Self-Assembled Peptide-Carbon Nitride Hydrogel as a Light-Responsive Scaffold Material

Peptide self-assembly is a facile route to the development of bioorganic hybrid materials that have sophisticated nanostructures toward diverse applications. Here, we report the synthesis of self-assembled peptide (Fmoc-diphenylalanine, Fmoc-FF)/graphitic carbon nitride (g-C₃N₄) hydrogels for light harvesting and biomimetic photosynthesis through noncovalent interactions between aromatic rings in Fmoc-FF nanofibers and tris-s-triazine in g-C₃N₄ nanosheets. According to our analysis, the photocurrent density of the Fmoc-FF/g-C₃N₄ hydrogel was 1.8× higher (0.82 μA cm^-1) than that of the pristine g-C₃N₄. This is attributed to effective exfoliation of g-C₃N₄ nanosheets in the Fmoc-FF/g-C₃N₄ network, facilitating photoinduced electron transfers. The Fmoc-FF/g-C₃N₄ hydrogel reduced NAD⁺ to enzymatically active NADH under light illumination at a high rate of 0.130 mol g^-1 h^-1 and drove light-responsive redox biocatalysis. Moreover, the Fmoc-FF/g-C₃N₄ scaffold could well-encapsulate key photosynthetic components, such as electron mediators, cofactors, and enzymes, without noticeable leakage, while retaining their functions within the hydrogel. The prominent activity of the Fmoc-FF/g-C₃N₄ hydrogel for biomimetic photosynthesis resulted from the easy transfer of photoexcited electrons from electron donors to NAD⁺ via g-C₃N₄ and electron mediators as well as the hybridization of key photosynthetic components in a confined space of the nanofiber network.