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

Abstract 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.