Enhanced built-in electric fields in alkali metal-doped C3N5 enable sustainable molecular oxygen activation for water purification

Abstract

The sluggish charge kinetics in photocatalysis is a severely limiting factor for the efficient molecular oxygen for water purification. Here, we report the conversion from amorphous to the crystalline phase of nitrogen-enriched carbon nitride (C₃N₅) via a molten salt strategy, enabling the ordered arrangement of dipole moments and reinforcing spontaneous built-in electric fields that harness directional separation and transfer of photogenerated charges. This unique combination of crystallinity enhancement, defective cyano groups grafting, and interlayer K⁺/Na⁺ doping synergistically boosts the built-in electric fields and the interlayer shuttling of photogenerated carriers. The interlayered K⁺/Na⁺–N₃ bridge site in C₃N₅ is able to activate the surface neighboring C and N atoms for boosting the rate-determining step of the photocatalytic molecular oxygen’s redox reaction to produce singlet oxygen sustainably. The engineered C₃N₅ demonstrates exceptional degradation activity for various persistent pollutants by releasing singlet oxygen even under harsh environmental conditions. Remarkable, our material displays an unprecedented pollutant removal efficiency with a 100 % degradation rate for up to 15 days of operation with negligible performance attenuation under outdoor sunlight. This successful engineering of the built-in electric field offers a new strategy for organic photocatalysts and the design of advanced materials for efficient and sustainable environmental remediation.