Interactions between carbon nanotubes and sulfonamide antibiotics in aqueous solutions under various physicochemical conditions.

Sulfamethoxazole (SMX) and sulfapyridine (SPY), two representative sulfonamide antibiotics, have attracted much attention recently because of their potential ecological risks. This work systematically investigated the adsorption characteristics of SMX and SPY on carbon nanotubes (CNTs), a newly introduced nano-adsorbent, under various physicochemical conditions. Laboratory batch adsorption experiments and mathematical models were used to determine the adsorption kinetics and isotherms of the two antibiotics to the CNTs. We found that SMX and SPY had very fast adsorption kinetics to the CNTs, which could be simulated with both the pseudo-second-order and the intraparticle diffusion models. These results suggest that the adsorption of the antibiotics to the CNTs were controlled by surface adsorption and intraparticle diffusion processes. Isotherm studies showed that sonication-aided dispersion slightly increased the adsorption of the antibiotics to the CNTs probably because the dispersion process might increase CNT surface area. When solution pH increased from 3.0 to 9.0, the Langmuir maximum sorption capacities of the antibiotics to the CNTs decreased from 98.0 to 18.6 mg/g (SMX) and from 108.6 to 83.2 mg/g (SPY), indicating pH is a controlling factor of the removal of the two antibiotics in aqueous solutions. We also found that the Langmuir adsorption capacity of the CNTs decreased slightly for both SMX and SPY when more adsorbents were in the solution. The findings from this study suggest that CNTs can be used as a high efficiency adsorbent to removal antibiotics from aqueous solution under various conditions.