Competitive partitioning of phenanthrene in carbon nanomaterials and anionic and nonionic micelles

Abstract

Presence of carbon nanomaterials in the environment can significantly impact the removal of polycyclic aromatic hydrocarbons by surfactant-enhanced remediation. The aim of this study was to investigate the impact that carbon nanomaterials have on surfactant remediation, which was done by analyzing the partitioning of phenanthrene, a model polycyclic aromatic hydrocarbon, in mixed carbon nanomaterials (carbon nanotubes and graphene) and surfactant (anionic SDBS and nonionic TX-100) solutions via batch solubilization and adsorption experiments. The presence of carbon nanomaterials was found to suppress phenanthrene solubilization as it absorbed both phenanthrene and surfactants; decreasing the amount of surfactants further lowered phenanthrene solubilization. Compared with SDBS, TX-100 showed a greater ability to solubilize phenanthrene in the presence of carbon nanomaterials. The adsorption of phenanthrene to carbon nanomaterials was suppressed with TX-100, demonstrating competitive adsorption between TX-100 and phenanthrene. Conversely, with SDBS present, the adsorption of phenanthrene to carbon nanomaterials increased, showing complementary adsorption between SDBS and phenanthrene; the maximum amount of phenanthrene adsorbed to both graphenes and carbon nanotubes was approximately 170 mg/g with SDBS present, compared to 122.8 and 95 mg/g without SDBS, respectively. The contrasting effects of TX-100 and SDBS on the distribution of phenanthrene was explained as follows: a) SDBS is less able to solubilize phenanthrene, b) carbon nanomaterials have high adsorption affinity for SDBS, and c) phenanthrene can be absorbed by SDBS. Overall, these findings demonstrate the mechanisms for the impact of carbon nanomaterials on phenanthrene partitioning in anionic (SDBS) and nonionic (TX-100) surfactants.