Montmorillonite-Supported PdO/ZnO Heterointerfaces for Enhanced Ciprofloxacin Removal from Water

Persistent antibiotics such as ciprofloxacin (CIP) require treatment materials that couple pollutant adsorption, efficient photoinduced charge utilization, and structural stability during aqueous operation. In this work, zinc oxide (ZnO) was incorporated into montmorillonite and subsequently coupled with PdO to obtain PdO–ZnO heterointerfaces within a clay-supported framework for CIP removal under UV irradiation. X-ray diffraction identified wurtzite ZnO and montmorillonite as the major crystalline phases. Nitrogen adsorption–desorption showed mesoporosity, with a specific surface area of 23 m 2 g −1 and pore volume of 0.127 cm 3 g −1 for the PdO-free composite, and 21–22 m 2 g −1 with 0.113–0.123 cm 3 g −1 after PdO inclusion. The average pore diameter increased from ~ 14 nm to ~ 21–23 nm. Diffuse reflectance UV–visible spectroscopy indicated a small but systematic band gap decrease from 3.196 to 3.137 eV with increasing PdO content. Under UV irradiation at 0.5 g L −1 catalyst, 20 mg L −1 CIP, and pH 6, the composite with the highest PdO loading (ZMP5) achieved ~ 90% removal within 120 min and the highest pseudo-first-order rate constant (0.01257 min −1 ), whereas the other compositions fell in the 0.00833–0.00978 min −1 range. Scavenger experiments reduced total removal from ~ 90 to ~ 81–85%, supporting parallel oxidative pathways involving superoxide-related routes, hydroxyl radicals, and photogenerated holes. Reuse tests showed total removal decreasing from 90 to 31% over four cycles, driven by adsorption loss (51 to ~ 1%) while the photocatalytic contribution remained comparatively less affected (39–30%). Post-reuse scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy indicated preserved lamellar morphology and retained Zn and Pd signals, consistent with structural stability of the oxide–clay architecture. These results show that PdO loading can tune adsorption–photocatalysis coupling in a montmorillonite-supported ZnO framework while preserving the textural and structural features required for repeated aqueous operation.