Copolymerization modification of carbon nitride by aromatic acids for enhanced photocatalytic NADH regeneration performance

The efficient regeneration of nicotinamide adenine dinucleotide (NADH) is a prerequisite for the practical application of redox-dependent enzymatic processes. Among the available strategies, photocatalytic regeneration stands out by harnessing abundant solar energy as a clean and sustainable driving force. Owing to its facile synthesis and exceptional chemical stability, graphitic carbon nitride (g-C₃N₄) has emerged as a widely adopted photocatalyst for this purpose. Herein, we report the synthesis of four aromatic acid modified g-C₃N₄ photocatalysts via copolymerization of urea with trimesic acid (TMA), phthalic acid (PTA), 2,6-pyridinedicarboxylic acid (PDA), and 2,5-furandicarboxylic acid (FDA). Structural and optical characterizations (XRD, FT-IR, XPS, UV-Vis DRS, PL, EIS, photocurrent) confirm successful incorporation of aromatic units, which extends π-conjugation structure, narrows the bandgap, enhances visible-light harvesting, and suppresses electron-hole recombination. Among the series, UCN-PDA_1.0 exhibits the highest photocatalytic activity (0.1473 μmol/min), achieving a NADH yield of 76.92%, which is 7.48 times that of pristine UCN. This work demonstrates that aromatic acid copolymerization is a highly effective strategy for enhancing the properties of g-C₃N₄-based photocatalysts.