Switching Charge Kinetic from type-I to Z-Scheme of g-C3N4 and ZnIn2S4 by Defective Engineering for Efficient and Durable Hydrogen Evolution

By virtue of spatial separation of active sites, light harvesting as well as highly preserved redox capability, direct Z-scheme heterostructural photocatalysts are found as promising materials for solar energy conversion and environmental remediation. However, challenge still exists to regulate the electron flow direction between semiconductors with staggered electronic structure. In this regard, by regulating the defective and crystalline feature of g-C3N4, a direct Z-scheme DC-g-C3N4/ZnIn2S4 heterostructure was gained, aiming at the modulation of electronic structure and robust hydrogen production performance. The insertion of defective groups in carbon nitride matrix led to a drastic downshift of band edge potentials in comparison to pristine g-C3N4. This variation gave birth to a staggered band edge alignment between DC-g-C3N4 and ZnIn2S4, resulting charge transfer kinetics variation from type-I to direct Z-scheme. By careful characterizations, it’s found that highly crystalline DC-g-C3N4 coupled with ZnIn2S4 to show fine interfacial contact. The optimal photocatalytic hydrogen evolution reaction (PHER) activity over DC-g-C3N4/ZnIn2S4 reached 1.65 mmol•g-1•h-1 with apparent quantum efficiency (AQE) of about 18.2 % at 420 nm and an AQE of ~ 2.2 % at 600 nm. In combination with photocurrent measurement, photoluminescence spectra and electron paramagnetic resonance, the improved hydrogen evolution activity is regarded as the consequence of decreased onset potential and improved spatial segregation of charge carriers by a direct Z-scheme carrier migration, where photoinduced electrons in DC-g-C3N4 can quickly combined with photoinduced holes in the valence band of ZnIn2S4, leading to spatial separation of photoinduced electrons and holes between the two semiconductors.