Adsorption of Chromate from Aqueous Solution by Polyethylenimine Modified Multi-Walled Carbon Nanotubes

In this paper, multiwall carbon nanotubes (MWCNTs) were modified by Polyethylenimine of different molecular weight of 1800 (MWCNTs-18) and 7000 (MWCNTs-70). The structure and morphology of the functionalized MWCNTs were characterized by thermogravimetric analysis (TGA), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The curve of TGA showed that the mass loss of MWCNTs-18 and MWCNTs-70 were 46.5% and 51.9% respectively, which was remarkably different with pristine MWCNTs. The XRD demonstrated that the structure of the pristine MWCNTs and functionalized MWCNTs were similar. In addition, the experiment of the removal of chromate from water solution using functionalized MWCNTs was also conducted. The experimental conditions such as concentration of chromate, temperature, pH were studied. The maximum uptake capacities for chromate anions were obtained at the concentration of 0.4 mmol·L−1. The solution pH showed a significant effect on chromate removal over a pH range from 4.0 to 9.0. Besides, the uptake capacities for chromate anions on MWCNTs-18 and MWCNTs-70 increased as the temperature increase within the range from 30 to 60 °C. Under the experimental conditions, the maximum uptake capacities of MWCNTs-18 and MWCNTs-70 for chromate anions were 0.27 and 0.33 mmol·g−1 respectively. The thermodynamic parameters of the uptake process were calculated, and the results showed that the process of uptake chromate was spontaneous.