Adsorption Removal of Selected Antibiotics From Water Using Carbon‐Mineral Composites

Carbon‐mineral composites (CHS, CHNT, CKT) were tested as adsorbents for the removal of doxycycline and ciprofloxacin from aqueous solutions. Adsorption behavior was investigated under equilibrium and kinetic conditions and analyzed using pseudo‐first‐order, pseudo‐second‐order, and Weber–Morris intra‐particle diffusion models, while equilibrium data were fitted to adsorption isotherms. CHS showed the highest removal efficiencies, reaching 95.7% for doxycycline and 80.6% for ciprofloxacin. Kinetic data for both antibiotics were best described by the pseudo‐second‐order model (R 2 = 0.9996 and 0.9923). The Weber–Morris analysis indicated a two‐stage mechanism involving rapid boundary‐layer diffusion followed by intra‐particle diffusion. Equilibrium studies at three temperatures (293, 298, and 303 K) showed that adsorption on CHS was best fitted by the Langmuir multi‐center model indicating monolayer adsorption on energetically heterogeneous sites. The maximum adsorption capacities (mg·g −1 ) predicted by this model were 34.5–44.7‐for doxycycline; and 8.50–20.1 for ciprofloxacin. Doxycycline showed a higher adsorption capacity than ciprofloxacin, probably as a result of differences in molecular structure and specific interactions with the composite surface. Evaluation of adsorption enthalpies using Boudart's rules confirmed that adsorption of both antibiotics on CHS is exothermic and enthalpy‐controlled, dominated by specific surface interactions.