Surface modification of pyrophyllite with amino silane coupling agent for the removal of 4-nitrophenol from aqueous solutions

The surface of naturally hydrophobic mineral pyrophyllite was modified to hydrophilic by treatment with prehydrolyzed N-(2-aminoethyl)3-ammopropyltrimethoxysilane (APEO) coupling agent to prepare a novel and effective adsorbent for the removal of 4-nitrophenol (4-NP) from aqueous solutions. XRD, FTIR, and SEM analyses were used to characterize the surface modification. It was found that after the grafting procedure, heat treatment at 110 degreesC results in condensation reaction between the OH groups of the APEO molecule and the hydroxyl groups and/or oxygen atoms on the pyrophyllite surface and the adsorption of 4-NP by APEO-modified pyrophyllite involves interactions between dissociated 4-NP molecules and protonated amine groups of APEO molecules attached to the mineral surface. Adsorption equilibrium data for 4-NP adsorption on APEO-treated and untreated pyrophyllite were most satisfactorily fitted using the Freundlich adsorption isotherm and adsorption capacity was found to be 0.268 mg/g for modified pyrophyllite whereas it was only 0.105 mg/g for untreated pyrophyllite. (C) 2004 Elsevier Inc. All rights reserved.