Aniline or potassium hexacyanoferrate engineering graphitic carbon nitride for highly efficient photocatalytic NADH regeneration

The development of highly efficient photocatalyst for reduced nicotinamide adenine dinucleotide (NADH) regeneration is vital to sustain and scale up the oxidoreductase-catalyzed reactions. As a representative metal-free photocatalyst, graphitic carbon nitride (g-C3N4) has many virtues including prominent chemical stability, low cost, non-toxicity and diverse precursors. However, pristine g-C3N4 suffers from a narrow absorption range and high recombination rate of photogenerated carriers, leading to a low catalytic efficiency. These issues can be addressed by integrating with a broad-spectrum photosensitizer. In this work, aniline (C6H7N) or potassium hexacyanoferrate (K4Fe(CN)6) was used for sensitizing g-C3N4. The effects of the mixing method of C6H7N, the type of precursor, preparation condition such as calcination temperature or centrifugal speed, and the addition amount of photosensitizer on the structures and properties of composites were investigated. After systematic optimization, the light absorption margin was greatly widened from 500 to 573 and 582nm, the recombination rate of photogenerated carriers was significantly reduced, and the photocatalytic performance was much enhanced. The catalytic activity of C6H7N/g-C3N4 and K4Fe(CN)6/g-C3N4 was separately 2.39 and 5.19mM/(g·min), 2.6 and 5.7 folds that of g-C3N4. The yield of NADH reached 71.8% (150min) and 54.1% (60min), respectively, while it was only 18.3% (150min) for g-C3N4.