g‑C<sub>3</sub>N<sub>4</sub>@α-Fe<sub>2</sub>O<sub>3</sub>/C Photocatalysts: Synergistically Intensified
Charge Generation and Charge Transfer for NADH Regeneration
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Abstract
Graphitic carbon
nitride (g-C<sub>3</sub>N<sub>4</sub>) 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-C<sub>3</sub>N<sub>4</sub> to increase solar-to-chemical
efficiency remains a hot yet challenging issue. Herein, a nanoshell
with two moieties of α-Fe<sub>2</sub>O<sub>3</sub> and carbon
(C) is in situ formed on the surface of a g-C<sub>3</sub>N<sub>4</sub> core through calcination of Fe<sup>3+</sup>/polyphenol-coated melamine,
thus acquiring g-C<sub>3</sub>N<sub>4</sub>@α-Fe<sub>2</sub>O<sub>3</sub>/C core@shell photocatalysts. The α-Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub> moiety to g-C<sub>3</sub>N<sub>4</sub> or from g-C<sub>3</sub>N<sub>4</sub> 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-C<sub>3</sub>N<sub>4</sub> is obtained. When
utilized for photocatalytic regeneration of reduced nicotinamide adenine
dinucleotide (NADH, a dominant cofactor in biohydrogenation reaction),
g-C<sub>3</sub>N<sub>4</sub>@α-Fe<sub>2</sub>O<sub>3</sub>/C
exhibits an equilibrium NADH yield of 76.3% with an initial reaction
rate (<i>r</i>) of 7.7 mmol h<sup>–1</sup> g<sup>–1</sup>, 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-C<sub>3</sub>N<sub>4</sub>