Coadsorption of Cu and sulfamethoxazole on hydroxylized and graphitized carbon nanotubes

Because of their various functional groups, antibiotics may complex with heavy metals and thus the environmental behaviors of both antibiotics and heavy metals may be altered. Noticing the experimental flaws of the previous studies, this study used Cu2 + and sulfamethoxazole (SMX) as model sorbates and carbon nanotubes (CNTs) as model sorbents to investigate the coadsorption of Cu and SMX. Combining the results of binary interaction experiments, we concluded that Cu and SMX preferentially occupy different types of CNT sorption sites at pHs 1.0 and 3.5, showing no apparent sorption change with the presence of coadsorbates. However, at pH 6.5, ternary complexes of Cu–SMX–CNTs and SMX–Cu–CNTs may be formed depending on Cu2 + concentrations. XPS data provided further support for the adsorption of both Cu and SMX on CNTs. These results indicated that the environmental behavior of antibiotics should be evaluated with careful consideration of the rule of metal ions.

► Cu–SMX complexation was highly pH-dependent.
► At pHs 1.0 and 3.5, Cu2 + and SMX were adsorbed on their preferred sites on CNTs.
► Different ternary complexes were formed depending on Cu concentrations at pH 6.5.