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

N-doped carbon quantum dots (NCQDs) decorated BiOCO heterojunction nanosheets have been successfully constructed by a facile hydrothermal method. The obtained NCQDs/BiOCO 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/BiOCO 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 BiOCO and NCQDs promotes electrons transfer and •O 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.