Novel intramolecular-tailored g-C3N4 with accelerated charge delivery for photocatalytic tetracycline degradation and hydrogen production: experimental studies and theoretical analyses

The precise intramolecular-tailored strategy is deemed to have abundant potential to promote the activity of metal-free photocatalysts yet remains a daunting task. In this work, we report a simple one-step calcination method for skillfully incorporating alkyl into the tri-s-triazine ring of graphite carbon nitride (g-C3N4). The photocatalytic tetracycline photodegradation rate of the optimal ethyl modified g-C3N4 (CN-E-75) is significantly higher than that of the original g-C3N4. Experimental and theoretical calculation results show that the significantly enhanced photocatalytic activity is mainly due to the optimization of the electronic band structure of g-C3N4 by introducing ethyl defects attached to N atoms in the tri-s-triazine rings. The ethyl defect mainly splits the Np orbitals to generate mid gap states under the conduction band edge, thereby consequently narrowing the band gap to extend visible light harvesting, but also meanwhile accelerates charge delivery to boost the photogenerated charge separation, inhibiting electron–hole recombination, and thus considerably increases the photocatalytic properties. Moreover, as-fabricated CN-E-75 verifies the satisfied stability after five cycling runs for photocatalytic water splitting for H2 evolution and tetracycline photodegradation. This work sheds light on deep understanding of intramolecular tailored defect engineering and offers guidance to design other efficient photocatalytic systems.