Fe‐Free Photocatalysis‐Self‐Fenton System for Ultraefficient Water Purification Enabled by Carbon Nitride With Strong Built‐in Electric Field

ABSTRACT Photocatalytic‐self‐Fenton system (PSFs) hold great promise for water purification through in situ generation‐consumption of H 2 O 2 , yet is constrained by two main obstacles: (1) the scarcity of cost‐effective and sustainable photocatalysts, which restricts the overall H 2 O 2 production, and (2) the dependence on exogenous Fe 2+ , leading to issues such as Fe sludge formation and narrow pH operating ranges. Herein, a highly crystalline CN bearing K + , cyano groups and polyethyleneimine is synthesized through doping and molten‐salt assistance calcination. The obtained catalyst exhibits a strong built‐in electric field (KPFM and SPV) and efficient spatial charge separation (series photoelectric tests and DFT calculations). The exposed active sites ( S BET = 102.2 m 2 ·g −1 ) and abundant terminal ‐NH 2 groups create quasi‐homogeneous system (SEM/TEM/AFM and free deposition experiment). The catalyst also exhibits high oxygen adsorption capacity and promotes the reaction pathway of O 2 →·O 2 − →H 2 O 2 →·OH, enabling photosynthesis H 2 O 2 rate up to 14.90 mmol·g −1 h −1 (22.2 times that of CN). The constructed Fe‐free PSFs achieves 100% degradation of high‐concentration tetracycline (100 mg L −1 ) within 10 min with a kinetic constant 3.46 times higher than that of common photodegradation system while overcoming the limitation of a narrow operational pH range. Furthermore, the Fe‐free PSFs can also 100% degrade sulfamethoxazole, ofloxacin, and diclofenac sodium. At last, the improved degradation mechanisms, key reactive species, degradation pathways, and toxicity are systematically elucidated. This study overcomes key limitations of CN‐based photocatalysts and provides novel insights into developing efficient Fe‐free PSFs for pollutant photodegradation over a wide‐pH.