Cd-doped Ag₂O/BiVO₄ visible light Z-scheme photocatalyst for efficient ciprofloxacin degradation

Foreign element doping can produce new photocatalysts with different band edge positions and adsorption properties. A composite of such a doped semiconductor with another component should enhance its photocatalytic properties towards a target substrate. The present investigation used a simple hydrothermal protocol to prepare Cd-doped Ag₂O nanoparticles. The Cd-doping of Ag₂O nanoparticles changed its valence band maximum position from 0.8 eV (for undoped Ag₂O nanoparticles) to 2.67 eV with a slight narrowing of the Ag₂O bandgap. A combination of DFT calculation and XRD results showed that the dopant Cd substituted Ag in the Ag₂O lattice. The doped material is an effective photocatalyst for ciprofloxacin degradation but with poor recyclability. The joining of a BiVO₄ part to the Cd-doped Ag₂O nanostructures gave a composite with improved photocatalytic activity and recyclability towards ciprofloxacin degradation. DFT calculations showed that BiVO₄ has a higher oxygen affinity than Cd-doped Ag₂O. The XPS characterization of the composite and appropriate active species scavenger experiments demonstrated a Z-scheme mechanism. Superoxide radicals play a critical role in CIP degradation.