NGQD active sites as effective collectors of charge carriers for improving the photocatalytic performance of Z-scheme g-C3N4/Bi2WO6 heterojunctions

Abstract

The broad absorption range and high carrier separation efficiency of photocatalysts are important for improving photocatalytic performance. Herein, nitrogen-doped graphene quantum dots (NGQDs) as effective active sites and collectors of charge carriers in modified Z-scheme g-C₃N₄/Bi₂WO₆ heterojunctions were obtained by a facile hydrothermal method, and dramatically enhanced the electron–hole separation efficiency and light harvesting ability. NGQD-modified Z-scheme g-C₃N₄/Bi₂WO₆ heterojunctions exhibited outstanding universal photocatalytic degradation activity for removing various antibiotics such as tetracycline (TC), ciprofloxacin (CIP), oxytetracyline (OTC), etc. under visible (vis) and near-infrared (NIR) light irradiation owing to the charge carriers' collection effect and up-conversion luminescence properties of NGQDs. In addition, the photocatalytic reaction mechanism was also revealed by active species trapping experiments and the electron spin resonance (ESR) technique, which indicated that the influencing order of active species on the photocatalytic reaction is ˙O₂⁻ > h⁺ ≫ ˙OH.