Facile reductive synthesis of both nitrogen deficient and protonated g-CN nanosheets for the synergistic enhancement of visible-light H evolution.

A new strategy is reported here to synthesize both nitrogen deficient and protonated graphitic carbon nitride (g-CN) nanosheets by the conjoint use of NHCl as a dynamic gas template together with hypophosphorous acid (HPO) as a doping agent. The NHCl treatment allows for the scalable production of protonated g-CN nanosheets. With the corresponding co-addition of HPO, nitrogen vacancies, accompanied by both additional protons and interstitially-doped phosphorus, are introduced into the g-CN framework, and the electronic bandgap of g-CN nanosheets as well as their optical properties and hydrogen-production performance can be precisely tuned by careful adjustment of the HPO treatment. This conjoint approach thereby results in improved visible-light absorption, enhanced charge-carrier separation and a high H evolution rate of 881.7 μmol h achieved over the HPO doped g-CN nanosheets with a corresponding apparent quantum yield (AQY) of 40.4% (at 420 nm). We illustrate that the synergistic HPO doping modifies the layered g-CN materials by introducing nitrogen vacancies as well as protonating them, leading to significant photocatalytic H evolution enhancements, while the g-CN materials doped with phosphoric acid (HPO) are simply protonated further, revealing the varied doping effects of phosphorus having different (but accessible) valence states.