Photocatalytic NAD(P)H regeneration by alkali-doped g-C3N4 and extending visible light to near-infrared light

Efficient regeneration of the coenzymes NADH and NADPH is crucial for sustaining biocatalytic processes, particularly in driving the biocatalysis reaction. In this study, the photocatalytic properties of alkali-doped graphitic carbon nitrates were explored to achieve efficient NAD(P)H regeneration. g-C 3 N 4 doped with potassium (KOH), sodium (NaOH), and calcium (Ca(OH) 2 ) was synthesized and characterized, showing significant enhancements in light absorption, charge separation, and photogenerated electron transport. Among the synthesized photocatalysts, KOH-doped g-C 3 N 4 (KCN) exhibited the best photocatalytic performance, regenerating 95 % NADH and 92 % NADPH within 30 min. This result compares favorably with those reported in previous studies. Based on this superior performance, K-0.2 was further applied to the in vitro CO 2 reduction to formate as a proof of concept. To clarify the mechanistic insights of the improved photocatalytic performance of KCN, the chemical model of g-C 3 N 4 and KCN was established, and DFT calculations were performed to reveal the electronic structure modifications responsible for the enhanced photocatalytic activity. Furthermore, to expand the light utilization capability of the system, upconversion nanoparticles (UCNPs) were incorporated into the system to utilize near-infrared light (980 nm), which successfully achieved NADH regeneration under near-infrared excitation and extended the light absorption range of the photocatalytic system. Overall, this study demonstrated that alkali-doped g-C 3 N 4 offered a highly efficient platform for NAD(P)H regeneration, and the integration of UCNPs further enriched the coenzyme regeneration scenario, suggesting a promising strategy for advancing sustainable coenzyme regeneration technologies.