Adsorption of monoaromatic compounds and pharmaceutical antibiotics on carbon nanotubes activated by KOH etching

The relatively low surface area and micropore volume of carbon nanotubes limit their potential application as effective adsorbents for hydrophobic organic contaminants. In this study, KOH dry etching was explored to prepare activated single-walled carbon nanotubes (SWNT) and multiwalled carbon nanotubes (MWNT) for adsorption of model monoaromatic compounds (phenol and nitrobenzene) and pharmaceutical antibiotics (sulfamethoxazole, tetracycline, and tylosin) in aqueous solutions. With activation, the specific surface area was increased from 410.7 m(2)/g to 652.8 m(2)/g for SWNT and from 157.3 m(2)/g to 422.6 m(2)/g for MWNT, and substantial pore volumes were created for the activated samples. Consistently, adsorption of the test solutes was enhanced 2-3 times on SWNT and 3-8 times on MWNT. Moreover, the activated carbon nanotubes showed improved adsorption reversibility for the selected monoaromatics, as compared with the pristine counterparts, which was attributed to the more interconnected pore structure and less pore deformation of the activated adsorbents. This is the first study on the adsorption/desorption of aqueous organic contaminants by KOH-activated carbon nanotubes. The findings indicate that KOH etching is a useful activation method to improve the adsorption affinity and adsorption reversibility of organic contaminants on carbon nanotubes.