Water purification is of extreme importance worldwide. p-Nitrophenol was used as a test chemical to design and test an organoclay for the removal of p-nitrophenol from an aqueous solution. Synthesis of the organoclay with methyltrioctadecylammonium bromide [CH3(CH2)(17)](3)-NBr(CH3) labeled as MTOAB results in multiple expansions of the montmorillonite clay from 1.24 nm to a maximum of 5.20 nm as is evidenced by the XRD patterns. Thermal analysis shows strong bonding of the surfactant to the clay siloxane layers and the interaction of the p-nitrophenol with the clay surfaces. It is proposed that the p-nitrophenol penetrates the siloxane layer of the clay and bonds through the ditrigonal space ofthe siloxane hexaLonal units to the inner OH units. Such a concept is supported by the observation of an additional infrared band at 3652 cm(-1) for the organoclay. Shifts in the p-nitrophenol OH stretching vibrations mean a strong interaction of the p-nitrophenol molecule. Significant changes in the siloxane stretchina bands are also observed. (c) 2007 Elsevier Inc. All rights reserved.