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

Abstract

Graphitic carbon nitride (g-C 3 N 4 ) 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 3 N 4 to increase solar-to-chemical efficiency remains a hot yet challenging issue. Herein, a nanoshell with two moieties of α-Fe 2 O 3 and carbon (C) is in situ formed on the surface of a g-C 3 N 4 core through calcination of Fe 3+ /polyphenol-coated melamine, thus acquiring g-C 3 N 4 @α-Fe 2 O 3 /C core@shell photocatalysts. The α-Fe 2 O 3 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 2 O 3 moiety to g-C 3 N 4 or from g-C 3 N 4 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 3 N 4 is obtained. When utilized for photocatalytic regeneration of reduced nicotinamide adenine dinucleotide (NADH, a dominant cofactor in biohydrogenation reaction), g-C 3 N 4 @α-Fe 2 O 3 /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-C 3 N 4 .

Carbon–Graphitic Carbon Nitride Hybrids for Heterogeneous Photocatalysis

“…Many studies demonstrated that metal‐free carbon nanostructures could be intrinsically excited in enriching effective number of photogenerated carriers over carbon‐induced g‐C 3 N 4 photocatalysts by proving empirical characterizations of photocatalytic improvement. [ 66,105,106 ] Feasible observation was reported in studies where multipath excitation of carbon‐induced g‐C 3 N 4 system was regulated synergistically by using the arranged morphologies, [ 67,107,108 ] quantum dots (QDs), [ 84,109 ] and intensified bridge link [ 110 ] of carbon moiety. These studies conclusively indicated that an active effect maintains between carrier efficiency and metal‐free carbon‐enhanced photocatalytic system.…”

Carbon‐Support‐Based Heterogeneous Nanocatalysts: Synthesis and Applications in Organic Reactions

“…Recently, Wu et al. also proposed an α‐Fe 2 O 3 /C core shell nanomaterial decorated over the sheets of GCN and used them as a heterogeneous catalyst for the regeneration of NAD + to NADH (Figure ) . The practical application of this biocatalysis could be evidenced from the high yield of the NADH formation in the reaction.…”

Comparison of Fe2TiO5/C photocatalysts synthesized via a nonhydrolytic sol–gel method and solid-state reaction method

“…17,18 However, the narrow band gap will lead to the shortcoming of rapid recombination of photoinduce e À /h + pairs. 19 Thus, among the plenty of strategies to solve this problem, [20][21][22] carbon doping is one of the most effective routes to modify photocatalyst. [23][24][25][26] Janus et al developed carbon-modied TiO 2 photocatalyst by exposure of P25 to the ethanol vapor for the carbon deposition.…”