Experiment and modeling of the interaction of copper(II) and salicylic acid with oxidized multi-walled carbon nanotubes

Batch experiments were conducted to elucidate the adsorption of a widely used salicylic acid (SA) and copper(II) on oxidized multi-walled carbon nanotubes (MWCNTs) as a function of pH and concentration. X-ray photoelectron spectroscopy and potentiometric titration were performed to study the concentration at the surface oxygen-containing functional groups of them. π–π Bondʹs sites were evaluated by the Dubinin–Ashtakhov model. Data analysis indicated that the adsorption mechanism was mainly due to chemical interaction among copper(II) and SA and the surface functional groups of them. The adsorbed SA on them leads to the modification of their surfaces and partial complexation of copper with the SA adsorbed on them and thus had a positive effect on the adsorption of copper. Copper was also shown to increase SA adsorption from pH 3 to 7. The surface complex model was used to describe the surface charge density, as well as adsorption equilibrium. The copper removal was due to adsorption of surface–metal complexes, while the SA uptake resulted from the formation of surface–organic complexes. Furthermore, when they coexisted in the system, it appeared that the surface/metal/organic chemical complexes were the main forms.