Enhanced photocatalytic degradation of furosemide using Gd3+/Cu2+co-doped ZnO synthesized via sonochemical-assisted coprecipitation

In this work, Gd³⁺/Cu²⁺co-doped ZnO photocatalysts with compositions Zn1 − x−yGdxCuyO (x, y = 0.00/0.00; 0.02/0.02; 0.02/0.04) were synthesized via sonochemical-assisted coprecipitation and applied in the degradation of the pharmaceutical furosemide under UV irradiation. X-ray diffraction confirmed the wurtzite ZnO phase in all samples, with a secondary CuO phase appearing at 4% Cu content and systematic shifts in lattice parameters. The Zn0.96Gd0.02Cu0.02O sample (ZGC22) exhibited the smallest crystallite size (~ 6 nm), a high BET surface area (~ 57 m²/g), and a band gap narrowing from 3.274 eV (undoped) to 3.242 eV, favoring enhanced UV absorption. The micrographic images reveal a morphology transition from well-defined rods (undoped ZnO) to dense, cauliflower-like nanoparticle agglomerates in the ZGC22 sample, and to more open, flaky aggregates at higher Cu levels. Under UV irradiation, the ZGC22 sample achieved 70% furosemide degradation after 180 min, surpassing undoped ZnO (55%) and the higher-Cu sample (44%). Scavenger tests identified •OH as the dominant reactive species. Reuse experiments conducted on the ZGC22 sample show more than 90% retention of degradation efficiency after multiple cycles. These results illustrate a synergistic effect of Gd3+/Cu2+ co-doping in adjusting structural and optical properties to improve photocatalytic performance.