Surface modification of natural magnetic particles with silica and trimethoxy[3-(phenylamino)propyl]silane for enhanced chloramphenicol and ciprofloxacin adsorption

Antibiotic contamination, particularly chloramphenicol (CAP) and ciprofloxacin (CIP), in aquatic environments contributes to the spread of antimicrobial resistance genes (AMRs), posing a global health threat. Adsorption has emerged as an effective, low-cost, and simple method for removing these antibiotics. This study reports the surface modification of natural magnetic particles coated with silica and trimethoxy[3-(phenylamino)propyl]silane (NMP@SiO2/TMPS) for the adsorption of CAP and CIP. TMPS was selected because it possesses a phenylamino group providing both aromatic and amine functionalities, enabling interactions such as electron donor–acceptor (EDA), π–π, n–π, hydrophobic, and hydrogen bonding. The TMPS concentration was varied at 1.5, 3.0, and 7.5 mmol for 0.5 g NMP and 2 mL sodium silicate solution. The sol–gel method was used to synthesize the adsorbent material. Characterisation of the adsorbent included FTIR, XRD, SEM–EDX mapping, VSM, and BET analysis. Optimal adsorption was achieved at pH 6 for CAP and at pH 5 for CIP, with contact times of 90 min and 60 min, respectively. The highest adsorption capacity was observed with NMP@SiO₂/TMPS(3.0), reaching 87.11 mg g–1 for CAP and 161.17 mg g–1 for CIP at a concentration of 350 mg L–1. Kinetic studies indicates that CAP adsorption follows the pseudo-second-order (PSO) model, whereas CIP adsorption is best described by the Elovich model. For both antibiotics, the Redlich–Peterson isotherm provides the best fit to equilibrium data. Thermodynamic analysis reveals that the adsorption is exothermic, spontaneous, and accompanied by an increase in system disorder. The successful preparation of NMP@SiO2/TMPS demonstrates its potential as an alternative adsorbent for the adsorption and desorption of antibiotics, advancing pharmaceutical wastewater treatment technology.