Thermally-treated MgO/nanocrystalline cellulose immobilized onto a Santa Barbara-16 mesoporous SiO2 template for the sequestration of antibiotics from polluted water

Abstract

Clean technologies using functional materials as adsorbents for removing antibiotics from polluted water are of great interest, especially for water scarce sub-African countries. In this study, adsorbent MgO/nanocrystalline cellulose immobilized on a Santa-Barbara-16 mesoporous SiO₂ template was synthesized at 450 °C, 650 °C and 850 °C (MNCS-450, MNCS-650 and MNCS-850), respectively, and characterized by pH point of zero charge (pHPZC), Fourier transform infrared (FTIR) spectrophotometry, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), X-ray diffraction (XRD), and N₂ physisorptometry. To evaluate the applicability for the removal of antibiotics, sorption experiments were carried out with two antibiotics representatives, namely ampicillin (AMP) and ciprofloxacin (CIP). The functional moieties, high surface areas (115 to 190 m² g⁻¹) and pore volumes (0.185 to 0.277 cm³ STP g⁻¹) of the adsorbents were responsible for AMP and CIP removal, probably by hydrogen bonding, hydrophobic and π–π stacking interactions. The experimental data of the sorption experiments best fit the three-parameter Langmuir–Freundlich model (LFM) and the mixed-1,2-order model (MOM), respectively. The maximum LFM monolayer adsorption capacity (q_maxLF) was achieved by MNCS-850 for AMP and CIP, which was 4.89 mg g⁻¹ and 4.90 mg g⁻¹, respectively. Ethanol effectively removed AMP and CIP from MNCS-450, MNCS-650 and MNCS-850 adsorbents. Therefore, the developed adsorbents can be reused and are environmentally friendly.