Intramolecular internal electric field and activated n-π* electronic transition co-promoted photocatalysis activity of carbon nitride: Mechanism and toxicity evaluation.

Graphitic carbon nitride (CN) exhibits enormous potential in addressing the global energy crisis and environmental issues, while poor charge behavior and insufficient light harvesting capability significantly impede its practical applications. Herein, CN with strong internal electric field and activated n-π* electron transitions was synthesized through one-pot thermal copolymerization of urea and 4,4-Bis(diethylphosphonomethyl)biphenyl. The integrated donor-acceptor structure induces powerful internal electric field, enhancing exciton dissociation efficiency and accelerating charge carrier transport. Simultaneously, n-π* electron transitions are successfully activated by lone pair electrons of phosphorus atoms, broadening the photo-response-range up to 500 nm. The above merits endow the optimal sample 45-BCN with boosted activity, achieving 100 % photodegradation efficiency for tetracycline (TC) within 40 min and significantly enhanced nitrogen fixation efficiency (about 5 times that of CN). Furthermore, the toxicity of photocatalytic-generated intermediates of TC was significantly alleviated according to the Quantitative Structure Activity Relationship model prediction and mung bean growth experiments. This work offers valuable insights into the construction of cost-effective, high-efficiency and environmental-friendly CN photocatalysts for mitigating water pollution and enabling solar-driven nitrogen fixation.