Research paper Al 13 -pillared montmorillonite modified by cationic and zwitterionic surfactants: A comparative study Lingya Ma a,b , Jianxi Zhu a, ⁎, Hongping He a , Qi Tao a , Runliang Zhu a , Wei Shen a,b , Benny K.G. Theng c a CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China b University of Chinese Academy of Sciences, Beijing 100049, China c Landcare Research, Private Bag 11052, Manawatu Mail Centre, Palmerston North 4442, New Zealand abstract article info Article history: Received 4 December 2013 Received in revised form 17 August 2014 Accepted 21 August 2014 Available online 22 September 2014 Keywords: Inorganic–organic montmorillonites Al 13 cation Cationic surfactant Zwitterionic surfactant Structure A series of inorganic–organic montmorillonites (IOMts) were synthesized by modifying polyhydroxy-aluminum (Al 13 )-pillared montmorillonites (AlPMts) with the cationic surfactant, hexadecyltrimethyl ammonium bromide (C16), and the zwitterionic surfactant, hexadecyldimethyl(3-sulphonatopropyl)ammonium (Z16). The products prepared using different surfactant concentrations (0.4–5.0 CEC) were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and C, H, and N elemental analyses. The results showed that the structure of the IOMt was strongly influenced by surfactant type. In the case of C16-modified AlPMt (C-AlPMt), the surfactant molecules entered and expanded the interlayer space, leading to the partial release of pre-intercalated Al 13 cations. At high surfactant concentrations (N 2.0 CEC), the basal spacing of C-AlPMt showed no further expansion although the gauche/trans conformer ratio of the intercalated surfactant decreased. In the case of Z16-modified AlPMt (Z-AlPMt), however, the amount of Z16 intercalated did not increase when the surfactant concentration exceeded 1.0 CEC, while the basal spacing was identical with that measured for the unmodified AlPMt. This observation could be attributed to a difference in the capacity of AlPMt for intercalating C16 and Z16. It was proposed that C16 was intercalated through both cation exchange (with Al 13 ) and physisorption, while the intercalation of Z16 was primarily mediated by electrostatic attraction between the interlayer Al 13 cation in AlPMt and the negatively charged group of Z16. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Montmorillonite is a naturally occurring layer silicate with excellent swelling capacity, a large specific surface, and a high cation exchange capacity (CEC). The physical and chemical properties of natural montmorillonites can be modified by cation exchange reactions with metal complex cations and organic cations, e.g., pillared interlayered clays (PILCs) (Pinnavaia, 1983) and organo-montmorillonites (OMts) (He et al., 2014). Because of the large specific surface area, high pore volume, and strong surface acidity, PILCs have significant applications in environmental remediation (Li et al., 2013; De León et al., 2014), such as being used as efficient adsorbents for oxyanionic contaminants and heavy metals (Zhou et al., 2010; Zhu et al., 2014). PILCs, however, do not efficiently remove the hydrophobic organic compounds from water because of its hydrophilic surface (Zhu et al., 2009b). In contrast, OMt shows excellent hydrophobicity and can be used as efficient adsorbents for organic pollutants (Stockmeyer, 1991; He et al., 2006; Liu et al., 2012; Fatimah and Huda, 2013). Wastewater in the environment, however, contains both organic and inorganic contaminants. Therefore, developing novel adsorbents that can efficiently remove both organic and inorganic contaminants is urgent. Inorganic–organic montmorillonites (IOMts), obtained by intercalating cationic metal complexes and organic cations, are capable of removing a wide range of inorganic and organic contaminants (Zhu and Zhu, 2007; Zhu et al., 2009b; Li and Wu, 2010; Ouellet-Plamondon et al., 2012). IOMt can also serve as novel adsorbents of volatile organic compounds (Zhu et al., 2007a), and as catalysts in the degradation of adsorbed organic compounds (An et al., 2008). Little information, however, is available regarding the interlayer structure of IOMt that holds the key to understanding their interactions with pollutants, and to developing novel industrial applications. Organo-montmorillonites (OMts) are commonly prepared by the intercalation of organic modifiers. Previous studies have shown that the type of organic modifier used can markedly influence the structural characteristics and adsorptive behavior of OMt (Dentel et al., 1998; Heinz et al., 2007; Zhou et al., 2007; Chitrakar et al., 2011; Liu et al., 2012). Thus, modifiers containing special functional groups, such as zwitterionic surfactants, can significantly improve the adsorption capacity of OMt (Shen, 2002). Sulfobetaine, containing both positively charged (quaternary ammonium) and negatively charged (sulfonate) groups Applied Clay Science 101 (2014) 327–334 ⁎ Corresponding author. Tel./fax: +86 20 85290181. E-mail address: zhujx@gig.ac.cn (J. Zhu). http://dx.doi.org/10.1016/j.clay.2014.08.023 0169-1317/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay