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

Abstract

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 α-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@α-Fe₂O₃/C core@shell photocatalysts. The α-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 α-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@α-Fe₂O₃/C exhibits an equilibrium NADH yield of 76.3% with an initial reaction rate (<i>r</i>) of 7.7 mmol h^–1 g^–1, among the highest <i>r</i> 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