Periodic Alkali Metal Modulation of Carbon Nitride for Volcano-Type Photocatalytic H2O2 Production.

Alkali metal ions (Li+, Na+, K+, Rb+, Cs+) are systematically doped into graphitic carbon nitride (g-C3N4, CN) to investigate the periodic regulation of photocatalytic H2O2 production. Using ethanol as a sacrificial agent under visible-light irradiation, the H2O2 generation rate exhibits a pronounced volcano-type trend along the Li-Na-K-Rb-Cs series, with K+-doped CN achieving the highest activity of 1795 µmol g-1 h-1, representing a 2.1-fold enhancement over pristine CN. Mechanistic studies reveal that alkali metal ions incorporation modulates the electronic structure of CN through orbital interactions, enhances π-conjugation, promotes charge separation, and facilitates interfacial charge transport. Density functional theory (DFT) calculations further indicate that the introduction of alkali metal ions lowers the energy barriers of key 2e- oxygen reduction reaction steps and establishes a kinetically efficient pathway for the selective formation of H2O2. This work presents a periodic law-guided orbital modulation strategy and provides a rational design principle for high-performance CN-based photocatalysts.