Adsorption and Conformation of a Cationic Surfactant on Single-walled Carbon Nanotubes and Their Influence on Naphthalene Sorption

Surfactants are used in synthesis and dispersion of carbon nanotubes (CNTs) and can thus be released into the environment with CNTs. In this study, it was observed that the coupled release of surfactants and CNTs altered the sorption of organic contaminants on the CNTs. The cationic surfactant, cetylpyridinium chloride (CPC), decreased naphthalene sorption on single-walled carbon nanotubes (SWCNT). In the most dramatic example, the adsorption capacity of naphthalene on SWCNT was reduced from 240 to 61.1 mg/g. The decrease of naphthalene sorption could be largely attributed to the competition of adsorbed CPC cations (i.e., C(21)H(38)N(+)) with naphthalene by occupying the SWCNT surface as surfaces decreased from 737 to 88.9 m(2)/g after the coating of CPC. However, the adsorbed CPC may form hemimicelles and result in a favorable media for naphthalene partition to counteract the decrease in naphthalene sorption. Configuration changes of adsorbed CPC hemimicelles might occur because the naphthalene partition into the adsorbed CPC decreased with the increase of adsorbed CPC. A partition-adsorption model was introduced to describe the partition fraction of naphthalene into adsorbed CPC hemimicelles as well as the adsorption fraction of naphthalene on unoccupied surfaces of SWCNT.