Efficient photochemical production of H ₂ O ₂ on carbon nitride photocatalysts with the optimized multi-synergistic effect of enhanced visible light absorption, charge separation, and surface kinetics

Photochemical production of hydrogen peroxide (H₂O₂) using visible light response photocatalysts offers a sustainable green strategy. In this study, g-C₃N₄-based (CN) photocatalysts were facilely synthesized for the photochemical production of H₂O₂ through multi-step calcination and alkali metal ion intercalation processes. The n-π* electronic transition was achieved by disrupting the symmetrical plane of the heptazine layers to enhance visible light absorption. The alkali metal ion intercalations greatly enhanced the photocatalytic activities of CN through a redshift in the π-π* electronic transitions under visible light and the introduction of cyano groups into the photocatalysts. In the alkali metal ion intercalated photocatalysts, the K⁺-intercalated photocatalyst demonstrates the greatest photocatalytic efficiency because of its effective introduction of cyano groups into the CN structure, which enhances the kinetics of the O₂ reduction reaction on the photocatalyst surface by reducing the interfacial charge-transfer resistance. A gradient energy band structure was introduced into the photocatalyst by gradient K⁺-doping, which improved the charge separation efficiency. The photocatalyst with the optimized multi-synergistic effect of improved visible light absorption, charge separation, and surface kinetics achieved a H₂O₂ production rate of 2720 μM h^-1 under simulated sunlight, which is 64 times higher than that of the photocatalyst prepared by the traditional thermal decomposition process. This study offers a straightforward approach for designing high-efficiency CN photocatalysts for photochemical H₂O₂ production.