Interaction between carbon nanotubes and soil colloids studied with X-ray spectromicroscopy Julia Sedlmair a, ⁎, Sophie-Charlotte Gleber b , Sue Wirick c , Peter Guttmann d , Jürgen Thieme e a Institute for X-ray Physics, Georg-August-University Göttingen, Friedrich-Hund-Platz 1, 37073 Göttingen, Germany b Argonne National Laboratory, APS, 9700 S. Cass Ave, Bldg. 401, Argonne, IL 60439-4837, USA c Brookhaven National Laboratory, NSLS I, Bldg. 725, Upton, NY-11973, USA d Helmholtz Zentrum Berlin, BESSY II, Albert-Einstein-Str. 15, 12489 Berlin, Germany e Brookhaven National Laboratory, NSLS I, Bldg. 817, Upton, NY-11973, USA abstract article info Article history: Accepted 19 August 2011 Available online 3 September 2011 Keywords: X-ray microscopy Carbon nanotubes NEXAFS Chernozem Soil To improve the understanding of the effect of carbon nanotubes (CNTs) on the environment, the characteri- zation of CNTs and their interaction with soils needs to be assessed. Here, we demonstrate an analysis of pristine and modified CNTs, in dry and wet state using soft X-ray spectromicroscopy with energies around the C 1s K-shell edge (280 eV–300 eV). Apart from that, suspensions of the CNTs and the colloidal fraction as well as the extracted humic substances of a chernozem soil sample were studied. The effect of the different sample environments on the CNTs were observable both in the microscopic images and the spectral data, e.g., in aqueous environment the CNTs built clusters. Since CNTs are mainly analyzed under sterile laboratory conditions, this study intends to show how to investigate CNTs and their interaction with other substances under ambient conditions. One of the major objectives was, whether differences between CNTs and organic soil particles are distinguishable at all, and subsequently, how to describe the observed interactions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction What happens, if carbon nanotubes (CNTs) are brought into contact with other substances — is it possible to distinguish them from matter of high carbon content and to monitor the interactions at the interfaces? With the increasing use and production of these designed materials, the ecological aspect comes into account, and reliable ways to study and characterize the interaction between CNTs and other substances have to be found. Since their discovery in 1991 (Iijima, 1991), the techniques to produce CNTs in sizable quantities have been improved continuously. Currently, several thousand tons of CNTs are produced per year, so the investigation of their interaction with the environment, either being introduced willingly e.g., for remediation of soils or unintendedly after disposal, is of key importance. Although several experiments concerning the effect of CNTs on tissue and cells (Lam et al., 2006; Smith and Handy, 2007) have been published, only few attend to the effects on soils and humic substances (Panessa-Warren et al., 2009; Saleh et al., 2010). Pristine CNTs are mainly chemically inert, which prevents them from being biodegraded; therefore, it is important to analyze their (long-term) effects on the environment. CNTs belong to the fullerenes, their atomic structure is comprised of C atoms, each tetrahedrally bound to three other C atoms (sp 2 - hybridization) resulting in a honeycomb-like pattern of their walls. Apart from their structure, the unique properties of CNTs also stem from their enormous aspect ratio, with a diameter in the nm-range, but a length of up to several mm. For this work, multi-walled CNTs with an outer diameter of 10–30 nm and a length distribution of 0.5–2 μm were used (Schierz and Zaenker, 2009). The properties of these still relatively new materials promise a large variety of applica- tions, of which some are already realized. Depending on their design, CNTs can be functionalized showing metallic or semiconducting properties (Bradley et al., 2003; Javey et al., 2004). Combining suit- ably designed CNTs with the right materials can optimize these materials, e.g., the addition of CNTs to concrete makes that building material lighter and more flexible (Nasibulin et al., 2009), alloys of steel and CNTs are extremely hard and rustproof (Reibold et al., 2006). In medicine and pharmacology, CNTs are currently tested for drug design and delivery (Prato et al., 2007) and as mentioned before, studies regarding site specific soil remediation aided by the applica- tion of CNTs are discussed (Fugetsu et al., 2004; Pillaya et al., 2008; Wang et al., 2005). Among other techniques, NEXAFS (near edge X-ray absorption fine structure) or FTIR (Fourier transform infrared spectroscopy) spectroscopy are used for these investigations, however, usually only as bulk measurements (Banerjee et al., 2004a, b; Schierz and Zaenker, 2009; Tang et al., 2002; Wiesemann et al., 2001). Methods Chemical Geology 329 (2012) 32–41 ⁎ Corresponding author. E-mail address: jsedlma@gwdg.de (J. Sedlmair). 0009-2541/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2011.08.009 Contents lists available at SciVerse ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo