Adsorption of zinc(II) from water with purified carbon nanotubes

Commercial single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were purified by sodium hypochlorite solutions and were employed as adsorbents to study the adsorption characteristics of zinc from water. The properties of CNTs such as purity, structure and nature of the surface were greatly improved after purification which made CNTs become more hydrophilic and suitable for adsorption of Zn^2+. In general, the adsorption capacity of Zn^2+ onto CNTs increased with the increase of pH in the pH range of 1-8, fluctuated very little and reached maximum in the pH range of 8-11 and decreased at a pH of 12. A comparative study on the adsorption of Zn2+ between CNTs and commercial powdered activated carbon (PAC) was also conducted. The maximum adsorption capacities of Zn^2+ calculated by the Langmuir model are 43.66, 32.68, and (13.04 mg g^-1)with SWCNTs, MWCNTs and PAC, respectively, at an initial Zn^2+ concentration range of 10-80 mg l^-1. The short contact time needed to reach equilibrium as well as the high adsorption capacity suggests that SWCNTs and MWCNTs possess highly potential applications for the removal of Zn^2+ from water.