Removal of mercury (II) from aqueous solutions by multiwalled carbon nanotubes coated with manganese oxide

Water pollution by heavy metals is one of the most important environmental problems. Among the heavy metals, mercury (Hg) is a very toxic metal and its high concentration can lead to impaired pulmonary and renal dysfunction. The aim of this study was to determine the amount of Hg removal by carbon nanotubes coated with manganese (Mn) oxide from aqueous solutions. Methods: In this study, multi-walled carbon nanotubes coated with Mn oxide were prepared and used to remove Hg from aqueous environments. In addition, the physical and structural characteristics of the nanotubes were determined by the X-ray diffraction (XRD). The impact of diverse variables was further investigated, including the initial concentration of Hg, the initial pH of the solution, contact time, mixing rate, as well as the amount of nano-composite and the impacts of confounders (nitrate and chloride). Finally, optimum conditions for each of these parameters were obtained by the Taguchi statistical method. Results: The XRD analysis showed that the nanotubes were properly coated with Mn oxide. Furthermore, the results demonstrated that under pH 7, the rate of mixing of 150 rpm, the contact time of 60 minutes, the amount of nano-composite of 60 mg, and the initial density of Hg 80 mg/L can be achieved by removing 95% Hg. Moreover, the confounder factors of nitrate and chloride reduced the amount of Hg removal by 4 and 5%, respectively. Conclusion: Based on the results, the nanotubes coated with Mn oxide can be used as easy and strong absorbents for the rapid absorption of Hg from drinking water and industrial wastewater.