Fragmented phosphorus-doped graphitic carbon nitride nanoflakes with broad sub-bandgap absorption for highly efficient visible-light photocatalytic hydrogen evolution

Abstract Graphitic carbon nitride (g-C3N4) has shown great promise in photocatalytic solar-energy conversion. However, photocatalytic activity of pristine g-C3N4 still remains restricted owing to its low surface area, insufficient visible-light harvesting, and ready charge recombination. Here, fragmented P-doped g-C3N4 nanoflakes (PCNNFs), which are prepared by a facile two-step processing combining P-doping via using phytic acid biomass as P source and urea as g-C3N4 precursor and nanostructure tailoring via a smart post-treatment, are reported. Particularly, PCNNFs exhibit narrowed sub-bandgap from valence band to the midgap states, extending light absorption up to 800 nm. The resultant PCNNFs sample shows a surface area of 223.2 m2 g−1, a highest value of P-doped g-C3N4 reported. The fragmented nanoflakes structure renders PCNNFs much shortened charge-to-surface migration distance in both vertical-plane and in-plane direction. Such PCNNFs are demonstrated to be highly efficient in charge transfer and separation. Attributed to the synergistic effect of P-doping and fragmented nanoflakes structure, PCNNFs exhibit a remarkable visible-light (>420 nm) photocatalytic H2 production rate of 15921 μmol h−1 g−1 and quantum efficiencies of 6.74% at 420 nm and 0.24% at 600 nm. Moreover, even under long wavelength light (>470 nm), PCNNFs still exhibit high H2 production rate of 9546 μmol h−1 g−1, over 62 times the rate of pure g-C3N4.