Methodological approach to the chloramphenicol adsorption by acid-leached halloysites: Preparation, characterization, performance and mechanism

Abstract

Adsorptive removal was found to be an environmentally friendly and effective approach to treat emerging contaminants such as chloramphenicol (CAP), an antibiotic widely used to care for human and animal diseases, which after using is discharged into the environment, disrupting thus ecosystems and inducing microbial resistance. In this study, we systematically investigated the effect of sulfuric acid treatment on the physico-chemical and adsorptive properties of halloysite with the objective of combining the results of acid-leached halloysite characterization, CAP adsorption and spectroscopic investigation to propose a coherent mechanism of the CAP−acid-leached halloysite interaction. After preparation, the acid-leached samples were characterized by X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), N2 adsorption–desorption, Transmission electron microscopy (TEM), zetametry, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), and used in CAP adsorption. The specific surface area increased significantly from 63 for H to a maximum of 240 m2 g−1 for the H2SO4-leached sample with 10 M concentration (H-10M). An amount of CAP adsorbed by the best adsorbent, H-10M, of 197.2 was found compared to 92.5 mg g−1 for H. The experimental isotherms were suitably fitted by the Langmuir-Freundlich equation. Thermodynamic parameters suggested physical, spontaneous, and endothermic adsorption. H-10M was easily desorbed by methanol whose involvement was explained by FTIR, and maintained its adsorption capacity for three cycles. By combining the results of the characterization, adsorption parameters such as the influence of pH, affinity, and thermodynamic data, and the FTIR and XPS (X-ray photoelectron spectroscopy) investigations between CAP and H-10M, a mechanism has been proposed which involves two interactions: a hydrophobic interaction taking place between −Si–O–Si− species and CAP aromatic ring and hydrogen bonding which occurs between the oxygen of the carbonyl group and the hydrogen of silanols (SiO–H). This integrated methodological approach has significant implications for the effective understanding and prediction of the environmental fate of these emergent contaminants in wastewater.