Adsorption of synthetic organic chemicals by carbon nanotubes: Effects of background solution chemistry Shujuan Zhang a , Ting Shao a , S. Sule Kaplan Bekaroglu a,b , Tanju Karanfil a, * a Department of Environmental Engineering and Earth Sciences, Clemson University, 342 Computer Court, Anderson, SC 29625, USA b Department of Environmental Engineering, Suleyman Demirel University, Isparta 32260, Turkey article info Article history: Received 6 October 2009 Received in revised form 1 December 2009 Accepted 9 December 2009 Available online 28 December 2009 Keywords: Carbon nanotube Adsorption Organic chemical Natural organic matter pH Ionic strength abstract With the significant increase in the production and use of carbon nanotubes (CNTs), they will be inevitably released into aquatic environments. Therefore, the fate and transport of CNTs in aqueous solutions have attracted extensive attention. In the present work, the effects of natural organic matter (NOM), solution pH and ionic strength on adsorption of three synthetic organic chemicals (SOCs) by both pristine and surface functionalized single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were investigated. The three SOCs (phenanthrene, biphenyl, and 2-phenylphenol) with different planarity, polarity, and hydrogen/electron-donor/acceptor ability, representing typical scenarios for the SOC–CNT interactions, were employed as probe molecules. Among the three background solution characteristics examined, NOM showed the most significant effect on SOC adsorption, while solution pH and ionic strength exhibited minimal or negligible impacts. The presence of NOM greatly suppressed the SOC adsorption by CNTs, and the impact on the SWNTs was higher than that on the MWNTs. The planarity and hydrophobicity of SOCs were two important factors determining the effects of NOM, solution pH and ionic strength on their adsorption by CNTs. ª 2009 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanotubes (CNTs), ever since their discovery, have attracted extensive attention due to their unique properties. They have shown potential applications in many areas, such as conductive and high-strength composites, nanometer- sized semiconductor devices, hydrogen storage media, and energy conversion devices (Baughman et al., 2002). With the significant increase in production and use of CNTs, one major concern is the health and environmental risks posed by these nanomaterials once they are released to the environment (Colvin, 2003; Wiesner et al., 2006). Evidences for potential risks of CNTs to humans and ecosystems are accumulating rapidly (Guzma ´ n et al., 2006; Donaldson et al., 2006). Due to their highly hydrophobic surfaces, CNTs exhibit strong adsorption affinities to synthetic organic chemicals (SOCs), such as polycyclic aromatic hydrocarbons (PAHs) (Gotovac et al., 2006; Yang et al., 2006; Wang et al., 2008, 2009; Zhang et al., 2009), chlorobenzenes (Chen et al., 2008a), nitroben- zenes (Chen et al., 2008b), and phenols (Chen et al., 2008a; Lin and Xing, 2008a; Yang et al., 2008). As a consequence, toxicity of CNTs may be further enhanced by adsorption of toxic chemicals. Therefore, understanding of SOC–CNT interac- tions is critical for the environmental risk assessment of both CNTs and toxic pollutants as well as for the applications of CNTs as potential adsorbents. SOC–CNT interactions are controlled by an array of factors, including physicochemical properties of CNTs and * Corresponding author. Tel.: þ1 864 656 1005; fax: þ1 864 656 0672. E-mail address: tkaranf@clemson.edu (T. Karanfil). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 44 (2010) 2067–2074 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.12.017