Enhanced Photocatalytic Activity of Direct Z-Scheme K4Nb6O17/Carbon-Rich Melon Heterostructures

Melon (also known as graphitic carbon nitride, g-C₃N₄) holds promise for photocatalysis, but challenges such as severe charge recombination, low oxidation potential, and sluggish exciton dissociation hinder its performance. Herein, a series of carbon-rich, melon-based photocatalysts are synthesized via one-pot, temperature-induced condensation of urea with the addition of a trace amount of citric acid. The addition of citric acid enhances crystallinity, extends melon chains, increases the C/N ratio, and improves π–π layer stacking of heptazine units, thereby enhancing charge transport properties and visible-light harvesting capacity. These carbon nitride samples are then coupled with molten salt synthesized K₄Nb₆O₁₇ crystals by a straightforward self-assembly method to construct 2D/2D heterostructure photocatalysts. Z-scheme electron transfer from K₄Nb₆O₁₇ to the melon samples is established based on their work functions and band edge positions. This efficient charge transfer in the Z-scheme heterostructure facilitates the spatial separation of charge carriers, resulting in a nearly fivefold enhancement in photocatalytic performance compared to the individual constituents.