Periodic p-orbital regulation induces volcano-type photocatalytic H2 and H2O2 production in an alkaline earth metal–doped g-C3N4 series

Periodic trends in elemental properties provide a fundamental framework for understanding catalytic behavior, yet their role in photocatalysis remains largely unexplored at the orbital-interaction level. Here, a systematic series of alkaline earth metal (Mg, Ca, Sr, and Ba)-doped graphitic carbon nitride (g-C 3 N 4 ) photocatalysts is developed to reveal how periodic electronic characteristics govern photocatalytic performance. Despite the similar chemical nature of the dopants, both H 2 evolution and H 2 O 2 production exhibit a pronounced volcano-type dependence along the Mg-Ca-Sr-Ba sequence under visible light, with Sr-doped g-C 3 N 4 delivering the optimal performance (329.86 μmol g −1 h −1 for H 2 evolution and 1363.58 μmol g −1 h −1 for H 2 O 2 production). This periodic behavior originates from an orbital-synergy mechanism between the outermost p orbitals of alkaline earth metals and the intrinsic C/N 2 p electronic states of g-C 3 N 4 . Moderate p -orbital reactivity enables enhanced π-conjugation, improved charge delocalization, and reduced kinetic barriers for key reaction intermediates, whereas excessive orbital perturbation disrupts electronic balance and deteriorates catalytic efficiency. These findings establish a periodic orbital-regulation principle governing volcano-type photocatalysis and provide a general design framework linking elemental periodicity with semiconductor catalyst optimization.