Removal of Co(II) from aqueous solutions by sulfonated magnetic multi-walled carbon nanotubes

Abstract

Sulfonated magnetic multi-walled carbon nanotubes (SMMWCNTs) were applied in the sorption of Co(II) from aqueous solutions. The SMMWCNTs were prepared and characterized by scanning electron microscope (SEM), Fourier transform infrared (FTIR), and X-ray diffractometer (XRD) test. A large number of influencing factors to the sorption process were investigated, such as pH, ionic strength, contact time, cations, anions, humic acid (HA), fulvic acid (FA) and temperature. The results indicated that the Co(II) sorption was strongly controlled by the pH and ionic strength. Moreover, foreign anions, such as F-, Cl- and Br-, had an obvious effect on the sorption process, which depended on the electronegativity of the anions. On the other hand, cations restrained sorption strongly, such as Mg2+ and Ca2+. The existence of HA/FA enhanced sorption process at pH 8. As revealed by the sorption results, the Langmuir adsorption model was more favorable than the Freundlich adsorption model, and the pseudo-second-order model could fit the data much better than the pseudo-first-order. The thermodynamic analysis suggested that sorption was spontaneous and endothermic. What’s more, the stability experiments of the SMMWCNTs showed that SMMWCNTs could maintain excellent magnetic stability and dispersion stability. Thus, this SMMWCNTs sorbent was believed to be a promising material for the selective removal of Co(II) from heavy metal-containing waste-water.