Rational design 2D/2D BiOBr/CDs/g-C3N4 Z-scheme heterojunction photocatalyst with carbon dots as solid-state electron mediators for enhanced visible and NIR photocatalytic activity: Kinetics, intermediates, and mechanism insight

Rapid recombination of photogenerated carriers and narrow visible light absorption range are two main defects in graphitic carbon nitride (g-C3N4)-based photocatalysts. To address these problems, construction of Z-scheme 2D/2D BiOBr/CDs/g-C3N4 heterojunction photocatalysts with carbon dots as solid-state electron mediators has been investigated. The resultant BiOBr/CDs/g-C3N4 hybrids exhibits remarkable interfacial charge transfer abilities and a broadened solar light absorption range owing to the short charge transport distance and the up-converted photoluminescence character of CDs. Simultaneously, the enhanced specific surface area and nanosheet structure impart more active sites to BiOBr/CDs/g-C3N4 composites. As a result, BiOBr/CDs/g-C3N4 composites reveal significant enhancement in the activity of photodegradation of ciprofloxacin (CIP) and tetracycline (TC) under visible and near infrared (NIR) light irradiation. Moreover, the photodegradation efficiency of BiOBr/CDs/g-C3N4 hybrids was significantly enhanced over that of pristine BiOBr nanosheets and g-C3N4 ultrathin nanosheets. The photocatalytic mechanism is expounded according to free radical capture experiments and electron spin resonance spin-trapping tests and the photodegradation intermediates of CIP were detected by liquid chromatography-mass/mass spectrometry. Moreover, BiOBr/CDs/g-C3N4 composites show excellent photostability and reusability after four runs for CIP degradation. (C) 2018 Elsevier Inc. All rights reserved.