Atomically Dispersed Zn−N4 Sites in g-C3N5@g-C3N4 Heterostructures Enable Charge Separation for Natural Sunlight-Driven Green H2O2 Production

The sustainable photocatalytic production of H2O2 through a completely green approach has become a promising solution to combat global energy and environmental challenges. Therefore, development of stable and environmentally friendly green photocatalysts is highly desirable. In this work, a catalyst has been developed by decorating a zinc single atom on a 2D heterostructure of g-C3N5@C3N4 (Zn C3N5@C3N4). The atomically dispersed Zn2+ forms a stable Zn−N4 coordination within the carbon nitride moiety, creating a single-atom active site for photocatalysis. The successful formation of single-atom active sites has been confirmed by morphological and elemental studies, while their crucial role in photocatalysis has been further established through the correlation with the intricate photophysical and optoelectronic properties. Femtosecond transient absorption spectroscopy data further demonstrate the suppressed charge recombination and accelerated charge transfer to the active catalytic sites, thereby enhancing photocatalytic efficiency. Notably, the Zn C3N5@C3N4 catalyst shows highly efficient photocatalytic H2O2 production at the rate of 25 mM/g/h, which is two times higher than the pristine CN, with an apparent quantum efficiency of ∼ 28% at 400 nm. The photoinduced active species taking part in the photocatalytic process has been confirmed by chemical scavenging experimental and electron paramagnetic resonance (EPR) studies. Finally, Zn C3N5@C3N4 has shown remarkable H2O2 production efficiency even under bare sunlight, which is noted as one of the highest amounts of H2O2 production rate under bare sunlight (130 mM/g/h) reported previously.