Investigation of the efficiency of powdered and granular magnetic activated carbon nano composites for the adsorption of metronidazole from aqueous solutions (Isotherms and kinetics study)

Abstract

Pharmaceutical pollutants, especially antibiotics, are a serious concern and one of the most polluting sources of the environment, and are harmful to the environment and human health. The purpose of this study was to evaluate the removal of metronidazole (MNZ) using powdered and granular magnetic activated carbon nanocomposites (magnetic powdered activated carbon (PAC) and magnetic granular activated carbon (GAC)) with adsorption from aqueous solutions. In this experimental-laboratory study, the adsorbent characteristics were determined by scanning electron microscopy (SEM), X-ray diffraction, vibrating sample magnetometer, Brunauer–Emmet–Teller (BET), Fourier transform infrared spectros-copy, and energy-dispersive X-ray spectroscopy analyses. The effects of different parameters includ-ing pH (3–11), MNZ concentration (10–30 mg/L), adsorbent dosage (0.2–3 g/L) were investigated on the adsorption process. Then, the adsorption isotherm and kinetics equations were investigated. The obtained results of SEM images showed the porosity on the magnetic activated carbon surface with varied sizes, almost uniform dispersion, and a diameter between 20 and 50 nm. Furthermore, the BET results showed that the specific surface area and the pore volume were 109.91 m2/g, and 0.2552 cm2/g for the Magnetic PAC, and 561.16 m2/g and 0.2898 cm2/g for the magnetic GAC. Also, the magnetization curve showed that the nanoparticles have super paramagnetic nature, whose magnetic saturation value was 30.717 emu/g for the powdered magnetic activated carbon nanoparti-cles, and 32.992 emu/g for the granular magnetic activated carbon nanoparticles. The results showed that the highest efficiency of magnetic GAC in the removal of MNZ (92/4%) was in conditions with an initial antibiotic concentration of 20 mg/L, pH = 7, adsorbent dosage 1 g/L, and for 90 min. The highest efficiency of magnetic PAC in the removal of MNZ (29.94%) was in conditions with pH = 3, adsorbent dosage of 0.2 g/L and for 30 min. The data obtained from equilibrium isotherms revealed that the MNZ absorption process through the magnetic GAC adsorbent (Langmuir (R² = 0.83), Freundlich (R² = 0.98)), magnetic PAC adsorbent (Langmuir (R² = 0.89), and Freundlich (R² = 0.94)) were in consistent with the Freundlich model. Also, the data obtained from the reaction kinetic cal-culations showed that the absorption of MNZ by the adsorbents was in accordance with a pseudo-second-order model (R2 = 0.98 for magnetic GAC adsorbent and R2 = 1 for magnetic PAC adsor-bent). The results obtained in this study showed that magnetic GAC as an effective adsorbent and magnetic PAC along with other methods could be used to remove MNZ from the aqueous solutions.