NaCl-templated hierarchical porous carbons enhanced removal of tetracycline and ciprofloxacin: Mechanistic insights from site energy distribution and competitive adsorption

In this study, hollow spherical NaCl was successfully synthesized via crystal growth inhibition technology. Porous carbons were prepared using hollow spherical NaCl templates with varying dosages, and their adsorption capacities for tetracycline (TC) and ciprofloxacin (CIP) were systematically investigated. The microscopic morphology and specific surface area of the samples were thoroughly characterized using SEM and BET analysis. Kinetic analysis revealed that the adsorption processes of TC and CIP by the porous carbon conformed to pseudo-second-order kinetic and intraparticle diffusion models, indicating that the active site was the main factor affecting the adsorption process. Isothermal adsorption studies demonstrated that the Generalized Langmuir model provided a more accurate description of the adsorption behavior compared to the Langmuir model, indicating monolayer adsorption occurring at heterogeneous adsorption sites. Among the synthesized porous carbons, MCS-3 exhibited optimal adsorption performance, achieving adsorption capacities of 404 mg/g for TC and 268 mg/g for CIP. Site energy distribution analysis further confirmed that the adsorption sites on MCS-3 possessed a higher density of adsorption sites and elevated average site energy. Competitive adsorption experiments revealed stronger adsorption affinity of MCS-3 toward TC over CIP. XPS revealed the adsorption mechanism, and the results indicated that the adsorption between the porous carbon and TC/CIP mainly occurred through the synergistic effect of Lewis acid-base interactions and the hydrogen bonding network. Investigation of pH effects indicated that pH modulated adsorption efficiency by altering the surface charge of the porous carbon and the ionization states of TC/CIP. Recycling experiments demonstrated that MCS-3 maintained stable adsorption performance over five cycles, highlighting its excellent recyclability. These findings collectively provide a critical theoretical foundation and practical guidance for the application of porous carbon in the remediation of TC/CIP-contaminated systems.