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This study explores the use of raw kaolin (RK) and alkali-activated kaolin (AAK) as eco-friendly adsorbents for the removal of cephalexin (CEP), a widely prescribed antibiotic frequently detected in wastewater and classified as an emerging contaminant, due to its detrimental effects on aquatic ecosystems, microorganisms, and human health. The adsorption of CEP on RK and AAK was systematically investigated in batch mode across different operational parameters, including contact time, CEP concentration, adsorbent dosage, pH of medium, and temperature. The adsorption process was monitored using UV–Vis absorption spectroscopy. The adsorption kinetics of CEP on both RK and AAK followed a pseudo-second-order model, and was governed by an initial rapid external mass transport, followed by slower diffusion into the internal pore structure at longer contact times. The equilibrium data were best described by the Langmuir isotherm model, suggesting monolayer adsorption on homogeneous surface sites of the adsorbents. The adsorption capacity of CEP was found to increase from 4.686 ± 0.203 mg g−1 on RK to 6.605 ± 0.231 mg g−1 on AAK, which is attributed to the higher surface area of AAK, resulting from the etching effect upon alkali activation of RK. Thermodynamic analysis confirmed that the CEP adsorption was spontaneous and exothermic and contributed to a reduction in surface irregularities. Importantly, adsorption-desorption experiments demonstrated that both RK and AAK can be effectively regenerated and reused for multiple cycles of the antibiotic removal. Characterization of the adsorbents before and after CEP adsorption using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared (FTIR) spectroscopy revealed that CEP molecules were mainly adsorbed through hydrogen bonding and weak electrostatic interactions. These findings highlight the ecological and economic advantages of using natural and AAK as sustainable and cost-effective adsorbents to tackle the growing challenge of pharmaceutical residues in wastewater treatment. Adsorptive removal of cephalexin (CEP), a frequently detected antibiotic in wastewater and classified as an emerging contaminant, using eco-friendly kaolin-based adsorbents in batch mode under various operational parameters.The adsorption kinetics, isotherm, and thermodynamics of CEP on both raw kaolin (RK) and alkali-activated kaolin (AAK) were well described by the pseudo-second-order, the Langmuir isotherm model, and the Van’t Hoff equation, respectively.Alkali activation enhanced the adsorption capacity of CEP by approximately 40%, attributed to increased surface area and cation exchange on the silica and gibbsite basal surfaces of the kaolin particles.Characterizations of the adsorbents revealed that CEP molecules were primarily adsorbed through hydrogen bonding and weak electrostatic interactions.The spent alkali-based adsorbents can be effectively regenerated and reused for multiple adsorption-desorption cycles without significant loss in adsorption capacity. Adsorptive removal of cephalexin (CEP), a frequently detected antibiotic in wastewater and classified as an emerging contaminant, using eco-friendly kaolin-based adsorbents in batch mode under various operational parameters. The adsorption kinetics, isotherm, and thermodynamics of CEP on both raw kaolin (RK) and alkali-activated kaolin (AAK) were well described by the pseudo-second-order, the Langmuir isotherm model, and the Van’t Hoff equation, respectively. Alkali activation enhanced the adsorption capacity of CEP by approximately 40%, attributed to increased surface area and cation exchange on the silica and gibbsite basal surfaces of the kaolin particles. Characterizations of the adsorbents revealed that CEP molecules were primarily adsorbed through hydrogen bonding and weak electrostatic interactions. The spent alkali-based adsorbents can be effectively regenerated and reused for multiple adsorption-desorption cycles without significant loss in adsorption capacity.
Majid et al. (Mon,) studied this question.