g-C3N4@alpha-Fe2O3/C Photocatalysts: Synergistically Intensified Charge Generation and Charge Transfer for NADH Regeneration

Graphitic carbon nitride (g-C3N4) is an emergent metal-free photocatalyst because of its band position, natural abundance, and facile preparation. Synergetic intensification of charge generation and charge transfer of g-C3N4 to increase solar-to-chemical efficiency remains a hot yet challenging issue. Herein, a nanoshell with two moieties of alpha-Fe2O3 and carbon (C) is in situ formed on the surface of a g-C3N4 core through calcination of Fe3+/polyphenol-coated melamine, thus acquiring g-C3N4@alpha-Fe2O3/C core@shell photocatalysts. The alpha-Fe2O3 moiety acts as an additional photosensitizer, offering more photogenerated electrons, whereas the C moiety bridges a "highway" to facilitate the electron transfer either from alpha-Fe2O3 moiety to g-C3N4 or from g-C3N4 to C moiety. By tuning the proportion of these two moieties in the nanoshell, a photocurrent density of 3.26 times higher than pristine g-C3N4 is obtained. When utilized for photocatalytic regeneration of reduced nicotinamide adenine dinucleotide (NADH, a dominant cofactor in biohydrogenation reaction), g-C3N4@alpha-Fe2O3/C exhibits an equilibrium NADH yield of 76.3% with an initial reaction rate (r) of 7.7 mmol h(-1) g(-1), among the highest r for photocatalytic NADH regeneration ever reported. Manipulating the coupling between charge generation and charge transfer may offer a facile, generic strategy to improve the catalytic efficiency of a broad range of photocatalysts other than g-C3N4.