Structural construction and regulation of PCN-222(M) (M = H2, Ni, Mn, Pd)/g-C3N4-AA heterojunctions: A strategy for optimizing photocatalytic water splitting to enhance hydrogen production

It is highly desirable to enhance the charge separation and introduce catalytic functions for efficient water splitting into hydrogen on g-C 3 N 4 . Herein, heterojunctions of PCN-222(M)/g-C 3 N 4 -AA were successfully synthesized through the in-situ hydrothermal method, where metallic ions (M) were strategically incorporated into porphyrinic metal-organic framework (MOF) ligands. This heterojunction design strategy is considered to establish directional charge transfer channels for photogenerated electron-hole (e − -h + ) pairs and thereby enhance its separation efficiency. Remarkably, the 1 % PCN-222(Pd)/g-C 3 N 4 -AA composite demonstrated superior photocatalytic hydrogen evolution performance, achieving a rate of 2338.17 μmol·g −1 ·h −1 . This rate was 3.23 times higher than that of pure g-C 3 N 4 and 2.79 times higher than that of g-C 3 N 4 -AA. The composite morphology was characterized by a series of physicochemical properties. Bandgap analysis via Tauc plot revealed that metal ion doping in the porphyrin center effectively modulates the HOMO-LUMO levels at the composite interface. First-principles calculations coupled with hydrogen adsorption free energy analysis elucidated how interfacial engineering between PCN-222(M) and g-C 3 N 4 -AA governs heterostructure formation and charge transfer pathways. This work systematically deciphers the synergistic effects of bimetallic MOF integration and provides insights into the underlying photocatalytic reaction mechanism.