Self-assembled S-scheme In2.77S4/K+-doped g-C3N4 photocatalyst with selective O2 reduction pathway for efficient H2O2 production using water and air

Abstract

The development of an efficient artificial H₂O₂ photosynthesis system is a challenging work using H₂O and O₂ as starting materials. Herein, 3D In_2.77S₄ nanoflower precursor was in-situ deposited on K⁺-doped g-C₃N₄ (KCN) nanosheets using a solvothermal method, then In_2.77S₄/KCN (IS/KCN) heterojunction with an intimate interface was obtained after a calcination process. The investigation shows that the photocatalytic H₂O₂ production rate of 50IS/KCN can reach up to 1.36 mmol g⁻¹ h⁻¹ without any sacrificial reagents under visible light irradiation, which is 9.2 times and 4.1 times higher than that of KCN and In_2.77S₄, respectively. The enhanced activity of the above composite can be mainly attributed to the S-scheme charge transfer route between KCN and In_2.77S₄ according to density functional theory calculations, electron paramagnetic resonance and free radical capture tests, leading to an expanded light response range and rapid charge separation at their interface, as well as preserving the active electrons and holes for H₂O₂ production. Besides, the unique 3D nanostructure and surface hydrophobicity of IS/KCN facilitate the diffusion and transportation of O₂ around the active centers, the energy barriers of O₂ protonation and H₂O₂ desorption steps are effectively reduced over the composite. In addition, this system also exhibits excellent light harvesting ability and stability. This work provides a potential strategy to explore a sustainable H₂O₂ photosynthesis pathway through the design of heterojunctions with intimate interfaces and desired reaction thermodynamics and kinetics.