The adsorption of paranitrophenol on organoclays synthesised by the ion exchange of the surfactant Molecule dimethyldioctadecylammonium bromide (DDOAB) of formula (CH(3)(CH(2))(17))(2)NBr(CH(3))(2) has been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis. The expansion of the montmorillonite depends on the loading of the montmorillonite with dimethyldioctadecylammonium bromide and is related to the arrangement of the surfactant molecules within the clay interlayer. This expansion is altered by the adsorbed paranitrophenol and is observed in the transmission electron microscopic images of the organoclay with adsorbed paranitrophenol. Changes in the surfactant molecular arrangements were analysed by thermogravimetry. The paranitrophenol is sublimed simultaneously with the loss of surfactant. The dehydroxylation temperature of the montmorillonite is decreased upon adsorption of the paranitrophenol indicating a bonding between the paranitrophenol and the hydroxyl units of the monmorillonite. (c) 2008 Elsevier Ltd. All rights reserved.