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Graphite carbon nitride (CN) has received tremendous interest, owing to its potential application in photocatalysis. However, excitonic effects stemming from Coulombic interactions limit the application prospect. Herein, mixed-dimensional metal-free two-dimensional/three-dimensional (2D/3D) heterojunction composites combining 2D covalent-organic framework (COF) nanosheets and 3D hollow porous tubular CN with a phosphate group (CNP) were fabricated to target regulation of exciton dissociation. Experimental and characterization investigations revealed that the presence of a phosphate group in hollow porous tubular CN could reinforce the interfacial interaction between CNP and COF and adjust the band structures for the formation of the Z-scheme mechanism. Benefitted from the effective exciton dissociation and accelerated charge transport at the 2D/3D heterostructure interface, the optimal photocatalytic H2 evolution rate achieved up to 3700 μmol h-1 g-1, which is much higher than the 3D CN, heterojunction CN, and other CN-based photocatalysts reported previously. It also exhibited an excellent peroxymonosulfate-assisted tetracycline (TC) degradation capability, and the rate constant of TC over the COF/CNP5 sample reached 5.61 and 1.40 times as much as that of COF and CNP. This study affords a meritorious instance to construct a mixed-dimension metal-free heterojunction photocatalyst and opens insights for excitonic regulation. [ABSTRACT FROM AUTHOR]