Application of near infrared spectroscopy for the determination of adsorbed p-nitrophenol on HDTMA organoclay—implications for the removal of organic pollutants from water

NIR spectroscopy has been used to measure the adsorption of p-nitrophenol on untreated montmorillonite and surfactant exchanged montmorillonite. p-Nitrophenol is characterised by an intense NIR band at 8890 cm−1 which shifts to 8840 cm−1 upon adsorption on organoclay. The band was not observed for p-nitrophenol adsorbed on untreated montmorillonite. Both the montmorillonite and the surfactant modified montmorillonite are characterised by NIR bands at 7061 and 6791 cm−1. The organoclay is characterised by two prominent bands at 5871 and 5667 cm−1 assigned to the fundamental overtones of the mid-IR bands at 2916 and 2850 cm−1. A band at 6017 cm−1 is attributed to the p-nitrophenol adsorbed on the organoclay. The band is not observed for the montmorillonite with adsorbed p-nitrophenol. It is concluded that p-nitrophenol is adsorbed to significantly greater amounts on the organoclay compared with the untreated montmorillonite. The implication is that organoclays are most useful for removing organic molecules from water through adsorption.