Comparison between different mesoporous carbons in the removal of doxycycline antibiotic: experimental assays and description of adsorbate features by density functional theory (DFT)

Abstract

This study presents a comparative analysis of the physicochemical and morphological features of three distinct mesoporous carbons, prepared from disparate natural sources. The material derived from sucrose (MPC), that obtained from chitosan (N-MPC-Chi), and the N-MPC-Glu derived from glucosamine exhibited surface areas of 1001, 904, and 873 m² g⁻¹, respectively. XPS analysis revealed that the MPC had the highest oxygen content, which provided a more electron-rich surface. The N-MPC-Chi and N-MPC-Glu contain 3.6% and 4.6% of nitrogen, respectively, and are related to pyridine and pyrrolic N moieties. The materials were applied in the adsorption of the antibiotic doxycycline (DOX), and the N-MPC-Chi showed the best adsorptive performance, with a maximum adsorption capacity of 191.4 mg g⁻¹. Kinetic and isothermal studies revealed the pseudo-second-order, and the Langmuir isotherm models as the best fits. Thermodynamic data suggest that chemisorption is the primary mechanism. DFT study of the DOX molecule revealed that the LUMO is located at the three flat-oriented rings of the naphthacene core. The HOMO was found to be situated at the out-of-plane carboxamide ring. Post-process characterizations, kinetic, isothermal, and thermodynamic studies indicate that ion exchange was the predominant mechanism, with hydrogen bond and electrostatic interactions also playing a significant role in the adsorptive process. N-MPC-Chi demonstrated a high removal capacity for DOX from a real river sample. The N-MPC-Chi is a promising adsorbent for DOX under real conditions.