Preparation of diameter-controlled free-standing MWCNT membranes and their application for dye adsorption

The synthesis of multi-walled carbon nanotubes (MWCNTs) was carried out over different Ni-loaded metallic oxide catalyst nanoparticles and under different reduction times to control the outside diameter of the nanotubes. Moreover, high-purity, free-standing membranes were fabricated by a simple filtration of the as-grown MWCNTs. Furthermore, the dye-adsorption properties of the nanotubes depended on the diameter of the carbon nanotubes (CNTs). The adsorption isotherms and kinetics of anionic dyes could be described by Freundlich and pseudo-second-order models, respectively. Thermodynamic studies suggested that the adsorption processes were spontaneous and exothermic. This work provides new insights into the synthesis and application of MWCNTs with the selective adsorption properties of carbon-based materials for the removal of organic dyes.