Introducing spin polarization into atomically thin 2D carbon nitride sheets for greatly extended visible-light photocatalytic water splitting

Abstract Atomically thin 2D carbon nitride sheets (CNs) became one of the most promising solar energy conversion materials. However, the application of CNs is still limited due to two reasons: (i) the bandgap of CNs is wider than its counterpart due to the quantum size effect, which reduces its effective utilization of the entire solar spectrum, and (ii) the visible-light photocatalytic activity of CNs is still low due to its faster recombination of photogenerated carriers than photocatalytic reaction. Here, we achieve a strong visible-light absorption band in CNs through fluorination followed by thermal defluorination in Se vapor (Se-CNs). Experimental results and theoretical calculations confirm that the formation of cyano groups accompanied with in-situ Se doping expands the absorption edge of CNs from 416 to 584 nm. More importantly, a downward electron spin polarization in the CNs structure improves dramatically the efficiency of charge separation and surface catalysis reaction. The hydrogen generation rate of Se-CNs with 3 wt% Pt under visible-light irradiation (> 420 nm) reaches up to 5411.2 μmol h−1 g−1 that is 176.5 times of the hydrogen generation of CNs. Additionally, the visible-light photocatalytic oxygen evolution of Se-CNs acquires tremendous improvements. This work provides a new approach for improving electron structure of atomically thin 2D non-metal semiconductor materials.