Amorphous Carbon Nitride as a Robust Photocatalyst for Biocatalytic Solar-to-Chemical Conversion

In situ regeneration of nicotinamide cofactor (NADH) is imperative because it is required as a reducing power for driving many redox enzymatic cycles useful in industry. Here, we report that amorphous carbon nitride (ACN) is a promising and robust photocatalyst for solar-driven biotransformation via NADH regeneration. Under visible light (lambda > 420 nm), NADH regeneration yields by ACN reached 62.3% within an hour, whereas partially crystalline polymeric carbon nitride (CCN) hardly reduced NAD+ to NADH. Subsequently, the regenerated cofactor was consumed by L-glutamate dehydrogenase, a NADH-dependent enzyme, achieving the conversion of alpha-ketoglutarate with a turnover frequency of 2640 h(-1). ACN showed excellent catalytic activity and long-term stability for light-driven biocatalysis; NADH regeneration efficiency after eight cycles remained above 92% of the first cycle's efficiency, and the enzymatic reaction proceeded for more than 12 h without significant loss of ACN's photoactivity. The remarkable photocatalytic activity of ACN originated from its unique microstructure that lacks hydrogen bonds that link polymeric melon units, leading to extended visible light absorption and less charge recombination. Our results suggest that ACN efficiently drives biocatalytic photosynthesis with exceptional catalytic sustainability.