Magnetic carbon composites as regenerable and fully recoverable adsorbents: Performance on the removal of antidiabetic agent metformin hydrochloride

Abstract

Abstract The present work describes three newly-prepared magnetic-carbon composites (M-CCs) applied as adsorbents. The M-CCs were prepared by the co-precipitation method, grafting Fe(II) and Fe(III) oxides onto the surface of different matrices: PAC, GNP and MWCNT in order to achieve M-PAC, M-GNP and M-MWCNT, respectively. The composites were characterized by Fourier Transform Infrared spectroscopy, X-ray Diffraction Spectroscopy. Scanning Electron Microscopy was used for characterization of M-MWCNTs, Transmission Electron Microscopy was used for characterization of M-GNP composites. Thermogravimetric analyses were performed for each of the three M-CCs. It is found that about 70% of M-CCs consist in Fe3O4 nanoparticles. M-CCs adsorption features and performance towards the removal of a pollutant model from aqueous solutions was established. They were tested for Metformin hydrochloride adsorption, a worldwide antidiabetic pharmaceutical agent. The parameters of adsorbent dose, adsorption duration, initial concentration of adsorbate solution, temperature, pH and co-existing ion concentration were considered as adsorption independent variables. The kinetic tests show that the Pseudo second order kinetic model (PSO) fit best the three-adsorption systems. M-GNP is the fastest adsorbent of the three (k2\u2009=\u20090.36\u2009g/mg min). The three investigated adsorption systems obey the Langmuir isotherm model. Pinpointing M-GNP (qm\u2009=\u20098.83\u2009mg/g) as the most efficient adsorbent in normal conditions, and M-MWCNT (qm\u2009=\u200926.17\u2009mg/g at 318\u2009K) at higher values of temperature. Acid conditions favor adsorption of Metformin hydrochloride onto M-MWCNT, alkaline for M-PAC, whereas M-GNP provides best performance under amphoteric conditions. Coexisting ions affected Metformin hydrochloride adsorption only in case of M-MWCNT and M-GNP. Desorption tests were also carried out by using phosphate buffer solution. M-GNP provides best desorption ratios, reaching nearly 66% of Metformin hydrochloride desorption after each use.