Adsorption kinetics of 4-n-nonylphenol on hematite and goethite

Abstract

The adsorption of 4-n-Nonylphenol (4-n-NP), a persistent emerging contaminant, onto the surface of hematite and goethite was studied using Attenuated Total Reflectance (ATR)-FTIR spectroscopy. The adsorption kinetics for hematite and goethite show that equilibrium was reached in less than 24 h, with the fastest kinetics to saturation achieved on hematite. Adsorption isotherms studies show that Langmuir model bests fits the data, with the highest adsorption capacity observed in goethite, with a calculated 4-n-NP maximum adsorption that was 3 times more than that of hematite. This higher maximum capacity on the surface of goethite was attributed to the presence of more OH species on the surface of goethite than on hematite. When the pH was varied, maximum adsorption was achieved close to pKa of 4-n-NP, with maximumvalues matching those acquired from adsorption isotherms and kinetic studies.