Oxygen-doped crystalline carbon nitride with greatly extended visible-light-responsive range for photocatalytic H2 generation

• Constructing a series of O-doped K + implanted CCN with narrowed bandgap (2.71-1.62 eV) for the first time. • Adopting oxygen doping strategy to activate the n→π* transition to enhance visible light and even near-infrared light harvesting. • An approximately 45- and 10- times enhancement than pristine CN and CCN for H2 generation at λ > 500 nm. • Excellent photoactive up to 650 nm owns prominent advantages over most CCN. Crystalline carbon nitride (CCN) materials with photoresponse of more than 600 nm are rare. Here, we successfully prepared a series of oxygen doped K + implanted CCN (KCN) with narrowed bandgap (2.71−1.62 eV) for the first time. Compared with most of the O-doped amorphous CN, the optical absorption can only reach 500 nm, and a few more than 500 nm, our oxygen doping strategy is adopted to activate more n→π* transitions to enhance visible light and even near-infrared light harvesting. This active-optimized O-doped KCN accounts for 45- and 10- times promotion than pristine CN and KCN in H 2 generation under λ > 500 nm. Most importantly, its maximum active wavelength is up to 650 nm, which has obvious advantages than most CCN-based photocatalysts in the utilization of solar energy. This excellent solar capture and H 2 production is attributed to the activated n→π* electron transition, and high crystallinity and conduction band (CB) position caused by oxygen doping.