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The practical application of graphitic carbon nitride (g-C 3 N 4 , CN) is restricted by its low photocatalytic activity and difficult recycling. Herein, we report a CN/Mn 2 O 3 p-n heterojunction grown by a plasma-assisted liquid-based method using a special precursor complex of melamine-cyanuric acid supramolecular on fluorine-doped tin oxide (FTO) substrate. The as-grown CN/Mn 2 O 3 /FTO p-n heterojunction exhibits a significantly enhanced photoelectrochemical performance with a photocurrent density of 25 μA/cm2 compared with its powder form (0.9 μA/cm2) formed by common drop coating method，and a tunable valence band (VB) with excellent mechanical strength which is benefit for photocatalytic oxidation reaction and recovery. The formation of CN/Mn 2 O 3 /FTO p-n heterojunction can promote the transfer of photoelectrons due to an internal electric field at the interface of p-n junction, leading to the accumulation of electrons and holes in the VB of CN and conduction band (CB) of Mn 2 O 3. The results have shed a light on promoting the practical application of CN, and the developed plasma-assisted liquid-based growth method can be extended to the preparation of other type of functional heterojunctions. [Display omitted] • ACN/Mn 2 O 3 p-n heterojunction was grown by a plasma-assisted liquid-based method using melamine-cyanuric acid supramolecular as precursor. • The as-grown CN/Mn 2 O 3 /FTO p-n heterojunction exhibits a significantly enhanced PEC performance and a tunable VB. • The internal electric field at the interface of p-n heterojunction can promote the transfer of photoelectrons and lead to the accumulation of electrons and holes in the VB of CN and CB of Mn 2 O 3. • The developed plasma-assisted liquid-based growth method can be extended to the preparation of other type of functional heterojunctions. [ABSTRACT FROM AUTHOR]

Amorphous carbon nitride (ACN) is a promising semiconductor photocatalyst for photocatalytic H 2 O 2 production. However, its actual activity is hindered by a high recombination rate of photoexcited charge carriers. Herein we report a K-doped ACN (K-ACN) photocatalyst synthesized via Ar plasma treatment to the modified melamine and KCl powder mixture at a moderate temperature. The as-synthesized K-ACN exhibits significantly enhanced photocatalytic properties for H 2 O 2 production with a yield of 6.21 mM h−1, which is 6 times higher than that of bulk CN. Moreover, the H 2 O 2 yield can be further increased to 13.95 mM h−1 by adjusting the pH value. The significantly enhanced photocatalytic property is mainly attributed to the introduction of K+, which is conducive to tuning the electronic structure, extending π conjugated system, passivating trap states and enhancing photocatalytic activity. The result has provided a facile and effective strategy for the modification of ACN to significantly boost its photocatalytic activity. [Display omitted] • K-ACN photocatalyst was synthesized via Ar plasma treatment to the modified melamine and KCl powder mixture. • The as-synthesized K-ACN exhibits 6-fold photocatalytic H 2 O 2 production relative to pristine carbon nitride. • The passivated trap states were observed in K-ACN and result in faster transport of light-induced active electrons. • K doping is conducive to tuning the electronic structure and enhanceing photocatalytic activity of ACN. [ABSTRACT FROM AUTHOR]