Interaction mechanisms of antibiotic sulfamethoxazole with various graphene-based materials and multiwall carbon nanotubes and the effect of humic acid in water

We studied the interaction mechanisms between carbonaceous nanomaterials (CNMs) and sulfamethoxazole (SMX) to elucidate their adsorption behaviors. Three graphene-based materials, reduced graphene oxide (rGO), graphene oxide (GO), and graphene nanoplatelet pastes (GNP), and five multiwalled carbon nanotubes (MWCNTs), MWCNT10, MWCNT15, MWCNT15-OH, MWCNT15-COOH, and N-doped MWCNTs, were used as sorbents. Oxygen-containing functional groups and graphene wrinkling suppressed SMX adsorption on GO and GNPs due to fewer Csp2 ring sites for π-π stacking and fewer accessible flat surface adsorption sites, respectively. Ring current-induced 1H NMR upfield chemical shifts increased as the π-donor concentration increased, as well as π-donor strength of polycyclic aromatic hydrocarbons (PAHs) (pyrene > phenanthrene > naphthalene) as model graphene compounds, suggesting that π-π interaction strength of SMX with PAHs associated with π-donor strength. Moreover, 1H NMR results further verified that carboxylic and hydroxyl groups in PAHs (9-phenanthrol and 3-phenanthrenecarboxylic acid) weakened the complexation between SMX and the graphitic surface. Additionally, the morphologies of rGO and MWCNT10 were observed using AFM, and transformed from being linear to scattered as the loading dose of the humic acid increased. Our results are useful to understand the distinct interaction mechanisms and subsequent adsorption behaviors resulting from various carbon nanomaterials with SMX in water.