Enhanced Photocatalytic H₂ Evolution Performance of the Type-II FeTPPCl/Porous g-C₃N₄ Heterojunction: Experimental and Density Functional Theory Studies

It is of great significance to improve the photocatalytic performance of g-C₃N₄ by promoting its surface-active sites and engineering more suitable and stable redox couples. Herein, first of all, we fabricated porous g-C₃N₄ (PCN) via the sulfuric acid-assisted chemical exfoliation method. Then, we modified the porous g-C₃N₄ with iron(III) meso-tetraphenylporphine chloride (FeTPPCl) porphyrin via the wet-chemical method. The as-fabricated FeTPPCl-PCN composite revealed exceptional performance for photocatalytic water reduction by evolving 253.36 and 8301 μmol g^-1 of H₂ after visible and UV-visible irradiation for 4 h, respectively. The performance of the FeTPPCl-PCN composite is ∼2.45 and 4.75-fold improved compared to that of the pristine PCN photocatalyst under the same experimental conditions. The calculated quantum efficiencies of the FeTPPCl-PCN composite for H₂ evolution at 365 and 420 nm wavelengths are 4.81 and 2.68%, respectively. This exceptional H₂ evolution performance is because of improved surface-active sites due to porous architecture and remarkably improved charge carrier separation via the well-aligned type-II band heterostructure. Besides, we also reported the correct theoretical model of our catalyst through density functional theory (DFT) simulations. It is found that the hydrogen evolution reaction (HER) activity of FeTPPCl-PCN arises from the electron transfer from PCN via Cl atom(s) to Fe of the FeTPPCl, which forms a strong electrostatic interaction, leading to a decreased local work function on the surface of the catalyst. We suggest that the resultant composite would be a perfect model for the design and fabrication of high-efficiency heterostructure photocatalysts for energy applications.