Adsorbed para-nitrophenol on HDTMAB organoclay—A TEM and infrared spectroscopic study

para-Nitrophenol adsorbed on hexadecyltrimethylammonium bromide modified montmorillonite has been studied using a combination of X-ray diffraction TEM and infrared spectroscopy. Upon formation of the organoclay, the properties change from hydrophilic to hydrophobic. It is proposed that para-nitrophenol is adsorbed onto the water in the cation hydration sphere of the organoclay. As the cation is replaced by the surfactant molecules the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Significant changes in the water vibrations occur in this process. Bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant (CEC) increases up to 1.0CEC. After this concentration the bands increase approaching a value the same as that of the surfactant. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.

Graphical abstractThe mechanism of adsorption of para-nitrophenol on both non-treated montmorillonite and the surfactant intercalated montmorillonite was studied by a combination of TEM and infrared spectroscopy. On the untreated and low CEC intercalated montmorillonite the para-nitrophenol adsorbed on the cation hydration sphere. At high CEC values the para-nitrophenol replaced the surfactant cation in the interlayer and bonded directly to the siloxane surface.Figure optionsDownload full-size imageDownload as PowerPoint slide