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-C 3 N 4 ) nanosheets by the conjoint use of NH 4 Cl as a dynamic gas template together with hypophosphorous acid (H 3 PO 2 ) as a doping agent. The NH 4 Cl treatment allows for the scalable production of protonated g-C 3 N 4 nanosheets. With the corresponding co-addition of H 3 PO 2 , nitrogen vacancies, accompanied by both additional protons and interstitially-doped phosphorus, are introduced into the g-C 3 N 4 framework, and the electronic bandgap of g-C 3 N 4 nanosheets as well as their optical properties and hydrogen-production performance can be precisely tuned by careful adjustment of the H 3 PO 2 treatment. This conjoint approach thereby results in improved visible-light absorption, enhanced charge-carrier separation and a high H 2 evolution rate of 881.7 μmol h −1 achieved over the H 3 PO 2 doped g-C 3 N 4 nanosheets with a corresponding apparent quantum yield (AQY) of 40.4% (at 420 nm). We illustrate that the synergistic H 3 PO 2 doping modifies the layered g-C 3 N 4 materials by introducing nitrogen vacancies as well as protonating them, leading to significant photocatalytic H 2 evolution enhancements, while the g-C 3 N 4 materials doped with phosphoric acid (H 3 PO 4 ) are simply protonated further, revealing the varied doping effects of phosphorus having different (but accessible) valence states. Nitrogen deficient and protonated g-C 3 N 4 was fabricated by the conjoint protocol utilizing NH 4 Cl as gas template and H 3 PO 2 as doping agent, leading to enhanced visible-light harvesting and charge carrier separation to achieve efficient H 2 evolution.