Broad-spectrum response NCQDs/Bi2O2CO3 heterojunction nanosheets for ciprofloxacin photodegradation: Unraveling the unique roles of NCQDs upon different light irradiation

N-doped carbon quantum dots (NCQDs) decorated Bi2O2CO3 heterojunction nanosheets have been successfully constructed by a facile hydrothermal method. The obtained NCQDs/Bi2O2CO3 heterojunction exhibits a wide-spectrum absorption ability and remarkably enhanced photocatalytic activities for ciprofloxacin photodegradation from ultraviolet to near-infrared region. The critical roles of NCQDs and two different charge separation and transfer processes of NCQDs/Bi2O2CO3 heterojunction under different light irradiations have been elucidated. Upon UV light irradiation, NCQDs act as electron reservoirs and a Z-scheme charge transfer process between Bi2O2CO3 and NCQDs promotes electrons transfer and •O2− reactive species generation. Under visible and NIR light irradiation, NCQDs act as photosensitizer (hole reservoirs) to harvest solar light and a type-II heterojunction leads to an efficient charge carrier separation and thus high catalytic ability. The mechanisms and pathways of ciprofloxacin degradation driven by different lights are discussed accordingly. This work provides a versatile pathway to well design an efficient wide-spectrum response photocatalyst.