Photofixation Pd Functionalization of ZnO Thin Films for Efficient Photocatalytic Removal of Doxycycline Antibiotic in Aqueous Phase

In this work, we demonstrate the co-catalytic modification of ZnO films via the photodeposition of palladium (Pd) to enhance the photocatalytic degradation of doxycycline (DC). Pristine ZnO films were synthesized using a sol–gel method and deposited onto glass substrates via dip-coating. The films were subsequently modified with Pd through chemical photodeposition under UV light, which facilitated the photoreduction of an aqueous 5 × 10−3 M Pd2+ precursor. The influence of varying UV photodeposition doses (2.5, 5, and 10 J/cm2) on the morphology and chemical composition of the Pd-modified films was investigated to control Pd surface coverage and chemical state. Characterization techniques included scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). At low UV doses (2.5 J/cm2), approximately 1.6 at.% of Pd was photodeposited, primarily as PdO, while higher UV doses (5–10 J/cm2) increased the metallic Pd0 content. The photocatalytic degradation of DC was evaluated in both distilled and tap water, where Pd/ZnO films demonstrated significantly higher removal efficiency (40–380% higher) than pristine ZnO films, with those containing higher Pd0 levels exhibiting the greatest activity. Across all samples, removal efficiency in tap water was approximately double that in distilled water.