Simultaneously Tuning Charge Separation and Oxygen Reduction Pathway on Graphitic Carbon Nitride by Polyethylenimine for Boosted Photocatalytic Hydrogen Peroxide Production

Abstract

The synthesis of hydrogen peroxide (H 2 O 2 ) from H 2 O and O 2 by metal-free photocatalysts (e.g., graphitic carbon nitride, C 3 N 4 ) is a potentially promising approach to generate H 2 O 2 . However, the photocatalytic H 2 O 2 generation activity of the pristine C 3 N 4 in pure H 2 O is poor due to unpropitious rapid charge recombination and unfavorable selectivity. Herein, we report a facile method to boost the photocatalytic H 2 O 2 production by grafting cationic polyethylenimine (PEI) molecules onto C 3 N 4 . Experimental results and density functional theory (DFT) calculations demonstrate PEI can tune the local electronic environment of C 3 N 4 . The unique intermolecular electronic interaction in PEI/C 3 N 4 not only improves the electron–hole separation but also promotes the two-electron O 2 reduction to H 2 O 2 via the sequential two-step single-electron reduction route. With the synergy of improved charge separation and high selectivity of two-electron O 2 reduction, PEI/C 3 N 4 exhibits an unexpectedly high H 2 O 2 generation activity of 208.1 μmol g –1 h –1, which is 25-fold higher than that of pristine C 3 N 4 . This study establishes a paradigm of tuning the electronic property of C 3 N 4 via functional molecules for boosted photocatalysis activity and selectivity.