Research paper Chemical and thermal properties of organoclays derived from highly stable bentonite in sulfuric acid Fethi Kooli a, ⁎, Liu Yan b a Taibah University, Department of Chemistry, PO Box 30002, Al-Madinah Al-Munawwarah, Saudi Arabia b Institute of Chemical And Engineering, Sciences 1 Pesek Road, Jurong Island, 627833, Singapore abstract article info Article history: Received 4 May 2012 Received in revised form 28 July 2013 Accepted 29 July 2013 Available online 27 August 2013 Keywords: Bentonite Acid activated clays Thermal stability Organoclays Organo-acid activated clays Cetyltrimethylammonium Generally, acid activation modified the physico-chemical properties of the raw clay minerals. The extent of these modifications depended on the type, origin of the clay minerals and the conditions of the acid activation. In this study, a bentonite exhibited a strong stability toward the acid treatment at 90 °C and at higher acid/clay mineral ratios, with slight depletion of Mg 2+ , Fe 3+ and Al 3+ cations (about 5%). The resulting organo-acid activated clays prepared after a reaction with cetyltrimethylammonium (C16TMA) hydroxide solution, exhibited uptaken amounts of surfactants between 0.80 mmol and 0.7 mmol/g with interlayer spacings of 2.20 nm and 1.80 nm, independently of the initial concentrations of the organic molecules. These organoclays were stable in acidic and basic solutions. However, after heating at 200 °C, the interlayer spacing shrunk due to the degradation of the organic surfactants as indicated by thermogravimetric analysis. The rehydration of the calcined organoclays at temperatures below 200 °C, did not lead to the increase of the basal spacings, due to change in configuration of the C16TMA cations. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The preparation of organoclay minerals with higher contents of organic cations has attracted a lot of interest, and the interlayer spacing values of these materials were an important parameter for the interca- lation of the polymers in the preparation of clay polymer nanocompos- ites (Lee and Kim, 2004). These materials have found many applications as adsorbents of hazardous compounds from water and soil (Beall, 2003; Sanchez-Martin et al., 2006), catalysts (Wang et al., 2009), pre- cursors for the preparation of porous heterostructure clays (Kooli et al., 2006a), nanocomposites (de Paiva et al., 2008), thickeners in paints, greases, oil-base drilling mud, and homogenizing fillers in the plastic industry. The main modification process of clay minerals was based on the exchange reaction of the Ca 2+ ,K + and Na + cations located between the clay mineral layers by the organic ones existed in the solu- tion. In general, the content of the organic cations in the organoclays, depended on the initial concentrations of the organic solutions (He et al., 2010; Xi et al., 2005a), the origin of the clay minerals, the counter anions of the organic salts (Kooli et al., 2006b), and the exchangeable cations of the clay minerals (Gammoudi et al., 2012). The most used organic salts solutions were bromide and chloride solutions. However, few studies were reported using organic cations from their hydroxide solutions (Kooli, 2013; Kooli et al., 2005). The acid activation of clay minerals led to a leaching of some metals from the clay mineral layers, resulted in a change of their composition and porosity (Komadel and Madejová, 2006). In addition, the cation exchange capacity (CEC) of the parent clay mineral decreased progres- sively with the severity of the acid activation (Kooli et al., 2009). Per consequent, the reaction of acid activated clay minerals with C16TMABr solution resulted to lower contents of the C16TMA cations in the resulting organo-acid activated clays compared to the organoclay prepared from the nonacid activated clay mineral (Kooli et al., 2009). Meanwhile, different results were obtained when the acid activated clay minerals were reacted with C16TMAOH solution, and the contents of the intercalated C16TMA cations were higher compared to the organoclay prepared from the nonacid activated clay mineral (Kooli et al., 2005). These unexpected results were related to the way the C16TMA cations were intercalated. An exfoliation of the acid activated layers due the higher pH of the C16TMAOH solution occurred, followed by adsorption of the C16TMA cations on the both sides of these clay mineral layers (Kooli et al., 2005). The severity of the acid activation of clay minerals depended on the origin of clay minerals, their chemical composition, strength of the mineral acids, and the temperatures of acid treatment (Pentrák et al., 2010). The rate of dissolution of the octahedral layers increased not only with the increasing concentration of the acid, temperature and contact time, but also with increasing Mg 2+ contents in octahedral layers (Breen et al., 1995a,b). The powder X-ray diffraction (PXRD) technique was the main tool to examine the stability of the clay minerals during the acid activation process. The basal reflections of smectite phase decreased gradually and eventually disappeared after intense treatment. The Fourier transformed infra-red (FTIR) technique indicated also changes in position and shape of the main Applied Clay Science 83–84 (2013) 349–356 ⁎ Corresponding author. Tel.: +966 569442963. E-mail address: fkooli@taibahu.edu.sa (F. Kooli). 0169-1317/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.clay.2013.07.022 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay