Here, we present a novel approach to achieve the ultrathin 2D CNs photocatalysts with wide spectrum absorption in visible-light range. The new method, i.e. thermal annealing of atomically thin CNs in Se vapor, can dramatically extend the absorption edge of the ultrathin CNs from 418 to 574 nm. Using structural characterization and spin-polarized density functional theory, we identify the loss of the nitrogen atoms at the edges and in situ Se doping into the network of ultrathin CNs, which could change the electronic band structure of the 2D CNs. As a consequence, the ultrathin 2D CNs photocatalyst via Se vapor annealing (Se-CNs) modified by Pt cocatalyst shows a superior photocatalytic hydrogen evolution activity under visible light irradiation. More significantly, the ultrathin Se-CNs photocatalyst also exhibits an impressive photocatalytic hydrogen evolution activity under visible-light irradiation in the absence of Pt cocatalyst. We believe that our study provide a facile and environmentally friendly strategy to realize the utilization of 2D CNs photocatalyst under wide spectrum range of solar radiation to harvest solar energy efficiently, and it can be further applied in various advanced fields, including CO2 photoreduction, organic photosynthesis, and pollutant controls.