Mechanistic insights into N-hydroxyphthalimide modified graphitic carbon nitride boosted photocatalytic hydrogen production Electronic supplementary information (ESI) available: Additional experimental section, TEM images, cyclic voltammogram, comparison of photocatalytic hydrogen evolution rates under different sacrificial reagents, etc. See DOI: ; 10.1039/c9cy01340g

Graphitic carbon nitride (g-C3N4) is considered as an attractive and appropriate material to split water and produce hydrogen (H-2) under visible light. Nevertheless, the H-2 evolution rate of g-C3N4 is low due to the rapid recombination of electron-hole pairs. In this context, we develop a novel g-C3N4 system combined with N-hydroxyphthalimide (denoted as NHPI) through pi-pi interactions and hydrogen bonds at the interface for circumventing this issue. NHPI conjugated small molecules act as an efficient hole mediator to reduce the recombination of electron-hole pairs and enhance the photocatalytic activity of g-C3N4. Under visible light excitation, the redox couple NHPI/NHPI+ serves as a redox shuttle, which can facilitate the transfer of holes from g-C3N4 to triethanolamine (TEOA), and the electrons can be shuttled to a Pt cocatalyst. Time-resolved photoluminescence (TRPL), photoelectrochemical (PEC) and electron paramagnetic resonance (EPR) measurements exhibit that the introduction of NHPI on g-C3N4 boosts the visible-light photocatalytic activity through accelerating spatial separation of the electron-hole pairs. Upon introducing optimal 2 wt% NHPI, the photocatalytic H-2 production rate of the g-C3N4/2 wt% NHPI (CN/2 wt% NHPI) composite is significantly enhanced up to 1145.4 mu mol h(-1) g(-1), exceeding that of pristine g-C3N4 (274.0 mu mol h(-1) g(-1)) by 4.2 times. Moreover, the reusability test shows that no obvious loss of activity is observed over the CN/2 wt% NHPI sample. Overall, an excellent stable and highly efficient photocatalyst of the CN/NHPI heterostructure has been obtained, which could find potential application in solar-to-fuel conversion.