Functionalization of acidified multi-walled carbon nanotubes for removal of heavy metals in aqueous solutions

Abstract

Water pollution is a worldwide issue for the eco-environment and human society. Removal of various pollutants including heavy metals from the environment is a big challenge. Techniques of adsorption are usually simple and work effectively. In the current study, MWCNTs were prepared by chemical vapor deposition (CVD) of acetylene at 600 °C. Fe–Co/CaCO3 catalyst/support was prepared by wet impregnation method. The crystal size of the catalyst was identified using XRD. Acidified functionalized multi-walled carbon nanotubes (MWCNT) were produced from oxidation of multi-walled carbon nanotubes by mixture of H2O2 + HNO3 in a ratio of 1:3 (v/v) at 25 °C. The structure and purity of synthesized functionalized CNTs were examined by TEM, N2-BET method and thermogravimetric analysis. The functional groups produced at CNTs surface were investigated using FTIR spectroscopy. Acidified functionalized MWCNTs with a high surface area of 194 m2g−1 and porous structure (17.19 nm) were used for water treatment from harmful cations (Pb2+, Cu2+, Ni2+ and Cd2+), single cation solutions and quaternary solution at different pH values and different times. The results were interesting because in single solutions the catalyst removed Pb2+, Ni2+, Cu2+ and Cd2+ with percentages of 93, 83, 78 and 15%, respectively, in 6 h. While in quaternary solution, adsorption was more complex and the order of the adsorbed metals was as following: Pb2+ (aq) > Cu2+(aq) > Cd2+ (aq) > Ni2+ (aq).