Coal Gangue-Derived Calcium Silicate Hydrate for Efficient Ciprofloxacin Removal: Adsorption Performance and Mechanism

The persistent accumulation of antibiotic pollutants in aquatic environments poses potential threats to ecological safety and human health, highlighting the importance of developing low-cost, high-performance adsorbents for their efficient removal. In this study, a hydrothermal method was employed to prepare highly dispersed coal gangue-based calcium silicate hydrate (CSH) adsorbents. The structural characteristics, adsorption performance, and adsorption mechanisms of the material were systematically investigated. The as-prepared CSH exhibited an interwoven nanorod/nanosheet composite morphology with a more developed pore structure and a higher specific surface area. Kinetic analysis indicated that the adsorption process followed a pseudo-second-order model and involved both Boyd diffusion and intraparticle diffusion, with liquid-film diffusion likely serving as the primary rate-limiting step. Isotherm analysis revealed that the adsorption behavior was well described by the Langmuir model, suggesting monolayer adsorption, with a theoretical adsorption capacity (Qm) of 129.29 mg/g. Thermodynamic analysis further demonstrated that the adsorption of CIP onto CSH was a spontaneous and endothermic process. Combined characterization results and theoretical calculations suggested that the adsorption of CIP by CSH was mainly governed by surface oxygen containing active sites, accompanied by electrostatic interactions, hydrogen bonding, and possible surface coordination effects. In addition, CSH maintained excellent adsorption performance and structural stability in the presence of coexisting ions, in tap water systems, and after repeated adsorption–desorption cycles. This study not only enables the high-value utilization of coal gangue but also provides new insights into the development of low-cost adsorbent materials for antibiotic removal.