Unraveling size-dependent catalytic activity of monolithic alginate hydrogels for PMS activation and ciprofloxacin removal

Ciprofloxacin (CIP) possesses significant ecological risks to aquatic environments, prompting the search for effective removal methods. Peroxymonosulfate (PMS) based activation emerges as a promising method for water-based CIP degradation. In this study, alginate was converted into spherical calcium alginate hydrogels (CAH) as an activator of PMS to remove CIP. The optimized CAH/PMS can degrade 86.73 % of CIP within 85 min with a first-order kinetic constant of 0.039 min−1. In addition, a relationship between spherical size of CAH (2.4, 3.5, 4.0 and 5.0 mm) and activities of CIP degradation is established, demonstrating 4.0 mm diameter CAH (4.0-CAH) possessing the highest CIP removal efficiency, far higher than 2.4-CAH (50.25 %, 0.014 min−1), 3.5-CAH (51.54 %, 0.021 min−1), and 5.0-CAH (78.71 %, 0.036 min−1). Besides, 4.0-CAH/PMS are not susceptible to various interference factors, including water bodies, pH, ion, and organic matter. The capture test shows excellent CIP degradation of 4.0-CAH is mainly dominated by a synergistic effect of superoxide radical, hydroxyl radical and singlet oxygen. This study highlights the practicality of scalable CAH as a metal-free catalyst for PMS activation and CIP removal, emphasizing its advantages in cost-effectiveness, easy regeneration, environmental friendliness.