Removal of Cu(Ⅱ) ions from aqueous solution by a magnetic multi-wall carbon nanotube adsorbent

Copper (Cu(Ⅱ)) pollution has a hazardous effect on human health. However, designing new adsorbents with prominent properties is a tremendous challenge in effectively removing Cu(Ⅱ) ions from the environment. In this study, new adsorbent—MnFe2O4/multi-wall carbon nanotubes (MMWCNTs), with excellent magnetic properties were synthesized and then systematically characterized. Introducing MnFe2O4 addressed the challenge of separating the nano-adsorbent from the liquid medium. Batch adsorption experiment results indicated that effective adsorption occurred in a relatively neutral range (pH=6–8). The adsorption behaviors were consistent with the pseudo-second-order model and the Freundlich model. The maximum adsorption capacity reached 46.41 mg/g at 308 K. The adsorption thermodynamics revealed the endothermic character of adsorption by MMWCNTs, and increasing the temperature benefitted the adsorption process. Furthermore, many surface functional groups of MMWCNTs facilitated adsorption performance. Compared with the MWCNTs before modified, the adsorbent had a nearly tenfold improvement from 3.4% to 34.8% in the removal efficiency of Cu(Ⅱ) ions. These results demonstrated that MMWCNTs are a suitable, efficient adsorbent that can be used in natural water bodies for adsorbing Cu(Ⅱ) ions.