Indirect Z-scheme nitrogen-doped carbon dot decorated Bi₂MoO₆/g-C₃N₄ photocatalyst for enhanced visible-light-driven degradation of ciprofloxacin

A novel nitrogen-doped carbon dot (NCD) decorated onto bismuth molybdate (Bi₂MoO₆) and carbon nitride (g-C₃N₄) (NCD@BMCN) nanocomposite was successfully synthesized for the photodegradation of ciprofloxacin (CIP) under the visible light irradiation. The homogeneous deposition of 10–20 nm NCD onto the surface of BMCN increases the specific surface area and photocurrent density, which can facilitate the good charge transfer efficiency for the enhanced photodegradation of CIP. The NCD@BMCN exhibits excellent visible-light-responsive photocatalytic activity over CIP degradation and the pseudo-first-order rate constants are in the range of 0.036–0.13 min⁻¹, which are dependent on initial pH, photocatalyst dosage and existence of anions. The indirect Z-scheme mechanism for CIP photodegradation with hydroxyl radicals (^•OH) and superoxide radicals (^•O₂⁻) as the dominant reactive species is also proposed, in which NCD plays a role as the mediator to transfer electrons from the conduction band of Bi₂MoO₆ to the valence band of g-C₃N₄. Moreover, the NCD@BMCN photocatalyst exhibits good stability and reusability after five consecutive cycles of photodegradation. Results have demonstrated that the NCD@BMCN is a promising Z-scheme photocatalyst for the degradation of CIP, which can be further explored to synthesize a rapid, productive and low-cost NCD@BMCN nanocomposite for the treatment of pharmaceutical-contaminated water and wastewater.