Synthesis and Characterization of the All Solid Z-Scheme Bi₂WO₆/Ag/AgBr for the Photocatalytic Degradation of Ciprofloxacin in Water

The continuous release of antibiotics to the environment via wastewater is becoming a priority. Since conventional depuration systems are unable to remove these substances, aquatic organisms in natural water bodies receiving effluents are facing a continuous risk of harmful effects. Advanced oxidation processes, such as heterogeneous photocatalysis have demonstrated to fully degrade antibiotics in water, thus attention is focused on developing more efficient photocatalysts. In this work, an all solid Z-scheme heterostructure was obtained to photocatalytically degrade and mineralize ciprofloxacin. Initially, Bi₂WO₆ was synthesized via the solvothermal method; then Ag° nanoparticles were photo-deposited on its surface, followed by the precipitation of AgBr. The AgBr/Ag/Bi₂WO₆ heterostructure was characterized by XRD, TEM, SEM, XPS, DRS and BET. Electrochemical characterization was used to determine the potential of the valence and conduction bands of the semiconductors, as well as to elucidate the mechanisms leading to the charge carrier transference within the heterostructure. These characterizations provided the evidence to classify the synthesized heterostructure as an all solid-state Z-scheme. Photocatalytic activity tests under visible light irradiation demonstrated a clear synergistic effect of the AgBr/Ag/Bi₂WO₆ heterostructure, compared to its single components. In pure water, degradation and mineralization yields of 57% and 38% were respectively obtained upon 5 h irradiation. Then, photocatalysis was performed using tap water and initial concentration of ciprofloxacin was set at 50 µg L⁻¹. In this case, the pollutant was completely degraded and mineralized. The photocatalyst was stable upon four reaction cycles in tap water.