Self-supported hierarchical crystalline carbon nitride arrays with triazine-heptazine heterojunctions for highly efficient photoredox catalysis

•A self-supported hierarchical crystalline MA-rod array is demonstrated for the first time.•The high crystallinity endows MA-rod array with the improved migration dynamics of charge carriers.•The formation of triazine-heptazine heterojunction accelerates the separation of photo-generated electron-holes.•MA-rod array exhibits excellent 51-fold higher hydrogen production than the reference with a high AQY of 60% at 420 nm.•The oxidation of aromatic hydrocarbons to aldehydes or ketones can be achieved under 460 nm irradiation with milligram yields. Self-supported hierarchical crystalline carbon nitride arrays (MA-rod array), which show the excellent properties of photocatalytic hydrogen evolution and oxidative organic synthesis, were synthesized by molten salt-assisted pyrolysis of rod-like supramolecular precursors from the hydrolysis of melamine. On the nanoscale, the highly crystalline MA-rod array has an omasum-like architecture with combined advantages of rapid electrolyte diffusion, efficient gas evolution, fast electronic transmission, and lower interface resistance. At the molecular level, the triazine-heptazine heterojunctions remarkably improve charge carrier transfer and separation. In the tests of photoredox catalysis, the MA-rod array exhibited 51-fold higher hydrogen production rate (11720 μmol h−1 gcat-1) than the reference with a high apparent quantum yield (AQY) of 60% at 420 nm. Furthermore, the oxidation of aromatic hydrocarbons to aldehydes or ketones can be obtained under single wavelength (460 nm) irradiation with milligram yields (e.g., the isolated yield of benzaldehyde is 34.5 mg with the conversion rate of 1805.6 μmol h−1 gcat-1), surpassing other photocatalysts so far.